CHAPTER 12
Explosive eruptions, landslides, magma movement, and faulting are the causes of earthquakes associated with ___________.
volcanoes
Seismic waves are characterized by how much the ground moves, which is indicated by the ______, and the time it takes for a complete wave to pass, which is the ______.
wave amplitude; period
Body waves are seismic waves that travel inside Earth: ____________ _ waves compress the material they travel through and are faster than __________ _ waves, which impart a motion perpendicular to the direction of wave propagation.
p; s
What features may be common along active faults, such as the San Andreas?
Linear ridge and/or valley Drainage channels running parallel to fault Scarp Offset stream channel
Seismic station
Location of scientific instruments that measure earthquakes
Hypocenter
Location where an earthquake is generated
The 9.0 magnitude earthquake that occurred northeast of Japan in March 2011 was the result of movement between two plates at a ______.
subduction zone
Dig shallow trenches across faults
subsurface layers preserve the history of motion and some may be dated to give clues to magnitudes and recurrence of past earthquakes
What kind of destruction can a tsunami cause?
-high death tolls are possible -nearshore boats may be carried inland -buildings and cities can be destroyed
Rank the following in order from the start (at the top) of an earthquake rupture to the end of the earthquake event.
1. A small section of the fault begins to rupture. 2. Rupture migrates outwards, generally following the actual fault surface 3. Rupture eventually may reach Earth's surface, creating a fault scrap. 4. Rupture grows along the fault plane, and fault scarp lengthens. 5. Earthquake stops as remaining stress no longer overcomes friction along the fault
If three seismic stations have the following P-S intervals: DUG = 57 sec, WUAZ = 73 sec, ISCO = 14 sec, place the stations in order from closest station (at the top) to the earthquake to the one farthest away.
1. ISCO 2. DUG 3. WUAZ
List the order of events, from first (on top) to last, that would lead to the formation of a tsunami due to an earthquake.
1. Megathrust is locked, causing the seafloor to bulge under stress 2. Megathrust ruptures, and bulging plate changes shape 3. Water above the plate lifts up towards the surface, forming a ridge of higher water 4. A tsumani radiates away from the disturbance; not noticeable in the open ocean 5. Tsunami approaches shore; energy concentrates in a shallows to create a higher wave
Rank seismic waves in order of recording by a seismometer (from first to last).
1. P-wave 2. S-wave 3. Surface wave
Rank the following in order for the steps taken to measure the local magnitude (Ml) of a shallow earthquake. Place the first step on top.
1. Seismic data are gathered from several seismometers 2. Maximum amplitude of the S-wave is measured on each seismogram 3. Relationships between distance and S-wave amplitude are plotted on a nomograph 4. MI is the point where each line crosses the center column (magnitude) of the nomograph
Rank the following in order for the process of locating an earthquake's epicenter. Place the first step on top.
1. Select records from at least three seismic station 2. Determine the P-S interval for each station 3. Estimate station distances from the epicenter using P-S intervals on a time-travel curve 4. Draw circles around each station, with a radius equal to distance from the epicenter 5. Locate the intersection of all of the circles to determine the epicenter of the earthquake.
The 1964 Alaskan earthquake caused significant property damage in an area over 600 km in length along the coast; it also created a fissure in the ground that was not only distant from the epicenter but also ______.
1000s of kilometers in length
An earthquake of Richter magnitude 7.0 has ______ times the ground motion and releases ______ times the amount of energy of a 6.0 magnitude earthquake.
10; 30
Seismographs record ground motion create by earthquakes in __________ directions
3
San Francisco, 1906
470 km of the San Andreas fault ruptured; devastating fires after the earthquake
An earthquake with a Richter magnitude of ______ has 100 times the ground motion and releases ______ times the amount of energy of a 4.0 magnitude earthquake.
6.0; 900
Which of the following may indicate the presence of a fault scarp?
A "step" in the landscape Freshly exposed, generally linear feature with little/no vegetation Break in slope along a hillside
Match the area within Earth to the hypothesized flow processes occurring there.
A - Large upwellings are occurring from the core-mantle boundary. B - Cold slabs of subducted material sink into the mantle. C - Material in the outer core is flowing and generating Earth's magnetic field. D - Mantle material is involved in convective flow.
Based on the map, what is true regarding earthquakes in the locations indicated? (Yellow dots = shallow-depth earthquakes; green dots = intermediate; red dots = deep.)
