EPS8 final

the NASA Shuttle Radar Topography Mission (SRTM)

- 11-day mission of the space shuttle in February 2000 -used InSAR to map the Earth's topography -provided first global Digital Elevation Map for Earth

list of significant california earthquakes

- 1857 Fort Tejon (San Andreas) - 1906 San Francisco (San Andreas) - 1971 Sylmar - 1992 Landers - 1994 Northridge - 2004 Parkfield

emile argand

- 1879 - 1940 - studied the structure of mountain ranges - adopted the very early continental drift ideas of Wegener -observed folded geological structures in the Swiss Alps and the Himalaya -sedimentary rocks are deposited in horizontal layers - with the action of tectonic forces, they fold

alred wegener

- 1880 - 1930 -studied paleontology, ancient climate, and geology - very interested in why there were fossils of tropical plants in the arctic -noticed coastlines matched -suggested continents like icebreakers plowing through oceanic rocks

professor Keilis-Borok

- 1921 - 2013 - founder of international institute of eq prediction theory and mathematical geophysics, moscow - working on eq prediction for more than 30 yrs - approach based on pattern recognition in eq catalogs - i.e. x% chance of this magnitude eq happening in this time span

coordinates

- 3 numbers ad a reference frame required to give complete location of a point in space --> X, Y, & Z relative to a reference --> latitude, longitude, elevation or depth on a sphere (geographic) - plus time - usually we choose geographical directions - many possible units

subduction under Pacific Northwest

- 4 cm/yr of plate convergence --> like small convection cell - up at ridge down at subduction zone -site of great underthrusting eq --> evidence for M9 in 1700 -volcanic arc & eruptions --> Mt. St. Helens

EarthScope

- 400 new seismometers in the US - 1000+ of GPS and strain instruments - 4 km hole to look at San Andreas Fault (SAFOD)

Synthetic Aperture Radar (SAR)

- A SAR forms an image by sending electric pulses to the ground and recording echoes - distance between antenna and ground is known very accurately from the travel time of radar (phase) - InSAR uses the phase of the radar wave to measure ground topography and movement

where are the faults on the san andreas from North to South?

- Alaska - British Columbia, Washington, Oregon - California - Baja California

how does the gps work

- GPS satellites and receivers have very precise clocks -they measure the travel time of a radio signal between satellites and the receiver on the ground -convert time into distance -4 satellites are need to get the position in 3D --> due to the fact that the signal lands on a sphere and need to observe overlapping spheres -can get velocity by having distance between antenna and satellite

Assam (Shilong) India

- June 12 1897, Mw8 -extreme ground acceleration, stones on the ground vibrated -largest blind eq ever -previously thought to have occurred on North dipping thrust, recent study suggest it occurred on south dipping thrust on North edge of Shilong plateau

1992 landers eq

- June 28, 1992 in mojave desert - Mw = 7.3, largest since 1952 --> smaller than 1906 San Francisco --> bigger than 1994 Northridge - 70 km right-lateral, strike-slip rupture on vertical plane -lasted 20 seconds -displacement up to 6 m

1872 owens valley eq

- M7.6 - M7.8 - devastated lone pine --> caused rockfalls across Sierra Nevada Mountains

the hector mine eq

- Mw 7.1 - Oct 16, 1999 2:46 AM local time - Eastern California Shear zone

Omori's Law

- Number (N) of aftershocks per unit of time decreases with time t - mathematically, rate of aftershocks follows: N ~ C/t where: N is the number of eq in time interval centered on time t - t is time after mainshock - C is a constant likelihood of getting a big eq decreases with time - combine Gutenberg-Richter and Omori's law

PcP versus PKP waves versus PdP waves

- PcP is reflection of P wave on the outside of the outer core - PKP is refraction through the outer/inner core - PdP wave is reflection on the outer layer of D'' layer surrounding outer core, and PcP is p wave reflection off of the inner layer of the D'' layer -little c means reflection off of the outer core

S wave shadow zone

- Swaves do not propagate in liquid -zone where no S-wave is received -S wave can be converted to p wave through the mantle (exception) -S waves vanish when they penetrate through the core because don't propagate through fluids

elastic property

- a material is elastic if it deforms when stress is applied to it and returns to its original shape when stress is removed -linear elasticity: when stress is proportional to strain -upper crust is elastic properties of an elastic body: -the more you stretch (or squeeze) it, the more it deforms -if you stop stretching/squeezing, then it returns to its original shape -it is not ductile i.e. it does not flow

changes in west coast over time

- a mid-ocean ridge subducted --> before that, only subducted along coast --> first hit near LA ~ 25 myr ago --> San Andreas Fault system started then -as ridge is subducting, two triple junctions are moving apart on coast --> mendocino Triple Junction moving north -----> NA-Pacific-Juan de Fuca function --> NA-Pacific-Gorda junction off Baja California -this will cause segment of transform to increase

seismometer basics

- a seismometer records the motion of the ground - it requires part of the instrument to be attached to the ground, and another part (the inertial mass) to be isolated from ground motion, so that the relative motion of the two parts can be measured - a restoring mechanism (a spring) that returns the mass to its original position when the shaking stops -a damping mechanism, so that the mass doesn't just keep bouncing around forever, obscuring waves arriving later -a pivot (hinge) so mass moves in one direction

traveling wave semantics

- a single frequency traveling wave will take the form of a sine wave - a snapshot of the wave in space at an instant of time can be used to show the relationship of the wave properties frequency, wavelength and propagation velocity

age of the earth, age of the oldest rocks

- age of the Earth is 4.6 billion years - oldest rocks are ~4.4 billion years old

PKiKP and SKiKP

- an I means a wave that goes through the inner core, a little i means a wave that reflects off of the inner core; and "K" refers to a P-wave in the fluid outer core -first letter is the wave it started as and then the last is what it is converted to -velocity increases with depth in mantle, decreasess in outer core then steadily increases again --> S wave velocity doesn't increase as much as P wave in mantle

seismometers

- an instrument for recording the motions of the Earth's surface through time --> used to record seismic waves - sometimes called a seismograph - seismogram: graph showing record of ground motion - principle: while the Earth moves back and forth under a suspended mass, the mass stays in place due to inertia --> measures horizontal movement

steel-frame commercial buildings

- best record of safety for tall buildings -most high rises are steel frame -steel l-beams are strong, yet light -can absorb much energy and flex far before breaking

exception 1 of seismicity not at a plate boundary

- blurring of the plate boundary --> more common on continental boundaries -because continents are weaker than oceanic plates - i.e. the pacific plate and north american plate boundary --> pacific plate boundary deforms plate: causes mountains because boundary not straight -explains seismicity

sir harold jeffreys

- british astronomer mathematician and geophysicist - objected to wegener's theory of continental drift arguing that the strength of the mantle was far greater than any conceivable dirivng force - effectively stalled plate tectonics for forty years

lessons of the 1994 northridge eq

- buried fault = blind fault --> hypocenter at deepest part of fault (18 km) --> rupture did not reach surface --> on previously unknown fault - interactions between faults (1971, 1994)? - more damage in direction of propagation of rupture

cold and rigid surface

- but the rocks at the surface of the Earth are cold and rigid. they don't want to flow - instead, the surface tries to stay immobile, but the forces of convection are too great. The surface breaks up into large chunks called plates

some common measures of the size of an earthquake

- damage (in $) - deaths or injuries -length of fault that breaks -area of fault break - displacement (average, or at a point) - intensity (measures power of shaking at a location) -magnitude (measures earthquake itself) -seismic moment (essentially area times displacement)

defining an object's motion

- displacement: how far object has moved - velocity: how fast an object is moving - acceleration : how fast the velocity changes - if we measure one quantity and keep track of time, we can calculate the other two

cause of aftershocks

- every time there is an eq, the volume of rock around the rupture is strained - sometimes, the strained rock breaks - often, it takes a while for it to break, so the aftershocks that occur are dependent on this -- when rock breaks it is because the shear stress exceeds the friction stress on a small fault plane -but we don't know for sure why there is a delay: -- static fatigue -- visco-elastic relaxation -- diffusion processes (pore fluids)

appearance of fault trace

- fault trace: where fault plane intersects the Earth's surface - surface fault appearance results from the accumulation of offsets in many repetitions of eq slip -fault scarp: steep slope formed by fault motion (displacement) -erosion smoothes fault scarps with time

convection

- heat a fluid from below, cool it on top --> cooler material is more dense --> hotter material is less dense - so the cool stuff on top sinks, and the warm stuff on the bottom rises - the liquid continually overturns, like in a pot on a stove

static versus sliding friction

- it is harder to start something moving than it is to to keep it sliding. this is is because friction decreases when things are moving - static friction > sliding friction - since the driving force required to overcome static friction is much larger than the force required to overcome sliding friction, there is often a sudden acceleration when things start moving

exception 4 of seismicity not on plate boundary

- man-made earthquakes -dam filling: stress in rock around dam, typically added stress that was already there but now triggered it -mining -oil industry: fracking (injecting high pressure fluids in rocks to break & promote fluid migration ; people usually reinject "waste water" afterwards that breaks rocks and causes eq) --> becomes a concern in Oklahoma

when did most forms of life begin, oldest oceanic seafloor

- most forms of life started to appear about 500 million years ago - oldest oceanic seafloor today is 200 myr

arthur holmes and convection

- proposed in 1928 that rocks flow because they are - heated from below and cooled from above -his description came very close to the modern views of Earth's plates and their dynamics -if you apply force to a rock that's hot, it can flow because of impurities in the crystal lattice

san andreas fault info

- right-lateral slip : LA moving Northwest --> 3.5 cm/yr relative to NA -segments: --> 1906 SF quake ("Big one" M7.9) --> creeping section (gradual aseismic slip) --> 1857 fort tejon quake (kariso plain / mojave segment) --> southern segment (southern segments split into different faults -big bend --> causes NS compression in Southern California --> San Andreas Fault curves around Los Angeles

hazards due to geological conditions at a construction site

- soft soils: stronger shaking - wet soils: liquefaction potential, landslide potential - cliffs and ridges: stronger shaking, landslide potential --> cliffs can concentrate or focus the energy

tsunamis vs. regular waves

- typical wind-driven waves in the ocean have short wavelengths (a few meters) while tsunamis have wavelengths of 10-100 km -tsunamis often do not break, the ocean simply rises rapidly. sometimes the tsunami arrives as a bore, a wall of churning water, like a normal wave after it has broken and is running into shore -the currents in tsunamis are very large and can carry much debris (boats, huge chunks of coral, houses, trees, people)

when did seismoscope work

- worked on March 1, 138 A.D. -seismoscope in city of luoyang - ball dropped from westernmost dragon's mouth - days later report arrived earthquake 500 km to the west

pangea

- ~350 - 175 myr all modern continents attached - north america was on the equator -dinosaurs roamed the earth

Bihar Nepal earthquake

-15 January, 1934 -among deadliest eq in India history -epicenter: 7 km from city -Mw = 7.9, Ms= 8.3 -most damage caused by sand liquefaction

great kanto earthquake, tokyo

-1923, destroyed part of tokyo and yokohama just before noon -water mains broken, extensive fires -at this fault, there are 4 plates intervening: pacific, philippine sea, japan sea, NA plate; all of which are subducting

lessons from past eq w/ brick structures

-1952 kern county (only 1/71 brick buildings survived) -1983 coalinga(most of town's 90 brick buildings removed) -most of 64 ppl in 1971 san fernando died in collapse of brick hospital -1989 loma prieta -->cause of most deaths was collapse of freeway --> cause of most remaining deaths due to falling bricks

India Guajarat (Bhuj) earthquake

-26 January, 2001 -epicenter on West side -Mw7.7, Ms8.0 -not on a plate boundary, no surface rupture -poor construction and unconsolidated soil resulted in extensive damage in many cities in Guajarat

1994 Northridge eq

-4:31 AM, Jan. 17 - Mw = 6.7, 20 x 20 km, 1-2 m slip -thrust fault -$40-50 billion damage -still a few aftershocks

moon seismology

-Apollo 11,12,14,15 and 16 had seismometers, so there were up to 5 seismometer locations -->found moonquakes ---> mostly tidally triggered --->about 1000 km deep --->mostly less than magnitude 2 -saw about 2000 impacts --> .5 to 5000 kg meteorites --> found a small lunar core about have the r/R ratio of Earth's core -active experiment (generating seismicity) -->placed seismometers in a 90 m long line --> thumped the ground along the line --> exploded grenades --> crashed old spacecraft into planet --> found very low P wave velocities (100-300 m/s) in loose sediments (regolith) at shallow depth --> about 1.5 km layer of basalt under surface

Izmit, Turkey eq

-August 17 1999 -M7.4 like Landers -20K to 45K fatalities -economic cost about $26B -Arabia-Eurasia collision pushes Anatolia block to the west. Strike slip movement is accommodated by the North Anatolian Fault

the worst example of failure of URM buildings in recent history

-Bam, Iran 2003 -mud-brick structures in 2000 years old city -December 26 -Mw 6.6, strike-slip -41K deaths, 30K injured -85% of buildings damaged -surface faulting observed -landslides occurred in epicentral area

Where are the faults more inland?

