GLG EXAM 2

Shear Stress:

Horizontal motion along fault; back and forth / *side to side* movement

Seismogram:

Interpreting Zig Zags Y axis = Wave Amplitude X axis = Time

A result of ground-shaking in areas with unstable, steep, and/or heavily loaded slopes.

Landslide

The "Quake Lakes" were formed as a result of this EQ hazard in Sichuan Province, China

Landslide

Formula to find Moment Magnitude (M)

M = (Area of Fault Rupture) x (Length of Fault Rupture) x (Strength / Rigidity of Rock) Scale is NOT linear *Example: * M6.0 releases 32x more energy than a M5.0

A ______ earthquake is the largest possible earthquake that could happen on earth, because if it happened it would rupture a distance equivalent to Earth's circumference

M10.0

Thousands of aftershocks were generated by the 9M earthquake on March 11th. What was the highest magnitude recorded for an aftershock?

M7

What type of plate boundaries produce megathrust earthquakes *(more than one answer)*?

Ocean-*Continent* convergent AND Ocean-*Ocean* convergent

What type of plate boundary is Chile on?

Ocean-continent convergent

Where was the epicenter of the March 11th earthquake?

Offshore of Japan's northeast coast

What type of seismic wave arrives first to a seismometer (travels the fastest)?

P = Primary; P waves travel ~twice as fast as S waves. Surface waves arrive last

How plate movement causes faulting

Plate motion > Stress (applied to lithosphere) > Strain (deformation of lithosphere) > EQ (rupture, faulting, release of energy)

What major cities in the Pacific Northwest are at risk for a megathrust earthquake?

Portland, Vancouver, and Seattle

Mercalli Intensity Scale:

Qualitative scale for reporting on earthquakes based on observations as opposed to measurements Intensity is not quantitative Scale is roman numerals [ I - XII ] Intensity = I: Shaking not felt, No damage, Peak, Acceleration: <0.17, Peak Velocity: <0.1 Intensity = XII: Extreme shaking felt, Very heavy damage

Elastic Rebound

Rocks relax and return to their original shape. Earthquake cycle then starts over again

This seismic wave shears (or cuts) the material it is moving through, causing lateral swaying

S wave

__________ _______ are used for long term forecasting

Seismic gaps; Identify areas along a fault with low or no seismic activity to determine where the next earthquake might occur Good for determining *location*, NOT *timing*

Why is ground shaking amplified in water-saturated sediment?

Seismic waves (P&S) SLOW down which INCREASES *wave amplitude*

Secondary waves (S) motion =

Shear (side to side)

Strike-slip faults - shearing motion

Sides of fault are offset laterally - either right-lateral or left lateral Strike-Slip = side-to-side movement

Three Sites (1,2,3) record intensity & magnitude for the same EQ. Site 1 is closest to the epicenter and site 3 is the farthest. All other factors are equivalent at the three sites. At which site would the earthquake *intensity* be the GREATEST?

Site 1 - because it is closest to the epicenter the shaking will be most intense at this location

Seismogram: Background Seismicity:

Some small amplitude activity is normal, this is why the beginning of a seismograph already has small waves Once the waves become significantly bigger, that is an indicator of an earthquake

Elastic Deformation

Stress causes build up of strain in the rocks as plates slowly move past one another (or converge, or diverge) tress of plate movement is not great enough to overcome strength of rock. Rocks will deform elastically (they'll bend)

Brittle Deformation

Stress of plate movement reaches critical stress of rock, rock breaks and slips Energy absorbed by the rocks in the form of strain is released = earthquake (Timeframe on the order of seconds)

A large earthquake on one fault can trigger earthquakes along neighboring faults.

TRUE

Fire is a secondary hazard associated with tsunami.

TRUE

Shear Stress:

Occurs at transform boundaries where rocks slide past one another (Transform)

Foreshock

Small magnitude earthquakes before the main shock

According to the seismic gap method of predicting EQs, this area in CA is due for a large magnitude event.

