Module 3 Earthquakes and Earth's Interior

Draw a cross section of the earth's layers

(see picture)

What types of geologic structures would you expect to find in an area that had undergone compression?

Answers will vary; however, students should mention folding, reverse and thrust faulting, and perhaps tectonic foliation. They should not mention normal faulting.

Why do deep-focus earthquakes occur along convergent plate boundaries? Why do they not occur along divergent or transform boundaries?

Convergent plate boundaries result in subduction where one plate descends below another. Deep-focus earthquakes occur within the subducted lithosphere as it sinks down through the asthenosphere. This does not happen along divergent or transform boundaries where the earthquakes are all relatively shallow.

What causes earthquakes? Explain elastic rebound theory. Where do earthquakes occur? Please explain your answer in the context of plate tectonics.

Earthquakes tend to occur along plate boundaries. This includes convergent, divergent, and transform boundaries. However, occasionally intraplate earthquakes—those occurring away from plate boundaries—do happen.

Where do earthquakes occur? Please explain your answer in the context of plate tectonics.

Earthquakes tend to occur along plate boundaries. This includes convergent, divergent, and transform boundaries. However, occasionally intraplate earthquakes—those occurring away from plate boundaries—do happen.

What is the difference between a dip-slip fault and a strike slip fault? Provide examples of each. Draw a cross section of a normal and reverse fault. For each, list the stress involved and changes in the length of the crust, if any.

Normal faults form in response to tension and involve lengthening of the crust. Reverse faults form in response to compression and involve shortening of the crust.

What phases of matter can a P-wave travel through? An S-wave? How has this helped us to have a better understanding of the layers of our Earth?

P-waves can travel through solids, liquids, and gases. S-waves can only travel through solids. By observing the way earthquakes arrive at seismometers around the globe, scientists are able to get a better understanding of the layers of the Earth. Specifically the inability of S-waves to pass through the outer core tells us that it must be at least partially molten. Scientists can also observe how P- and S-waves reflect, refract, or change velocity at various boundaries within the Earth, giving us clues about the nature of the layers.

Describe two earthquake-related hazards.

Student answers should include two of the following. Earthquakes involve ground shaking, which can be extremely detrimental to human structures. Landslides can result from seismic shaking. Liquefaction happens when ground shaking causes sand grains to try to settle more tightly together, which allows water pressure to build up so that it pushes the grains apart, causing the once solid ground to behave like quicksand; this can cause damage to structures. Fires have been associated with earthquakes because ground shaking can upset open flames, topple power lines, and rupture gas lines; all of these can start a fire. Tsunamis are large waves that are triggered by displacement of seawater; they are associated with earthquakes that take place near coastal regions. After the earthquake is over, disease may threaten lives in an earthquake-damaged region.

How is the Mercalli intensity scale used to determine the magnitude of an earthquake? What errors might be associated with this technique?

The Mercalli intensity scale defines earthquake intensity by assessing both the damage that the earthquake caused and people's perception of the shaking. The main issue is that testimonies can be very subjective among a group of people.

What is the Moho? How was it discovered?

The Moho is the boundary between the crust and mantle. It was discovered by Mohorovicic, who observed that P-waves arriving at seismometers distant from an earthquake epicenter arrived with greater velocities than those arriving proximal to the epicenter. From this, he assumed that P-waves reaching distant seismometers traveled in part through the mantle and that their velocity was greater in the mantle.

Explain why tsunamis are NOT tidal waves.

Tsunamis are created by large displacements of water caused by earthquakes, landslides, or volcanic eruptions. Tsunamis are associated with displacements of the seafloor, which displace water in the ocean; this is different from tides which are the result of gravitational attraction between the Earth, Moon, and Sun.

Much of the capitol city of Port-au-Prince was destroyed during the 2010 Haiti earthquake even though similarly sized earthquakes in other cities did very little damage. What caused so much damage during the Haiti earthquake? a. A tsunami wiped out the city. b. Landslides covered large areas. c. The buildings were poorly built. d. The residents did not evacuate in time.

a. A tsunami wiped out the city.

Which type of wave is a compressional body wave? a. P-wave b. S-wave c. L-wave d. R-wave

a. P-wave

A tsunami is a. a sea wave generated by a displacement of water. b. a sloshing of water back and forth within a lake or a bay. c. a wave caused by unusually large tidal forces. d. the tendency of wet, clay-rich soils to behave like a liquid during an earthquake.

a. a sea wave generated by a displacement of water.

