Earthquake and Volcano Ch 3
transform
First recognized by J. Tuzo Wilson in 1965, ______ faults are a special type of horizontal-movement fault that connects the ends of two offset segments of plate edges.
period
For a wave, the ________ = 1/frequency
dip, strike
Geologists measure the orientation of tilted rock layers. _____ is the angle of inclination from the horizontal of a tilted rock layer, and ______ is the compass bearing of a rock layer where it pierces the horizontal plane.
1. Granite rock 2. packed sand 3. loose sand 4. water 5. air
P wave velocity depends upon the material through which the wave passes. Rank these materials from the fastest P wave velocity at the top to the slowest at the bottom.
compressional
P waves are ______ and can travel through air, just like sound waves do, and hence are audible.
sound
P waves can travel through air, where they take the form of _____ waves. You might experience this as a sonic boom.
P waves with 1- to 10-second periods
The body-wave (mb) scale for earthquake magnitude is based on the amplitudes of _______.
seismograph
The instrument used to record seismic waves is called a(n)
bedrock type distance from the epicenter magnitude building style
The intensity of an earthquake varies with _____.
mainshock
The largest earthquake in a series that occurs on the same portion of a fault is called the _____.
lateral continuity
The law of _____ _____ states that sedimentary layers extend laterally until they thin out at their edges.
superposition
The law of _____ states that within a sequence of undisturbed sedimentary, the oldest layer is at the bottom
epicenter
The point on the Earth's surface directly above where the fault first ruptures is known as the
hypocenter
The point where a fault first ruptures is known as the ____.
a fracture in bedrock along which sliding has occurred
what is a fault
tension
Normal faults form in response to which type of stress?
One may have the same period as the seismic waves and thus experience resonance.
Why might two adjacent buildings that are constructed of the same materials but have different heights suffer very different amounts of damage during an earthquake?
low-frequency surface waves
Tall buildings have low frequencies of vibration and are therefore most strongly affected by _________.
seismic, waves
The energy released when a fault ruptures radiates outward from the hypocenter as ______ ________.
Isolate the building from the ground Infill walls to create shear walls Add buttresses Add bracing
Which of the following are methods used to seismically retrofit a building?
Cannot travel through fluids The second to reach a recording station Has a shearing motion
Which of the following best describe an S wave?
Wood
Which of the following building materials is both flexible and can handle the large accelerations of seismic waves?
Moves in a push-pull fashion The first to reach a recording station Can travel through any material
Which of the following describe a primary (P) wave?
Climate
Which of the following is the only factor listed that does not affect the intensity of an earthquake?
Change the height of the building Change the degree of attachment to the foundation Change the type of building materials
Which of these are ways in which a building can be designed to eliminate the occurrence of resonance?
Low frequency Slow-moving
Which of these correctly describe the nature of surface waves?
Law of original continuity
Which of these laws tells us that when a sedimentary rock layer abruptly terminates, something must have happened to it after it formed.
strike-slip, right-lateral
Which of these statements describe the fault shown here? (Person standing with 1 leg on either side of straight crack in surface; right side moved back, left side moved up)
reverse dip slip
Which type of fault is shown here? (3 horizontally bedded rock layers offset by angled surface that cuts through them; block on right is above cut and has moved up (compress))
body wave
Which type of seismic wave is the fastest?
The movement along the fault increases stress on adjacent sections of that fault.
Why are aftershocks common after a large earthquake?
The outer core is liquid, and S waves cannot travel through a liquid.
Why do S waves disappear at the core-mantle boundary?
To assess earthquake hazards
Why do geologists map the location of active faults?
Because the area of the rupture zone is defined by aftershocks, which continue for many weeks following a great earthquake
Why does it often take weeks to determine the moment magnitude for great earthquakes?
Friction holds the rocks together
Why don't the rocks on either side of a fault simply slide past each other when stress is applied?
Most buildings are already designed to handle the vertical forces associated with their own weight.
Why is it of greater concern to design buildings to withstand horizontal ground movement than it is to design them to withstand vertical ground movement?
It uses short-period seismic waves.
