Question 1

For a shallow-focus earthquake, the hypocentre and epicentre are virtually coincident, especially as detected at distant seismograph stations.

Accepted Answer

A shallow-focus earthquake has its hypocentre (the point where the earthquake originates underground) relatively close to the earth's surface, which means that the epicentre (the point on the surface directly above the hypocentre) is also very close. As a result, the two positions can be considered virtually coincident, especially when detected at distant seismograph stations.

Question 2

The energy released by an earthquake is very intense, and felt just as strongly in distant places, in accordance with its magnitude.

Accepted Answer

The energy released by an earthquake diminishes with distance from the epicenter, so it is not felt as strongly in distant places. The intensity of shaking and damage decreases as you move away from the earthquake's source.

Question 3

When vibrations (ground motion)from a distant earthquake reach a seismograph, the inertia of the suspended mass keeps it relatively stationary, while the Earth and the case of the instrument move, oscillating around it.

Accepted Answer

This is the principle behind how a seismograph works. The stationary mass of the seismograph allows it to detect the ground motion caused by an earthquake.

Question 4

The Cascadia Subduction Zone is typical in its earthquake activity for most young subduction zones.

Accepted Answer

The Cascadia Subduction Zone is atypical because it remains locked for long periods, leading to infrequent but very large earthquakes, unlike many young subduction zones that have more frequent, smaller earthquakes.

Question 5

The epicentre of an earthquake is on the surface of the Earth directly above the hypocentre.

Accepted Answer

The epicenter is indeed the point on the Earth's surface directly above the hypocenter (or focus), which is the actual location where the earthquake begins its rupture.

Question 6

The system of locating earthquakes depends on nearby reports of the shaking and high speed communication lines.

Accepted Answer

The answer of The system of locating earthquakes depends on...

Question 7

S waves are waves that can travel through solid and liquid media.

Accepted Answer

S waves, or secondary waves, can only travel through solid materials because they require the material to have shear strength, which liquids do not possess.

Question 8

Just before a major earthquake, locked portions of major faults exhibit a period of fault creep.

Accepted Answer

Fault creep is a slow, steady displacement along a fault that occurs without significant accompanying earthquakes, whereas locked portions of faults typically do not exhibit movement until they rupture suddenly in an earthquake.

Question 9

Earthquakes result from the sudden release of elastic strain energy previously stored in rocks surrounding a zone of fault movement.

Accepted Answer

This is a well-established explanation for the causes of earthquakes.

Question 10

Following a major earthquake, aftershocks diminish in magnitude but may still be powerful enough to destroy or further damage weakened buildings.

Accepted Answer

Aftershocks are smaller earthquakes that occur after a major earthquake. Although they may decrease in magnitude over time, they can still be strong enough to cause damage to structures that were already weakened during the initial earthquake. Therefore, it is important to take precautions during the aftershock period and continue to assess the safety of buildings and structures.

Question 11

As a P wave passes, material particles vibrate at right angles to the path followed by a point moving with the wave.

Accepted Answer

P waves, or primary waves, are a type of seismic wave that causes material particles to vibrate in the same direction as the wave is moving, not at right angles. This type of wave motion is called longitudinal or compressional.

Question 12

As determined by dated sedimentary evidence in west coast marshes, there have been at least 13 great "Megathrust" earthquakes on the Cascadia Subduction Zone during the past 6000 years.

Accepted Answer

Dated sedimentary evidence in west coast marshes confirms that there have indeed been at least 13 great "Megathrust" earthquakes that have occurred on the Cascadia Subduction Zone over the past 6000 years.

Question 13

The fact that ________ is good evidence for a solid inner core.

Accepted Answer

P waves are faster in the inner core than in the outer core because the inner core is solid, while the outer core is liquid. The fact that P waves speed up when passing through the inner core gives evidence that it is solid. This suggests that the inner core is made of a dense and rigid material, likely iron and nickel alloy, while the outer core is mostly liquid metal.

Question 14

P waves can travel through solids and liquids but not through gases.

Accepted Answer

P waves, or primary waves, can travel through solids, liquids, and gases; they are compressional waves that can propagate through all states of matter.

Question 15

If the P, S, and surface waves arrive almost simultaneously, the seismic recording station is virtually at the epicentre of the earthquake.

Accepted Answer

When the P, S, and surface waves arrive almost simultaneously, it indicates that the seismic recording station is very close to the epicentre of the earthquake. Hence, the statement is true.

Question 16

Reid's elastic rebound theory of earthquake generation was based on his studies following the 1906 San Francisco earthquake.

Accepted Answer

Reid's elastic rebound theory was formulated after studying the 1906 San Francisco earthquake.

Question 17

Horizontal vibrations, such as induced by strike-slip faulting, S-waves and some types of surface waves are generally much more dangerous to tall buildings than vertical up and down ground shaking.

Accepted Answer

Horizontal vibrations can cause much greater stress on tall buildings than vertical vibrations, as they can induce significant lateral forces and cause structural damage or collapse. This is why building codes and designs often take into account the effects of horizontal shaking and incorporate measures to mitigate them.

Question 18

Some large earthquakes are preceded by smaller magnitude foreshocks.

Accepted Answer

This statement is true. Some large earthquakes are often preceded by smaller magnitude foreshocks. Foreshocks are smaller earthquakes, which occur in the vicinity of a larger earthquake, and may give advance warning of an impending, larger earthquake.

Question 19

The time between the first P-wave and S-wave arrivals is a measure of the distance from a receiving station to the epicentre of the earthquake.

Accepted Answer

This statement is true. The time interval between the P-wave and S-wave arrivals is determined by the distance of a receiving station from the epicentre of an earthquake, with larger time intervals indicating greater distances. This information can be used to calculate the location of the earthquake's epicentre.

Question 20

On earthquake distribution maps, the boundaries of the Earth's tectonic plates are shown as zones of high seismic activity.

Accepted Answer

This is true because tectonic plates are constantly moving and interacting with each other, which causes stress and friction along their boundaries, resulting in earthquakes.

Quiz 10: Earthquakes and Earth's Interior