A - Mostly shallow earthquakes occur along the mid-ocean ridge. B - This is a diffuse zone of seismic activity associated with continental rifting. C - This is a large zone of seismicity associated with a continental collision. D - Shallow, intermediate, and deep earthquakes occur along a subduction zone. E - Very little seismicity occurs in this area, which is far from a plate boundary.
Most earthquakes are generated by movement along faults. Match the fault type with its image.
A - Normal Fault B - Reverse Fault C - Strike-slip fault
Match the location with the best description for earthquakes formed in that area within a continent.
A - Strike-slip motion mostly causes shallow earthquakes; some may be large B - Moderate-size normal-fault earthquakes are created at a rift C - Magma intrusions may cause small earthquakes as molten material moves through rock D - Preexisting faults readjust and move as plate is subjected to new stresses; may produce large earthquakes
What is true regarding earthquakes in the locations indicated? (Yellow dots = shallow-depth earthquakes; green dots = intermediate; red dots = deep.)
A - Subduction zone causes earthquakes along the Aleutian Islands B - Most earthquakes occur due to volcanic activity C - Strike-slip earthquakes are common along the San Andreas fault D - Shallow earthquakes follow the Mid-Atlantic Ridge E - Shallow, intermediate, and deep earthquakes occur along this subduction zone
Match the location on the image with the best description for causes of earthquakes in that location.
A - The oceanic plate is bent and stressed as it moves toward the trench B - Shearing occurs within the accretionary prism C - Magma is moving D - Shearing and downward-pulling forces produce deep earthquakes E - Compressive stresses associated with plate convergence cause thrust faulting behind the magmatic arc.
Match the location on the image with the best description for causes of earthquakes in that location.
A - Thrust faults form near the plate boundary and create large, shallow earthquakes. B - Megathrust forms along the plate boundary and creates large earthquakes between the two plates. C - Thrust faults or reactivated older faults may form within the interior of either continent. D - Oceanic plate material is detached, and deep earthquakes cease.
What is a seismic gap?
A fault segment that has had fewer earthquakes than other sections
Match the location on the seismogram with the appropriate description.
D - Background vibrations A - Arrival of first P-waves C - Arrival of first S-waves B - Arrival of first surface waves
Which of the following are potential sources of destruction that may be caused either directly or secondarily by earthquakes?
Aftershocks Landslides and rock falls Tsunamis Fires
Chile
An active megathrust exists along the west coast of South America.
Which location on the image represents the epicenter of the earthquake? (Note that each circle has a radius equal to the distance of that station from the earthquake, as calculated from the P-S interval.)
B
Which of these areas is the least likely to have a large earthquake in the near future?
B - Reason: Right. Earthquakes are very common here, so energy is not building up to create a large event.
Based on what you know about the interior of Earth, which image correctly displays how seismic waves would travel through Earth's layers as they go deeper?
B, because rocks get more dense deeper in Earth
Chile, 1960
Tsnami struck part of the shore of South America 15 minutes after the earthquake; 10-meter-high wave killed at least 2,000 people
Which of the following are true for seismic waves?
Body waves include P-waves and S-waves. Surface waves only travel on the surface of Earth. Body waves travel within and through Earth.
What features in the image might a geologist use to study earthquakes and measure movement along a fault?
C: This linear feature marks the fault line. D: Stream channel abandoned as movement along the fault continued shows fault offset. B: Offset stream shows the plate on the left side of the fault has moved northwest. E: Displaced rock unit can show direction and distance of movement over time.
Iran
Collision of the Arabian plate causes thrust and strike-slip faults.
Nepal
Continental collision zone continues to build the Himalaya Mountains.
S-waves
Create one large shadow zone; cannot pass through core
Which location on the image experienced the most shaking intensity (extensive damage), according to the Modified Mercalli Intensity Scale?
D
Match the location on the image with the best description for causes of earthquakes in that location.
D - Spreading and slip between adjacent blocks occurs along normal faults; earthquakes occur as magma intrudes into fissures. B - Strike-slip earthquakes occur along faults that link adjacent segments of the spreading center. C - Plate cools, subsides, and bends as it moves away from the ridge; stress from the bending forms steep faults. A - Rocks along this linear feature flow because they are too hot to fracture; earthquakes are shallow, small, and numerous.
Based on the image, which of the following are true?