The San Francisco Bay area/northern CA

Frequency:

The amount of time it takes one wave to pass a certain point All things that exist have a frequency at which it vibrates Including buildings

What caused the Fukushima nuclear disaster?

The tsunami disabled the back-up generators causing the reactors to overheat.

Shear stress

Transform boundaries

Major changes in the elevation of the landscape over wide regions can occur as a result of strong earthquakes.

True

The largest magnitude earthquakes will occur at this type of plate boundary

a subduction zone

Which of the following is true about tsunamis?

a tsunami can flood areas that are several kilometers inland

What types of rocks will store more strain?

crystalline rocks (interconnected crystals)

A large magnitude earthquake at a subduction zone

megathrust

Of the scales used to measure EQs, this one is a calculation of the energy released during a rupture

moment magnitude

Stress occurs in the Earth mostly due to:

plate movement

A tsunami warning sign that occurs on the coastline just before the first wave hits

receding/withdrawal of ocean water (trough of tsunami wave arriving first)

Large movement on this type of fault will generate a tsunami

reverse/thrust/megathrust fault (in a subduction zone)

Surface waves can go through any material and have a ________ motion

rolling (also can be side to side and up and down all together)

The top cross section below shows earthquakes along the San Andreas fault before October 17, 1989 and the one on the bottom shows earthquakes along the same fault after that date. These two cross sections illustrate that:

1. the most dangerous part of a fault may be one that has not had recent earthquakes 2. San Francisco is due for an earthquake 3. one way to predict the locations of future earthquakes is to identify seismic gaps

What lithospheric plate is Japan on?

Eurasian Plate

Earthquake timing can be accurately predicted.

FALSE

What is the definition of a fault?

Faults are fractures upon which the rocks have moved A fracture along which rocks have moved relative to one another

Secondary hazard created by earthquake damaged utility lines

Fire

Of the scales used to measure earthquakes, this one will change depending on your location because it is based on observations

Mercalli Intensity scale

These seismic waves are also referred to as "Body Waves" because they travel through Earth's interior

P and S waves

This seismic wave has the fastest velocity and will be the first to arrive, causing sharp, vertical jolts

P wave

Which seismic wave can be detected and used as a warning signal that destructive shaking is about to occur

P wave

Interpreting waves on seismogram

P waves = Smallest waves on seismogram S waves = Medium sized waves on seismogram Surface waves = Large waves on seismogram Highest magnitude earthquakes: reverse fault because of compressional stress

The time it takes for a complete wave to pass, is the:

Period

Data output of seismograph monitoring equipment (what is produced)

seismogram

Instrument that records/measures vibrations of the crust (ground shaking)

seismometer

The wavelength of a tsunami will decrease as it moves toward this location

shallow water/shoreline

What is the tectonic setting of the large 2011 Tohuku earthquake in Japan?

slip along a subduction zone (megathrust)

What kind of fault will generate the highest magnitude earthquake & why?

Reverse fault because of compressional stress; Rocks will store the most strain (have the most potential energy) when compressed.

Outdated scale for energy released during an earthquake that is no longer in use, but often still reported in the media

Richter Scale

Extensional (Tensional) Stress:

Rocks are pulled apart (divergent)

Compressional Stress:

Rocks are squeezed together (convergent)

Crystalline

Strong due to interlocking crystals Can store more strain

A tsunami can travel up a river.

TRUE

The most destructive natural disaster in history, in terms of $$$

The March 11, 2011 Tohoku, Japan EQ and tsunami

Liquefaction occurs in this type of sediment

water saturated, uncolsolidated material

The only physical property of a tsunami wave to increase as it moves into shallow water

wave amplitude or height

The distance and height inland that a tsunami wave travels

wave run-up

Approximately how many >M3 aftershocks do you think are related to the M9 Tohoku EQ (Japan, 2011) (within 1 week of the event)?

~ 3000

order of processes that generate an earthquake

*Stress* is applied, *strain* is stored, rocks *break*, and then rocks *rebound*... After every earthquake the process begins again

Dip slip movement

*Up and down* motion; vertical displacement; move parallel to the dip of the fault plane

What are the odds of a megathrust earthquake in the Cascadia region in the next 50 years?

