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The mechanism by which rocks store and eventually release energy in the form of an earthquake is termed ________. |
elastic rebound |
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Earthquake epicenters closely correlate with __________________. |
edges of the plates |
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What determines the amount of destruction caused by seismic shaking? |
intensity of the shaking; nature of the ground material; duration of the shaking; nature of the building material |
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Which of the following terms are types of seismic waves? |
surface waves, primary waves, secondary waves |
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What is true about erosion? |
Erosion varies from place to place |
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Where do valleys tend to form in a landscape? |
Valleys form where rock layers are easily erodible (soft). |
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The point within Earth from which earthquake wave energy radiates is known by which of the following terms? |
Focus |
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On average, how many damaging earthquakes occur each year? |
1000 |
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Most earthquakes are the result of movement along which of the following features? |
Faults |
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During the 1906 San Francisco earthquake, the Pacific Plate moved 4.7 meters (15 feet) north relative to the North American Plate. Which of the following types of stress was exerted on the rocks during this earthquake? |
shear stress |
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Which of the following events allows rocks on either side of a fault to rebound elastically, causing an earthquake? |
Friction along the fault plane is overcome. |
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The average composition of the continental crust most closely approximates that of ________. |
granite |
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What term describes the type of deformation experienced by rocks before an earthquake? |
slow deformation |
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How are elastic rebound and elastic deformation different? |
Elastic deformation causes objects to bend, whereas rebound causes objects to return to their original shape. |
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Elastic deformation before an earthquake is like _______, whereas rupture is like__________. |
stretching a rubber band; breaking a rubber band |
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What will happen to a straight fence that undergoes elastic strain during an earthquake? |
The fence will break. |
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What is a terrane? |
… |
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Where does most terrane accretion occur? |
in association with a continental-oceanic subduction zone |
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Why are terranes added to continental margins, rather than subducting under them? |
Terranes are too buoyant to subduct. |
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Which of the following statements about terranes is most accurate? |
The margins of many continents have grown through the accretion of terranes. |
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Which two processes commonly generate magma? |
decompression melting and wet melting (the addition of volatiles) |
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Where does the water involved in melting at subduction zones come from? |
Water contained within minerals in the subducting plate is released during metamorphism. |
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What is peridotite? |
the rock making up the mantle |
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Why is water a necessary component of the melting process in subduction zones? |
The addition of water lowers the melting temperature of rock. |
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Why is decompression melting common at mid-ocean ridges but not at subduction zones? |
Tectonic plates are moving apart at mid-ocean ridges, resulting in a lowering of pressure beneath the ridge. Tectonic plates are moving together at subduction zones, resulting in an increase of pressure under new mountains. |
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Which of the following could cause rock to melt? |
… |
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The upper mantle is very close in chemical and mineralogical composition to ________. |
peridotite |
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What is a fault? |
fractures along which rocks move |
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What are rocks below and above a fault called? |
the footwall below and the hanging wall above |
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Which type of force is responsible for normal fault formation? |
tensional force |
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Which type of force is responsible for reverse fault formation? |
compressional force |
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Which type of force is responsible for normal strike-slip formation? |
shear force |
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Which type of fault has NO vertical motion of rocks associated with it? |
strike-slip fault |
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Earthquakes with a Richter magnitude of less than ______ are generally not felt by humans. |
2.0 |
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How do continental crust and oceanic crust differ? |
Continental crust is composed of granite; oceanic crust is composed of basalt.; Continental crust is less dense than oceanic crust.; Continental crust is thicker than oceanic crust. |
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How are tsunamis generated? |
through displacement of the seafloor under water |
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What is a tsunami? |
a series of water waves that travel away from a fault in all directions at high speed |
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Why do ships at sea tend not to notice tsunamis? |
Tsunamis in deep water have small wave height and long wavelength. |
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Why does the wave height of a tsunami increase as the tsunami enters shallow water? |
In shallow water, the energy of the tsunami must be contained within a smaller water column. |
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What type of plate boundary are most tsunamis associated with? |
convergent boundary |
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Which ocean is associated with most tsunamis? |
Pacific Ocean |
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Will Sumatra experience another tsunami like the destructive one of December 2004? |
This is likely, because Sumatra is near many ocean trenches. |
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Which of the following responses best describes the epicenter of an earthquake? |
The point on Earth’s surface directly above the focus of an earthquake. |
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In calculating the location of the epicenter of an earthquake, which of the following factors is most useful? |
the difference in arrival time of P and S waves |
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In addition to a travel-time graph, at least how many seismograph stations are needed to determine the location of the epicenter of an earthquake? |
three |
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As the distance between the epicenter of an earthquake and a seismograph station increases, so does the difference in the arrival times of the P and S waves. What causes this? |