-Basin and Range faults (Nevada) - Wasatch Fault Zone --> Utah, Idaho, Montana, Wyoming

more evidence for continental drift theory

-During WWII, scientists mapped the ocean floor bathymetry and magnetic field - long linear volcanic mountain chains called Mid-Ocean ridges - Seafloor spreading was proposed, postulating a driver for continental drift -further evidence came from the magnetic orientation of the sea floor

ShanXi Central China

-January 23, 1556 -deadliest in history, homes in caves in lose cliffs that collapsed, worst loss of life ever documented from an eq (830K) -fatality rates reached 60% in many cities -magnitude is not well known ~8

Tangshan eq

-July 27, 1976 -Mw7.8 -more than 650K deaths -intensity up to XI --> occurred in large city (~1 million) with generally low seismicity --> destructed most of industrial buildings, residential buildings, and water system -had a M7.1 aftershock 15 hours later

example of one of the first felt reports

-Lisbon, Portugal Nov 1st 1755 -M8.2-M8.5 -followed by a huge tsunami -destroyed 85% of the city -prime minister marquis de pombal ordered a query

very near disaster story dam

-Lower Van Norman Dam (at intersection of 405 & 5) -800K cubic yards of dam embankment slid into reservoir due to liquefaction of fill on upstream side -dam was 1/2 full but lose 30 ft of dam height -immediately evacuated 80K people living downstream -water level was lowered -dam was replaced by Los Angeles Dam

1971 Sylmar eq

-M6.7, Feb. 9 1971 -65 deaths -$500 million in damage -unexpected damage to some modern buildings

1933 long beach earthquake

-March 10 M6.3 -a shock, people had forgotten about quakes -120 deaths -engineered buildings had little structural damage -unreinforced masonry walls (bricks) failed catastrophically

example of devastating eq on soft ground

-Mexico city badly damaged in 1985 --> M8 eq more than 200 miles away --> extremely soft, clay-rich soil downtown --> 10K deaths -soft sites are common (i.e. LA, Bay Area, Salt Lake City, Anchorage, Boston, New Orleans

Nepal earthquake (Gorka)

-Mw7.8, Ms8.1 -April 2015 -allowed scientists to map the zone of the interface that was activated during the eq, big concern if still locked --> since the rupture did not extend up to the surface, more is expected to come

2011 Tohoku, Japan eq

-Mw9.05 -officially named the Great East Japan Earthquake -most powerful eq ever observed in Japan -11 March -epicenter 70 km east of coast -underwater depth of hypocenter 32 km -japan frickin shifted 2 m eastward & East coast lowered by .8 m (static displacement)

the type of elastic wave for P and S

-P waves compress rock and exhibit longitudinal motion (all parallel) - S waves sheer the rock and exhibit transverse motion (all perpendicular)

other supercontinents

-Rodinia formed at 1.3-1.0 gyr and fragmented around 750 myr --> included most of continents in a different configuration than Pangea -there may have been earlier supercontinents

which area of LA theoretically best to build on?

-Santa Monica mountains theoretically better to build on because of bed rock

Haicheng and Tangshan eq

-a blow for eq prediction -Feb 4, 1975 Haicheng: --> a succcessful prediction based on foreshock activity --> a sign of the ingenuity of the Chinese people -14 months later the city of Tangshan --> possibly the worst disaster in the 20th century --> unfortunately, the idea that eq are predictable dies hard

pancaking building

-a collapsed building that layers on top of one another -building code and quality of construction are main causes of casualties

Earth's Magnetic Field

-a liquid metallic core which rotates very fast because of convection which causes a magnetic field -similar to putting bar magnet at center but slightly tilted -the Earth's field flips sign (compass points South) at random intervals ranging from .5-30 Myr

wood-frame with stucco

-a little good: --> looks good --> 1" stucco strong as 1/4" plywood -bad: --> stucco adds weight, therefore makes building more vulnerable --> can fall off if poorly attached

first seismogram of a distant earthquake

-a magnitude ~5.8 earthquake in April 17, 1889 was strongly felt in Japan one hour before being recorded in Postdam, Germany -the instrument was a pendulum designed to measure slight changes in the direction of the vertical -scientists recognized that recording of waves that had traversed a long path through the Earht's interior carried valuable information about the properties of the materials through which the waves had traveled

how is the seafloor age determined

-ages measured from foraminifera fossils --> single celled ocean creatures --> retrieved by drilling to bottom of sediments -range from new to 150-200 myr --> cms per year created --> or 10's of km per million years -seafloor grows old with time until it sinks back into mantle

how deep are quakes?

-all types of boundaries have shallow quakes --> 0 to 30 km depth -subduction zones also have deeper events -->as deep as 650 km ---> subduction is dragging cold material down ---> cold material is more brittle -deeper events: breakage of subducting slab -->mostly from the pull of the weight of the sinking slabs --> some are also caused by bending of sinking slab --> not from rubbing together of plates

focal mechanism solutions

-also called "beach-ball diagrams" - show the geometry of the fault in a simple diagram - originally determined using P-waves first motions -now are computed from full waveforms -pictured as lower hemisphere projection by convention

Alaska eq

-among the most dangerous faults in US --> 8 quakes over M8 in the last 100 years -sparsely populated -main fault is subduction thrust --> reaches Earth's surface on ocean floor --> many secondary faults (e.g., Denali Fault) -also has volcanoes, tsunamis -large Alaska eq in 1962 9.2M, comparable to Japan

determining the size of eq from paleoseismology

-amount of slip at a single site --> bigger the slip, the bigger the eq --> not always true for strike-slip faults -appearance of same event at several sites --> the longer the rupture length, the bigger the eq

amplitude of seismic waves

-amplitude is the strength of shaking --> depends on magnitude of earthquake --> determines amount of damage -amplitude decreases with distance from the earthquake --> energy spreading out over larger area - P wave smallest - S waves larger than P waves - Surface waves largest of all

explain india's trajectory into Asia

-an example of convergent boundaries -if a fragment of a continent comes off and sits on top of subducting oceanic crust, it will get squished against the overriding continental plate

significance of the Asal Rift (Afar)

-an example of rift valleys (initial breaking of the continental plate) -origin of humanity (Lucy) found here

refraction

-bending of rays -refraction of light water: --> because speed of light waves is slower in water than in air -seismic waves refract too --> refraction and reflection can occur in the same surface

oil exploration underwater

-boat with satellite navigation antenna -has a sounder source that transmits sound which bounce off of the seafloor and then underwater acoustic phones (seismometers) detect seismic echoes from rock layers --> looking for oil traps

unreinforced brick, stone (masonry) or adobe buildings

-both residential and commercial -most dangerous type in eq --> suffer most severe damage --> cause majority of deaths -difficult and costly to repair and strengthen -brick and stone are heavy and inflexible -lateral motions create large inertial forces that crack mortar --> which is usually weak -bricks can separate, walls collapse unless wood-frame interior walls can hold up building

reflection of waves

-bouncing -ray of light reflecting off a mirror -body wave reflects off the surface of the Earth -seismic waves reflect off the Earth's surface and interfaces at depth

static stress triggering

-calculate where stress was raised or lowered by a large rupture -compare with aftershocks distribution -coulomb stress increase correlates with aftershocks? --> yes but debatable -many aftershocks where stress level was dropped

use gutenberg-richter for forecast

-can calculate the expected number of eq in a given time period from the slip rate by adding up all the eq on up to the max that a fault can sustain i.e. max = M7 1M7 + 10 M6 + 100M5 .... --then calculate the shaking for each of them and sum it up

plate reconstructions

-can trace plate motions well for last 200 myr -since we have oceanic plates up to about that age to reconstruct motions -motions less well-known 200-600 myr --> no oceanic plates left around to help

thrust faulting cycle

-causes vertical strain or a hump on the continental plate into the other continental plate -this vertical strain is overcome by causing an earthquake that decreases the hump and causes a slip at the actual fault

possible precursors that may be associated with stress change in crust

-change (increase or decrease) in number of quakes -slow ground motion -radon emission from ground (radioactive, increased before some eq, released from cracks in rock) -change in electrical resistivity -change in electromagnetic field (i.e. increase in signal right before) -change in water chemistry (found ~6 months precursor in chloride and other chemicals in bottled water) -change in seismic waves velocity

the two ways to change friction

-change the normal stress or change the coefficient of friction (mew) - the process of lowering the coefficient of friction is called lubrication (in the earth, water) - fractured rocks also have lower coefficient of friction. So faults that have slipped a lot (big, active ones) should have the lowest mew, because lots of fracturing has taken place

eq insurance

-changing state regulations, deductibles high -vulnerability of insurance company -FEMA (federal emergency management agency) as back-up for insurance - trade-offs --> could use funds to reinforce house --> be sure to do basic things to reinforce

magnetic "stripes" found on Mid-Atlantic ridge

-colored bands indicate normal magnetic polarity -no color indicates reversed polarity -bands form successively as plates spread apart, magma wells up to form new seafloor, which cools and records the normal or reversed magnetic field existing at that time -due to the mid-ocean ridge upwelling

Southern California Faults

-complex system driven by Pacific-North American interaction and the Big Bend -NW-SE trending faults mostly right-lateral strike-slip -E-W trending faults mostly thrust -Garlock Fault (N-E trending) is left lateral -some faults don't reach surface --> usually thrust faults, "blind thrusts"

lessons from the 2004 parkfield eq

-concept of characteristic eq at parkfield has to be revised --> return period may vary --> eq source characteristics can change from one event to the next - eq are not periodcially repeating phenomena - the idea that a quake is 'overdue' is false, as is the idea that you are safer just after a large quake --> eq are always due

concrete blocks

-concrete blocks have two hollows, so save money and weight -when properly reinforced, building very strong -unreinforced concrete is like unreinforced stone or brick -common bond: blocks staggered (better) -stack bond: blocks aligned vertically (worse b/c cracks can run straight through wall)

living in a fault zone

-could be zoned for parks or at a minimum, streets -ideally, best to live 5 miles or more away from faults --> often unrealistic in California, so saturated

The Sumatra-Andaman eq and tsunami

-dec. 26, 2004 - the eq initiated along the NW side of Sumatra -the rupture propagated to the north over ~1000 km -M9, along the subduction zone where the Indo-Australian plate is sinking beneath Indonesia on the Burma plate -over 1000 km of the subduction zone suddenly slipped up to 15 m -the Earth's rotation actually sped up, making the day shorter by 2.8 microseconds because the eq changed the shape of the Earth (w t f)

mantle velocities

-deeper rock is stiffer due to increasing pressure thus higher velocity -mantle is thought to be nearly uniform in composition -Mg, Fe, Si, O in various phases of minerals -phase changes produce ~5% jumps in velocity and density --> changes in molecular arrangement in crystals --> at depths of 410, 520, and 67- km -670 km depth separates upper and lower mantles -seismic tomography shows where seismic waves travel faster or slower, like a CAT scan

how strong will the shaking be?

