Ch.5 - Earthquake's and Earth's Interior

The ________ of an earthquake is on the surface of the Earth directly above the focus.

epicenter

How much more energy does a magnitude 7.0 earthquake release than a magnitude 6.0 earthquake?

An earthquake with a magnitude of 7.0 releases 32 times more energy than an earthquake with a magnitude of 6.0.

Which of the following statements best describe the continental crust and oceanic crust?

Continental crust is thicker than oceanic crust.

What are the major zones of Earth's interior?

Crust, mantle, and core

In elastic rebound theory, what must occur to produce an earthquake?

Enough stress must build up over time on a fault to overcome friction.

The Mercalli Scale is a scale from ________.

I to XII that rates the structural damage due to an earthquake

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.

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 one of the following statements is correct?

P and S waves travel through solids and P waves travel through liquids.

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.

What is the major difference between the crust and the lithosphere?

The crust is compositionally distinct from the mantle, but the lithosphere is the rigid part of the crust and mantle.

What does the above diagram show as relating to locating an earthquake epicenter?

This is an example of using triangulation to correctly pinpoint an epicenter.

________ is the maximum possible damage designation on the Mercalli scale.

XII

Major earthquakes are often followed by somewhat smaller events known as ________.

aftershocks

The Richter magnitude of an earthquake is determined from the ________.

amplitude of the largest seismic wave

P waves ________.

are faster than S waves and surface waves

Oceanic crust is composed primarily of ________.

basalt

In the open ocean, tsunamis travel at about the same speed as a ________.

commercial airliner

The upper part of the ________ has the approximate composition of granite.

continental crust

____ averages 35 to 40 km in thickness.

continental crust

_______ has an average density of 2.7 g/cc.

continental crust

On a typical seismogram, ________ will show the highest amplitudes.

surface

What type of earthquake wave causes the greatest damage?

surface

Overall, this type of seismic wave is the most destructive.

surface wave

Aftershocks occur because ________.

the area surrounding a region that experienced a large earthquake needs time to adjust to the displacements on the main fault

The 2011 earthquake and tsunami in Japan killed approximately 21,000 people while the 2010 earthquake in Haiti killed approximately 316,000 people because ________.

the construction methods in Haiti were not as good as those used in Japan

The earth's major layers formed because ________.

the earth was heated after its formation resulting in melting and subsequent sinking of heavier materials

Megathrusts between subducting oceanic crust and an overriding plate are a potential source of tsunamis because ________.

the earthquakes on these faults are underwater and could displace large amounts of water from the oceans

Strike-slip faults are common along ________ plate boundaries.

transform

Structural damage from seismic vibrations would be worse ________.

where older buildings were built on a thick layer of sediment

During the Alaskan earthquake of 1964, the buildings that survived the best were made of ________.

wood

The best building material to use in an earthquake prone region is ________.

wood

What is a tsunami wave?

Massive ocean waves usually triggered by underwater earthquakes

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

Megathrust fault

Which of the following best describes why the 2010 earthquake in Chile caused a large tsunami while the 2010 earthquake in Haiti only caused a small and local tsunami?

The earthquake in Haiti was the result of motion on a transform boundary, which does not produce any vertical motion of the sea floor, whereas the Chilean earthquake was the result of motion along a convergent plate boundary, which does.

What is the difference between the epicenter and the focus of an earthquake?

The epicenter is the surface location of an earthquake and is located above the focus

How do the inner core and outer core differ?

The inner core is solid, whereas the outer core is liquid.

Faults are "locked" because ________.

high confining pressure increases friction on the fault

The location where slippage begins is called the ________.

hypocenter

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

intensity

Which of the following is determined by making direct observations in the area affected by an earthquake?

intensity

________ is the rigid, cool outer approximately 100 km of the earth.

lithosphere

Short term earthquake prediction research has focused on ________.

looking for precursors such as changes in topography, animal behavior, foreshocks, radon emission, etc that might signal an imminent earthquake

Which of the following is determined by measuring the amplitude of waves recorded from an earthquake?

magnitude

Use one of the following five terms to fill in the blank for the question below: The upper part of the ________ has the approximate composition of peridotite.

mantle

________ makes up the largest proportion of Earth by volume.

mantle

Which of the following does not determine the amount of destruction caused by seismic shaking?