1 in 3

What controls ground shaking intensity? ( things)

1. *Magnitude* 2. *Distance from the epicenter* - Amplitude of seismic waves decreases with increasing distance from the epicenter 3. *Depth of the Focus* 4. *Rock type* 5. *Direction of fault rupture*

What characterisitics of a shoreline/city will cause the wave height of a tsunami to be higher *(more than one answer)*?

1. Inlets and bays 2. Tall buildings 3. Narrow streets

The shaking in Tokyo lasted for 5 minutes. Why is this amount of time significant *(more than one answer)*?

1. a long period of shaking means the epicenter is close. 2. a long period of shaking means there might be a tsunami generated. 3. a long period of shaking means the magnitude of the earthquake is large.

Tsunami may be generated by:

1. earthquakes that cause the seafloor to shift 2. activity associated with volcanic eruptions 3. landslides that displace large amounts of water

How would this diagram change if the seismic station was farther from the earthquake?

1. there would be a larger gap between the arrivals of the P- and S-waves 2. the S-waves would arrive later 3. the P-waves would arrive later 4. (Correct) *all of these*

characteristics of S-waves

1. they cannot travel through liquids (travel through *solids* ONLY) 2. they displace the rock in a direction that is perpendicular to their travel direction (shear wave motion) 3. they shear rock from side to side or up and down

Long-range earthquake forecasting:

1. uses tectonic settings and historical records 2. is based mainly on the knowledge of when and where earthquakes occurred in the past 3. measures patterns of seismic activity along a fault to determine locations and recurrence intervals

P-waves do this to the medium they are traveling through

compress

Primary waves (P) motion =

compressional waves (up-down)

An earthquake is generated at this point where the Earth first ruptures

focus/hypocenter

This will turn moist, unconsolidated material into a slurry of mud (i.e., cause liquefaction)

ground shaking

On this map of southeastern Asia and adjacent areas, which site would have earthquakes along a continental collision?

in Tibet

The time interval between P and S waves does this (increases or decreases) as you move further from the epicenter of an EQ

increases

Short-term earthquake prediction:

is complex, but techniques are still developing that hold promise

Why did the Christchurch earthquake (2011) in New Zealand cause much more damage than the larger Canterbury earthquake (2010)?

it was closer to a large city with buildings that had been damaged by the earlier earthquake

The Sumatran tsunami of 2004 had ~230,000 casualties for this reason alone

lack of a Warning System

This process causes 2nd, 3rd, and 4th tsunami waves to be larger than the 1st

oscillation or wave resonance

Earthquakes are a release of energy when rocks snap, or fracture. At what depths do most earthquake occur?

100 kilometers marks the base of the lithosphere, which is a rigid solid that can snap and break.

How long was strain being stored on this plate boundary before the March 11th earthquake struck?

200 years

How deep was the water that was displaced by the March 11th earthquake?

4 miles

How much warning did people in Tokyo have before the shaking started?

60 seconds

Wave run-up will be the lowest height and furthest inland over this type of topography

wide/flat land or bay

How do geologists study earthquakes in the geologic record?

1. Measure orientation, dimensions, and offset of surface fault ruptures 2. Dig trenches across a fault to study its history of movement 3. Look for changes in the landscape as a result of faulting 4. Drill and instrument deep holes across faults to record data on active faulting

What happens every time faults move?

1. Rocks break 2. Rocks move 3. An earthquake 4. Rocks release energy 5. (Correct) *All of the above*

Earthquake cycle process

1. period of inactivity along a segment of fault 2. period of small earthquakes where stress begins to release causing strain 3. fore shocks occur prior to a major release of stress (does not always occur) 4. main shock and aftershocks where fault releases all pent up stress, releases the major quake

If an area has shallow, intermediate, and deep earthquakes, what can you infer about the area?

1. the *shallow* EQs will be *closer to the trench* than deeper ones 2. this area has the *potential for large* EQs 3. the *depth pattern* of EQs can be used to determine which way the slab is inclined 4. it is near a subduction zone 5. *Correct* ALL OF THESE

What do the two stars near the center of this block represent?