-depends on the eq size and the distance to eq -site: nature of the ground under the structure --> the geology of the shallow layer below the surface is imperative to determine shaking

human factors to tsunami intensity

-destruction of coral reefs which would have reflected some of the incoming energy -destruction of the coastal mangrove forests, which impede the tsunami runup (intact mangroves saved many animals at a Sri Lanka zoo) -removal of natural sand dunes for improved beach access (thailand)

2011 Tohoku earthquake tsunami

-devastation of coastal area -receding currents produce giant swirls - velocity is ~(gravity * depth)^1/2

faults

-discontinuity (break) in the Earth's curst along which motion takes place -can be active (still has motion) or inactive (moved in the past) -can be seismic (makes earthquakes) or aseismic (slips slowly- creeps)

relationships between displacement, velocity, and acceleration

-displacement is the change in position. it is a vector with a magnitude and direction - velocity = displacement / time taken - acceleration = change in velocity / time taken

data recovery

-driving (or flying) to recording site --> still often used -telephone lines --> bad during large quakes -microwave transmission -satellite transmission -internet ~real time

what is the cause of normal faults around mountains?

-ductile lower crust and upper mantle flow laterally under the pressure imposed by excessive topography -brittle crust on top accommodates extension by normal faulting, creating a succession of ranges and valleys -the excess weight from elevated topography compresses the ductile section which spreads laterally and deforms brittle layer

Himalayas

-earthquakes are similar to those at subduction plate boundaries

slider block basics

-elastic energy storage in springs (like strain accumulation in the Earth) -resistance due to friction (like locked fault segments) -multiple, interacting elements (faults have many interacting segments too) --> therefore chaos, but chaos is not completely unpredictable ----> statistical measurements can be made - on a fault plane, interaction between adjacent fault patches goes in 2 dimensions, making things even more complex

energy released during elastic rebound of plates

-energy is released in the form of fracture energy, heat, and seismic waves -the larger the upper mantle, the less strain (more area) and less seismicity

energy of earthquakes

-energy that goes into an earthquake is released from the elastic crust rebound --> like a spring -energy that comes out of an earthquake distributed between --> radiated energy: seismic waves -------motion of crust --> breaking rocks & frictional heating (both of which are hard to measure)

quiescence

-eq are due if they have not happened in a while -seismic gaps (theory): --> eq are due in places they haven't happened because that part of the fault is all that's left holding back the plate motion --> this theory ignores aseismic motion - slow eq: times where the subduction zone relaxes its shear stress and the fault starts to move and therefore does not cause seismic waves

HAZUS eq model

-estimates damage and loss to buildings, lifelines and essential facilities from scenario and probabilistic eq, including: -ground shaking & ground failure -estimates of casualties -estimated cost of repairing damaged buildings -quantity of debris -direct costs associated with loss of function

quality of execution

-examples of poor execution: --> throwing trash in concrete mold, leads to holes in concrete, weak spots --> using salt water for mixing cement --> increasing sand-cement ratio to cut down cost --> reducing amount of reinforcing steel bars

deformation under compression

-exhibited in convergent plates -horizontal shortening -vertical thickening -exhibited in thrust faults (the faults at convergent faults) - oblique fault plate - compression accommodated by slip on fault plane -footwall on the bottom, hanging wall on top

more on cliffs and ridges

-experience greater shaking --> as waves reach surface, they are reflected back from cliff face and cause further amplification of shaking --> energy trapped within peak of the ridge (i.e. Bel Air) -landslide and rockfall potential

focal mechanisms and explosions

-explosions also produce seismic waves - an explosion is a different kind of seismic source: there is no fault plane -underground cavity expands suddenly -first motions are compressive in all directions --> this is how we can distinguish explosions from eq

geological moment

-fault length and slip measured from field observations --scales well with seismic moemnt -map displacement (D) and rupture length (L) on the ground --> assume rupture depth (W) : M0 = mew * D * L * W - slip and depth vary along fault strike - estimates are good along short fault segments - sum moments of all segments

fault scarp of the 1872 owens valley quake

-fault length: 160 km - largest horizontal slip of 7 m near Lone Pine - vertical component (east down) of up to 1 m

Hayward fault & berkeley stadium

-fault slips aseismically on the upper layer & offsets structures, deeper is seismic. -eq still possible on the Hayward fault -walls of stadium are deeply offset

Mid-Ocean Ridge Spreading Center information

-few, shallow, and small earthquakes (because plate is young & pliable) - high volcanic activity -far from civilization, little damage --> except in Iceland and Afar -called ridges because youngest, hottest crust is lighter than old crust & floats higher on the mantle, forming ridges -occurs at depths shallower than most of sea-floor -therefore the age of the seafloor increases with distance from ridge until it subducts

lesson from 1857

-for big quakes, location is not just a city --> rupture area is extensive -->the name of the eq only tells part of the story: Fort Tejon was the locus of the largest destruction and happens to be in the middle of the broken zone

rule of thumb for distance to earthquake

-for not too distant earthquakes, distance (in km) is P-S arrival time difference (in sec) times 12 --> if too far, then travels into mantle, otherwise just on crust - this is an approximation. seismic velocities vary with depth in Earth

force

-force is the cause of motion -force is a vector: it has a direction and intensity -2 kinds of force: -contact force: involve physical contact between objects -field forces: don't involve physical contact between objects (i.e. gravitational force)

a look at hills

-generally, it is better to be on hard rock in mountains than on a soft basin, despite some amplification from cliffs and ridges

ground settlement

-grains rearrange to denser packing -often uneven leading to different vertical motion in different parts of the building -by shaking, you rearrange the grains so you reduce the void between the grains --> compaction -differential settlement can lead to tilting buildings

more active faults and segments in the interior of the NA plate

-great basin extension -eastern california shear zone -"Big bend" on SA fault

death valley

-great basin extension -valley formed by conjugate normal faults -water evaporates in middle (nowhere 2 go) and leavers salt remnants

rest of US faults

-great basin faults: distributed extension -wasatch fault zone: nevada, utah, idaho, montana, wyoming --> about 10-25% as active as San Andreas --> mainly normal faults -new madrid: had some big quakes. we don't know how often they strike -charleston, plus a few others

P-wave radiation pattern around focus (see figure 1)

-green line is fault -slip shown by pink arrows intensity of shaking is: a. strong in some directions : lobes b. weak in other directions: nodes -NN directions are Nodal planes - one nodal plane is the fault plane, the other is the auxiliary plane

inertia and reason for damage in houses

-ground moves back and forth, shaking the house -the center of inertia moves from base of building, top lags behind a bit

earthquake effects

-ground shaking --> structural collapse --> falling objects -ground setting, liquefaction --> buildings collapse or sink into the ground -landslides and avalanches -fault offset --> surface break -tsunamis and seiches -human-assisted hazards --> floods from dam failure or water pipes break --> fires --> toxic spills

he elastic rebound theory

-harry fielding Reid, after studying the fault trace of the 1906 earthquake, postulated that the forces causing eq were not close to the eq source but very distant -the forces gradually increase the stress near the fault, which eventually fails in an earthquake to elastically rebound to original shape

hazard and risk

-hazard - probability that a given area will be affected by a given destructive process - risk: probability that a loss will occur -preparation lowers risk, not hazard -hazard is what seismologists predict --> includes eq probability -risk is what insurance companies, the govt etc. need to know -how do we close the gap? risk = hazard * vulnerability * value

taipei 101

-height = 508 m - used to be World's tallest building (<2007) - inertial damper limits swaying (add a heavy mass to damper amplitude of shaking)

exception 3 of seismicity not on a plate boundary

-hotspots -i.e. hawaii -due to slow mantle convection and magma rising up in oceanic plate and cooling to form islands -long chains of volcanoes appear on the sea floor; many large enough to emerge as islands -the islands form along a line, in order, and all the island chains on the same plate are aligned

the coral reef instrument

-if seafloor is going up and down, coral head cannot survive above water, so grows laterally, has weird fluctuating shape -grows like rings on a tree

local or richter magnitude includes correction for distance to epicenter

-if seismometer not 100 km from epicenter: local magnitude = log(A) + C -where: --> A is the maximum seismic wave amplitude in microns (10^-6 m) recorded on a standard seismograph --> C is a correction factor that is a function of distance from the seismometer to the epicenter

wood-frame buildings

-if well-built and maintained, safest structures due to lightness and flexibility of wood --> needs a good foundation --> needs to be attached to foundation --> needs some lateral support - we know this from performance in eq and experiments

tsunami from deep ocean to shallow ocean

-in the open ocean, a tsunami is less than a few tens of cm high at the surface, but its wave height increases rapidly in shallow water. Tsunami wave energy extends from the surface to the bottom in even the deepest waters. As the tsunami attacks the coastline, the wave energy is compressed into a much shorter distance and a much shallower depth, creating destructive, life-threatening waves

magnitude of an earthquake

-instrumental measurement of wave amplitude -ML and MW -energy, duration, slip and rupture length all scale with magnitude

forecasting: past history

-instrumental records (early 20th century) -historical records (late 1700s - missions) -geological records (goes back in time a few 1000 years)

IRIS

-international organization linking sensitive seismometers worldwide into a global database -part of the network was funded to support the CTBT (comprehensive test ban treaty), with the idea that the way to enforce the treaty is by constant seismic monitoring -a side benefit has been learning about the Earth through earthquakes -wave form tells nature and depth -time tells distance

exception 2 of seismicity not on a plate boundary

-intraplate earthquakes: eq in the middle of continents -caused by the beginning of new plae boundaries -ice loading and unloading: the temperature of Earth was much colder and ice was heavy & sinks into the crust; when warms up, ice mels, then the crust rebounds slowly causing seismicity

seismoscope

-invented by the Chinese - balls held in dragon's mouths were connected to a vertical pendulum - shaking released balls - direction back to epicenter indicated by first ball released - just don't know time

big california eq general location

-it takes a large fault to have a M7 eq -mainly near SA fault --> a lot near Mendocino Triple junction (with Juan plate) ----> not as damaging --> some in the Sierra Nevada Mts. -smaller faults have magnitude 5-6 and have a wider distribution

Aleutian Islands 1946

-large (but not huge) quake, M7.4 - epicenter about 90 miles offshore -generated large tsunami felt across the pacific -one of the first earthquakes that raised concern, caused tsunami

overall lessons learned from these world eq

-large eq have large rupture area -eq can progress along faults -eq can occur in unexpected places (or are more damaging when they do) -exposed fault is not necessarily an indicator of size --> kern county, blind thrusts, jumping faults -density of ppl and building practices determine number of deaths, not just size -secondary effects can cause more deaths than the shaking (fires, tsunamis)

the lessons from the owens valley quake

-large eq off San Andreas -intensity and max slip comparable to SAF 1906 and 1857, but rupture much shorter -slip partitioning on the range front; --> extensional direction is oblique to fault direction --> down-dip slip and strike-slip split on separate fault planes near the surface

California seismicity recently

-last 150 yrs, 2-3 quakes of M8 -main fault is strike-slip: San Andreas -many secondary faults --> some offshore, most are farther east -san andreas fault slips ~3.5 cm/year, 5.4 cm between pacific plate and north america

where are fault zones?