Why is the Richter magnitude scale less reliable for large earthquakes that occur far away?
Seismic waves slow down in soft sediments, which increases their amplitude.
Why is the shaking during an earthquake stronger in a building built upon soft sediments?
transverse
The ______ nature of S waves make them apt to damage buildings.
moment magnitude (Mw)
The _______ scale is the most accurate measure of the size of large earthquakes.
the bigger the earthquake, the greater the shaking of Earth
Charles Richter based his earthquake magnitude scale on the idea that _______.
compressional, tensional
Dip-slip faults generally form in response to ______ forces.
magnitude intensity
Earthquake _____ is a measure of the energy released during an earthquake. Earthquake _____ is a measure of the effect of an earthquake on people and buildings.
near the epicenter
Earthquake intensity is generally greatest ________.
decreases
Earthquake intensity with distance from the epicenter.
energy released; damage to people and buildings
Earthquake magnitude is an objective measurement of the _______, whereas intensity is a subjective measurement of ______.
length of fault rupture
Earthquake magnitude is strongly influenced by the ________.
tensional
Examine the right-lateral fault in this figure. What kind of stress do you think is occurring at the point where it bends to the right? (Person standing next to a stepped crack (like a soft Z) : side she is on (left) has moved up, right side moved down)
fluids containing dissolved metals can more easily flow through fault zones
Veins of valuable ores are common along faults because ______.
earthquake
Vibrations we feel when sudden movement occurs along a fault
faults offset rock units
Faults can be recognized in the field, even if the fault plane itself is not exposed, because ______.
normal
A _____ dip-slip fault occurs when the hangingwall moves down relative to the footwall
reverse
A ______ dip-slip fault occurs when the hangingwall moves up relative to the footwall
fault, fracture
A _______ is a planar feature where the two sides move past each other. If no movement occurs, then the planar feature is called a ______.
concrete
A building constructed of ______ is likely to have a shorter period.
concrete
A common solution for retrofitting buildings and bridges to decrease earthquake damage is using a combination of _____ and steel.
1,000
A magnitude 7 earthquake has an amplitude ______ times greater than a magnitude 4 earthquake.
acceleration due to gravity
Acceleration during an earthquake is usually measured relative to _______.
D (lowest layer)
According to the law of superposition, which of the layers marked in this image is the oldest?
energy
An earthquake occurs from the release of ______ when stress on a fault builds high enough for the rocks to snap and move suddenly.
seism
Another term for an earthquake is a ______.
potential energy
As stress builds up over many years on a fault, _______ is stored in the rocks. This is released as seismic waves when the fault ruptures.
divergent
At which type of plate boundary would you be most likely to find normal faults?
convergent
At which type of plate boundary would you be most likely to find reverse dip-slip faults?
large
Because of their low frequency and slow speed, surface waves carry _____ amounts of energy away from the epicenter.
Both P and S waves slow down.
How do scientists identify the depth to the top of the asthenosphere in the Earth's interior?
By analyzing the seismic wave traces on a seismogram
How is earthquake magnitude measured?
When you straddle the fault, the left-hand side has moved toward you.
How would you recognize a left-lateral strike-slip fault?
left-lateral strike-slip
If a feature truncated by a strike-slip fault is displaced to the left on the other side of the fault, what type of fault is it?
shear walls
Parking structures are often vulnerable to earthquake damage, as shown in this image. This is because they often lack sufficient _______. (3 story parking structure collapsed.)
compression
Reverse faults form in response to which type of stress?
mudstone sandstone granite rock
S waves can travel through ______.
moment
Seismic ______ (Mo) is equal to the shear strength of rocks times the rupture area of the fault times the average displacement on the fault.
body, surface
Seismic waves that pass through the interior of the planet are called ______ waves, whereas those that travel across the surface are called _______ waves.
faster
Seismic waves travel _____ through hard rocks than they do through soft rocks and sediment.
high-frequency
Short rupture lengths produce mostly ______ seismic waves.
lower
Similar to a rupturing fault, when the path of sound waves through a trombone is extended the frequency is ______ and the tone is lower.
foreshocks aftershocks
Smaller earthquakes that precede the mainshock are called _____ and those that follow the mainshock are called _______.
primary, secondary
The two types of body waves are ______ waves and ______ waves.
love, rayleigh
The two types of surface wave are _____ waves and ______ waves.
base isolation
The use of ____ _____ in the form of ball bearings or shock absorbers protects a building from the worst of the ground shaking.
compressibility density
The velocity of P waves depends on the ______ and _______ of the material through which they pass.
