Geology Module 9

a. What is a foreshock? b. What is an aftershock?

A. A foreshock is a small series of earthquakes that come before a major earthquake. B. an aftershock is a small series of earthquakes that come after a major earthquake.

a. Describe a normal fault. b. What kind of stresses lead to a normal fault?

A. A normal fault is a fault whose hanging wall slipped down the slope. B. They are formed during the extension, stretching of the crust.

a. What is an earthquake focus? b. What is an earthquake epicenter?

A. An earthquake focus is a point in which rock first starts to rupture and slip on a fault B. An earthquake epicenter is a point that lies directly above the focus and can be pinpointed on a map of the earth

Define the following terms: a. Earthquake magnitude b. Earthquake intensity

A. Earthquake magnitude is the measured amount of ground shaking that occurs during an earthquake. B. Earthquake intensity is the effect or consequences of an earthquake and its ground-shaking ability.

a. Describe a strike-slip fault. b. What kind of stresses lead to a strike-slip fault?

A. a Strike-slip fault is an almost vertical fracture and one block slides laterally past the other. B. Shear stress

a. Describe a reverse fault. b. What kind of stresses lead to reverse faulting?

A. a reverse fault is a fault whose hanging wall slipped up the slope. B. They are formed during compression of the crust.

Identify the FALSE statement. -Seismic waves travel faster in solids than through liquids. -P-waves in a porous sandstone will travel slower than P-waves traveling through a crystalline rock. -Both P- and S-waves can travel through liquids. -The velocity of seismic waves can change (speed up or slow down) as they pass through different rock types.

Both P- and S-waves can travel through liquids.

A 200-km-thick, warm layer of mantle just above the core-mantle boundary and discovered by seismic tomography is called:

D" layer.

What is "elastic rebound" and how does it relate to earthquakes?

Elastic rebound is a theory developed by geologists that describes the elasticity of rocks and their tendency to rebound to their original, unbent shape after the stress has been relieved through a seismic event. This related to earthquakes because they are the vessel through which the stress is relieved.

Identify the FALSE statement. -Normal faults result from stretching the Earth's crust; thrust faults from squeezing and shortening it. -ML, mb, and Ms earthquake magnitude scales can accurately define extremely large earthquakes. -Moment magnitude (Mw) rating is the number now used for the official (archival) record. -All earthquake magnitude scales are logarithmic, which means a difference of one unit in magnitude reading represents a 10-fold difference in ground motion.

ML, mb, and Ms earthquake magnitude scales can accurately define extremely large earthquakes.

Which statement is TRUE? -R- and L-waves are surface seismic waves. -S-waves are compressional body waves; P-waves are shear body waves. -Surface waves are the first to show up on a seismogram recording of a quake. -Shallow-focus quakes do less damage than deep-focus quakes.

R- and L-waves are surface seismic waves.

Which statement is TRUE? -R- and L-waves are surface seismic waves. -S-waves are compressional body waves; P-waves are shear body waves. -Surface waves are the first to show up on a seismogram recording of a quake. -Shallow-focus quakes do less damage than deep-focus quakes.

R- and L-waves are surface seismic waves.

Describe stick-slip behavior and how it relates to earthquake occurrence over time.

Stick-slip behavior is cyclical behavior that occurs at faults. Along the fault plane, friction prevents movement but stress continues to build up until it reaches a point where the stress is overwhelming. The cycle then "resets" and friction prevents movement and stress builds up again.

Identify the FALSE statement. A positive gravity anomaly would be formed by: -an observed gravitational pull that is stronger than the reference geoid. - a large reserve of metal ore. - extra mass at depth. - a zone of open space, such as a cave or cavern.

a zone of open space, such as a cave or cavern.

Identify the FALSE statement. Seismographs: -may be the mechanical type, consisting of a weight, spring, frame, pen, and revolving cylinder. -may be electronic, consisting of a heavy cylindrical magnet, coil of wire, spring, and computer readout of the voltage generated. -are only sensitive enough to record ground movements down to about 1 mm. -operate because of inertia; one part of the instrument remains motionless while the recording device moves in response to seismic waves.

are only sensitive enough to record ground movements down to about 1 mm.

The locations of major earthquakes and volcanic eruptions:

are usually along plate boundaries.

Which statement is FALSE? Liquefaction: -can cause clay-rich sediment to turn into an unstable slurry of clay and water. -is the sudden loss of strength of some soils that happens because of earthquake shaking. -caused the greatest amount of damage in the San Francisco quake of 1908. -can affect sand layers below ground surface and cause them to erupt as sand volcanoes or sand boils.

caused the greatest amount of damage in the San Francisco quake of 1908.

Identify the FALSE statement. Fault creep: -is slow but steady movement along a fault. -causes additional buildup of stress in an area, thereby increasing the likelihood that a strong quake will happen there soon. -may be happening in seismic gaps. -may happen because the rock is weak and can slip smoothly, without creating shock waves.

causes additional buildup of stress in an area, thereby increasing the likelihood that a strong quake will happen there soon.

The P-wave shadow zone:

forms because of changes at the core-mantle boundary.

Which of the following earthquake phenomena is the least likely to actually injure or kill humans?

ground shaking

When the mass of water that an iceberg displaces is equal to the mass of the iceberg, it floats. This is an example of:

isostasy

A tsunami:

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

Identify the FALSE statement. The Richter scale: -measures the size of a quake in terms of the damage it does (its intensity). -measures the amplitude of the largest deflection on a seismogram in response to specifically defined seismic waves at a specifically defined distance and depth. - is today termed a local magnitude reading (ML). -works well only for shallow, nearby earthquakes.

measures the size of a quake in terms of the damage it does (its intensity).

Earthquake prediction is not highly reliable, but geologists do know:

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

Which of the following is NOT a mineral found in the mantle? -olivine -quartz -perovskite -magnesium spinel

quartz

Which statement is TRUE? Earthquakes in California are: -the result of reverse faulting along the San Andreas Fault. -the result of widening along the San Andreas Fault, which will eventually cause western California to sink into the ocean. -always above magnitude 7.5 because the San Andreas is such a large fault. -shallow and occur in the upper 15 km of crust, even though the San Andreas fault cuts through the crust to deeper depths.

shallow and occur in the upper 15 km of crust, even though the San Andreas fault cuts through the crust to deeper depths.

Identify the FALSE statement. The low-velocity zone (LVZ), found 100-200 km beneath ocean crust, represents: - the upper part of the asthenosphere. -conditions where mantle peridotite partially melts and fills voids between grains. - the crust-mantle boundary. - a weak layer in the Earth's interior.

the crust-mantle boundary.

Seismic wave velocity is affected by each of the following EXCEPT: -thickness of the rock layer. -density of the material. -the rock's rigidity (resistance to bending). -compressibility of the rock unit.

thickness of the rock layer.

Which of the following is NOT a good technique for building earthquake-resistant structures? -use concrete-block rather than wood-frame construction. -bolt bridge spans to the top of support columns. -wrap bridge supports with steel cables. -use supports that are capable of holding more than the static (unmoving) weight of the building.

use concrete-block rather than wood-frame construction.