The moment magnitude is based on the __________ and __________ of the earthquake. a. amplitude; displacement b. amplitude; distance c. displacement; amount of damage d. amount of damage; distance

a. amplitude; displacement

Body waves include a. both S- and P-waves. b. both L- and R-waves. c. both surface and interior waves. d. P-waves only.

a. both S- and P-waves.

Moderate- and deep-focus earthquakes occur along ONLY a. convergent-plate boundaries. b. divergent-plate boundaries. c. transform-plate boundaries. d. hotspots.

a. convergent-plate boundaries.

The point within Earth where an earthquake takes place is termed the a. focus. b. epicenter. c. eye of the fault. d. vertex.

a. focus.

At any point along the surface of any nonvertical fault, as shown in the following figure, the a. hanging wall lies vertically above the footwall. b. footwall lies vertically above the hanging wall. c. hanging wall lies to the left of the footwall. d. footwall lies to the left of the hanging wall.

a. hanging wall lies vertically above the footwall.

The 2010 Haiti earthquake was so destructive because a. of poor construction standards that caused many buildings to collapse. b. stress had been building on the underlying fault for over 1,000 years. c. it generated a tsunami that was responsible for the majority of the lives lost. d. earthquake damage to the local nuclear power plant caused it to explode.

a. of poor construction standards that caused many buildings to collapse.

The Mercalli intensity scale tends to be very subjective and thus is generally only used for historical earthquakes that were near people but were not recorded by seismometers. The Mercalli scale may be considered subjective because it a. relies on testimony from people. b. does not take distance into account. c. can only be used for large earthquakes. d. cannot be used in heavily populated areas.

a. relies on testimony from people.

Which tectonic setting has the potential to create the largest earthquakes on Earth? a. shallow thrust faults associated with a convergent boundary b. deep focus faults associated with a convergent boundary c. thrust faults associated with a transform boundary d. ridge segment transform boundaries associated with divergent boundaries

a. shallow thrust faults associated with a convergent boundary

Which of the following does NOT affect the severity of damage from an earthquake? a. weather b. distance c. duration d. magnitude

a. weather

According to the moment magnitude scale (Mw), a magnitude 8 earthquake would be 1,000 times greater than a magnitude __________ earthquake. a. 9 b. 5 c. 7 d. 4

b. 5

Which earthquake scale is used to assess the effects of an earthquake on humans and human-made structures? a. Richter scale b. Mercalli scale c. moment magnitude scale d. surface-wave magnitude scale

b. Mercalli scale

Which type of seismic wave has the fastest velocity? a. L-wave b. P-wave c. R-wave d. S-wave

b. P-wave

Which of the following is a good technique for building safer structures in an earthquake zone? a. Use concrete-block construction. b. Use wood-frame construction. c. Use unreinforced walls so the walls can sway. d. Place shock absorbers on the tops of buildings to add stability.

b. Use wood-frame construction.

The locations of major earthquakes a. can be anywhere on the globe. b. are usually along plate boundaries. c. are usually near the centers of tectonic plates. d. are only on the overriding plate at a convergent boundary.

b. are usually along plate boundaries.

The P-wave shadow zone marks the a. crust-mantle boundary. b. core-mantle boundary. c. outer core-inner core boundary. d. lithosphere-asthenosphere boundary.

b. core-mantle boundary.

A surface along which rock on opposed sides is offset by an earthquake-induced slip is called a a. joint. b. fault. c. fold. d. wall.

b. fault.

The Richter scale a. depends on the distance from the epicenter of an earthquake. b. measures the size of earthquake by the amount of ground motion. c. takes the size of the slipped area on the fault into account. d. is a linear scale.

b. measures the size of earthquake by the amount of ground motion.

Aftershocks are usually a. much stronger than the mainshock. b. much weaker than the mainshock. c. about the same as the mainshock. d. along a different fault than the mainshock.

b. much weaker than the mainshock.

Surface waves a. travel more rapidly than body waves. b. produce most of the damage to buildings during earthquakes. c. are the first waves initially produced in an earthquake. d. are the first waves to arrive at a seismograph station after an earthquake.

b. produce most of the damage to buildings during earthquakes.