1. the star at DEPTH is the *hypocenter* 2. the location of the earthquake 3. the *star at depth* is the place where the earthquake is GENERATED 4. the star on the SURFACE is the *epicenter* 5. *correct* all of these

Dip-slip faults: Normal motion

Hanging wall moves down relative to footwall moving up Dip slip = up and down movement

What type of rock do you think will be able to hold the most energy before it breaks?

*Intrusive igneous rocks* are dense, crystalline rocks. The denser the rock, the more energy it can absorb (pore space and air will weaken rocks)

Strike Slip movement

*Side to side* motion (displacement); parallel to the strike of the fault plane

Most earthquakes occur at depths of:

*less than* 100 km in depth

Which are true of faults?

1. A lateral fault may result from horizontal compression. 2. Orientation of a fault depends on directions of stresses. 3. Vertical compression may result in a more vertically oriented fault. 4. *These are all true of faults* - CORRECT -

Hazards of earthquakes

1. Fire = natural gas lines or electrical lines break 2. Flooding = landslides damming rivers; dams breaking 3. Landslides = unstable slopes fail 4. Tsunami = elastic rebound of seafloor lifts ocean water 5. Building Collapse: Lateral Failure 6. Liquefaction 7. Landscape change = Can cause subsidence or increase in elevation 8. Foreshocks

What features in the image help you identify the location of the fault?

1. Linear ridges and valley 2. Scarp 3. Stream channel runs parallel with faults 4. *(Correct) All of these*

The continental block shown in this figure has a transform boundary, a reverse fault, and a continental rift. What type of activity could cause an earthquake here?

1. Reverse faulting 2. Normal faulting 3. Strike-Slip faulting 4. Movement of MAGMA near the Rift 5. (Correct) *all of these*

What measurements are used to calculate the amount of pressure (or energy) stored along plate boundaries *(more than one answer)*?

1. Stored strain on the fault 2. Rock strength 3. Amount of time to last earthquake 4. Rock deformation (through GPS measurements)

characteristics of P-waves

1. They compress and then expand the rock in the direction the wave travels. 2. Can travel through any material 3. Fastest and arrive first

In which of the following ways may earthquakes be generated within a continental plate?

1. Transform faults 2. Movement of preexisting faults subjected to new stress 3. Intrusions of magma 4. Continental rifting and normal faulting 5. *All of these* - CORRECT -

definition of wave amplitude

How much the ground moves from a baseline

Compressive stress

Convergent boundaries: subduction & continental Collisions

Short Term Forecasting:

Detect small movements in ground elevation Escalated seismicity (foreshocks) Change in fluid pressure in rock Change in radon concentrations leaking from rock

Extensional stress

Divergent boundaries: Ocean ridges, continental rifts

What location is at the least risk for an earthquake?

East coast of South America (not on a plate boundary; passive margin)

Seismic Energy:

Energy released by sudden rupture of strained rocks. Transmitted in all directions from point of rupture.

The earthquake hazard responsible for most of the destruction in the 1906 San Francisco EQ

Fire

Earthquake cycle:

First, *Elastic Deformation* Second, *Brittle Deformation* Third, *Elastic Rebound* Stress >> Strain Energy >> Earthquake >> Energy Released

What geologic hazards are closely related to and generated by a megathrust earthquake *(more than one answer)*?

Flooding & Tsunami

Dip-slip faults: Reverse/Thrust motion

Hanging wall moves up relative to footwall moving down Dip slip = up and down movement

Three Sites (1,2,3) record intensity & magnitude for the same EQ. Site 1 is closest to the epicenter and site 3 is the farthest. All other factors are equivalent at the three sites. At which site would the earthquake *magnitude* be the GREATEST?

The magnitude would be the *same at all three* sites - magnitude is the calculated measure of energy released and is the same regardless of your location

Elastic Deformation:

Timeframe 10s-100s of years When stress is applied and deformation occurs, but the deformation is elastic because once the stress is removed, the original form returns.

What type of plate boundary is Haiti on?