Type of fault

Refer to the map of Earth's plates below, and determine which type of plate boundary is most often associated with these earthquake events.

ocean-continent convergent (subduction) boundaries

______ have the highest velocities

p waves

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

rapid; fault

S waves can travel through ________.

solid media only

Earthquakes along the San Andreas fault zone, for example, are repetitive—they reoccur in roughly the same regions over and over again—separated by decades or centuries because ________.

stress continues to build up all the time and when it is great enough to overcome friction there will be an earthquake and then the process will start over again

Which of the following terms are types of seismic waves? Choose all that apply.

surface, primary and secondary

In North America the highest potential for large tsunamis is in the coastal regions of ________.

the Pacific Coast and Hawaii

The Modified Mercalli Intensity Scale is used to measure _______.

the amount of damage caused by an earthquake

One measurement that is widely used to determine how far the focus of an earthquake is from the seismograph where it is recorded is ________.

the difference in travel time between the P and the S wave

The earth's major layers formed because ________.

the earth was heated after its formation resulting in melting and redistribution of major chemical compositions

Which of the following is not a significant factor contributing to the damage caused by an earthquake?

the proximity to a plate boundary

If you are on a beach, you might recognize that a tsunami is approaching because ________.

the water will WITHDRAW from the beach farther than usual

There are ________ earthquakes around the world every day.

thousands

In the 1906 San Francisco earthquake, much of the damage was due to fires because ________.

water lines were badly damage so that firemen could not put out the fires

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 along a fault

How did Earth acquire its layered structure?

Denser materials, such as nickel and iron, sank to the Earth's center and became its core, whereas less dense, more buoyant materials such as silicon and aluminum, rose to the Earth's surface and became its primitive crust.

What does this illustrate about the nature of earthquake destruction?

Different building codes matter greatly. Buildings that can take earthquake stresses often survive without damage while others build differently face total destruction.

What causes an earthquake?

Earthquakes result when a block of rock rapidly slips past another along a fault plane.

The ________ scale is an earthquake magnitude scale is based on the energy released by the earthquake.

Richter

How do the lithosphere and asthenosphere differ?

The lithosphere is a cool, rigid outer shell that overlies the asthenosphere, which is warmer and less rigid than the lithosphere.

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.

Modern seismographs rely on ________ to record the ground motion from an earthquake.

inertia

What is the most likely area where you will see major earthquakes?

mountain belt

During the 1906 San Francisco earthquake, the movement of the Pacific Plate relative to the North American Plate along the San Andreas Fault was approximately ________.

10 meters

Felt earthquakes usually last for ________.

10-60 seconds

Approximately how much more energy is released in a 6.5 Richter magnitude earthquake than in one with a Richter magnitude of 5.5?

32

What is the probability that a large earthquake (M > 6.7) will occur in the San Francisco area between 2003 and 2032?

62%

What is a tsunami?

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

The deepest well that has ever been drilled on the earth is ________ deep, about 1/500th of the radius of the earth.

12.3 km

Earthquakes with a Richter magnitude of less than ______ are generally not felt by humans.

2.0

Part A: When the Tohoku earthquake occurred, as much as 30 meters of the Pacific plate was subducted westward under the Okhotsk plate, upon which sits the island nation of Japan. The crust of the Okhotsk plate directly west of the plate boundary bulged upward. In light of this, what is a possible explanation for the uplift indicated in red just west of the plate boundary? B: The Tohoku earthquake generated a massive tsunami that devastated the nearby coast of Japan. In light of your answer to Part A, what is the explanation for the generation of the tsunami? C: In light of your answers to Parts A and B, explain how the earthquake changed the coastline in a way that increased the destructiveness of the tsunami as it came ashore. D: What is the magnitude of the maximum slip indicated here, in meters? E: According to this chart, in what general direction did slip occur? F: Describe the relationship between the location of volcanoes on the island of Japan and the depth to the subducted plate below Japan. G: What might be a possible explanation for the fact that the there are no volcanoes over areas where the subducted plate is less than 100 kilometers deep?