D indicates the core-mantle boundary, which S-waves cannot penetrate because the outer core is molten. P-waves received at C are indirect. No S-waves are received at A, B, or C, as this is the S-wave shadow zone. No direct P-waves are received at A or B, as these are P-wave shadow zones.
Wave is refracted away at a steeper angle.
Descending seismic ray passes from a fast material to a slower one.
Wave is refracted to a shallower angle.
Descending seismic ray passes from a slow material to a faster one.
Love waves
Displace the surface horizontally; cause buildings to slide sideways off their foundations
Rayleigh waves
Displace the surface vertically; cause most of the damage during an earthquake; create a rippling surface (during large earthquakes)
P-waves
Drop in velocity as they enter the core; may travel through all layers; create two shadow zones
Papua New Guinea, 1998
Earthquake and underwater landslides in the southwestern Pacific generated three tsunamis, which destroyed villages, killing 2,200 people; wave at one location was 10 meter high.
What evidence exists to indicate that the eastern U.S. has earthquake risks? (Choose all that apply.)
Earthquake-hazard maps indicate two major zones of possible future activity. Modern-day tectonic stresses, such as ridge push, may reactivate ancient faults in continental interiors. Major earthquakes have occurred in this area in the last 200 years.
True or false: Geologists cannot determine anything regarding rocks in the subsurface without using drill holes.
False
True or false: Short-term earthquake prediction can use foreshocks to accurately predict exactly when a major earthquake will occur.
False
True or false: The largest magnitude earthquakes will always produce the largest numbers of fatalities.
False
True or false: When an earthquake occurs along a fault, the entire plane of the fault slips at once.
False Reason: An earthquake rupture starts in a small area (hypocenter) and expands along the fault over time.
The image shows a surface expression of slip along a normal fault caused by an earthquake. What is the indicated feature (labeled "A")?
Fault scarp
What happened in and along the sea during the Great Alaskan Earthquake of 1964?
Faulting and uplift of the seafloor occurred, creating a large tsunami in the Pacific Ocean. Some areas subsided and were flooded by seawater. Massive landslides were created. Some land that was below the sea was uplifted above sea level.
Thrust faults
Gently dipping faults in which the hanging wall moves up with respect to the footwall; most common along convergent plate boundaries
What did scientists put into the hole they drilled through the San Andreas fault in order to better understand earthquake there?
Geophysical instruments
What hazard associated with the 1964 Alaskan earthquake occurred as far away as 800 km from the epicenter?
Ground shaking
Based on the three seismograms, which seismic station was closest to the epicenter of the earthquake?
ISCO
look for offset of both natural and human-made features
In the field, provide reference points to measure motion, both how much and in what direction.
The 2004 earthquake in ________ occurred due to subduction of the Indian-Australian plate under the Eurasian plate, creating a(n) ___________ that killed over 220,000 people.
Indonesia; tsunami
How are we able to limit risks from earthquakes?
Install warning systems to shut down gas systems and pipelines. Use earthquake hazard maps to determine areas of least risk. Engineer buildings with systems to dampen seismic energy.
Which of the following correctly describe the March 2011 Tohoku earthquake in Japan?
It created a very destructive tsunami. It was one of the five largest ever recorded. The earthquake occurred due to the subduction of the Pacific plate.
Which of the following describe the San Andreas fault?
It is located in California. It is made of different segments that have different tectonic behaviors. It is located along the boundary between the North American plate and the Pacific plate.
Which are true of the Modified Mercalli Intensity Scale?
It may be used to describe earthquakes that occurred before seismometers were invented. It describes the effects of shaking in everyday terms. A value of XII indicates complete destruction of buildings.
Which of the following describe the 2004 Indonesian earthquake?
It occurred due to subduction. It created a destructive tsunami. It was over 9 in magnitude.
Which of the following best describe the size and speed of a large tsunami newly created by an earthquake in the open ocean?
It travels at 600 to 800 km/hr. The wave height is around a meter. The wavelength is more than 700 km.
What actions can you take before or during an earthquake to reduce your chances of being hurt?
Keep 72 hours' worth of food, water, and supplies. Avoid using open flames, since there may be gas leaks. Stand clear of buildings or objects that may fall. Seek cover under a heavy desk or a door frame.
sink a deep drill hole through a fault
Lower geophysical instruments deep into a fault to possibly record data on a large earthquake as it happens.
geophysical surveys
Measure subsurface magnetic, seismic, gravity, and electrical properties to determine the nature of rock, sediment, and structures
Seismic wave
Mode of earthquake energy transmission through Earth
Seismic tomography has aided with which of the following regarding the interior of Earth?