During an earthquake, if the hanging wall slides upward relative to the footwall and if the fault is steep (closer to vertical than horizontal), then the fault is termed a __________ fault. Refer to the following figure for an example of such a feature. a. normal b. reverse c. strike-slip d. thrust

b. reverse

Vertical motion seismographs record earthquakes by producing a squiggly diagram called a a. wave sheet. b. seismogram. c. pictogram. d. seismograph.

b. seismogram.

An earthquake occurs with an epicenter in the town of New Madrid, Missouri, in the interior of the North American Plate. Where might the hypocenter of this earthquake plausibly be found? a. in New Madrid (hypocenter and epicenter mean precisely the same thing) b. 20 km south of New Madrid c. 20 km beneath New Madrid d. 200 km north of New Madrid

c. 20 km beneath New Madrid

To find the location of an earthquake's epicenter, you need to calculate the distance from the epicenter to ____ different seismometer stations. a. 1. b. 2. c. 3. d. 4.

c. 3.

Interpret the travel-time curve shown. Approximately how many minutes elapsed between the arrival of the first P-wave and the arrival of the first S-wave at Station 3? a. 3 b. 5.5 c. 7 d. 17

c. 7

Which of the following statement is the most accurate? a. Earthquakes are caused when water or oil penetrate into the subsurface and cause a lubricating effect. This causes the rocks to slip. b. Earthquakes are caused by an increase in magma pushing its way through transform boundaries. c. Earthquakes are caused when stresses on rocks are too great and the rock breaks, typically along fault lines or plate boundaries.

c. Earthquakes are caused when stresses on rocks are too great and the rock breaks, typically along fault lines or plate boundaries.

Which of the following statements is true? a. An earthquake would most likely occur along plate boundaries. b. An earthquake would most likely occur in the middle of a continent. c. Earthquakes can occur at both plate boundaries and in the middle of a continent

c. Earthquakes can occur at both plate boundaries and in the middle of a continent

How can geologists know what the interior of the Earth looks like when we can't see it? a. Geology uses rocks at the surface to infer what the interior of the Earth looks like. b. Geologists are able to use core sample from drilling through the oceanic crust to see what the interior looks like. c. Geologists use a variety of methods to "see" the interior of the Earth including the study of seismic waves and the magnetic field.

c. Geologists use a variety of methods to "see" the interior of the Earth including the study of seismic waves and the magnetic field.

On December 26, 2004, a magnitude 9.3 earthquake generated a tsunami that devastated coastlines on the __________ Ocean. a. Atlantic b. Arctic c. Indian d. Pacific

c. Indian

Which peripheral hazard of earthquakes caused the damage shown in the photo?a. Liquefaction b. Fire c. Landslide d. Tsunami

c. Landslide

Which type of waves are compressional in nature? a. S b. L c. P

c. P

What kind of waves travel with a compressional motion? a. Love waves b. Rayleigh waves c. P-waves d. S-waves

c. P-waves

The areas shown in gray occur because a. S-waves cannot pass through the liquid outer core. b. S-waves can pass through the solid inner core. c. P-waves are refracted at the core-mantle boundary. d. P-waves are reflected at the asthenosphere-mantle boundary.

c. P-waves are refracted at the core-mantle boundary.

Andrija Mohorovicic discovered the crust-mantle boundary, which is now named after him, because he realized that a. S-waves were traveling faster than P-waves. b. no P-waves could travel through the boundary. c. P-waves were refracted at the boundary. d. no S-waves could travel through the boundary.

c. P-waves were refracted at the boundary.

When reading a seismogram printout of an earthquake recording, which wave will the first to register? a. S. b. L. c. P.

c. P.

Which type of wave moves like this? a. S. b. L. c. P.

c. P.

Which seismic wave phase causes the ground to roll like a wave? a. P-wave b. S-wave c. Rayleigh wave d. Love wave

c. Rayleigh wave

Which type of waves are shear waves? a. L b. P c. S

c. S

Earthquakes that occur in a band called the __________ can be used to track the motion of subducted oceanic lithosphere. a. Wegener belt b. seismic gap c. Wadati-Benioff zone d. Richter zone

c. Wadati-Benioff zone

IF you were buying a home home in California, where would you prefer to build your home? a. a brick building in an area underlain by artificial till b. a brick structure in area underlain by sand and silt sediments c. a brick building in an area underlain by granite

c. a brick building in an area underlain by granite

Which of the following would be a likely indication of an impending earthquake? a. an aftershock b. a single shock c. a foreshock

c. a foreshock

Where would an earthquake most likely occur? a. in the middle of a continent b. in the middle of an ocean c. along plate boundaries

c. along plate boundaries

Long-term earthquake predictions a. can forecast the month in which an earthquake will occur. b. involve monitoring fault movement in real-time. c. are based on the study of historic recurrence intervals. d. are based on the last known earthquake in a region.

c. are based on the study of historic recurrence intervals.

