Chapter 11 Geology

What is meant by elastic rebound?

Elastic rebound refers to how the slippage along a fault (i.e., earthquake) allows the deformed rock to regain its original shape in a new location.

What characteristics do faults that experience fault creep exhibit?

Fault creep tends to produce slow, gradual displacements of rock blocks with little seismic shaking.

Why are short-range earthquake predictions often unsuccessful?

Foreshocks do not occur before every earthquake. Animal behavior is unreliable.

Who was the first to explain the mechanism by which most earthquakes are generated?

H. F. Reid first explained the mechanism by which most earthquakes are generated by conducting a landmark study shortly after the 1906 San Francisco earthquake.

How do seismologists create long-range earthquake predictions?

Identifying seismic gaps

What is an earthquake, and how do earthquakes generally occur?

a sudden shaking of the ground that is caused by the rapid movement of one block of rock past another block of rock at a fault

Aside from the answer to the previous question, in what other setting(s) do(es) strong earthquake activity occur?

along transform faults in continents, along strike-slip faults in continents

The slippage of an earthquake starts ________.

at the focus or hypocenter

In addition to the destruction created directly by seismic vibrations, how else can earthquakes cause destruction?

by triggering a firestorm within populated areas. by triggering a landslide, by triggering a tsunami

Which type(s) of seismic waves tend(s) to cause the greatest destruction to buildings

surface waves

Which is the zone of the greatest amount of seismic activity?

the circum-Pacific belt

What information does a time-travel graph provide?

the distance from the earthquake to the recording station

Which type of earthquake destruction can cause houses to sink into the ground?

liquefaction

How does a seismograph work?

A seismograph works by suspending a weight from bedrock, which remains motionless during an earthquake. A rotating drum that is affixed to the moving bedrock moves as the rock moves, recording the relative displacement between the stationary weight and the rotating drum. A seismograph can measure P waves, S waves, and surface waves.

How much more energy does a magnitude 8.0 earthquake release than does a magnitude 7.0 earthquake?

An earthquake with a magnitude of 8.0 releases 32 times more energy than an earthquake with a magnitude of 7.0.

How are the long-range forecasts of earthquakes useful?

Long-range forecasts of earthquakes provide important guides for building codes so that structures such as buildings, dams, and roadways can be built to withstand expected levels of shaking.

______ faults are associated with ______ plate boundaries.

Megathrust; convergent

Are accurate, short-range earthquake predictions currently possible using modern seismic instruments?

No, there are currently no reliable methods available for making short-range earthquake predictions.

How does triangulation determine the epicenter of an earthquake?

On a map, a circle is drawn around each of three recording stations, with the radius being the distance from the station to the epicenter of the earthquake. The epicenter is located where the three circles intersect.

Which type of seismic wave can pass through the liquid outer core?

P waves

What are the differences between P waves, S waves, and surface waves?

P waves are the fastest and have the lowest amplitudes; S waves are the second-fastest and have the second-lowest amplitudes; surface waves are the slowest and have the highest amplitudes.

Which are the last seismic waves to arrive at a seismic station?

Surface waves

What is a tsunami?

a large ocean wave generated when a megathrust fault suddenly lifts a slab of seafloor

If both earthquakes are of the same magnitude, why can an earthquake that occurs east of the Rockies produce damage over a larger area than the damage produced by an earthquake in California?

The bedrock in the eastern and central United States is more rigid than that in the western United States, which allows seismic waves to travel greater distances with less attenuation.

Why could a repeat of the 1811-1812 New Madrid, Missouri, earthquakes be destructive to the Memphis, Tennessee, metropolitan area?

The buildings in Memphis are on top of unconsolidated floodplain deposits and thus are more susceptible to damage than buildings on top of solid bedrock. Memphis does not have adequate earthquake provisions in its building code.

For which reason(s) might an earthquake with a magnitude of 7.0 result in more death and destruction than a quake with a magnitude of 8.0?

The construction materials used in buildings in the area with the 7.0 magnitude earthquake are of poorer quality than those used in the area of the 8.0 magnitude earthquake. The area with the 7.0 magnitude earthquake has a higher population than the area with the 8.0 magnitude earthquake. The 7.0 magnitude earthquake lasts longer than an 8.0 magnitude earthquake

How are faults, hypocenters, and epicenters related?

The hypocenter is the exact point underground along a fault where the slippage of the two blocks of rock occurs. The epicenter is the point on Earth's surface that is directly above the hypocenter.

Why is the moment magnitude scale favored over the Richter scale for large earthquakes?

The moment magnitude scale measures the total energy released, whereas the Richter scale only measures the amplitude of the largest seismic wave.

What does the Modified Mercalli Intensity scale tell us about an earthquake?

how intense an earthquake feels

What information is used to establish the lower numbers on the Modified Mercalli Intensity scale?

how the earthquake is felt by people in an area

Which type of fault tends to produce the most destructive earthquakes?

megathrust fault

The highest magnitude earthquakes typically occur _______.

near subduction zones

What two types of faults are common at divergent plate boundaries?

normal and transform faults

Which type(s) of plate boundary is/are associated with Earth's largest earthquakes?

ocean-oceanic convergent plate boundary, oceanic-continental convergent plate boundary

Which of the following would be the best to use to compare large earthquakes around Earth?

the moment magnitude scale

What influences the amount of destruction that seismic vibrations cause to human-made structures?

the nature of the building processes and construction processes used, intensity of the vibrations, the nature of the ground underneath human-made structures, duration of the vibrations

During an earthquake, _____.

the slippage continues along the fault until it reaches a point where rocks are not sufficiently strained to continue slippage