Modeling areas of hot plumes and cool subducted slabs The existence of the D'' layer along the core-mantle boundary Creation of flow models of the mantle
The boundary between the mantle and the crust is called the ____________, named after the scientist who discovered it. (Use the short name.)
Moho
Short-term earthquake prediction may utilize which of the following?
Monitoring activity along an earthquake-prone fault Study of foreshocks and stress buildup Lasers that can record even slight movement along a fault
Which are true of "Richter" or "local" magnitude calculations?
Most commonly mentioned Use a nomograph to relate distance, magnitude, and amplitude Use maximum S-wave amplitude on a seismogram
Based upon the image that shows colored dots to represent earthquake epicenters, which are true of the locations of earthquakes?
Most earthquakes occur along plate boundaries. A few earthquakes occur far away from plate boundaries.
Volcanoes and magma generate earthquakes in which of the following ways?
Movement of magma within the volcano Explosive eruptions Landslides on unstable slopes
How are fires caused by earthquakes?
Natural gas lines rupture due to shaking.
Based on the graph and what you know of Earth's layers, which are true of P-wave velocity with increasing depth in Earth?
P-wave velocity increases both through the mantle, and through the core, due to increasing density of the material of each layer with depth. P-wave velocity drops once it enters the outer core from the mantle, indicating a change in material at the boundary.
Choose the phrases that correctly describe the seismic waves as shown here.
Period is the time it takes A to pass a point. A represents amplitude.
Epicenter
Point on Earth's surface directly above an earthquake's focus
Both images represent surface waves moving through Earth materials: A are ________ waves and B are ________ waves.
Rayleigh; Love
Which are true of reflection versus refraction?
Refraction bends a portion of the wave energy as the wave either slows or speeds up as it crosses the encountered boundary. Reflection sends a portion of the wave energy back away from the encountered boundary. Either may happen to a seismic wave as it encounters a boundary between materials of different physical properties.
Wave is refracted upward toward the surface
Rising seismic ray passes from a fast material to a slower one.
Which fault, located in California, is both the world's best known and extensively studied? This fault is found along a transform plate boundary and will likely produce a significant earthquake in the next 30 years.
San Andreas
Match the region/city of the U.S. with its earthquake risk and the cause of that risk level.
San Francisco - High risk; location near the San Andreas fault New Madrid - High risk; location near a reactivated ancient fault zone in the continental interior Southern Alaska - High risk; location near an active subduction zone Hawaii - Medium to high risk; seismic activity associated with volcanism Upper Midwest - Low risk; few active faults in the continental interior From Utah through Yellowstone - Choice, Medium to high risk; intermountain seismic belt due to many active normal faults Medium to high risk; intermountain seismic belt due to many active normal faults
study fault ruptures and topographic features
Scarps, troughs, ridges or steps may show the precise location of the faults at the surface, expressed as a linear feature.
Wave continues in a straight path.
Seismic ray passes through material that does not change from place to place.
What useful phenomenon is shown by the two images?
Seismic waves travel faster through the mantle and, at a certain distance, will reach the surface faster than waves traveling through the crust.
Based on the image representing seismic waves moving through Earth, which of the following is true? (The large arrow represents a seismic ray, the path taken by any part of the seismic wave.)
Since the seismic rays are straight, we can determine that the physical properties of the material do not change.
Study of indirect waves
Since these waves have reflected off boundaries or changed wave type as they cross a boundary, geologists may learn more about Earth's interior by studying them.
Yellowstone Area, 1959
Slip along a normal fault generated the Madison Canyon slide, which formed Earthquake Lake; 28 people were buried in the slide.
What features in the image help you identify the location of the fault?
Stream channel running parallel with fault Linear ridges and valley Scarp
Mexico City, 1985
Subduction zone; seismic waves amplified by geologic setting of lake sediments in a bowl-shaped basin
Charleston, 1886
Tectonic cause is still not certain; largest earthquake in the southeastern United States; 60 people were killed.
New Madrid, 1811-1812
Tectonic stresses reactivated an ancient fault zone
Based on the image showing seismicity along the San Andreas fault, what may be determined? The top cross section shows earthquakes prior to Oct. 17, 1989; bottom section shows earthquakes after that date.