A: During the earthquake, a large part of the Pacific plate was thrust under the Okhotsk plate. This both lifted and deformed the edge of the Okhotsk plate. B: The sudden lifting of the seafloor around the bulging crust pushed huge volumes of water up, out, and away in all directions. C: The effective height of the tsunami would have been increased by the amount of subsidence of the coastline: here, around 1 meter. D: 24 E: The motion was both upward and toward the east. F: The volcanoes appear to line up along the 100-kilometer dashed depth isoline, and there are more over areas where the plate is deeper. There are no volcanoes over plate that are less than 100 kilometers deep. G: Magma is not generated in significant amounts until the subducted plate has reached a depth of 100 kilometers.

Part A: Which of the following best describes how scientists help the public prepare for an earthquake event? B: Look at the accompanying map showing the locations of the 15 largest earthquakes in the world since 1900. Imagine an earthquake occurs at location 2 on the map (southern Alaska) that could generate a tsunami. Which of the following statements are most accurate? C: Look again at the map. An earthquake at which of the following locations could cause a tsunami?

A: Scientists cannot predict when exactly an earthquake will occur, but they can identify tectonically active areas that are likely to produce earthquake activity and let the public know they are in an earthquake-prone area. B: All locations (except 9) could benefit from an alert that an earthquake occurred at location 2, because they are near the ocean and might experience a resultant tsunami. & All islands in the middle of the Pacific Ocean should also receive warnings. C: All of the locations except 9 could produce tsunamis, because all are subduction zones involving at least one oceanic plate.

Part A: Which of the following best describes how scientists help the public prepare for an earthquake event? B: Imagine an earthquake is about to occur at location 2 on the map (southern Alaska). Which of the following statements is most accurate? C: Look again at the map. Bear in mind that all the earthquake locations that are not inland are on a convergent plate boundary (subduction zone). Which of these statements is true?

A: Scientists cannot predict when exactly an earthquake will occur, but they can identify tectonically active areas that are likely to produce earthquake activity and let the public know they are in an earthquake-prone area. B: Most of the people living at location 2 probably are aware that they live in a location where earthquakes are likely. & All locations (except 9) could benefit from an alert that an earthquake occurred at location 2, because they are near the ocean and might experience a resultant tsunami. C: All of the locations except 9 could produce tsunamis, because all are subduction zones involving at least one oceanic plate.

Part A: Using the accompanying map of the San Andreas Fault, and the knowledge that earthquakes occur about every 200 years in this area, which of the four segments of the fault do you think has the best chance of experiencing a major earthquake in the near future? B: If major earthquakes occur along active segments of the San Andreas Fault about every 200 years, when can another major event be expected along the Fort Tejon section? C: Which segment do you think is experiencing fault creep? Faults that creep have slow and continuous rock movement instead of the sudden and large movement associated with earthquakes.

A: Southern section (bottom section, red on the map) B: This segment should generate another major event around 2050-2060. C: North central section (orange on the map)

Part A: Which of the following best describes why the ground surrounding the students looks dry and solid, while the ground underneath them is wet and muddy? Note that when the students arrived at this place, all the ground appeared solid and no earthquake occurred while they were at the site. B: Which of the following is the best description of what happens to water-saturated soils during an earthquake? C: Jogging on a beach where the sand is packed together, near where ocean waves meet the sand, you notice that your footprints quickly fill with water after each step. Waves are not filling them up. Instead, there is another reason. Where is the water coming from?