-legal definition (Alquist-Priolo act): zone shall ordinarily be one-quarter mile or less in width, except in circumstances which may require the State Geologist to designate a wider zone -physical definition depends on how active and well-developed the fault is -->width of San Andreas fault zone ~1-2 km

distribution of sizes for aftershocks

-like for mainshocks, there are many more small aftershocks in a sequence than big aftershocks

size of aftershocks

-like for mainshocks, there are many more small aftershocks in a sequence than big aftershocks (Gutenberg-Richter) -if mainshock has M6, one may observe: --> 1 or 2 aftershocks with M between 5 and 6 --> 10's of M 4 to 5 - if a mainshock has M8, M7 aftershock is likely

reflection & refraction

-like light waves, seismic waves reflect and refract at interfaces -Snell's law applies in exactly the same way -interface means change in medium

soil liquefaction

-liquefaction: deformation of water-saturated soil during intense shaking allows water to flow upward and the soil loses its shear strength and flows, becoming liquefied into a kind of quicksand --> water pressure increases between sediments and so cohesion decreases & can no longer sustain the weight of the building -liquefaction potential in soft, sandy water-saturated soils (low-lying and flat) -buildings may tilt or sink into liquefied sediments, empty tanks may float -can cause a buoyancy effect of objects buried

a few things missing in the calculation to predict large earthquakes (slip in earthquakes = fault rate * time between earthquakes)

-little earthquakes take up some of the slip -some aseismic creep happens between earthquakes -earthquakes trigger each other to happen before they are "due" -the last event gives a very rough estimate of how active a boundary is -it is most useful as a warning

possible damage for steel frames

-localized yielding or buckling --> especially at welds -cracking of plaster, ceilings, facades -sometimes too flexible, if not enough steel was used (to cut costs)

P waves

-longitudinal: material moves back and forth (vibrates) in the same direction that wave travels, produces compression/dilation cycle -fastest type of wave, so arrives first (primary wave) -typical velocities in crust: 5-7 km/sec -travels through solids and fluids

proper plywood bracing

-lots of nails to attach plywood to structure -attach structure to foundation

oregon-washington

-main fault is subduction zone -M9 every 600-1000 years, last in 1700 -recent quakes --> M6.5 in 1965, 6.8 in 2001 in Seattle --> M7.1 in 1949 in Olympia -also volcanoes -denoted Cascadia subduction zone

design

-making a building plan that takes into account lateral forces (horizontal shaking) -can suffer from too much attention to aesthetics (i.e. stilts at Bunche)

how slow do rocks flow

-mantle rocks flow a few centimeters per year - it takes ~100 million of years to flow from the top to bottom of the mantle

recording the magnetic field

-many rocks, including basalt, have small amounts of magnetic materials in them -when such a rock solidifies from magma, the grains of magnetic materials align with the Earth's magnetic field -after the rock solidifies, the grains stay in their original orientation: they preserve the direction of the magnetic field at the time the rock formed --> geomagnetic reversal time scale

china discouraging predictions

-many unofficial eq warnings that brought factories and businesses to halt -new law approved by premier Zhu Rong-Ji --> requires high standard of scientific reasoning --> else predictors will be penalized

Magnitude

-measure of the earthquake size -determined from seismograms -determined by: -->taking the logartithm of the largest ground motion recorded during a particular seismic wave type --> applying a correction for distance from seismometer to the epicenter -several types of magnitude --> depends mainly on seismic wave type (P, S, or surface) -logarithms are used because earthquakes and resulting ground motion range over many orders of magnitude in size -correction for distance used because amplitude decreases with distance from the earthquake --> as energy spreads out over larger area --> seismometers are not always at the same distance from earthquake

mercalli scale from I to XII (12 levels)

-measures local shaking intensity from visible effects of quake -obtained from: --> the damage done to buildings --> .changes in Earth's surface --> felt reports -modified Mercalli intensity scale --> to account for modern construction -useful for historical earthquakes, described in old newspapers, personal accounts, etc.

seismic moment

-modern method for measuring magnitude -based on physical size of ruptured area, amount of slip, and rigidity of the rock determined from: -seismograms by special processing -observations of surface offset (slip) and fault length (surface rupture length or area covered by aftershocks) -most accurate

the Garlock fault

-mojave fault -the exception of left-lateral strike-slip, conjugate fault with San Andreas -causes one side to squeeze out because compressing and slip, one side is preventing it from going that way

intensity of the 1872 owens valley quake

-most devastating effects of this eq occurred at lone pine -the shock was felt over most of california and much of nevada -stopped clocks and awakened people

wave propagation & oil

-most energy is transmitted through the water and rocks -but a little is reflected back to make these images -oil people generally only use P waves --> s waves do not travel through water --> do not travel as well through rock, either

more on divergent boundaries

-most frequently manifested as mid-ocean ridges -less frequently manifested as rift valleys on land --> early stage of rifting, later become mid-ocean ridges after plates have spread far apart enough and a mature spreading center (the ocean) widens

does the water always go outward very far before a tsunami?

-no, this depends on the generation mechanism and the direction the wave goes out - in thrust fault generated tsunamis, the ocean on the hanging wall (landward side) comes in first, but on the footwall (ocean side), the sea will go out first -farther from the source, the waves can interfere with each other and you don't know whether it comes in or out first

limitations of intensity

-not a true measure of size because --> depends on distance from epicenter, and --> varies with building practices, and --> varies with rock or soil type that you are on -so an earthquake will shake different places with different intensities -so an earthquake will shake different places with different intensities -but maximum intensity experienced in a given earthquake correlates with that earthquake's size (magnitude) --> felt very close to epicenter

intensity of an earthquake

-observational assessment of damage -measures shaking at a spot

Mega-thrust eq

-occur on shallow dipping fault plane - rupture extends widely in the brittle crust -result in large rupture areas - a break that is during subduction zone can have large length and width; seismic zone is determined by fault zone size so large seismicity

geologic setting of North America

-old stable interior -east coast passive margin -west coast active margin -- pacific - N. Am. plate interactions --->transform motion at SAF --->subduction under Alaska & Aleutian ls. --Juan de Fuca - N. Am. interactions ---> subduction under Northern California, Oregon, Washington, and British Columbia

New Zealand

-on the boundary between the Pacific and Australian plates -each eq near Wairarapa raises the coast line, exposing more land above sea level -paleo-shorelines are evidence of past quakes

Milne-Shaw seismometer

-one of the first seismometers globally distributed in 1890s

transform boundaries

-one plate slides sideways past another plate --> no crust created or destroyed -can be ocean-ocean contact or continent-continent contact --> called strike-slip faults in continents (i.e. San Andreas) -least common boundary -shallow eq -no volcanoes

static displacement

-opposite of elastic rebound -doesn't rebound to what it was

the main plates on west coast california san andreas boundary & what time of boundary is san andreas mostly

-pacific plate & NA plates -mostly a transform boundary ( in the north becomes convergent & subduction)

is prediction impossible?

-perhaps there is no information about exact time, place, and size - perhaps eq are the result of a chaotic system - chaos is a common feature of complex systems in nature : a deterministic system that is extremely sensitive to initial conditions, making it impossible to predict ahead of time

quakes in Europe

-plate boundaries complicated --> the remnants of subducting African plate -Italy and Greece: --> damaging moderate quakes --> old buildings, high population density -Turkey like California --> big strike-slip quakes --> sequence in 1940s showed alarming series of events marching along Anatolian Fault

subduction zones

-plates move toward each other -where crust is destroyed -numerous and large earthquakes within the plates -eq occur from surface of 700 km --> they outline sinking lithospheric slab --> the dipping seismic zone is called the Benioff zone -almost always form volcanoes, the oceanic plate sinking into mantle melts mantle rocks due to interaction with water --> causes rising magma for volcano -M8 or M9 eq

eq fatalities and population growth

-post 1800 medicine and sanitation result in large increase in population -increasingly people live in large urban centers. many of them are on plate boundaries --> this causes more fatalities

longer-rage time dependent forecasting

-predict continuation of a sequence -calculate how the stress from one eq changes probability of another

friction increases with depth

-pressure on the fault plane increases with depth, increasing the friction -more strain can be accumulated before slip -so, deep quakes can release a lot more energy than shallow ones

Harry Hess

-proposed the idea of the seafloor spreading - 1945: Hess measured the oceans bottom topography - 1953: discovery of volcanic valleys running along the mid-ocean ridges (Great Global Rift) - 1960: seafloor spreading proposal -magma rises up through vents in the Rift -it cools at the surface

lateral bracing

-purpose is not to increase vertical load building's walls and columns can bear, but to maintain vertical supports to remain stable & intact --> supporting weight of building during lateral shaking, increasing the shear resistance of the walls

rayleigh waves and lone waves type of elasticity

-rayleigh waves appears like an ellipse because particles are moving up and down and threes a back and forth movement "like an ocean" -love waves appear transverse (S-like) "like a snake"

seismic networks

-regional short-period networks --> 50-400 instruments, vertical component only --> emphasis on eq detection & location -regional broadband networks --> fewer instruments (10-100) --> emphasis on understanding bigger quakes -global networks --> global detection and Earth interior studies --> run by many countries (USA, France, Japan, plus stations in regional nets)

right or left lateral

-right-lateral: if you are sitting on one side, you see the other side moving to the right -left-lateral: if you are sitting on one side, you see the other side moving to the left

the mechanics behind fault break

-rupture begins at hypocenter (focus) --> place on fault where stress has exceeded strength (friction) - crack spreads outward over planar fault surface from focus --> cracks propagate at about 3 km/sec -larger broken area implies larger magnitude and longer duration of rupture

lessons from the 1906 eq

-secondary effects can be more devastating and costly than primary effects - a comparison of this shock to the Fort Tejon eq, which occurred on the San Andreas fault in 1857, shows that the fault break in 1906 was longer but that the maximum and average displacements in 1857 were larger

lower hemisphere projection

-see figure four -in 3 dimensions, the source radiates waves in all directions - a method for projecting half a sphere on a plane -planes cutting through the sphere plot as lines

extensional deformation

-seen in divergent boundaries 1. horizontal extension 2. vertical thinning -exhibited in normal faults - the faults on divergent boundaries (the foot wall is above the hanging wall) --> oblique fault plate --> accomodates extension and divergent movement --> produces shallow earthquakes -valleys bounded by normal faults

using seismic waves to image the inside of the earth

-seismic waves travel through the entire earth - we can analyze the time they take to travel to different points on the surface (our seismometers) to determine the velocity along raypath -faster and slower paths tell us about what kind of material the waves pass through and about the physical state (warm/cold, mineral structure, solid/liquid)

aftershocks tell us about mainshock

-seismologists estimate the area of rupture by mapping aftershock locations --aftershocks cover the rupture area and expand slightly outside of it ---> obtainn length and width of faulted area = magnitude of mainshock --> obtain orientation of faulted area (can help determine fault plane direction in focal mechanism)

modern portable seismic station

-seismometers are buried under the ground --> to rid of surface noise -batteries are often charged using solar panels -data are collected on a computer and transmitted to data center via satellite

how to measure chain?

