Deck 8: Earthquakes and Earths Interior

Question 1

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

Answer 1

Convergent plate boundaries line the Pacific basin,since the Pacific is shrinking and the Atlantic is growing due to plate tectonics motions.As plates subduct,they create earthquakes along their distance.The Pacific basin also has some transform faults along it,including the San Andreas in California.

Question 2

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

Answer 2

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 the Rocky Mountain Arsenal near Denver,Colorado,was responsible for numerous small earthquakes in the area.

Question 3

What are the differences between P-waves and S-waves?

Answer 3

P-waves are primary waves;they arrive first to a seismograph because they are the fastest.They are compressional and can travel through solids,liquids,and gases.S-waves are secondary waves;they arrive second to a seismograph.They are shear waves because they move the material perpendicular to the direction of travel.S-waves can only travel through solids.

Question 4

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 5

Describe what seismographs do and how they work.

Question 6

Describe the three categories of earthquakes based on focal depth and what causes them.

Question 7

What causes intraplate earthquakes?

Question 8

How does elastic rebound theory explain when earthquakes occur?

Question 9

Why is the Modified Mercalli Intensity Scale no longer the main method used for measuring the size of earthquakes?

Question 10

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 11

What is earthquake intensity,how is it measured,and what factors are involved in the intensity of a quake?

Question 12

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

Question 13

Describe surface waves and their most important two types.

Question 14

What does the Richter Magnitude Scale measure,and why are scales of this type used more frequently than intensity scales?

Question 15

How is the seismic-moment magnitude scale different from the Richter Magnitude Scale?

Question 16

What happens along an earthquake fault after rupturing begins? How is the length of time of ground shaking related to the length of the fault?

Question 17

How would an earthquake epicenter be located,using three seismograms,a map,and a protractor?

Question 18

What causes tsunamis,and why are they so destructive?

Question 19

What is an earthquake? What are aftershocks?

Question 20

What causes earthquakes?

Question 21

What is the biggest cause of Earth's internal heat?

Question 22

Why are the paths of seismic waves curved?

Question 23

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

Question 24

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

Question 25

What are the focal depth ranges for shallow-focus,intermediate-focus,and deep-focus earthquakes?

Question 26

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

Question 27

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

Question 28

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

Question 29

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

Question 30

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

Question 31

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 32

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

Question 33

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

Question 34

Why are there so few earthquakes within plate interiors?

Question 35

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

Question 36

What is usually the ultimate cause of the stresses and pressures that build up in rocks and produce earthquakes?

Question 37

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

Question 38

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 39

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

Question 40

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

Question 41

The fastest seismic waves,which can travel through solids,liquids,and gases,are ____________________ waves.

Question 42

An earthquake of magnitude 7.0 has an amplitude ____________________ times as large and releases ____________________ times as much energy,respectively,as a magnitude 6.0 earthquake.

Question 43

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

Question 44

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 45

The structural layer that comprises the greatest volume of Earth is the ____________________.

Question 46

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

Question 47

The name of the point on Earth's surface vertically above the hypocenter is the ____________________.

Question 48

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

Question 49

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 50

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

Question 51

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

Question 52

The term that best describes a tsunami is not "tidal wave" but ____________________.

Question 53

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

Question 54

The name of the location within Earth where earthquakes originate is the ____________________.

Question 55

The two types of body waves are ____________________ wave and ____________________ waves.

Question 56

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

Question 57

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

Question 58

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

Question 59

The ____________________ of an earthquake on the Richter Scale is determined by measuring the ____________________ of the largest recorded seismic wave.

Question 60

The study of earthquakes is called ____________________.

Question 61

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 the above

Question 62

The composition of the mantle is:

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

Question 63

The Modified Mercalli Intensity Scale is a subjective scale to measure the destructive effects of an earthquake.

Question 64

The temperature range at the base of the crust is:

A)100 to 250°C.
B)250 to 550°C.
C)500 to 800°C.
D)800 to 1,200°C.
E)1,000 to 1500°.

Question 65

The focus of the most destructive earthquakes is almost always:

A)shallow.
B)intermediate.
C)deep.
D)internediate and deep.
E)shallow,intermediate,or deep.

Question 66

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

Question 67

Benioff zones indicate the angle of plate descent along a convergent plate boundary.

Question 68

The major boundary that occurs at a depth of about 30 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 the above

Question 69

The magnitude of an earthquake measures:

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

Question 70

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

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

Question 71

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

A)100%.
B)95%.
C)80%.
D)55%.
E)25%.

Question 72

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 73

Only 5% of all earthquakes occur within the:

A)Mediterranean-Asiatic belt.
B)circum-Mediterranean belt.
C)interiors of plates and mid-oceanic ridges.
D)passive margins of continents and mid-oceanic ridges.
E)shields of continents and mid-oceanic ridges.

Question 74

Aftershocks do not cause much damage.

Question 75

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 the above

Question 76

The average geothermal gradient near Earth's surface is:

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

Question 77

The composition of the core is:

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

Question 78

The type of building construction and population density in the area of an earthquake are factors that can affect the intensity on the Modified Mercalli Intensity Scale.

Question 79

The estimated average geothermal gradient in the mantle is:

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

Question 80

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 will snap back to their original shape after faulting.
E)rocks will bend before they break,will snap back to their original shape after faulting,AND will break when their capacity to store energy of deformation has been exceeded.