A: The motion of the students' bodies in the water-rich soil caused it to flow like a fluid. B: The shaking causes water from between grains to move and push grains apart, weakening the material and allowing it to flow like a slurry. C: The water is from the pore spaces between the sand grains.

Part A: Which of the following best describes the general relationship between the velocity of seismic waves and depth in Earth? B: Look at the accompanying figure. Based on this figure, the properties of Earth's layers, and the mode of travel of body waves, which of the following best describes where the velocity of body waves should be fastest and where the velocity of body waves should be slowest within Earth's interior?

A: Which of the following best describes the general relationship between the velocity of seismic waves and depth in Earth? B: In general, body (P) waves would travel fastest in the inner core and slowest in the outer core.

A: What is a seismograph? B: What is the underlying principle of seismograph construction? C: When will the first earthquake waves arrive at a seismograph station? D: How long does it typically take for the first earthquake waves to arrive at a seismograph that is some distance away from the epicenter after the earthquake occurs

A: an instrument used to record earthquake waves B: A heavy weight suspended within a moving box needs to overcome inertia, resulting in a slight delay in the motion of the weight after the box moves. C: a short time after the earthquake occurs D: several minutes

A: What are the two primary types of waves generated by earthquakes? B: Name two types of body waves. C: Where do body waves and surface waves travel? D: What do vertical and horizontal surface waves have in common? E: How do rocks within Earth change as P waves pass? F: How does rock within Earth change as S waves pass? G: How are S waves and vertical surface waves different?

A: surface waves and body waves B: P & S waves C: Body waves travel within Earth, and surface waves travel along Earth's surface. D: Both waves travel along Earth's surface and decrease in amplitude with depth below the surface. E: Rocks within Earth both expand and contract as P waves pass. F: Rocks within Earth are displaced up and down as S waves pass. G: S waves are body waves, whereas vertical surface waves are surface waves. The amplitude of S waves does not decrease with depth, but the amplitude of vertical surface waves does decrease with depth.

A: What term describes the tectonic feature along the seafloor at the blue plate boundary at the arrow? B: What type of plate boundary is the blue boundary here? C: Describe the relative motions of the Pacific Plate (east of the boundary) and the Okhotsk Plate (west of the boundary). D: What was the depth of the initial rupture (at the focus)? E: The curving and dashed lines in the diagram display how much time elapsed between the initiation of the earthquake at the focus and motion experienced along the fault. How many seconds after the initial rupture at the focus did the maximum slip (shown in red) occur? F: The colored legend at the bottom of the diagram represents the amount of slip experienced along the fault. What was the greatest amount of slip in centimeters and in meters? G: What was the depth of the area of maximum slip? H: In what direction did the motion propagate along the plate boundary? I: In light of your answers to parts D, E, F, G, and H, what is a possible explanation for the uplift indicated in red just west of the plate boundary?

A: trench B: convergent boundary C: The Pacific plate is moving westward and is being subducted under the eastward-moving Okhotsk plate. D: 32 km E: 45-60+ seconds F: more than 3000 centimeters (30 meters) G: 10-20 km H: The motion was both upward and toward the east. I: During the earthquake, a large part of the Pacific plate was thrust under the Okhotsk plate. This both lifted and deformed the edge of the Okhotsk plate.

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

Surface waves

Why is the Moment magnitude scale favored over the Richter magnitude scale?

The Moment magnitude measures the total energy released by an earthquake.

Oceanic crust is ________ than continental crust.

denser

Which of the following is not a way that seismic waves travel in the earth?

diffusion

An earthquake magnitude scale is a measure of ________.

energy released

The position on Earth's surface directly above the earthquake source is called the ________.

epicenter

The ________ is the site of initial rupturing associated with an earthquake.

focus

When an earthquake occurs, energy radiates in all directions from its source. The source is also referred to as the ________.

focus

A tsunami can occur ________.

when an earthquake occurs in the seafloor like along an oceanic plate boundary