Transform

Buildings fail in very specific and predictable ways and can be engineered to withstand lateral shaking (from an S wave) and rolling motions (from surface waves).

True

What region experienced a set of small earthquakes that were triggered by a magnitude 7.2 earthquake?

USA / Mexico border

Tensional Stress:

Up and down movement; one side *moves down*.

Compressional Stress:

Up and down movement; one side *slides on top* (up/over).

what is the difference between long & short term forecasting?

We can make short- and long-term forecasts but the longer the term the less certain we are

Clastic

Weak Do not store much strain

A tsunami will move the furthest inland over what type of topography?

Wide, flat land

This fault is created when rocks are pulled apart or extended (tensional stress). HINT: divergent boundaries

a normal fault

Data recorded on a seismogram shows these two properties of seismic waves

amplitude and wavelength

Moment Magnitude is calculated by

area of rupture on the fault, amount of slip, and estimates of rock rigidity. All magnitudes reported by the USGS are Moment Magnitude (NOT Richter).

(P) and (S) waves are *together* called:

body waves

Hazard of EQs responsible for causing the most casualties

building collapse

Landslides and volcanic eruptions can cause a tsunami by:

causing a large mass of rock to catastrophically displace the water

As stress accumulates along a fault plane, this process occurs until the stress exceeds the strength of the rock

elastic deformation OR strain accumulation

The process responsible for changes in ground elevation during/after an EQ

elastic rebound

The image shows a surface expression of slip along a normal fault caused by an earthquake. What is the indicated feature?

fault scarp

Vertical offset visible at the Earth's surface that indicates movement along a fault

fault scarp

Most large earthquakes on subduction zones occur because of:

faulting along the plate boundary

The name for the fault block located above the fault plane

hanging wall

As it grows, a fault rupture that began at depth:

has an oval shape below the surface

Which of the following would NOT be a good idea in an area that has a high risk for earthquakes?

have many new buildings be made of rigid concrete or masonry

This hazard played a large role in the destruction during a M 6.3 EQ in 2011 in Christchurch, New Zealand

liquefaction

Largest magnitude earthquake in the sequence

main shocks

Most earthquakes occur along:

plate boundaries

When the frequency of a seismic wave matches the natural frequency of a structure, they will:

resonate

The special geologic terms used to represent the direction of a horizontal line on an inclined surface (like in a fault) and the angle of that surface to the horizontal are:

strike and dip

Type of faults that produce lateral (side-toside) movement between fault blocks

strike-slip faults

These seismic waves are formed by the vibration of body waves, and are the *slowest* and *most destructive* seismic waves

surface waves

On this map of earthquakes near Japan, why do shallow earthquakes occur to the east and deeper earthquakes occur to the west?

the subduction zone dips to the west

The southern San Andreas fault near Los Angeles is considered a candidate for a major earthquake because:

this segment of the fault has not moved for more than 100 years

The huge 1964 Alaskan earthquake, one of the largest earthquakes ever recorded, was caused by:

thrusting along a subduction zone (megathrust)

Produced by a dramatic uplift/down drop of oceanic crust; stops once it runs out of energy

tsunami

Seismic waves are amplified (more destructive) in this type of geologic material

unconsolidated deposits

How do we determine the location of a recent earthquake?

use seismic records from three or more stations

Type of motion required to generate a tsunami wave

vertical displacement

Strain Energy

Accumulates, causing elastic deformation

Magnitude:

Amount of strain stored that is released

what is an aftershock?

An earthquake that occurs after a main shock along the area of fault that ruptured during the main shock

Seismic Network:

Array of many seismic and geological instruments communicating with one main data station.

Strike Slip Faults: Shearing Motion:

Based on relative motion on opposite side of fault plane Side faults are offset laterally - either right lateral or left lateral Lateral direction is determined by looking what direction the plate has moved relative to you from either side If the plate is to the right = right lateral

On this map of South America and adjacent areas, which site would have the deepest earthquakes?

Below the *magnetic belt*

Hanging wall:

Block above fault plane

Footwall:

Block below fault plane