P waves are faster than S waves. |
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Which statement provides the best explanation of why most earthquakes occur at plate boundaries? |
Plate boundaries are locations on Earth where portions of the lithosphere interact as they move past each other. |
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What causes an earthquake? |
Earthquakes result from the rapid release of energy in the Earth’s crust. |
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What characterizes the size of an earthquake? |
the amount of damage; the amplitude of the seismic wave |
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What is a seismograph? |
an instrument used to record earthquake waves |
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What is the underlying principle of seismograph construction? |
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. |
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When will the first earthquake waves arrive at a seismograph station? |
a short time after the earthquake occurs |
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How long does it typically take for the first earthquake waves to arrive at a seismograph after the earthquake occurs? |
several minutes |
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What are tsunami? |
massive ocean waves usually triggered by underwater earthquakes |
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The position on Earth’s surface directly above the earthquake source is called the ________. |
epicenter |
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________ refers to the tendency for a foundation material to lose its internal cohesion and fail mechanically during earthquake shaking. |
Liquefaction |
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Which two observations help constrain the dimensions of Earth’s core and mantle? |
Earth’s density and the wobble of Earth’s rotation axis |
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What does the wobble of Earth’s rotation axis tell us? |
The core must be denser than the mantle. |
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How do we know that the core has a density less than 15 g/cm3? |
This density is higher than any known substance. |
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How do we know that the radius of Earth’s core has to be at least 3100 km? |
A smaller core would require material with an unnatural density. |
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How do we know that the radius of Earth’s mantle has to be at least 1771 km? |
If the mantle were smaller, the rock making up the mantle would have a density that is too low. |
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How do we know the actual dimensions of Earth’s core and mantle? |
from earthquake waves passing through Earth |
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Earthquakes with a deep focus are most often associated with which of the following tectonic settings? |
trenches |
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As stress is applied to rocks and deformation occurs, which of the following terms best characterizes the energy that is stored in the process? |
elastic energy |
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Earthquakes occurring at depths up to 700 km (435 mi) are associated with which of the following plate boundaries? |
convergent boundaries |
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Which of the following responses provides the best reason for why the asthenosphere is not capable of storing elastic energy? |
Elastic energy is quickly used up in the asthenosphere. |
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How can the epicenter location of earthquakes at an oceanic-oceanic convergence zone be used to determine which plate is being subducted? |
The epicenters will be located on the plate that is not being subducted. |
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Overall, this type of seismic wave is the most destructive. |
surface wave |
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Which layer of Earth possesses the greatest thickness? |
mantle |
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Which of the following rocks best represents the typical composition of oceanic crust? |
basalt |
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Which region of Earth is composed of abundant amounts of granite? |
continental crust |
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What is the major source of energy that drives the movements of the lithospheric plates on Earth? |
thermal energy from within Earth |
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The magnetic field of Earth is thought to originate in which of the following layers? |
outer core |
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Which of the following responses best describes why the lithospheric plates are able to move around on the surface of Earth? |
Because the asthenosphere is composed of weak, hot, and dense rock, the cold, rigid, less dense lithospheric plates are capable of moving on it. |
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How do we know that the outer core of Earth is liquid? |
A shadow zone exists where S waves do not arrive on the side of Earth opposite the focus of an earthquake. |
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What do we call seismic waves that are transmitted along the outside of Earth? |
surface waves |
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Which of the following motions best describes the movement of S waves as they travel through rocks following the release of energy during an earthquake? |
shaking particles at right angles to the direction of travel |
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Which of the three types of seismic waves travels through rock with the greatest velocity? |
P waves |
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Which of the following types of seismic body waves travels only through solids? |
S waves |
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Early in the study of earthquakes, seismologists learned that P waves arrive at seismograph stations all over Earth, but a shadow zone exists for S waves. Which of the following responses best explains this phenomenon? |
The outer core of Earth is liquid. |
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Which type of seismic waves generally cause the most structural damage as they travel through Earth? |
surface waves |
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Approximately how much more energy is released in a 6.5 Richter magnitude earthquake than in one with magnitude 5.5? |
30 times |
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Transform boundaries are classified under which type of fault? |
strike-slip |
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What role do transform boundaries play? |
… |
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Do fracture zones near transform boundaries play a role in plate motion? |
… |
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What is the relationship between transform boundaries and mid-ocean ridges? |
Transform boundaries connect segments of mid-ocean ridges. |
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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. |
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What are the major zones of Earth’s interior? |
crust, mantle, core |
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Which one of the following statements is correct? |
S waves travel through solids and P waves travel through liquids. |
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What are the two primary types of waves generated by earthquakes? |
surface and body waves |
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