What rock makes up the oceanic crust? a. granite b. gabbro c. basalt

c. basalt

The crust, core and mantle are the main layers of the Earth and are separated based on their ________. a. texture. b. temperature. c. composition.

c. composition.

The Earth's magnetic field is thought to be a direct result of ________. a. conduction in the outer core. b. convection in the inner core. c. convection in the outer core.

c. convection in the outer core.

A cyclic loop of molten rock rising close to the surface of the earth, cool and and sinking again is an example of ________ heating which is found in the ________. a. conduction; mantel. b. conduction, crust. c. convection; mantle.

c. convection; mantle.

The quantity of motion that occurs along a fault is termed a. the fault gouge. b. the fault gauge. c. displacement. d accumulation.

c. displacement.

The spot on the surface directly above where the earthquake occurred is called the what? a. earthquake b. focus c. epicenter

c. epicenter

The __________ the earthquake, the LESS severe the damage will be. a. larger the magnitude of b. longer the duration of c. farther you are from d. closer you are to

c. farther you are from

Earthquakes often occur along a. bedding planes. b. terminal moraines. c. faults. d. river valleys.

c. faults.

Which of the following is considered a secondary hazard associated with earthquakes? a. tsunamis b. liquefaction c. fire

c. fire

A primary force opposing motion on all faults is a. covalent bonds. b. gravity. c. friction. d. the Van der Waals force.

c. friction.

What rock makes up the continental crust? a. basalt b. gabbro c. granite

c. granite

Temperatures ________ as you go deeper into the Earth. a. decrease b. stay about the same c. increase

c. increase

Which of the following is NOT associated with earthquakes? a. tsunamis b. liquefaction c. lahar

c. lahar

Wet and unconsolidated substrates are uniquely susceptible to __________ during an earthquake. a. displacement b. collapse c. liquefaction d. faulting

c. liquefaction

Which of the following is characterized by brittle, rigid, and solid? a. asthenosphere b. mantle c. lithosphere

c. lithosphere

Which of the following is least likely to produce an earthquake? a. movement along a fault line b. plate motion c. magma moving in the mantle

c. magma moving in the mantle

The P-wave and S-wave shadow zones are similar in that ________. a. all seismic waves are recorded there. b. only certain seismic waves are recorded there. c. no seismic waves are recorded there.

c. no seismic waves are recorded there.

Long-term prediction methods include(s) a. early warning systems. b. behavior of animals. c. seismic risk assessment. d. recognition of foreshocks.

c. seismic risk assessment.

The inner core is ________. a. liquid. b. semi-solid. c. solid.

c. solid.

If a fault is nearly vertical in orientation and the two walls of rock on opposite sides slide past one another horizontally, the fault is termed a __________ fault. Refer to the following figure for an example of such a feature. a. normal b. reverse c. strike-slip d. thrust

c. strike-slip

According to the image below, which seismic wave phase is likely to cause the most damage? a. P-wave b. S-wave c. surface wave d. aftershock

c. surface wave

Generally, which type of earthquake waves travel with the slowest velocity? a. S-waves b. P-waves c. surface waves d. All earthquake waves travel at the same speed.

c. surface waves

You are visiting a relative in California, and while you are at the park, an earthquake occurs. You notice what looks like wave motion on the surface of the Earth. What types of waves are you actually seeing? a. body waves b. shearing waves c. surface waves

c. surface waves

As a seismologist, you are asked to write a report on the latest earthquake. Your boss want to know the details of the earthquake in terms of damaged caused to the city and surrounding area. In order to get this type of information, which scale would you use? a. the magnitude scale b. the Richter scale c. the Modified Mercalli scale

c. the Modified Mercalli scale

What is the feature called where most active earthquakes (and volcanoes) are found? a. the Atlantic Ring of Fire b. the Arctic Ring of Fire c. the Pacific Ring of Fire

