Geology of Natural Hazards Exam 2

Thrust Faults

A reverse fault at a lower angle. compression stress, often at convergent plate boundary. when thrust faults dont break the surface, they are called blind thrusts which are dangerous because they often remain unknown until they cause an earthquake.

Time Dependent

Accepts degree of predictability. Use seismic gap and recurrence interval. 2nd most uncertain better able to say how earthquakes are behaving when and where may happen

Deterministic Prediction

Assumes earthquakes are inherently predictable. Can predict every aspect of the earthquake. this is an ultimate goal but despite things sold, cant actually do it yet.

Deformation

Bending, breaking, expanding, squeezing- change shape of form somehow

Foot Wall

Bottom part of fault. beneath person standing on fault's feet.

Recurrence Interval

Delta time, average delta time, amount of time between events. when use, on average earthquake occurs every delta time in this place. doesnt mean it will happen at that time. looking at history of events, in past on average events occurred every x number of years. not good indicator when it will come, some delta times are shoreter or longer. assume random data set that has been collected. if not random then cant use recurrence interval. Average recurrence interval- how fault has behaved in past, not necessarily how earthquake will come in future. time independent- based on backward looking average gives sense of how active a fault is. "overdue because been more than Delta time years" is not accurate statement. average so some take longer, some shorter, based on average value, backward looking statistic when use to go forward there is much uncertainty. depending on where fault is, different recurrence values. not all parts of fault respond in same way. doesnt mean how it has to happen in the future. when earthquakes may happen

Time Independent

Earthquake prediction that assumes quakes are random. Just looks at the recurrence time interval. most uncertain just when may happen

Real Life Mitigation

Educating about risks of earthquakes- Califonia campaign Shakeout to prepare for possible scenario. earthquake drills. earthquake insurance- issue money, bolt down houses, stock up on water, emergency supplies, first aid, bolt house objects to walls. issue if dont have money to do it.

Vertical Motion Faults

Fault pieces move up and down. Normal Faults, Reverse Faults, Thrust Faults

Elastic Deformation

First phase of strain in elastic rebound theory before earthquake might happen. Exert force like bending. Period of time the rock bends before it breaks. During time bending it will bounce back to original shape. Anything you do to it, all the stress is gone, the strain goes away, goes back to original shape. 1 to 1 ratio of strain to stress in elastic deformation. brittle failure, fault slips, earthquake happens.

Fault

Fracture along which movement happens. Fracture in earth, break that slips causes earthquakes. classified based on relative motion. 4 types of faults. An earth fracture along which rocks on one side move relative to those on the other side. Fractures in the crust along which rocks on one side of he break move past those on the ohter. Measured according to amount of displacement along fractures.

Nomograph

Graphical way to determine magnitude. line between S-P time and amplitude intersects is magnitude line. As S wave gets close to P arrival, S-P time decreases. line between the 2 points is the magnitude. straight line is plotted between P-S time and S-wave amplitude. This line intersects the central line at the approximate magnitude of earthquake

Surface Wave Magnitude

MS. to find use amplitude and period of 20 seconds on graph. Also use distance in degrees, S-P time. use equation to calculate magnitude for Richter Magnitude scale. number usually quoted in media. surface waves with a period of 20 seconds generally provide the largest amplitudes on seismograms. uses amplitude of largest surface wave in 20 seconds.

Body Wave Magnitude

Mb. to find need to know amplitude and period of P wave in first 15 seconds of seismograph. amplitude is height of biggest wave and period of wave in first fifteen seconds. also need distance (degrees) from S-P time. then with certain equation can calculate magnitude for Richter Magnitude scale. uses amplitude of first body wave.

liquefaction

Possible for damage: Soil build on changes building response. when soil behaves as solid stops behaving as solid in response to shaking. water saturated sediments, material in subsurface when starte behave as liquid , whatever built on top of it lost all strength and collapses. can also move through surface and come up and make sand boils and mud volcanoes. resolidifying on surface. shaking makes clay size grains move out of contact with each other making liquid behavior