The San Francisco area is a likely location for a future earthquake. Prior to Oct. 17, 1989, there were three "locked" segments of the fault.
What is an earthquake recurrence interval?
The average time between repeating earthquakes
Select all the factors that influence the velocity of P-waves as they travel through Earth.
The density of the material How easily the rocks are compressed How rigid the material is
Normal faults
The hanging wall moves down with respect to the footwall; most common along divergent boundaries
Reverse faults
The hanging wall moves up with respect to the footwall; most common along convergent plate boundaries
This cross section represents a model developed by a USGS geologist after the large 1964 Alaska earthquake, showing how uplift from the earthquake was caused by thrusting of the continent over the oceanic crust. How did this support the development of the theory of plate tectonics?
The motion indicated is the same as an ocean-continent convergent plate boundary with subduction, as is predicted for this area by plate tectonics.
Based on the map, which are true of the subduction zone and indicated earthquakes? (Yellow dots = shallow-depth earthquakes; green dots = intermediate; red dots = deep.)
The subducted plate is generally inclined from west to east, with the deepest portion of the slab to the east. Shallow earthquakes are closer to the trench, whereas deep ones are farther away.
What happens to the size and speed of a tsunami as it approaches the shore?
The velocity decreases. The height increases.
In the image, if seismometers 4 and 5 receive seismic waves sooner than would normally be expected from an earthquake that occurs at location A, what may be said?
The waves must have passed through a rock body giving them a higher velocity than the surrounding material (granite is an area of faster velocity).
Which of the following are true of earthquakes related to subduction zones?
They may be due to magma movement. These are typically the only place to produce deep earthquakes. They may occur either in front of or behind the trench. A megathrust earthquake may be very damaging.
Which of the following are true of earthquakes related to mid-ocean ridges?
They may be due to strike-slip motion along transform faults. They may occur along steep faults away from the ridge axis as the new crust cools and bends. Most have hypocenters less than 20 km deep. Many occur along the axis of the ridge due to normal faulting or magma intrusions.
Which of the following are true of earthquakes related to continental collisions?
They may occur in large thrust faults created near the plate boundary. They may occur in either continental plate. A megathrust between the two plates creates large earthquakes. Earthquakes are widely distributed along the collision zone.
Papua New Guinea
This area straddles active plate boundaries in the southwestern Pacific Ocean.
use satellite data
This can create an interferogram to show deformation of Earth
Presence of S-wave shadow zone
This helps determine that the outer core is molten, as this type of wave cannot travel through molten material.
Presence of P-wave shadow zone
This helps determine the depth of the core-mantle boundary and diameter of the core; some indirect waves of this type reach this area and may also be studied.
P-wave velocity as a function of depth
This shows that rocks tend to become more dense with depth and that there is a dramatic change in material at the core-mantle boundary.
Northridge, 1994
Thrust fault lifted up a large section of land; structural damage included a section of concrete and steel freeway; 60 people were killed.
Alaska, 1964
Thrust faults associated with the Aleutian Island subduction zone
Alaska, 1964
Thrust faults generated landslides and a tsunami; most of the 128 deaths were caused by the tsunami.
What is required to calculate the depth to an earthquake's hypocenter?
Time interval between the arrival of the P-wave and a second compressional wave.
In which of the following ways may earthquakes be generated within a continental plate?
Transform faults Movement of preexisting faults subjected to new stresses Continental rifting and normal faulting Intrusions of magma
P-wave
Travels at 6 to 14 km/s; compresses the rock in the same direction it propagates; travels through solids and liquids
S-wave
Travels at about 3.6 km/s; movement perpendicular to the direction of travel; cannot travel through liquids
True or false: Most deaths from earthquakes are caused by collapse of buildings or other structures.
True
True or false: Tsunamis are monitored in the Pacific and Indian Oceans by tsunami-warning centers, which can provide advance warning to coastal areas.
True
Hokkaido, 1993
Tsunami in the western Pacific hit 5 minutes after the 7.8 magnitude earthquake; wave killed at least 100 people and swept boats across a concrete barrier on the shoreline.
Hawaii, 1960
Tsunami reached the middle of the Pacific 15 hours after a South American earthquake; 11-meter-high wave killed 61 people and damaged buildings.