-separate equation for each observation (8 eq) - each measure votes for or against prediction --> at least 8 (unknown) thresholds -add the votes and find (another) threshold to determine if intermediate-term pattern is there - if threshold is too high, you miss some quakes, if too low, generate false alarms

2004 parkfield eq

-sept 28, Mw6 -fulfilled some, but not all elements of the original 1985 eq forecast for Parkfield -rupture same section of SAF -similar magnitude -but unlike before, propagated from south to north & did not have a M5 foreshock

S waves

-shearing (transverse): material moves back and forth perpendicular to the direction the wave travels -slower than P wave, arrives second --> called secondary wave -typical velocities in crust: 3-5 km/sec -travels through solids, but not fluids --> because there is no restoring force for the perpendicular motions (gravity instead of elastic)

intensity map

-shows contours of areas with a similar level of damage on the modified mercalli scale --> depends on soil and population -estimated from measurements at 10 to 100's of locations -mainly comes from places with buildings -not a direct measurement of ground motion -intensity maps are still being made --> no longer used much --> mainly useful for: ----comparing historical eq w/ current one ----damage assessment and anticipation of future events

number of times in 100 years shaking will exceed 20% gravity

-significant damage to older buildings begins at .2 g - ~3 times/100 yrs in LA

Cascadia (WA & OR)

-small section of plate that is a subduction zone -small plate convergence ~5-9 mm/yr (varies along arc) -few large historic earthquakes -motivated research on the geologic record --> exceptionally low seismicity for a subduction zone is explained by low convergence rate and that it is near its origin so very young & malleable

more on aftershocks

-smaller eq following the largest eq of a sequence (the mainshock) near mainshock rupture zone -- follow almost all shallow eq -- cover ruptured area -- can number in thousands -- can last for years or decades -- almost always occur

more on foreshock

-smaller eq that precede the mainshock (by a few days or just hours) - not always there --> half of mainshocks in Western US have foreshocks -near mainshock hypocenter --> part of the nucleation process

recording systems

-smoked paper rotating drums -ink and paper rotating drums -photographic film rotating drums -analog tape -digital tape -hard drive (magnetic or optical)

problems with concrete shear wall

-soft stores still pose hazard -walls distributed around only two or three sides --> vulnerable to strong twisting forces, esp. if irregularly shaped building

SCIGN

-southern california integrated geodetic Network -has about 250 stations across southern california -mainly to watch --> displacement produced by earthquakes --> continuous deformation between earthquakes -accuracy is better than 5 mm both laterally and vertically

real risk from quakes

-standard unit of risk --> 1 in a million chance of death in a year --> equivalent to, on average, each person losing 30 min of life expectancy

the future: active buildings

-start with steel frame -use seismometer to either: --> actively control inertial mass --> change stiffness in response to motions -could theoretically tolerate any eq

skyscrapers

-steel frames -special problems: --> most buildings are damaged by short-period (high frequency) seismic waves --> high-rises can resonate and be damaged by long-period motion -computer models help design tall structures

strapping water heater to wall

-straps should be metal and firmly anchored into studs or masonry walls -there should be at least two -gas and water line connectors should be flexible hoses

what affects seismic waves velocity?

-strength of the material. weaker is slower. generally speaking --> high pressure makes rocks stronger --> high temperature makes them weaker -density of the material, density is slower -the kind of wave -if we study the propagation of the waves in the Earth, we can have information about the medium theough which they travel

stress: too hard to measure in nature

-stress is what we want to know to predict displacement -useful answers we would like to know: --> how much stress does it take to break rock? --> is there enough stress in the ground for another big earthquake? -we measure strain (deformation) instead --> strain can be measured by measuring surface movement

soft ground shaking

-stronger shaking on: --> soft soil (young alluviums, sand dunes) --> landfill --> waterside sites -seismic waves grow in amplitude when they pass form rock into softer material

the mechanics behind ground shaking affecting buildings

-structural elements designed to support weight of buildings, furnishings, occupants -therefore, vertical forces of eq are usually resisted effectively by buildings -conventional building are not designed to resist horizontal forces (ground shaking)

active seismology

-structure of Earth at shallow depth -controlled source of seismic waves is used to send waves down into the ground -a line of seismometers picks up the reflected and refracted signals -the time of the arrival tells you where the reflectors are (like echolocation or ultrasound) -->and tells you the velocities of the layers --> certain layers are useful (i.e. mineral or oil deposits)

lessons from the Sylmar earthquake

-structures are damaged not only by how hard you shake, but also by how long (fatigue of structures) -earth filled dams are subject to liquefaction and collapse (mountains behind LA are full of them) - alquist-priollo act

island arcs

-subduction zones are shaped as arcs -above sea level

ghost forest

-subsidence of land causes salt water to fill (and kill) forest - alaska and washington coast

facts on timing for tectonic plates and mantle convection

-tectonic plates move 0 to 20 cm/year -this is about 25 miles per million years -the mantle is moving at similar velocities -it takes about 100 million years for the mantle to overturn -the outer core is a liquid, and it is also convecting, but much faster --> creates the Earth's magnetic field

section of the San Andreas Fault that is creeping

-the Hayward fault

lessons from Landers eq: jumping faults

-the Landers eq broke 3 separate faults in a single rupture -like aftershocks, but faster. no time lag between them - not previously thought possible

example of transform boundary zone

-the Pacific-North America boundary (San Andreas fault)

global seismographic network and testing loyalty to nuclear test ban treaty

-the amplitude of the seismic waves tells us how big the explosive source was -nuclear explosions involve a tremendous amount of energy liberated from a small volume, so it effectively goes off instantaneously -conventional explosions are chemical reactions and liberate energy more slowly b/c more matter -by looking at the by looking at the waveforms, seismologists can try to distinguish between the more sudden nuclear signature and the more slowly building conventional signature

differences in movement in the ductile layer and brittle layers of crust

-the ductile layer moves slowly over time, the brittle layer releases strain in bursts and moves abruptly - how often this strain is released / how long it builds up is variable but the longer it builds up the more energy that is released

soft soil mechanics

-the energy carried in a wave is: wave velocity * density * amplitude^2 -therefore, if a wave travels from solid rock into softer, lower velocity soils, wave velocity and density decrease - conservation of energy implies that amplitude of shaking must increase in soft ground

the 2004 tsunami from sumatra

-the eq spawned a huge tsunami that swept toward Indonesia and Thailand in one direction and toward India, Sri Lanka, and Africa in the other -250K to 300K killed, some as far away as Somalia -no warning system set up in the Indian ocean like the Pacific -scientists in the US knew the tsunami was a probability within minutes although magnitude was not correctly estimated -they had no way to get the news to the shoreline communities

recurrence, size, and slip velocity

-the faster a fault slips, the more often it must have eq, or the bigger the quakes must be, or both (b/c the faster the stress is accumulated) - we can estimate a maximum eq size from the length and depth of a fault

stress

-the force per unit area (pressure) --> i.e. walking on fresh snow distributes force

how large can earthquakes get?

-the largest well-recorded earthquake occurred in Chile in 1960 had Mw = 9.5 -we have only been recording for about 80 years so even larger earthquakes may have occurred in the past -upper limit controlled by area of plate boundary likely to break at once -the whole Earth breaking in half: Mw = 12-13

how small can earthquakes get?

-the magnitude scale has no intrinsic upper or lower limit but physics has bounds - earthquakes with magnitude as small as -2 have been recorded by very sensitive seismometers -log(.01) : -2 --> released energy equivalent to that produced when a brick is dropped from a table to the ground --> fault size of about 1 m x 1 m

geodesy

-the measure of the Earth's shape -conventional techniques rely on the measure of angles and then seeing how much displaced from earthquake

elastic rebound and old and new roads

-the old road recovers its shape on each side of fault (elastic rebound), the new road is bent (co-seismic strain)

definition of seismic moment

M0 = mew * D * S where: - mew = the rigidity of the rock (measures elastic stiffness) - D is the amount of displacement (offset) between the two sides of the fault - S is the surface area that ruptured - units are force * length --> newton-meters, dyne-cm -varies over many orders of magnitude

sandpiles and critical states

-the slope of the dry sandpile steepens until it reaches a critical state (angle of repose of sand) - adding a grain of sand to a steep sandpile can cause any size landslide -if the earth's crust is always in a critical state of stress, there is no way to predict if the next eq will be small or large -grains in critical state: almost ready to go but held by friction: any perturbation of the system can trigger

paleoseismology

-the study of geological indicators of ancient eq -can go back several thousands of years -probably the best way to understand the "seismic behavior" of a fault system

pull-apart basin

-the transform fault has an offset which causes a pull-apart basin (with normal faulting) -this results in normal faulting around basin - i.e. dead sea

Wilson Cycle

-theory: continents collide, insulate mantle underneath, then separate as mantle gets hot and upwells

plate facts

-there are 10 to 15 major plates -the US is split, mostly on the North American Plate, but a western sliver on the Pacific Plate -the boundaries between plates are faults --> but faults are not all plate boundaries - major earthquakes are essentially caused by the moving plates rubbing together

the 3 kinds of elastic waves

-there are two directions associated with waves: the direction the wave travels (raypath) and the direction in which the material is displaced (particles always vibrate up & down) -three kinds of waves (but two of them are basically the same) 1. longitudinal waves: material is displaced along the ray path (particle motion is parallel to wave direction) 2. transverse horizontal waves: material is displaced perpendicular to ray path and parallel to surface 3. transverse vertical waves: material is displaced perpendicular to ray path and perpendicular to surface - the 3 kinds of waves can interact at a free surface to create other types of motion

utility of dead/damaged trees for dating earthquakes

-they can be used because their rings signify time

why did 61 ppl die in Hawaii even though they were forewarned?