Forecasts

Relies on precursory signals. Warning base on precursory signals like microearthquakes, changes in gasses emitted from wells which can indicate an earthquake will happen but does not mean they will happen. problem is dont manifest in same way, cant say when water drops to this leverl earthquake in this way, may not be microearthquakes prior to event, sometimes all happen and no event, none happen and event, unreliable to determine event

Plastic Deformation

Second phase of strain from stress in elastic rebound theory before earthquake might happen. After elastic deformation is keep applying stress and bending it, applying stress force, eventually when it lets go of stress it will stay the same shape. The bending is not recoverable. A little bit of stress creates a lot of strain in plastic deformation.

S waves

Secondary waves. slower than P waves and travel through interior. move by shear. change shape. only move through solid. move with wiggling motion making it hard to stand. buildings jarred by earlier p waves distort and may collapse. wiggling motion makes them more desructive.

Strike-Slip Fault

Side to side motion. Left-lateral strike-slip fault and right- lateral strike-slip faults. if block split horizontally, top section moves to left relative to bottom then left lateral. if top half moves to right then right lateral. If start at a market bed at one side of the fault and step across the fault, always have to go left to get to the other marker bed on the other fault that was at same point if left lateral fault. vice versa for right. Type of stress is shear stress. Commonly find shear stress at transform boundaries so at transform boundaries often find strike-slip faults. rocks on one side of fault slip laterally past those on other side.

horizontal Motion Fault

Strike Slip Fault

Stress

The force from plate tectonics at plate boundaries that causes deformation that creates earthquakes. Plates are always in motion so stress is always being applied to rocks, but breaking doesnt always happen all the time because of elastic rebound theory.

Normal Fault

The hanging wall is going down relative to the foot wall. Makes the distance between two points on hanging wall and foot wall bigger. Normal fault has widening effect so the stress that does that is called extension stress which pulls the faults apart. Often times divergent plate boundaries experience extension stress to find normal faults on divergent plate boundaries. rocks above fault surface slip down and over the rocks beneath the fault.

Reverse Fault

The hanging wall is moving up relative to the foot wall. The two point on the foot wall and hanging wall get closer . Just measure the horizontal distance, doesnt matter what the vertical distance is. The stress in reverse fault is called compression which pushes the faults creating the strain of the reverse fault. Often times convergent plate boundaries experience compression stress so find reverse faults at convergent plate boundaries. move rocks on the upper side of the fault up and over those below.

Strain

The resulting deformation caused by stress that creates earthquakes

size earthquake

The size of an earthquake is related to the amount of movement on a fault. the largest earthquake expected for a particular fault generally depends on the total fault length, or the longest segment of the fault that typically ruptures. Relationship between fault segment lenght and eaqrthquake size puts a theoretical limit on the size of an earthquake at a given fault. a short fault only a few km long can have many small earthquakes but not an especially large one because the whole fault is not long enough to break a large area of rock.

Brittle Deformation

Third and final stage of strain from stress on rock in elastic rebound theory before an earthquake might happen. The stress applied to the rock from tectonic forces is enough to finally break the rock. As the rock breaks, stress is being release. This is where the earthquake happens. After brittle fracture, the two broken pieces go back to their original shape before the stress The deformation of pieces is recoverable. Elastically rebounds back to original shape even though its broken. in response to smaller stresses rocks may merely bend, while in response to large stresses, they fracture or break. As stress levels increase, rocks ultimately succumb to brittle failure, causing fault slippage during an earthquake.

Hanging Wall

Upper part of fault, if person standing on fault where their head would be, where hang lantern.

Surface waves

arrive after body waves that travel through interior. long series of rolling motions. two types Love waves and Rayleigh waves which move in perpendicular planes. generally involve greatest ground motion so cause large proportion of earthquake damage. find buildings loosened and weakened by body waves that are vulnerable to final blow of surface waves.

