Question 1

The large left step in the San Andreas fault in the Los Angeles area causes compressive ruptures along east-west-oriented ________ faults as in the 1971 San Fernando and 1994 Northridge events.

Accepted Answer

The large left step in the San Andreas fault in the Los Angeles area causes compressive ruptures along east-west-oriented thrust faults, as evidenced by the 1971 San Fernando and 1994 Northridge earthquakes. These events are characterized by the horizontal compression and vertical displacement of rock layers.

Question 2

In the 1989 Loma Prieta quake,the Marina District building collapses were extensive,and numerous destructive fires broke out,due to all but which one of the following?

Accepted Answer

The question asks for the reason why numerous destructive fires broke out in the Marina District during the 1989 Loma Prieta quake, and all options except for D provide plausible explanations. Choice D, "widespread looting and arson," is not a valid reason as it suggests that humans intentionally caused the fires, which is not supported by the facts of the earthquake. Therefore, the correct answer is D, and the other options (A, B, and C) could all contribute to the building collapses and fires observed in the Marina District.

Question 3

Today,North America has several small- to medium-sized plates subducting beneath its ____________.

Accepted Answer

The correct answer is B) western margin. This is because the Pacific Plate and other smaller plates are subducting beneath the North American Plate along the western margin, particularly along the coastlines of Alaska, Canada, and the western United States. This subduction is responsible for the significant volcanic and seismic activity in these regions.

Question 4

How does a locked zone of a large strike-slip fault catch up with a creep zone?

Accepted Answer

A locked zone of a large strike-slip fault catches up with a creep zone through infrequent but large fault movements, often resulting in large earthquakes. This is because the stress accumulated in the locked zone is released suddenly when it overcomes the frictional resistance along the fault plane.

Question 5

In San Francisco's Marina district in 1989,some fill underwent permanent deformation and settling,and some formed slurries as underground water and loose sediment flowed like a fluid in a process known as ______________.

Accepted Answer

The process described in the question, where loose sediment and water flow like a fluid, is known as liquefaction. Solifluction refers to the slow downhill movement of soil due to freezing and thawing, while creep refers to the gradual movement of Earth materials due to gravity. Plasticity and asthenocity are not related to the process described in the question.

Question 6

Another class of active faults is created by southern California pushing into the "Big Bend" of the San Andreas fault.These faults are __________________.

Accepted Answer

The answer of Another class of active faults is created...

Question 7

Constraining bends in large strike-slip faults commonly "lock up";thus,movements there tend to be _________________.

Accepted Answer

When large strike-slip faults experience constraining bends, it causes the rock to accumulate strain energy. As this energy builds up, the fault will eventually "lock up," meaning that the rock is unable to move past the constraining bend without a significant amount of force. As a result, movements at these locations tend to be infrequent and large, as the strain energy must build up to a certain point before the rock can slip past the constraining bend.

Question 8

In 1985 in Mexico City,building damages were the greatest and the number of deaths the highest where all but which one of these factors combined and created resonance:

Accepted Answer

The correct answer is C because single-story buildings typically have a much shorter resonant period than 1 second, and thus, they were not the ones that vibrated themselves to pieces due to resonance with the seismic waves. The resonance effect was most pronounced in taller buildings, particularly those between 6 to 16 stories, which matched the frequency of the seismic waves.

Question 9

The San Andreas fault's earthquakes in historic time include which of the following?

Accepted Answer

All three options are correct.

Question 10

Organic material in sediment layers can be dated by measuring the amount of radioactive ________ present.

Accepted Answer

Organic material in sediment layers can be dated by measuring the amount of radioactive carbon-14 present. The carbon-14 dating technique is widely used by scientists to determine the age of materials containing carbon-based substances. As carbon-14 decays over time, by comparing the amount of carbon-14 in a sample with the initial amount of carbon-14, an estimate of the sample's age can be calculated.

Question 11

In the last 5.5 million years,rifting action has torn Baja California and California west of the San Andreas fault (including San Diego,Los Angeles,and Santa Cruz)from the ______________.