-though given about 5 hrs warning, the prediction that the wave would arrive at midnight was off by an hour -curiosity and complacency lured ppl back to the shore -the prediction was off because the depth of the ocean was poorly known in the south Pacific

US and mexico coast

-three little plates: explorer, juan de fuca, gorda -san andreas fault -spreading range -cocos plate -in mexico extensional (divergent)

shear-wall bracing

-ties together, stiffens, and strengthens vertical frame, limits lateral deformations, transfers eq forces back to foundation --> wood-frame buildings benefit greatly from plywood sheathing --> shear walls of large buildings made of steel-reinforced concrete

to make an eq prediction, you need to state

-time interval in which quake will occur -region in which quake will occur -magnitude range of predicted quake -->small quakes more common

criticisms of Keilis-Borok's method

-training set is small (many fake alarms) - many parameters -transparency : hard to figure out method and data used

more on surface waves

-travel on surface of earth, at the interface of solid rock and air --> motion is strongest near the surface --> most strongly generated by shallow (near the surface) earthquakes -travel a bit slower than S waves -are the largest amplitude waves --> so the P wave can serve as a warning to take cover or shut down critical facilities --> warning ranges from a few to 100 seconds - the most destructive waves of earthquakes

lessons from 1812

-trees can be a good source of information when historical records are scant -large eq can cause damage at gr8 distances from the fault -damaging eq are common in southern California

lessons learned from the 1946 Aleutian Islands eq & tsunami

-tsunamis can go a long way and do a lot of damage -in deep water, they travel as fast as a get (800 km/hr), but a phone call is faster -foundation of the pacific tsunami warning center in HIlo

normal fault (divergence) trace

-typically steep dip-angle fault plane -perched terraces --> like near thrust fault traces -alluvial fans --> can be very large, as in Death Valley -often large, clean fault surfaces (almost the same as thrust faults except for angle of fault plane)

adjectives for different magnitudes

-under M5 = small -M5 - M6 = moderate - M6 to M7 = large -M7 to M7.8 = major -M7.8 or above = great

basics to measure how the Earth is moving

-use an inertial mass that is isolated from movement below

sounding the earth at shallow depth oil exploration

-use artificial source of seismic waves -mapping the upper frew km of the crust -looks almost entirely at sedimentary rock --> relatively young, not fully cooked rocks --> starts out in layers (sand, silt, pebbles) -oil and gas seep upwards --> from buried, rotting and cooked organic material - gets trapped in pools in structures like faults and warped layers

modern method for locating eq

-use many stations to correct for local speed variations. simultaneously solve for location, time (and sometime seismic wave velocity) --> use 50-200 arrival times from short-period regional network seismometers --> location (time, lat, lon, and depth: 4 numbers) requires observation of at least 4 P wave times

deep sounding of the Earth

-use natural sources: eq -waves do not travel along straight lines inside the Earth because velocities vary with depth -surface waves, P, S, & PP paths --> PP path is the P wave reflecting off the surface

p and s waves and distance to eq

-use property that P and S waves travel at different speeds -the farther they travel, the greater the separation in time and distance

concrete-frame commercial buildings

-uses concrete beams and columns in same manner steel beams are used on steel frame buildings --> but more brittle and much heavier - second most dangerous structure - designing adequate connections for these heavier building elements far more difficult - cypress freeway in Oakland has this type of construction; many collapsed in Mexico city in 1985 M8 quake

oblique faulting

-usually faults do not exhibit one pure movement -it is common to have some combination of fault movements occurring together -here, normal and strike-slip

refraction & curved ray paths

-velocity of body waves increases with depth in mantle -wave ray paths are curved upward by refraction -waves are also reflected and refracted at interfaces between layers with different properties --> shallow layers in the crust --> in mantle --> core/mantle boundary

meaning of compression/dilation in terms of p-waves

-vertical ground motion of first P-waves arrival is either Up or Down - compression : up / pull - dilation : down / push

seismic waves

-vibrations of the ground -elastic waves propagating inside the Earth and along its surface

mars seismology

-viking 1 and 11 in July and September, 1976 --> showed that Mars has a very low background seismicity --> seismometers essentially recorded wind noise, providing information about wind velocity -ESA ExoMars mission to Mars, scheduled for launch in 2018 will carry seismometers -NASA InSight mission to be launched on May 5th 2018 will carry a 3-component seismometer and a thermal probe

once shaking stops

-walk slowly outdoors, beware of broken glass -stay in open areas, away from building --> parts may fall during aftershocks -only re-enter safe buildings -if in a car: --> stop in an open area --> stay in car for a while, let emergency vehicles get where they need to go -->proceed slowly & cautiously: road may be damaged or hazardous -check for gas lines, electric lines, then water lines -try to minimize phone use, aftershocks are certain & may be dangerous, landslides and tsunamis may be possible

concrete tilt-up commercial buildings

-walls are concrete slabs poured horizontally then tilted up - low cost, fast to build --> often used for warehouses and other light industrial buildings

1946 tsunami

-washed over a 42 m cliff at Scotch Cap, destroying the lighthouse and killing the crew -About 5 hrs after the eq, the tsunami reached the Hawaiian Islands --> without any warnings, killed 164 ppl in Hawaii - wave height was 18 m at Hilo

uses of seismic networks

-watching earthquakes --> mostly long-term, fundamental research --> monitoring regional earthquake hazards --> improve seismic assessment -watching for nuclear weapons tests --> are treaties being violated? are unknown groups testing weapons? --> detection of explosions --> discrimination of explosions from earthquakes --> estimating yield of explosions

tuning the seismometer

-we need a seismometer that is sensitive at seismic frequencies (a few Hz). it is most sensitive at its natural frequency which is given by the square root of k (stiffness)/ m (mass) -we adjust the mass, m, and the spring constant k, until the natural frequency of the seismometer is near the frequencies of seismic waves -we use a damping device that stops the oscillation after a few swings

materials

-wood and steel preferred over concrete and brick because --> light, which lessens weight that walls must support and has less inertia --> flexible, so it can deflect without cracking or breaking to sustain deformation --> too much flexibility is a disadvantage, making bracing necessary (if heavy, inertia of heavy part makes it lag behind the horizontal & can shear the structure)

age distribution on the seafloor

-youngest age is at the ridge where much of the new land is formed

when did humans emerge from the apes

1 - 4 million years ago

main method of testing plate tectonic predictions (velocity)

1 Global positioning system (GPS) that can measure ground motion with mm accuracy, therefore plate velocities (mm/year) -to get velocity have to come back later and get new position coordinates from benchmark position, obtain a displacement vector: how much was displaced -the benchmark has a GPS antenna in the center of it -the GPS signal is broadcasted by satellites -velocities (mm/year) measured by GPS compared to the geological velocities from plate model reconstructions

list some of the worldwide quakes

1. Aleutian Islands 1946 & alaska 1964 (2nd biggest): tsunamis 2. chile 1960 - biggest eq instrumentally recorded 3. japan 1923 (kanto), 1995 (kobe), 2011 (Tohoku) 4. sumatra 2004 (3rd biggest): tsunami 5. India/Tibet 6. Central and Eastern China - deadliest eq in 1556 Shaanxi - 1975 Haicheng and 1976 Tangshan: prediction success and failure 7. European quakes (turkey) - propagating sequence along North Anatolian fault

main types of damage to a tree during earthquakes

1. beheading : the top is cut off 2. cutting roots 3. indirectly, if water table is displaced and one tree drowns while another dries 4. other ways: landslides, tsunamis, liquefaction, hydrological changes

types of seismic waves

1. body waves -travel inside the earth 2. surface waves -travel along the surface of the Earth

what waves are body waves and what waves are surface waves

1. body waves -P (primary) waves -S (secondary) waves 2. surface waves -love -rayleigh

scientific method general steps

1. careful observations 2. hypothesis building 3. tests of the competing hypotheses 4. refine or abandon and rebuild

fixes for: hanging pictures, tall furniture, cabinets

1. closed hook 2. anchor 3. latches

modes of action for eq preparedness

1. consider the safe and dangerous places in your home 2. consider how to get to exits 3. adequate supplies, located in a secure spot 4. have a plan! 5. learn how to shut off utilities -gas : wrench -fuse box: switch -water gate valve

facts on the 3 types of subduction

1. continent over ocean --> explosive volcanism 2. ocean (older, colder & heavier) over ocean --> explosive volcanism 3. continent - continent --> collision -leading to high mountain building because continental crust does not subduct -continental crust floats because it is lighter than mantle rocks

sumatra famous earthquake

1. creates a tsunami 2. december 26, 2004 3. magnitude 9.3 4. 250K to 300K killed, some as far away as Somalia

types of lateral bracing

1. diagonal bracing: a single diagonal or two crossed diagonals (x-bracing) of steel attached at angle across frame of building 2. shear-wall: solid, continuous walls of plywood or concrete

3 types of plate boundaries and facts about each

1. divergent -plates move away from each other -mantle material rises to fill the space between the separating plates --> creation of new plate 2. convergent - plates move toward each other -one plate subducts into the mantle while the other remains on top --> plate destruction 3. transform -plates rub against each other -both plates stay on surface and move side-by-side past each other --> neither formation nor destruction

three reasons why earthquakes are interesting

1. expensive 2. not uniform in space and time 3. a basic scientific problem

complications with the act defining "official" fault lines

1. faults can splay (split near the surface) 2. gouge zones (if there are tens of thousands of eq then the fault gets convoluted)

measuring earthquakes general

1. felt reports - intensity -not precise, but best data for historical earthquakes 2. seismologic measurements 3. mapping of rupture zone -if surface break exists and is accessible -fault displacement from past events 4. geodetic measurements of ground shift (GPS, InSAR)

two strategies for predicting an eq

1. find a specific precursor (short-term prediction) -water level changes, electromagnetic field, wave velocities, foreshocks etc. -need a physical mechanism in order to prove connection between precursor and event and generalize 2. forecast a general pattern -statistical distribution of quakes in space and time

earthquake location methodology

1. find p-s time difference at a station 2. convert to distance 3. draw a circle centered around station with radius given by step 2 4. do steps 1-3 for 2 more stations 5. quake lies at intersection - triangulation

Shear deformation

1. horizontal shear 2. extension/contraction directions rotate -constitutes the faults at transform boundary -also called strike-slip faults -usually vertical or nearly vertical -generally do not create topography because slip vector on fault is parallel to surface

intensity vs. magnitude Mw (moment magnitude)

1. intensity is based on damage -has one value for each neighborhood for each earthquake, so range of intensities for each quake -can be used for historical earthquakes 2. magnitude is based on source -has one value for each earthquake -informs us about the slip and area

how tsunamis are formed

1. interseismic elastic deformation, where the oceanic plate is subducting under continental plate 2. eq releases strain in over-riding plate, rebounding the continental plate 3. this elastic rebound causes the tsunami - tsunami wave formation and propagation

northridge famous earthquake

1. january 17, 1994 at 4:31 AM 2. 50 deaths 3. $20-40 billion in losses

example of soft soils

1. landfills -often poorly compacted material -organic material often decays producing voids and weak spots prone to settlement -expect: --> strong shaking in eq --> ground can settle substantially 2. riverbanks and waterside sites -often thick layers of soft, silty clay with a lot of water -many downtowns are on riverbanks -riverbank towns often have old buildings

types of magnitude

1. local or richter magnitude --> original magnitude, developed in the 1930s --> used S wave recorded within 300 km of epicenter 2. body-wave magnitude (Mb) --> uses P wave recorded at 30 degrees to 90 degree distance 3. surface wave magnitude --> uses surface waves for large distance 4. moment magnitude (Mw) --> determined differently, using seismic moment --> currently the most common

two statistical laws

1. magnitude statistical distribution : Gutenberg-Richter 2. rate of occurrence of aftershocks : omori

the 3 basic considerations in building for quakes

1. materials 2. design 3. quality of execution

facts on the two types of crust

1. oceanic -thin (~8 km) -basaltic (low SiO2 contnet) 2. continents - thick (~30 km) -granitic (high SiO2 content) -less dense than basalt -float on mantle (like icebergs on water)

conversions of seismic waves

1. p waves and s waves can partially convert to each other when they encounter a sharp change in seismic velocity (as occur between rock layers) -usually just a small percent of total energy of the wave 2. the seismic waves quickly get very complicated

ingredients for forecasting

1. past history 2. fault map 3. current seismic activity 4. geodesy and other geophysical indicators 5. physics (rock mechanics)

example of continental plate over oceanic plate and of oceanic plate over oceanic plate

1. peru-Chile trench causing The Andes 2. Western Pacific arcs

forecast versus prediction

1. prediction = specific statements about when, where, and how big - usually based on short-term (weeks - month) precursory phenomena 2. forecast = general statement about likelihood of eq - based on probabilistic estimates -combines historical seismicity, paleoseismicity, geodesy, rock mechanics, modeling - used for long-term (~decades)