Modified Mercalli Intensity scale

based on how strongly people feel shaking and the severity of damage it causes. Use Roman numerals. higher is greater intensity. Reflects subjective observations of people who felt earthquake and objective description of level of damage. typically show strongest intensities in areas near epicenter and areas where ground conditions cause strongest shaking. 1-12. measures how earthquake is experienced not actual size of event. describes amount damage occurs in area. take scale and convert MMI to acceleration of ground. equation: 10^(x/3)- 0.5 is ground acceleration in cm/s^2. x= MMI scale. then convert ground acceleration int percent g, cm/s^2 into unit of g forces. (A/980.6)x 100= %g do this to compare to actual measured by seismometer to find epicenter.

Focal Mechanism

beach ball looking diagram to tell which type of fault it is and in relation the stress and perhaps type of tectonic plate boundary.

types of earthquake waves

body waves - S and P waves, and surface waves - Love and Rayleigh waves. different types of shaking are a result of different types of earthquake waves.

precurssors

change in levels of radioactive gas radon, microearthquakes, foreshocks, water level drop, change in ground elevaion

Shake Map

computer generated maps of ground motion which show distribution of maximum acceleration for many potential earthquakes. useful in land planning because help forecast pattern of shaking in future earthquakes along same fault, so can be used to infer likely level of damage. a real-time shake map can help send emergency response teams quickly to areas that have likely suffered the greatest damage.

subduction zones

convergent boundaries. usually reverse or thrust faults. often generate giant earthquakes and that such sudden shifts of ocean floor can generate huge ocean waves called tsunamis.

S-P time

difference in arrival time for p and s waves. helps find distance from seismometer from earthquake. for any given distance, time it takes p to arrive is less than time s arrives. farther away, bigger distance, bigger delay from when p arrives than s arrives. if know delay can use graph to find distance from seismometer. bigger S-P time, farther away. distance to epicenter

Magnitude

different types of magnitude based on different types of wave. Body wave magnitude and Surface wave magnitude. The relative size of an earthquake, recorded as the amplitude of shaking on a seismograph. The bumber is recorded as a logarithm of the amplitude. Amplitudes differ for different seismic waves. amount of energy released and shaking. size. no matter where measure will get same magnitude. different from intensity because less intense farther from epicenter.

secondary ground effects

earthquakes can trigger landslides. back and forth acceleration has pumping effect on water between grains, water is forced into spaces between grains with each pulse of earthquake. sudden increase in water pressure in pore spaces can push grains apart and permit mass to slide downslope. cause liquefaction- in which soils that ordinarily seem perfectly stable become almost liquid when shaken and then solidify again when shaking stops, earthquake can shake soft sediment deposits down to much tighter grain packing, expelling water which caries sediment along as rapidly flows to surface creating sand boils and mud volcanoes. liquefaction can cause significant damage to buildings and roads on soft sediment

seismic waves

energy that travels out released when a fault slips from the place where the fault first slipped called the focus. energy that propegates by deforming the earth

tsunami

hazard associated with earthquake. at subduction zone, reverse faults in response to compression, any kind of dip-slip fault under water can create tsunami. need vertical motion to displace water. pacific ocean lots of potential tsunamis because of subduction zones of convergent boundaries. vertical motion dip slip fault, water displaced. need shallow water feeling the bottom to get taller. big wave approaching slows down when feels bottom because of frigtion and volume coming in behind it so it gets higher and gets so high it cant maintain its height anymore and crashes over in wave. wave height increases as slows down and feels bottom. wave length decreases, gets shorter ass feels bottom. subsequent waves can be larger. recession water to prepare for larger wave an abnormally long wavelenght wave most commonly produced by sudden displacement of water in response to sudden fault movement on seafloor. can also form when a landslide, volcanic eruption, or asteroid impact displaces water. reverse or thrust fault so compression stress so convergent boundaries subduction zone fault. displaces huge volume of water creating waves that move in both directions from location generated. height depends on magnitude of shallow-focus earthquake, area of rupture zone, rate and volume displaced, sense of ocean floor motion, and depth of water above rupture.

