Deck 9: Earthquakes and Earth's Interior

Question 1

What is a possible cause of intraplate earthquakes?

Answer 1

Intraplate earthquakes may be caused by localized stresses that build up along ancient faults that are generated by plate movements elsewhere.

Question 2

Explain how geologists calculate the distance between the epicenter of an earthquake and a given seismograph.

Answer 2

by measuring the difference between the arrival times of P-waves and S-waves at a seismograph location and using a time-distance graph

Question 3

Why has it been suggested that large earthquakes might be prevented by injecting water along isolated portions of fault zones,which have been inactive for an unusually long time? When was this technique discovered?

Answer 3

Local increase of fluid pressure can cause small earthquakes,which release stresses that would otherwise build up to cause a larger earthquake.This phenomenon was first recognized when it was discovered that liquid waste disposal by deep-well injection at Rocky Mountain Arsenal near Denver,Colorado,was responsible for numerous small earthquakes in the area.

Question 4

Besides the distance to the epicenter of an earthquake,what are two other things that a seismograph can tell us?

Question 5

How would you locate an earthquake epicenter using three seismograms,a map,and a protractor?

Question 6

How does elastic rebound theory explain when earthquakes occur?

Question 7

Compare the continental crust with oceanic crust in terms of composition and thickness.

Question 8

What causes tsunami,and why are they so destructive?

Question 9

Why are there so few earthquakes within plate interiors?

Question 10

What are two major and very useful differences between P- and S-waves?

Question 11

What is the purpose of trenching across an active fault?

Question 12

What is the evidence that Seattle is prone to earthquakes since there have been no quakes in historic times?

Question 13

What is the cause of most earthquakes?

Question 14

Within which belt or zone do the majority of earthquakes occur?

Question 15

Why do most earthquakes occur along the circum-Pacific belt?

Question 16

Explain the differences between the magnitude and the intensity of an earthquake,in terms of cause and effect.

Question 17

Why are earthquakes more likely to occur in Tokyo,Anchorage,and Los Angeles than they are in New York,London,or Paris?

Question 18

Which type(s)of seismic waves do seismographs record?

Question 19

Explain why the portions of the San Andreas fault that are "locked" are or are not safer than the parts where the two plates slide more or less continually.What is the name of the theory that deals with this issue?

Question 20

Why are most intermediate- to deep-focus earthquakes generated at convergent plate boundaries?

Question 21

An instrument that detects,records,and measures vibrations produced by an earthquake is called a(n)____________________.

Question 22

The elastic rebound theory of earthquakes postulates that rocks store the energy of ____________________ by bending until their internal strength is surpassed and they ____________________ and return to their former place.

Question 23

What is the highest temperature found on or in Earth,and why is that location so hot?

Question 24

Explain the differences between the magnitude and the intensity of an earthquake,in terms of how each is measured or observed.

Question 25

The theory of elastic rebound was proposed as a result of studies following the ____________________ earthquake in the year ____________________.

Question 26

Seismic waves that cause a rolling or swaying motion of the surface of the ground are called ____________________.

Question 27

What is Earth's average density,what are the average surface rock densities,and what does this tell us about the interior of Earth?

Question 28

Why do structures located on thick,soft sediment,especially water-saturated or artificial fill,suffer much greater damage than structures built on bedrock?

Question 29

Why are the paths of seismic waves curved?

Question 30

For what purpose is seismic tomography used?

Question 31

What evidence do scientists use to estimate the density and composition of the core?

Question 32

Almost all intermediate- to deep-focus earthquakes occur along ____________________ plate boundaries.

Question 33

The study of earthquakes is called ____________________.

Question 34

Explain the differences between the magnitude and the intensity of an earthquake,in terms of how many intensities and magnitudes a single earthquake can have.

Question 35

What is paleoseismology,and why is it important?

Question 36

The ____________________ or focus of an earthquake is the location within the crust where the energy of an earthquake is released.The ____________________ is the point on Earth's surface directly above the focus.

Question 37

Why do earthquakes of similar size often have such large differences in their destructiveness? Why are they so different in the number of people they kill?

Question 38

What happens to P-waves and S-waves when they encounter the core-mantle boundary,and what does this change in behavior indicate about the core?

Question 39

The two major types of seismic waves are ____________________ waves and ____________________ waves.

Question 40

Why do we know that the geothermal gradient near the surface cannot continue very deeply into Earth?

Question 41

The structural layer of earth that is liquid is the ____________________.

Question 42

The increase of temperature with depth is known as the ____________________.

Question 43

The term that best describes most tsunamis is ____________________.

Question 44

The number of seismograph records needed to locate the epicenter of an earthquake is ______.

Question 45

The structural layer that the P- and S-wave low-velocity zone,in the upper part of the mantle,closely corresponds to is the ____________________.

Question 46

Seismology has produced a great amount of information about ____.

A) the mechanisms of plate tectonics
B) the physical and chemical state of Earth's interior
C) the causes of mountain building
D) earthquakes
E) all of these

Question 47

Only 5 percent of all earthquakes occur within ____.

A) the Mediterranean-Asiatic Belt
B) the Circum-Mediterranean Belt
C) the interiors of plates and mid-oceanic ridges
D) the passive margins of continents and mid-oceanic ridges
E) the shields of continents and mid-oceanic ridges

Question 48

The velocity of S-waves is ____________________ than that of P-waves.S-waves cannot pass through materials that are ____________________ or ____________________.