3 complications for seismic waves as traveling inside the earth

1. reflection 2. refraction 3. conversion

Northern California Faults

1. san andreas -runs through point arena, point reyes, san francisco, san jose, watsonville 2. east bay faults - calaveras-hayward-rodger's creek -some farther east 3. offshore faults?

sylmar california famous earthquake

1. san fernando valley near Sylmar, California 2. 6 AM PST 3. February 9, 1971 with a magnitude of 6.6

san francisco famous earthquake

1. san francisco 2. april 18, 1906 3. 5:12 AM 4. ground break was 477 km long (296 miles)

define: sequence, foreshock, mainshock, aftershock and some corollaries :)

1. sequence: set of quakes that appear related in space and time 2. foreshock: quake followed by a bigger quake in same sequence 3. mainshock: biggest quake in a sequence 4. aftershock: quake after the biggest quake in a sequence - corollaries: one never knows that an event is a foreshock until the mainshock comes along ; aftershocks can turn into foreshocks

mathematical conditions for slip considering slip equation

1. shear stress (tau) < cohesion (C) + mew (friction coefficient) * normal stress (on) --> fault does not slip 2. tau = C + mew* on --> fault slips

single block versus multiple blocks

1. single block: - a single slider block is quasi periodic - sticks until stress overcomes friction, then slip - slip events are similar in magnitude and occur sort of regularly 2. multiple blocks -when blocks begin to interact, the system rapidly becomes complex. even a few blocks results in unpredictable behavior -faults in the Earth act like systems with many, many interacting blocks

order of the earth layers from inner to outer

1. solid inner core 2. liquid outer core 3. mantle 4. crust

abbreviated Mercalli intensity

1. some ppl feel it 2. felt only by a few ppl on upper floors 3. felt quite noticeably indoors 4. felt indoors by many, outdoor by few 5. felt by nearly everyone, many awakened 6. felt by all, many frightened. damage slight 7. damage negligible in buildings of good design; considerable damage in poorly built buildings 8. damage slight in specially designed structures; damage great in poorly built, heavy furniture overturned 9. damage considerable in well built buildings, buildings shifted off foundations 10. well-built wooden structures destroyed 11. few, if any masonry structures remain standing 12. damage total, lines of sight and level are distorted

maximum size of quakes for different zones

1. subduction zones -some bigger than M9 --1960 Chile 9.5 ; 1964 Alaska 9.2 ; 2005 sumatra M9.1 --> larger fault area within cold crust (fault plane has small dip) 2. transform and ridge quakes -biggest quakes seen are M8 --> SF 1906 was M7.9 --> one of the sumatra 2012 was M8.6

why don't quakes extend deeper?

1. temperature : increases with depth 2. pressure : increase makes variations in composition and changes in crystal structure -if material is within a few hundred degrees of its melting temperature, it quietly flows rather than storing elastic strain and suddenly cracking in an eq

thrust fault (convergence) trace

1. topographically irregular scarp -in contrast, strike-slip has straight trace 2. low dip-angle fault plane 3. perched terraces -formed during previous interseismic intervals 4. deeply incised canyons -from rapid uplift

Tohoku famous earthquake

1. tsunami 2. march 11, 2011 3. largest event recorded in Japan 4. magnitude 9 5. 16K killed

less easy-to-fix home hazards

1. water heater -heavy, hooked up to gas & water lines -strapping to the structure is now mandatory 2. plaster -can be shaken loose -sometimes heavy in old houses 3. air conditioners -load on walls, can fall 4. antennas, can damage roof 5. free-standing walls can topple

define wavelength, period, & frequency

1. wavelength: length of a cycle, or distance between two peaks on the curve 2. period: time it takes for the wave to advance by one cycle 3. frequency: number of cycles per second (1/T)

Moment magnitude

Mw = 2/3(log M0) - 6.0 where M0 is the seismic moment in Newton-meters -replaces other magnitude scales, such as richter magnitude or surface wave magnitude -provides a consistent measure of size of earthquakes from the smallest micro-earthquakes to the greatest earthquakes ever recorded

Omori's Law: mathematical expression

N = N0 / (1 + kt) where: - t is time after main shock - N is the number of earthquakes in time interval centered on time t - N0 and k are constants

P wave shadow zone

P waves are refracted at velocity interface (mantle/core boundary) -zone where no P-wave is received -from line tangent and line that is refracted through the core due to the faster velocity of the core

types of construction and eq resistance for different structures

(from best to worst) 1. residential structures -wood frame -reinforced concrete blocks, bricks -unreinforced brick, stone or adobe 2. commercial buildings -steel frame -reinforced concrete shear wall, concrete tilt-up -unreinforced masonry

how bracing reduces lateral shear

(mostly for diagonal bracing) -without bracing, a square's diagonals change in length --> therefore, attach diagonals for bracing, resulting in less damage to building structure and contents -stiffens structure, provides a more direct diagonal path for the transfer of the inertial weight of the structure to the foundation --> wood diagonal bracing usually not adequate for houses, instead plywood shear wall recommended

post-dictions

(observational study) -retrospective predictions --> after an eq happens, look for strange signals before it -a VERY dangerous practice --> there is always something strange happening -might be the only way to learn --> seismology is an observational science

parkfield eq sequence

SAF creeps to the north and breaks in quakes to the south -parkfield is at the transition -breaks occur at predictable intervals

tectonic plate movement speed

a few millimeters per year - a few meters per thousand years - a few kilometers per million years

soft story

a floor (usually at ground level) with many large openings -large openings reduce shear strength of walls --> openings include garage, windows, doors -greater damage often occurs at soft story in both residential and commercial buildings

seismic moment in comparison to magnitude

a more physical way of describing the source of an earthquake

wood-frame with masonry veneer

a relatively thin layer of stone, brick, or adobe attached after wood framing -problems: --> can be heavy (stones) --> greater inertia forces --> insurances often do not cover such buildings

what is a wave?

a wave is a disturbance that travels far through a medium while particles of the medium move a small amount back and forth and do not experience a net translation - a source is needed to create the disturbance - waves propagate away from the source in all directions

define: a. focus ; b. hypocenter ; c. epicenter ; d. rupture ; e. surface rupture ; f. seismic waves

a. focus - point where the rupture started b. hypocenter- location and time of quake beginning (same as focus) c. epicenter - surface projection of hypocenter d. rupture - the breaking of the rocks and sliding of one side of the fault against the other side, the result of the process e. surface rupture - the trace of the fault which broke at the surface (morphology) f. seismic waves - vibrations of the rocks inside and at the surface of the earth

brittle

abrupt rupture when stressed -earthquakes break rocks -due to brittle nature of crust --> shallow aprt of crust

extra reinforcement around windows

additional bars around wall openings

aftershocks and dipping plane

aftershocks often align on dipping plane which can be observed in a cross section

USA seismicity

all the action is in the West -most dramatic topography in the West -few eq in the east some faults as far east as Yellowstone no action to west in Pacific plate either -Hawaii is special case- hotspot volcano

focal depth

depth of focus or hypocenter

jumping faults

earthquake jumps from one fault to the next along a fault formed of individual segments that are sufficiently close --> increase magnitude of event -like aftershocks, but no time lag between them

swarms

earthquake swarm is a sequence of earthquakes with no clear mainshock-aftershock relationship -no clear relationship of rate and magnitude over time -need a driving mechanism to maintain conditions: -- most common in volcanic areas -- one of the best ways to predict eruptions ----> but many false alarms

quasars

emit radiowaves 2 different sources, reconstruct your position

strike-slip fault focal mechanism

even quadrants of compression/dilation in focal mechanism

during quake

if you are inside: -get under table or secure piece of furniture --> if you are in bed, stay in bed, protect your head --> avoid swinging doors -watch out for --> heavy furniture, swinging lights, falling plaster -avoid big windows and chimneys -do not rush outdoors or into stairwells -if you are outside, stay away from the sides of buildings -if you are in a car, stop in an open area away from overpasses or bridges & stay in the car

lithosphere

includes crust and upper mantle

how did the pacific plate get so close to us?

it has been subducting beneath the north American plate, bringing the boundary closer to us - accreted pieces of crust due to vocanoes not subducting

San Andreas Fault in Carrizo Plain

locked and capable of very large earthquakes -Parkfield, CA is a small town that marks the transition between locking and creeping -above parkfield, right-lateral slip

where does convection occur in the earth

mantle -rocks flow -heat drives them

"stress shadow"

model of stress change -eq was so large, it shut off the seismicity in the area for almost a century - blue showed where stress was released - in turkey, very large events propagate to the west, african plate is pushing the antolian plate upwards

rule of thumbs for magnitude and amplitude, length/duration & energy

on average, a magnitude M+1 earthquake compared to a magnitude M has: - 10 times greater peak amplitude of shaking - 3.3 times longer length of fault and duration of slip - 33 times greater energy in the waves and moment release

seismologist

one who studies earthquakes

how to characterize a chain?

over 6-24 months before event - rate of eq - area of fault - change in rate --> number of eq --> magnitudes of eq -change in spacial distribution : clustering --> mainshocks & aftershocks -maximum distance between eq -relative number of big and little eq

Gutenberg-Richter's Law

relation between: -magnitude M and number of quakes N with magnitude greater than M mathematically: - Log(N) = a*-b*M -typically the b value (or slope) is about 1 -this means that there are 10 times more quakes with magnitude greater than M-1 than M

note to self gurl!

review the recap quizzes for wk 7. tuesday this info was difficult

part 1 of holmes hypothesis

rocks flow: -under high pressure and temperature, rocks flow slowly, over millions of years -when pulled slowly, rocks flow; when pulled quickly, rocks break

see figure 2 & 3

shows thrust fault and normal fault focal mechanism -thrust fault results in compression in the center of the focal mechanism (where black is) -normal fault results in compression on the outer edges of the focal mechanism (black compression on the outsides)

aftershocks

smaller earthquakes following the largest earthquake of a sequence (the mainshock) near mainshock rupture zone - follow almost all shallow earthquakes - cover ruptured area - can number in thousands - can last for years or decades --aftershocks of Northridge M6.7 are still occurring -the most predictable (and therefore well-studied) earthquakes

ductile

smooth motion in space & time -below the brittle surface, flows around the fault rather than maintaining the fault -large-scale plate motions are smooth -due to ductile flow in ductile mantle underneath

hard to reinforce URM buildings because

strengthening them is inhibited by: -high retrofit costs -historical preservation -budge cutting -lack of concern

elastic force

with little pressure wants to recover shape so rebounds

wasatch fault zone

zone of normal faulting from Arizona and Nevada to Montana -locking north from the mouth of Rock Canyon the abrupt mountain front illustrates the active extensional fault system

parkfield forward predictions

~ 22 yr repeat time -historical data could be bad: intensity in central California sparse in 19th century -data could be good, but random: --> not hard to find spurious patterns in short series

interpreting seismic velocities

~ sqrt. of elastic stiffness divided by density - velocity inc. with depth and so does density --> therefore velocity is dominated by stiffness -stiffness controlled by: --> temperature --> composition --> water content --> crystal structure

moment of an earthquake

-measures source size

explanation for plate divergence in baja california

-plate boundary is not straight which caused extension in baja california and riveria plate but mostly transform

overpass retrofit

-reinforce pillars and attach horizontal slabs to pillars - horizontal slabs are usually on a horizontal platform to give the structure a bit of flexibility

strike-slip fault trace

-repeated slip events on fault gradually offset surface features (river, terrace etc.) -old features are offset more than young features -average fault slip rate = offset / age of feature -terraces can be formed by rivers dropping off sediment

Queen Charlotte Fault System

-right-lateral strike slip -along the coast of Canada, there is much seismicity, there is a strike slip fault however

the rupture process and seismic waves

-rock breaks and one side slides against the other side -elastic energy released by cracking and sliding rocks sets vibrations, which travel outward. these are seismic waves. -these vibrations are felt and cause damage at the surface of the earth -only a small amount of damage is caused by offset on the fault, vibrations shaking the ground do most of the destruction

geologic fan

-rocks from eorsion of mountains

angle and friction

-rough texture acts as friction - as the angle increases, the driving force increases while the normal force decreases - eventually the driving force exceeds the friction, and the block slides

what are the ellipses on top of arrowhead of vectors for plate velocities

-show possible location of arrowhead within error bars

can a creeping fault have seismicity?