NGDC Travel time map

how far and long it takes tsunami to travel

relationship between earthquake size and amount of time between earthquakes

in general a direct correlation of a larger delta time, larger displacement. shorter displacements can happen any time but shorter time doesnt get big displacements. the more stress building up when there is more time between events which means there is more force possible for bigger potential for a bigger earthquake to happen.

New Construction

install base isolator- between structure and foudation, keeps structure in place and allows all shaking on ground only. do it because of resonoance

microearthquakes

large number of minute earthquakes not able to be determined precisely the focus can revel presence of previously unknown fault system.

structural damage

load-bearing masonry walls likely to shake apart and collapse, dropping heavy roofs on people, bridge decks and floors of parking garages not strongly anchored at ends because have to expand and contract with temperature. strong earthquake can shake them off supports. external ways loosely attached to building frameworks can break free and collapse. reinforced concrete often breaks in large earthquakes leaving formerly enclosed reinforcing steel free to buckle and fall. reinforced concrete fares much better if wrapped in steel to prevetn crumbling. fit steel sheaths around reinforced concrete columns. new construction often involves wrapping steel rods around vertical reinforcement bars in concrete supports. weak floor at any level major problem. upper floors move back and forth during shaking, leading to collapse of either individual floors or whole building. diagonal beams can provide support needed to resist lateral movement. heavily reinfoced concrete walls and corners supports with unreinforced fill-in walls of brick common in developing walls, bricks have no strength in earthquake provide no nlateral strength so collapse. shattering glass common causes of serious injuries. broken glass rain down on street from windows. safety glass now required in ground floor windows of commercial buildings but not upper loors. glass systems in modern high rise buildings designed to accomodate routine sway from wind and perform fairly well in earthquake. old houses rest on concrete foundations. onlything holding house is weight. large can shake older houses off foundations and destroy them. weak foundation can be strengthened with diagonal bracing or sheets of plywood nailed to wall studs. taller buildings experience earthquake damage caused by sway of building. even buildings without weak floors may collapse if upper floors move in one direction as ground snap backs in another. oscillation can cause damage even if doesnt collapse. buildings too close taller break at level of top of shorter neighbor.

Seismic Gap

location on fault that earthquake hasnt occurred in a while. likelihood of happening in gap is higher than places where occurred more recently. Stress builds up in gap that hasn't been released yet. pattern of earthquakes along fault segments also provide clues into further earthquake activity. segments of major fault that have less earthquake activity than neighboring segments represent seismic gaps. experience shows seismic gaps are far more likely to be the locations of large earthquakes than the more active segments of same fault. lenght of seismic gap provides indication of possible future break. show where earthquake may happen.

Richter Magnitude Scale

logorithmic scale, how much bigger or more shaking. measure magnitude based on distance and shaking. every step up means the earthquake is bigger by a factor of 10. to find how much bigger, more ground motion or seismograph swing, 7 earthquake is from 3 earthquake. 10 ^ (7-3). also tells how much more energy is released. jumps by a factor of 32. more energy released 7 earthquake from 3 earthquake 32^(7-3). from 1-10. empirical scale based on maximum amplitude of earthquake waves measured on a seismograph. although wave amplitude decreases with distance, designed as though seismograph 100 km from epicenter. seismograms vary greatly in amplitude for earthquakes of different sizes. to make variation more manageable, use logarithmic scale to compare earthquakes of different sizes.

tsunami mitigation

need to educate people on behaviors of tsunami, have clear evacuation routes, know where to go, warning system of bouys in some places in ocean moves with waves, measuring height and length and can detect anomaly and detect tsunami wave, network identify and predict when might arrive at certain locations, sirens and evacutaion routs.