Accepted Answer

The San Andreas fault marks the boundary between the Pacific plate and the North American plate. Rifting action has caused the Baja California and California regions west of the San Andreas fault to separate from the North American plate and move onto the Pacific plate. Therefore, the correct option is D: North American plate and piggybacked them onto the Pacific plate.

Question 12

We know that the part of California on the Pacific plate will not break off in a giant earthquake and sink into the Pacific Ocean because ______________________.

Accepted Answer

Isostasy refers to the equilibrium between the Earth's crust and mantle, preventing large landmasses from sinking.

Question 13

Much of the San Francisco Marina District is built on artificial fill debris from the buildings ruined by the 1906 earthquake.Seismic waves in 1989 were ____________ in this artificial fill.

Accepted Answer

Seismic waves were amplified in the artificial fill of the San Francisco Marina District. This is because the loose and poorly compacted soil of the fill allows seismic energy to be transmitted more efficiently, leading to greater ground motion and amplification of seismic waves.

Question 14

The largest earthquakes along western North America are due to subduction beneath the continent.They include ________________.

Accepted Answer

All of the given options are correct statements about the largest earthquakes along western North America, which are caused by subduction of the Pacific and Cocos plates beneath the continent. The 1964 Alaska earthquake (option A) is one of the largest earthquakes ever recorded and was due to subduction of the Pacific plate. The 1985 Mexico City earthquake (option B) was also caused by subduction, but of the Cocos plate. The subduction zone off the coast of Oregon and Washington (option C) generated a magnitude 9 earthquake in 1700, which was identified through various geological and historical records.

Question 15

In 1985,as a result of the Michoacan earthquake many buildings collapsed and killed about 8000 people in Mexico City,even though the city lies 350 miles from the epicenter.This was caused by all but which of the following?

Accepted Answer

The collapse of thousands of single-story frame houses is not mentioned as a cause of the collapse in Mexico City. The other options are all mentioned as contributing factors.

Question 16

The spreading-center segment at the southern end of California's Salton Sea is marked by all but which of the following?

Accepted Answer

The spreading-center segment at the southern end of California's Salton Sea is marked by glassy volcanic domes, high heat flow, boiling mud pots, and major geothermal energy reservoirs. However, it does not have a lack of small earthquakes because magma is too close to the Earth's surface. In fact, the area experiences many small earthquakes due to the movement of magma and the tectonic plates in the region.

Question 17

When is the best time for an earthquake to occur in California to minimize loss of life?

Accepted Answer

During the night, when most people are home and asleep, there are fewer people on the roads and in buildings, which would minimize the risk of injury or death.

Question 18

Recent work has shown that the last major earthquake in the Cascadia subduction zone occurred about 9 p.m.on 26 January 1700 and was about magnitude 9.This is known by __________________.

Accepted Answer

This choice combines the information from option A (analysis of growth rings in trees) and option B (the occurrence of a tsunami in Japan). Specifically, the absence of growth rings in trees after 1699 and the occurrence of a tsunami in Japan point to a major earthquake occurring at 9 p.m. on 26 January 1700 in the Cascadia subduction zone.

Question 19

Prehistoric earthquakes may be interpreted using faulted pond sediments.The amount of offset of sediment layers from one earthquake is proportional to the ________________.

Accepted Answer

The amount of offset of sediment layers is proportional to the earthquake magnitude. Therefore, choice C is the best answer. The other options - amount of time since the last major earthquake, amount of radioactive material in the sediment, and isostatic anomaly - are not directly related to the amount of offset of sediment layers in faulted pond sediments caused by earthquakes.

Question 20

When the part of California west of the San Andreas fault plows into Alaska it _______________.

Accepted Answer

When the part of California west of the San Andreas Fault plows into Alaska, it will become part of Alaska's southern margin. This is because Alaska is located on the North American Plate and the Pacific Plate is moving northward towards it. As the two plates collide, the Pacific Plate will be subducted beneath the North American Plate, causing the western part of California to become accreted to the southern margin of Alaska.

Quiz 5: Earthquakes Throughout the United States and Canada