Strike-slip faults
Two sides of the fault move horizontally past one another; fault plane is near vertical; most common along transform plate boundaries
Why does the United States have such varying risks of seismic activity?
Volcanic activity can cause seismic risk in some areas. Some areas are near plate boundaries, while others are not. Some regions in the continental interior have active fault systems.
What is the process of liquefaction associated with an earthquake?
Water-saturated ground loses its strength due to shaking.
Why is it important to study prehistoric earthquakes?
We can determine the recurrence intervals and likely size of earthquakes to help people create a regional plan for future seismic events.
Based on the earthquake hazard map, which areas have a high risk for earthquakes?
West coast of South America Southern Alaska and the west coast of North America The Middle East
Subduction zone earthquakes ______.
account for about 90% of all significant earthquakes. are shallow near the trench and get progressively deeper with distance from the trench
Satellites can be used to study faults by ______.
analyzing changes in elevation before and after earthquakes
On the image, red areas show seismically slow materials and blue areas show seismically faster materials. Geologists have interpreted that ______.
blue areas may represent the location of dense, subducted plates in the lowermost mantle red areas represent rising masses of hot, mostly solid mantle material; may be sources of mantle plumes and hot spots
The majority of people in the magnitude 7.0, 2010 Haitian earthquake died because ______.
buildings collapsed and crushed people
Seismic tomography ______.
can show areas of "fast material" and "slow material" creates an image of what is inside Earth uses deviation from expected seismic wave arrival times to determine variation in material at depth
Landslides generate seismic waves by ______.
causing the ground to shake
Most earthquake deaths are caused by ______.
collapse of structures
Geologists can investigate the interior of Earth by ______.
creating computer and numerical models to model processes that occur at depth subjecting rocks to high temperature and pressure in laboratory settings examining rocks that once resided at great depths
drill cores
cylinder-shaped samples of rock from depth; may go as deep as 5 km but most are less than several hundred meter
The earthquakes that occur in a subduction zone get progressively ______ (in general) with distance from the trench.
deeper
Seismic waves that travel through the mantle will arrive at a recording station located a long distance from an earthquake's hypocenter before waves that travel just through the crust because the mantle is ____________ and thus the waves in it have a higher velocity.
denser
Using the time interval between the arrival of the first P-wave and another type of compressional wave is how we calculate the _________ to an earthquake hypocenter.
depth
The Moho ______.
depth may sometimes be identified as reflections on seismic-reflection profiles depth may be determined by observing arrivals of seismic waves and whether the first waves came through the crust or the mantle is an abbreviation for the Mohorovicic Discontinuity, the boundary between the crust and mantle
A seismometer ______.
detects and records ground motion during earthquakes may create a graphic plot called a seismogram is often placed with two others, oriented at 90o to detect three components of motion
Prehistoric earthquakes may be studied by ______.
digging trenches along a fault in order to map the offset of layers of sediment and soil to provide a timeline for interpreting when the fault moved
The sudden release of energy stored in rocks causes a(n) ____________.
earthquake
Tsunamis may be generated by ______.
earthquakes that cause the seafloor to shift activity associated with volcanic eruptions landslides that displace large amounts of water
When rocks return to their original shapes after being strained, we call it ________ behavior.
elastic
One of the most destructive hazards following an earthquake are ____________, which are caused when both natural gas lines and then water mains break due to shaking.
fires
A section of a fault that has had relatively little earthquake activity is called a seismic _________.
gap
Landslides create seismic waves by causing the __________ to shake.
ground
Tsunami warning systems ______.
have buoys and ocean bottom sensors to detect small changes in sea level use seismic information to determine an earthquake's potential to cause a tsunami help detect potential tsunamis in the Pacific and Indian Oceans
Geologists look at rocks that were once at great depth, create high temperature and pressure conditions for rocks in the laboratory, and develop computer models in order to ______.
investigate deep conditions and processes within Earth
Moment magnitude ______.
is calculated from the amount of fault displacement and size of the fault area that slipped for energy released by earthquakes is almost always greater than the energy of lightning strikes but is less than that of an average hurricane is useful for both large and small earthquakes
Short-term earthquake prediction ______.
is complex, but techniques are still developing that hold promise
The Great Alaskan Earthquake of 1964 ______.
is the strongest ever recorded for North America had an epicenter between Anchorage and Valdez reported a fault surface that was over 900 km long and 250 km wide
Megathrust earthquakes are characterized as ______.