frequency

number of peaks per second in cycles per second or Hertz Hz

displacement from earthquake

offset. the distance of movement across the fault

epicenter

point on the map directly above the focus. position on surface directly above where fault moved, the focus

relationship between magnitude and frequency

power law. if plot all known earthquakes of a certain size against their frequency of occurence, we get a more or less straight line on which we can extrapolate to events larger than those on record. small earthquakes are far more numerous than large earthquakes and giant earthquakes are extremely rare. most of total energy release for fault occurs in the few largest earthquakes. each qholenumber increase in magnitude corresponds to an increase in energy release of 32

damage

primary cause of deaths and damage is collapse of buildings and other stuctures. shaking during can trigger other damage as well. aftermath, fire becomes serious hazard. electric wires fall to an accompaniment of great sparks that are likely to start fires. buckled streets, heaps of fallen rubble, broken water mains hamper firefighter's efforts. days after commonly bring epidemics caused by impure water because broken sewer mains leak contaminants into broken water mains. decomposing bodies burried in rubble contribute to spread of disease.

P waves

primary waves. fastest moving through interior. move by compressing and dilating. change volume. move through gas, liquid, and solid. come as a sudden jolt

earthquake insurance

rates dependent on risk maps USGS put togeter percent probability of shaking

Mitigation

risk maps- probabilities of where and when earthquake will strike to estimate risk for given area. based on past activity measured in terms of frequency and magnitude. invaluable for choosing sites for major stuctures and important for insurance purposes. mitigation efforts are expensive and hard to enforce. cost wieghed against potential lives saved

earthquake machine

rubber bands show elasticity of rocks and show randomness as well as patterns of earthquakes. cranking is the stress applied to the rocks. block is plate motion. or is block the fault splitting.

energy of plate motion on earthquake graph

shows position moves suddenly then no energy until the next sudden motion. plate motion is constant but the block doesnt move constantly. Energy goes to rubber band (the rock). the stress keeps increasing on the rock and then a critical fracture occurs and the rock releases energy. rock undergoes periods of elastic strain. the energy of plate motion is released into the rock and then the rock releases the energy.

creep

sometimes a fault moves almost continuously rather then suddenly snapping. strain in fault is released by creep and doesnt accumulate to cause large earthquakes.

Zoning

strategy to mitigate. using location of faults and geology to say where to and not to build

acceleration

strength of the shaking in gravity. duration of strong shaking in an earthquake depends on size of earthquake. time that the ground moves in one direction during earthquake, before oscillation moves back in other direction is similar to time of initial fault slip in one direction. total duration of motion is longer because ground oscilates back and forth. an increase in magnitude above 6 doesnt cause much stronger shaking, it increases area and total time of shaking. larger provides more time to evacuate but evacuation is harder with acceleration increasing. longer shaking lasts, more damage occurs; structures weakened or cracked in first few seconds are commonly destroyed with continued shaking. amount of shaking also relates to distance from earthquake's focus. waves radiating outward from earthquake source show significant decrease in violence of shaking with distance, especially in bedrock and firmly packed soiil. earthquakes that occur deep underground may cause less property damage than smaller earthquakes near earth's focus. shaking severity is also affected by type of material waves are traveling through. violence of shaking depends on frequency of earthquake waves compared with frequency of ground oscillation. lower frequency oscillations of surface waves often correspond to natural oscillation frequently of loose, water saturated ground.

foreshocks

swarms of minor earthquakes than can warn of major earthquake if they announce the onset of fault slippage. not always precede large earthquakes.

early warning systems

system TriNet with seismometers installed to moniter earthquakes throughout region. within minutes of tremor, information from seismometers is used to produce ShakeMap of ground-shaping severity in area of earthquake. Advanced National Seismic System installed nationally in areas of moderate to high seismic risk. provide litter advance warning of earthquake shaking, for most not enough time to evacuate building which is why building codes and earthquake preparedness are so important.

amplitude

the amount of positive or negative wave motion. wave height, farthest get from zero. magnitude uses amplitude of types of waves. converting swing of seismometer and converting to energy released, bigger swing, bigger size on richter scale. always use biggest amplitude.

location

the difference time it take p waves to get to seismometer than s waves farther seismometer is away from earthquake, the longer it takes the s wave to get there after p wave. use relative arrival time to get location. farther seismometer is away from the earthquake, the longer delay time between p and s wave arrival. the shorter amoung of time to get there, closer to seismometer. Time arrival difference is S-P time. shorter S-P time means closer to earthquake, longer S-P time means seismometer farther away from earthquake. after find degrees of distance waves traveled on travel time curves, multiply by 111.19 to get km. need at least three seismometers to find location of earthquake epicenter.