Question 49

The velocities of P- and S-waves are determined by these two properties of the material they are passing through: ____________________ and ____________________.

Question 50

For every integer increase of magnitude on the Richter Scale,______ times more energy is released by the earthquake.

Question 51

If you could drill from the outer surface of Earth all the way to the center,you would pass through the major divisions of Earth,the ____________________,the ____________________,and finally the ____________________.

Question 52

According to the elastic rebound theory,____.

A) rocks will bend before they break
B) rocks will snap back into their original shape after faulting
C) rocks will break when their capacity to store energy of deformation has been exceeded
D) rocks will bend before they break AND snap back into their original shape after faulting
E) all of these

Question 53

The focus of the most destructive earthquakes is almost always ____.

A) shallow
B) intermediate
C) deep
D) intermediate and deep
E) none of these

Question 54

One of the strongest earthquakes ever recorded in North America was the intraplate quake known as the

A) 1811 New Madrid, Missouri, earthquake
B) 1886 Charleston, Carolina, earthquake
C) 1906 San Francisco earthquake
D) 1964 Anchorage, Alaska, earthquake
E) 1984 Mount St. Helens, Washington, earthquake

Question 55

The energy used in seismic tomography is ____________________.

Question 56

The depth to the Mohorovicic discontinuity is ______ km beneath the continents and between ______ and ______ km beneath the seafloor.

Question 57

The two types of body waves are _______ and _______ waves.

A) Raleigh; Love
B) compressional; extensional
C) secondary; primary
D) tensional; extensional

Question 58

The study of ancient earthquakes is known as ____________________.

Question 59

The focal depth ranges for shallow focus,intermediate focus,and deep focus earthquakes,respectively is

A) <70 km; 70 to 300 km; >300 km
B) <5 km; 5-50 km; >50 km
C) <1 km; 1-10 km; >10 km
D) <20 m; 20 m -100 m; >100 m

Question 60

The percentage of all earthquakes that occur along a plate boundary is nearly what?

A) 100 percent
B) 95 percent
C) 80 percent
D) 55 percent
E) 25 percent

Question 61

On the Richter Scale,an earthquake of 6.0 releases ten times as much energy as an earthquake of 5.0.

Question 62

Scientists use seismic tomography to

A) develop 3-dimensional models of Earth's interior.
B) determine the location of an earthquake's epicenter.
C) predict the timing and intensity of a future earthquake.
D) determine the depth of an earthquake.

Question 63

Subtracting the arrival time of the first S-wave from the arrival time of the first P-wave gives the P-S time interval for each seismic station.

Question 64

The average geothermal gradient near Earth's surface is what?

A) 100C/km
B) 50C/km
C) 25C/km
D) -25C/km
E) -50C/km

Question 65

The second major seismic belt,accounting for 15% of all earthquakes is the Mediterranean-Asiatic belt.

Question 66

Approximately 90% of all earthquake foci are at depths of greater than 100 km.

Question 67

The temperature of the core of Earth is estimated to be very close to that of the ____.

A) interior of the Sun
B) surface of the Sun
C) Earth's mantle
D) Earth's oceanic crust
E) outer space

Question 68

What is the estimated average geothermal gradient in the mantle?

A) 10C/km
B) 5C/km
C) 1C/km
D) -2C/km
E) -5C/km

Question 69

Which of the following is not a factor affecting earthquake intensity?

A) distance from the epicenter
B) depth of the hypocenter
C) population density
D) duration of shaking
E) the time elapsed since the last earthquake

Question 70

According to elastic rebound theory,rocks deform and bend.When their internal strength is exceeded they rupture.This energy release is called an earthquake.

Question 71

Seattle,Washington ____.

A) has not had an earthquake historically
B) is very unlikely to have a large earthquake because there have been none in historic times
C) has frequent small earthquakes and so is very unlikely to have a large earthquake
D) has large earthquakes about once every century
E) has large earthquakes very infrequently but will likely have one again

Question 72

What does the magnitude of an earthquake measure?

A) intensity
B) the damage created
C) the energy released
D) the duration of trembling
E) intensity and the duration of trembling

Question 73

The most damage from the 1906 San Francisco earthquake was caused by what?

A) fire
B) a tsunami
C) ground shaking
D) cracks opening up
E) landslides

Question 74

Although most aftershocks are smaller than the initial earthquake,an aftershock may be as big and may cause considerable damage.

Question 75

The Modified Mercalli Scale is a quantitative measure of an earthquake's intensity.

Question 76

The temperature range at the core-mantle boundary is estimated to be between ____.

A) 2,500 to 5,000C
B) 5,000 to 6,500C
C) 7,000 to 8,500C
D) 8,500 to 10,000C
E) 10,000 to 11,500C

Question 77

Seismologists most commonly report the magnitude of an earthquake using the Richter Scale.

Question 78

A seismic risk map can be used to

A) predict when an earthquake will take place in an area.
B) choose locations for hospitals and other important buildings.
C) determine the most likely location of the epicenter of the next earthquake.
D) show seismic gaps.

Question 79

The major discontinuity that occurs at a depth of 2,900 km below earth's surface is the ____.

A) low velocity zone
B) Moho
C) inner core outer core transition
D) core-mantle boundary
E) none of these

Question 80

What is the composition of the mantle?

A) peridotite
B) basalt
C) granite
D) iron
E) iron and nickel metal