S
This image best illustrates the way in which ______ waves travel through material. (Hands holding a rope as an up and down motion in the rope progresses from left to right over time.)
1960 Chile
The earthquake with the largest moment magnitude calculated to date was the _______ earthquake.
3.5
Examine this nomograph. If it is determined from a seismograph that the S-P time is 30 seconds and the amplitude of the seismic waves is 0.5 mm, what is the magnitude of the earthquake?
dominantly vertical
A dip-slip fault is one where movement is ______________.
6
A fault-rupture length of 10 km produces approximately a magnitude ____ earthquake
S
Because their motion is up and down and side to side, _____ waves are the type of body wave that can do severe damage to buildings.
3,000 km
Examine this graph. If the S-P time is approximately 4.5 minutes, how far from the epicenter are you? (Graph with distance from earthquake on x-axis and time on y-axis. Time between arrival of S-wave and P-wave increases with distance: 11 min at 8800 km)
right-lateral strike-slip
If a feature truncated by a strike-slip fault is displaced to the right on the other side of the fault, what type of fault is it?
rayleigh
If, during an earthquake, you feel like you're being rocked in a boat at sea, you are most likely feeling the passage of _____ waves.
intensity
In general, earthquake ______ decreases with distance from the epicenter.
sediment
In general, earthquake intensity is greatest in areas underlain by _______.
travel with a shearing motion at right angles to their direction of advance cannot travel through fluids but can travel through solid material
Love waves are a type of surface wave. They are similar to S waves in that they ____________.
A- strike (line created by water surface hitting tilted bedrock) B- angle of dip (angle between water surface and rock surface) C- direction of dip (direction rock is tilted)
Match the arrows marked A-C with their correct labels. (A on line created by water surface hitting tilted bedrock; B is angle between water surface and rock surface; C points in direction rock is tilted)
time of day of the event
One of the most critical factors in determining the loss of life from a earthquake is ________.
inertia
Seismographs like the one shown here record seismic waves because the heavy weight does not move with the framework of the instrument. This is due to the _____ of the weight. (Device with weight and pen hanging as pendulum on a framework and base, with rotating paper cylinder, that moves with Earth)
higher
Similar to sound waves passing through a trombone, the shorter the rupture length along a fault, the ______ the frequency of the seismic waves that are generated.
transform
Spreading centers are linked to each other or to subduction zones by ______ faults which allow the rigid lithosphere to move over a curved surface.
shear
Strike-slip faults form in response to which type of stress?
amplified
Surface waves are often _____ when they pass through soft sediment, increasing earthquake intensity.
L (long)
Surface waves are referred to as ______ waves because they take more time to complete one cycle of motion and are the slowest moving.
are moderate in size occur nearby
The Richter magnitude scale is only useful for assessing earthquakes that _______.
amplitude
The Richter magnitude scale uses the _______ of seismic waves to determine the amount of shaking and thus the size of an earthquake.
right-lateral strike-slip
The San Andreas fault in California is the most famous example of a _______ fault.
strike slip
The San Andreas in California and the Alpine in New Zealand are examples of ____-_____ faults
Mercalli
The ______ Intensity Scale ranges from I (not felt) to XII (damage nearly total).
Mercalli Intensity
The ______ Scale is a descriptive scale based upon the effects of an earthquake on people and buildings.
9.8 m/sec2
The acceleration due to gravity is ______, which is referred to as 1.0 g.
48
The amount of energy released by a magnitude 5 earthquake is ______ times that released by a magnitude 4 earthquake.
period
The amount of time it takes for a building to sway back and forth one time is called its ______.