Wavelength

the distance between two crests, one cycle

strike and dip

the orientations of rock layers and faults are described in terms of strike and dip. Strike is the compass orientation of a horizontal line on a rock surface. dip is the inclinaiton angle down from horizontal to the rock surface.

focus

the place where the fault first slipped, the hypocenter of the earthquake. point at depth that moves where seismic waves are generated

intensity

the severity of earthqake in terms of damage that it inflicts on structures and people. use Mercalli intensity scale. perceived effects. changes. more intense at epicenter than farther awaym Modified Mercalli intensity scale

Realtionship between earthquake size and frequency

the smaller the delta time is more abundant than larger delta time. earthquakes happen more frequently on smaller time fram then on large. there are more frequent smaller earthquakes than larger earthquakes.

Elastic Rebound Theory

the theory applied to most earthquakes in which movement on two sides of a fault leads to bending of the rocks until they slip to release the bending strain during an earthquake. (Rocks near a fault are slowly deformed elastically then plastically until the fault breaks during brittle deformation during an earthquake when the rocks on each side slip past each other, relieving the stress. After the earthquake the rocks regain their original, undeformed shape, but in a new position. ) With increasing stress, a rock deforms elastically, then plastically, before ultimately failing or breaking in an earthquake. A completely brittle rock fails at its elastic limit.

surface rupture length

the total length of the break. the largetst earthquake expected for a particular fault generally depends on the total fault length, or the longest segment of the fault that typically ruptures.

Period

time for one complete cycle between successive wave peaks to pass. amount of time it takes wave to make a full cycle. gone to equivalent starting position

retrofitting

type of mitigation. different types to minimize shaking and make sure buildings resist shaking as much as possible. Diagonal bracing in walls keep walls from shearing. install shear wall panneling attached to all studes to keep wall from shearing. anchor bolts to anchor house to foundation.

Love Waves

type of surface wave, moves from side to side, shear motion. as moves down in depth the amount of motion is smaller shaking. Side to side transverse motion, most near the surface a bit of torqueing happens- rotate and twist.

Rayleigh waves

type of surface wave, moves up and down in motion that somewhat resembles ocean swells. backwards rolling motion. decreases in magnitude as it gets deeper.

Resonance

vibrating with same frequencey, where earthquake has same frequency of building making it vibrate more. base isolator design buildings that dont resonate at same natural frequency as earthquakes. taller buildings shake more, resonance at same frequency with wave so shake more than shorter buildings with less frequencey. shorter buildings respond with higher frequency because farther away from natural frequency

Paleoseismologists Graphs

want to date movement of fault. date by absolute radiocarbon dating, know the age, can figure out when fault may have occured. dont know exact age in between two layers, pick time between. put faults in order with youngest at top and find data. calculate delta t for average RI between each years. then average all delta ts to make prediction. paleoseismology- study of prehistoric fault movements, seismolegists can establish fault movement trends that predate written records

Prediction

warning to help make it safer. provide people with some reasonably reliable warning of impending events. efforts going into development of early warning systems for areas away from epicenters to provide warning after earthquake but before shaking reaches areaNapa recently able to predict 10 seconds before in lab. big deal. different types of predictions. Time- Independent, Time Dependent, Forecasts, Deterministic Predictions can have understood prediction but its accuracy will not be good. moving forward more difficult to predict..

Body waves

waves from seismic wave that travel through the interior. made up of P and S waves used to locate and assign magnitude of earthquake

Game

what worked: education programs, retrofitting, hospitals and school, early warning system and defense in water, upgrading housing, protecting electrical and utilities. not realistic: budget, only one variety of geography with only certain types of earth and buildings. could start earthquake whenever ready. casualties were acceptable. given more time to prepare than probably would be given, and not really given yet as warning sytems.