large in magnitude the most damaging and deadly
Most earthquakes occur at depths of ______, and earthquakes in subduction zones may occur at depths of ______.
less than 100 km; up to 700 km
Water-saturated sediment can lose its strength due to shaking during an earthquake in a process called ___________.
liquefaction
The greatest variety of processes involving the flow of materials most likely occurs in the ______.
mantle
Long-range earthquake forecasting ______.
measures patterns of seismic activity along a fault to determine locations and recurrence intervals uses tectonic settings and historical records is based mainly on the knowledge of when and where earthquakes occurred in the past
Representing the huge thrust fault created by subduction, ________ earthquakes are deadly and damaging, and commonly create tsunamis.
megathrust
The amount of slip on a fault, and the size of the fault that slips, is used to calculate an earthquake's ________ magnitude.
moment
Shallow earthquakes are the ______ common, and deep earthquakes, which occur exclusively in subduction zones, are the ______ common.
most; least
The direction of subduction indicated in the circular area is to the ______.
northwest
Most earthquakes occur along ______.
plate boundaries
The surveying that occurred following the 1964 Alaskan earthquaked indicated significant vertical changes in the land surface and thrust faulting of the ocean crust underneath the continent; this information played strongly in the development of ___________ __________ theory shortly thereafter.
plate tectonic
Fatalities caused by earthquakes are most closely related to ______. Chose the three most important factors.
population density earthquake magnitude proximity to high-risk areas, e.g., subduction zones
Investigate mines
provide detailed, cotinuous exposure of rocks and structures in place; may go deeper than 5 km but most are much shallower
study inclusions
provide pieces of rock from depth that have been brought to the surface by such things as volcanic process
The average time between earthquakes along a certain fault is the ______.
recurrence interval
When a seismic wave hits an interface and some of the energy is sent back toward the surface, that wave is said to have been ______, whereas when a seismic wave hits an interface and some of the energy is bent as it crosses that boundary, the wave has been ______.
reflected; refracted
The image, indicating the path of a seismic wave through a segment of Earth, shows ______.
refraction causes seismic waves to take curved paths through Earth seismic waves are refracted to shallower and shallower angles at depth waves are eventually bent back toward the surface
Overall, a P-wave increases in velocity with depth. This implies that ______.
rocks are increasing in density with depth
Elastic behavior is when ______.
rocks return to their original shape after being strained
One method of studying faults uses __________ radar data sets to map an area before and after an earthquake to measure how the surface was deformed.
satellite
In the San Andreas experiment, ______.
scientists drilled a hole through part of the fault and installed instruments in hope of recording an earthquake as it happens
Flooding because of dam failures, flooding due to subsidence, and rupturing gas lines are ______ due to earthquakes, whereas shaking of structures and buildings, liquefaction, and the destruction of structures by faulting are ______ due to earthquakes.
secondary effects; direct damage
The energy released by an earthquake travels through rocks as ______.
seismic waves
A modern seismic detector is called a ______.
seismograph, and works by measuring ground motion in three directions Reason: Seismographs employ three seismometers.
Seismic waves are recorded by a digital instrument called a ______ and may be viewed either on a computer screen or as a paper plot printout called a ______.
seismometer; seismogram
study surface features
some may have been uplifted from depth; can provide large areas of rock and structures that were created deeper in earth
The two basic types of seismic waves include ______ waves, which are created when seismic wave energy reaches Earth's surface and is transformed into new horizontal and vertical waves, and ______ waves, which are usually generated at faults and travel through Earth (primary and secondary).
surface; body
An earthquake is ______.
the sudden release of energy stored in rocks
A large sea wave produced by uplift, subsidence, or some other disturbance of the seafloor, especially by a shallow submarine earthquake, is a(n) ___________.
tsunami
The image indicates that ______.
two major zones exist for earthquake risk in the eastern U.S.
Not only did the 1964 Alaskan earthquake create a dangerous tsunami, but it also caused ______ as seen in the attached photograph.
uplift of the seafloor
During the 1964 Alaskan earthquake, faults movements caused ______.
uplift of the seafloor that brought it to the surface uplift of the seafloor that caused a tsunami subsidence that resulted in flooding
The 2010 and 2011 earthquakes in New Zealand caused a lot of damage because they ______.
were shallow and located near city centers