c. the Pacific Ring of Fire

Which two scales are the most similar? a. the Modified Mercalli and the Richter Scales b. the Modified Mercalli and the Magnitude Moment Scales c. the Richter and the Magnitude Moment Scales

c. the Richter and the Magnitude Moment Scales

The Modified Mercalli Scale measures what? a. the largest jolt of energy caused by an earthquake b. the total energy released by an earthquake c. the damage caused by an earthquake

c. the damage caused by an earthquake

The RIchter Scale measures what? a. the damage caused by an earthquake b. the total energy released by an earthquake c. the largest jolt of energy caused by an earthquake

c. the largest jolt of energy caused by an earthquake

The S-wave shadow zone indicates a. the mantle and core are composed of the same material. b. the crust is similar to the core in composition. c. the outer core is liquid. d. the mantle is liquid.

c. the outer core is liquid.

The Magnitude Moment Scale measures what? a. the damage caused by an earthquake b. the largest jolt of energy caused by an earthquake c. the total energy released by an earthquake

c. the total energy released by an earthquake

At a minimum, how many seismic stations are necessary to locate the epicenter of an earthquake? a. one b. two c. three d. four

c. three

Scientists are currently trying to find ways to better predict earthquakes. Currently, studies are underway that would potentially give us some warning. However, even these new advances ________. a. would only work in certain areas. b. would not work for all types of earthquakes. c. would only give us a few seconds warning.

c. would only give us a few seconds warning.

An increase in size of one unit of magnitude translates to __________ times the ground motion. a. 1 b. 2 c. 32 d. 10

d. 10

The earthquake foci pattern east of Australia and just north of New Zealand indicates which tectonic setting? a. Hot spot activity b. Divergent plate boundary c. Transform plate boundary d. Convergent plate boundary

d. Convergent plate boundary

The vast majority of earthquakes occur a. associated with isostatic rebound. b. near hotspots. c. along passive margins. d. along all types of plate boundaries.

d. along all types of plate boundaries.

The larger the __________ of the wave, the MORE severe the damage will be. a. travel-time curve b. epicenter c. seismometer d. amplitude

d. amplitude

Liquefaction a. increases the cohesion between sediment grains in wet sediments. b. decreases the pressure of the water that fills the pore space between sediment grains. c. can cause roads, fences, and pipelines to crack and separate if they straddle a fault. d. can affect sand layers below the ground surface and cause them to erupt as sand volcanoes or sand boils.

d. can affect sand layers below the ground surface and cause them to erupt as sand volcanoes or sand boils.

Earthquakes in California are a. the result of reverse faulting along the San Andreas fault. b. the result of rifting along the San Andreas fault. c. always less than magnitude 6.5. d. due to stick-slip behavior along the San Andrea fault.

d. due to stick-slip behavior along the San Andrea fault.

The Modified Mercalli Intensity scale measures a. the amount of energy released by an earthquake. b. amplitude of P-waves. c. the dimensions of the slipped area on a fault. d. earthquake damage.

d. earthquake damage.

When a fault slips and the rock units on either side return to their original shape by generating vibrations, it is called a. a foreshock. b. rupture formation. c. elastic deformation. d. elastic rebound.

d. elastic rebound.

Earthquakes can often produce __________ by breaking gas lines. a. landslides b. flooding c. sinkholes d. fires

d. fires

S-waves are unable to pass through the Earth's outer core, which indicates that the outer core is a. a void space within the Earth. b. compositionally different from the mantle. c. composed of an ultra-dense solid. d. liquid.

d. liquid.

A tsunami a. is narrower but taller than the largest wind-driven waves. b. grows no taller than 30 feet high. c. is dangerous near its source but dies out within about 200 km. d. may be just a broad, gentle swelling out at sea but grows as it approaches shore.

d. may be just a broad, gentle swelling out at sea but grows as it approaches shore.

Earthquake prediction is not highly reliable, but geologists do know a. that earthquakes never happen outside of seismic belts. b. that recurrence intervals can provide accurate short-term predictions. c. that in the long term, earthquakes happen at predictably spaced time intervals. d. more earthquakes happen along plate boundaries than happen at intraplate locations.

d. more earthquakes happen along plate boundaries than happen at intraplate locations.

One difference between P- and S-waves is that a. only S-waves can travel through a solid. b. only P-waves can travel through a solid. c. only S-waves can travel through a liquid. d. only P-waves can travel through a liquid.

d. only P-waves can travel through a liquid.