-some creeping faults may still have earthquakes when locked section fails -some faults may creep all the way down to the ductile zone without a locked section

how do rayleigh waves achieve a circular motion

- longitudinal and transverse

raypaths and wavefronts

- raypaths: lines that show the direction of propagation of the seismic wave - wavefronts: connect the positions of the seismic wave that are doing the same thing at the same time (i.e. crestline of wave) - in general, raypaths are perpendicular to wavefronts

deadliest disasters mostly occurred where in China?

-at the Yellow river, flooding

cost-benefit analysis

-benefit-cost ratio: --> calculate annual benefits --> multiply by lifetime --> calculate projected cost of special eq constuction --> take ratio to get benefit/cost ratio -need to compare costs of losses in the case of disaster w a probability P to happen - see figure 5

planetary seismology

-best way to see layering inside of planets -already been some seismometers on moon & mars -want to measure the path of seismic waves to get information about physical quantities i.e. composition

ocean bottom seismometers (OBS)

-better coverage of Earth's surface -useful for: --> mid-ocean ridges --> hotspots --> subduction zones --> detection of nuclear explosions --> global seismology -very expensive

many faults are not visible at the surface

-blind thrust faults (beneath the surface, cause a fold on the surface) -subduction mega-thrust faults (visible only deep under the ocean)

India-Asia and eq

-eq are the result of the India-Asia collision -California eq pale in comparsion -many great eq -prototype for intensity XII shaking --> the difference of these thrust events and thrust events in subduction faults is that there is no water and live right near source

san francisco 1906 indirect effects

-fire was the biggest problem --> water mains broken shutting off water supply to city - burned for 3 days --> stopped by dynamited fire breaks -caused some new building codes

the plate tectonics revolution

-large parts of the Earth's surface move as rigid bodies: tectonic plates -plates are not continents

more facts on the rupture

-largest amount of slip is generally near the middle of the fault rupture plane -near the edges, there is less slip -slip is generally in the same direction across the entire fault rupture plane -fault planes do not open or close, the two sides just slip sideways -a point on the fault plane slips at a rate of about 1 m/sec during an earthquake -the larger the eq, the bigger the rupture area -a larger quake will generally take longer to rupture and have greater slip -only part of a fault ruptures in each quake

more on mainshock

-largest eq in sequence - larger mainshocks strain more volume of rock, have more aftershocks - foreshocks and aftershocks usually 1 magnitude unit (or more) smaller than mainshock

charles francis richter

-made richter scale in 1935 after 1929 Whittier CA earthquake --> dawn of eq science: some new instruments --> richter analyzed felt reports on a drive through whittier with einstein & understood the need for a direct measure of eq size

long run rupture

-the fault breaks entirely and slip distribution on fault surface is uniform -over many years the slip is evenly distributed

the chile 1960 eq

-the largest eq ever recorded w Ms 8.5 -epicenter: 140 kms SSW of Concepción, Chile -$550 million damage in southern Chile -tsunami caused: --> 61 deaths, $75 million damage in Hawaii; $50 million damage in Japan -32 dead and missing in the Philippines -US west coast $500K damage

recurrence intervals

-the time between similar eq -typically hundreds to thousands of years for major eq --> less for smaller quakes --> therefore instrumental record is useless and the historical one is nearly so

product of a forecast

-when and where the eq will be -how big (magnitude) -how much shaking at a given spot --> predicted intensity, depends on distance from fault

concrete shear wall for commercial buildings

-when properly designed, building very strong -rely upon massive stiff concrete walls, as well as concrete frames -performance depends on: --> number of walls --> location within building --> configuration of walls --> size & number of openings in walls

motions 3 components and under which are p waves and s waves amplitudes largest and which surface wave

1. E/W : p-wave amplitude smallest, S wave large; love waves 2. N/S : p-wave amplitude larger; S wave amplitude small; rayleigh 3. up/down : p-wave largest; S wave large; Rayleigh waves

important questions for paleoseismologists

1. is a fault active? 2. how often do we get big eq? 3. how regularly spaced in time are they? 4. does a given segment always rupture entirely in one piece? or does it require several smaller eq to break?

local or richter magnitude

Ml = log10 (A) -A is the maximum seismic wave amplitude in microns (10^-6 m) recorded on a standard seismograph (wood-anderson) at a distance of 100 km from the epicenter -measured in microns, so if amplitude is 1 mm, then 1000 microns = 10^3 and log(10^3) = ML 3

log of small numbers has what interesting property?

become negative

lessons from landers and hector

big eq can interact: - how did Landers trigger Hector Mine 7 years later? -topics of research: --> stress transfer (Coulomb) between faults --> visco-elastic relaxation in deeper crust

the forces involved with friction

friction = normal force * coefficient of friction - Normal force is the downward force of the block on the ramp -driving force is what is making the block "want" to move -coefficient of friction is the force directly opposing the driving force - if friction > driving force then no motion

why are faults locked near the surface?

friction forces: -the rocks near the surface act like the hare and not the turtle because of friction -friction is a force that resists motion until the driving force overcomes it -friction changes once things start moving: it decreases -friction depends on the material and on the forces that act perpendicular to the fault

global seismographic network

goal: to deploy over 128 permanent seismic recording stations uniformly over the earth's surface -nuclear test ban treaty

conjugate faults

have opposite directions of slip and intersect at high angle

Oakland: Problems with the Hayward fault

hayward fault is both seismic and creeping -creep is shallow & below high temperatures for seismicity

strain

how much something changes shape - fraction of size that a body is deformed = (L2 - L1) / L1

what is a tsunami?

known as harbor wave because was first observed in a harbor - a tsunami is an ocean wave caused by the motion of the seafloor in an eq, volcanic eruption, or landslide - when the source is in deep water a very large tsunami can be generated that travels over great distances

1933 long beach lessons

led to key improvements in zoning -field act of 1933 --> authorize california state department of works to review and approve building plans, and supervise construction --> affects public schools -post-1933 buildings much safer than pre-1933 -no Field Act building has ever failed

the magnitude of an earthquake is expressed in what scale

log scale

december 1812

a bad month for missions -Dec. 8 Wrightwood Earthquake on the San Andreas Fault -M ~7.5 --> was long thought to have been on an unknown fault close to San Juan Capistrano until people studied trees -one struck december 21 near santa barbara --> M6-7 --> possibly offshore, possibly the result of stress changes due to the Dec. 8 quake

how much does the Chile 1960 eq contribute to total seismic moment released by eq in the last 110 years or so?

about a quarter

SF to Salinas: creeping section continues southward

no known large earthquake

can s wave travel through outer core

no, converts to p and then back to s at mantle

two types of crust

oceanic and continental

with all these exceptions, why do we believe in plate tectonics?

provides unified explanation for: - matching geology & fossils - magnetic stripes - locations of most earthquakes - locations of most volcanoes it predicts: - plate velocities (from geological record & plate reconstructions)

tension is push or pull?

pull

special studies zone act- Alquist-Priolo Act of 1972

restricts construction on fault lines within 30 ft from "official" fault line

long-range triggering

shaking, rather than just long-term loading triggers aftershocks in more distant locations -evidence from eq with strong directivity

slickensides

striations on flat surfaces made as two sides of fault slide past each other during fault motion -indicate direction of slip on fault

angle of the earth as an explanation for why surface waves take so long

surface waves travel the largest angle around the earth

simple harmonic motion

the bobbing of the float on a pond is like the bobbing of a mass on a spring, it is called simple harmonic motion (up & down)

seismicity

the occurrence of earthquakes in space and time

seismology

the study of earthquakes and wave propagation through the earth

the only difference between mainshocks, foreshocks and aftershocks

the time at which they occur in sequence

interseismic velocity

velocity change with earthquake

how many components does a seismometer record:

3: N, E & upward

radius of earth

6370 km

when was extinction of dinosaurs

65 myr

continents average elevation

840 m above sea level

path of India into Eurasia

~50 mya -india drifting path inferred from Plate Tectonics reconstruction model -collision started about 50 mya -since then, India continued to drift northward, penetrating 2000 km into Eurasia continent

percent of planet that is ocean and average depth

~70% - average depth of 4 km

Gondwana and Laurasia

-Gondwana is the southern part of Pangea --> comprised of South America, Africa, India, Antarctica, Australia (further back was Gondwanaland) -Laurasia is the northern part of Pangea -they became independent supercontinents from the split of Pangea and opening of the Tethys Sea in the late Mesozoic era

Synthetic Aperture Rader Interferometry (InSAR)

-InSAR started to emerge in the 1990s and revolutionized the the way we measure topography and ground displacements -SAR systems produce images of ground backscattering properties -InSAR can produce images showing ground displacement -radars operate in electromagnetic radiation not visible light -radar bounces off ground & rebounds giving measure of distance -with two radar images of the same region, you can form an interferogram --> an interferogram depicts variations of the difference in antenna-ground distance --> therefore InSAR can be used to measure 1) the topography of the Earth or 2) displacements of the ground ---> accurate within mm

more on the fort tejon eq

-Jan 9 1857 -M7.9 -epicenter not known exactly -extends over a large area -->rupture length ~360 km --> slip of up to 9 m in Carrizo plain --> 6 m of slip in Palmdale -the last rupture on this segment

the three non-conventional sequences

1. swarms 2. long-range triggering 3. jumping faults

two ways to graph a wave

1. time 2. distance

remeber these eq

1906 SF haicheng and tancheng chile 1960 sequence eq on NOrth antolian fault Bhuj India 2001 -only need to remember what we learned not dates

trench

deepest point in oceans -cause seismicity and volcanoes behind trenches

plasticity

deforms permanently under stress

equation for calculating how far the earthquake is

distance = (Time S - Time P) / (1/Vswave - 1/Vpwave) - interval between S and P arrival time increases as distance increases

explanation for seismicity in the northeast

elastic rebound of ice

mature fault

fault planes break many times, that is, the surface which ruptures usually has broken many times in the past -often rupture plane is just part of a much larger fault

geodetic moment

fault slip model determined using geodesy - total moment is sum of moments on all patches

part 2 of holmes hypothesis

flow driven by heating: - convection is flow driven by heating - The Earth's mantle contains radioactive elements which are constantly producing heat - this heat causes the interior to be warmer than the surface, allowing convection to occur -causes motion at the surface

relationships between wavelength, period, & frequency

wavelength = velocity * period frequency = 1 / period velocity = frequency * wavelength

speed of sound

~300 m/s