S wave, P wave
The arrival times of which two types of seismic wave are used to calculate the location of an earthquake's epicenter?
3 a.m.
The best time for an earthquake in California is _______, when the loss of life is likely to be lower.
hangingwall
The block above the fault plane in this image is referred to as the ___
footwall
The block below the fault plane in this image is referred to as the ___________. (5 horizontally bedded rock layers offset by angled mineshaft that cuts through them; block on left is below cut and has moved down)
horizontal ground movement
The damage done to this house was most likely due to ________. (Multi-level home skewed in different directions.)
asthenosphere
The decrease in velocity of both P and S waves at about 100 km depth marks the top of the _______. (Cross section of Earth next to graph of wave velocity versus time.)
wavelength, amplitude
The distance between two waves, labeled A in this figure, is called the ______. The height of a wave above its starting point, labeled B in this figure, is called the ________. (Single lines with 2 bumps moving left to right; A: space between 2 bumps; B: height from flat line to peak of bump)
outer core
The drastic decrease in P wave velocity and the disappearance of S waves at the depth shown with an arrow on this graph marks the top of which layer of the Earth's interior?
lower
The greater the length of fault rupture, the ____ the frequency of the seismic waves it produces.
seismometer
The instrument used to detect seismic waves is called a(n)
original horizontality
The law of ________ states that sediments deposited in water form as horizontal layers.
looking at the difference in arrival times of different types of seismic waves
The location of the epicenter and hypocenter of an earthquake can be determined by ______.
collapsed structures
The majority of people who died in the Northridge 1994 earthquake did so due to ______.
the amount of strain energy released by the movement along the rupture surface
The most reliable measure of earthquake size is seismic moment, which measures the ________.
aftershocks
The movement associated with an earthquake puts stress on adjacent faults and causes ____.
frequency
The number of times a building sways back and forth during a given amount of time is called its ______.
frequency
The number of waves passing a given point during one second is referred to as ______.
retrofitting
The process of reinforcing existing buildings to increase their resistance to seismic shaking is known as _____.
acceleration
The rate of change in velocity of the ground as it is moved by seismic waves is called _____.
secondary
The second type of seismic wave to reach a recording station after an earthquake is a(n) _____ wave.
seismology
The study of earthquakes is known as
Rayleigh waves with 18- to 22-second periods
The surface-wave (Ms) scale for earthquake magnitude is based on the amplitudes of ______.
P
This figure demonstrates how ______ waves move through material. (4 springs with an arrow pointing left to right showing how a push and pull type of motion progresses across the spring with time.)
rayleigh wave
This figure demonstrates the sense of motion of which type of seismic wave? (Cross section of rolling hills and valleys; under each hill is counterclockwise circular motion; under entire area motion is progressing left to right)
soft first story
This hospital is an example of a building with a ______. Collapse of buildings like this caused many deaths in the 1971 San Fernando Valley earthquake. (8-story building with first floor open; looks like it is built on tall stilts.)
bracing
This image shows _____, a method used to provide resistance to the up, down, and sideways movements of the ground. (A 6-story building with braced frames running diagonally across traditional 90° bracing.)
base isolation
This image shows how a building can be protected by ______, which allow(s) a building to roll with seismic waves. (The bottom corner of building resting on small, multipart isolator base.)
love
This type of surface wave travels parallel to Earth's surface in a side-to-side motion.
magnitude
To determine the _______ of an earthquake, seismologists use a nomograph, which compares the distance from the hypocenter and the amplitude of the seismic waves.
Wood --> Lightweight, flexible Steel --> Flexible, vulnerable to compressive stress Concrete --> Great compressional strength, vulnerable to brittle failure
To protect buildings from earthquake damage, it is important to consider the building materials you use. Match these building materials to their properties.
three
To study earthquakes, seismologists must record the movement of earthquake waves in ______ directions.
allow spreading centers to wrap around the curved surface of Earth
Transform faults are fractures that form in order to _________.
False
True or false: Low-frequency seismic waves tend to die out first, at shorter distances from the hypocenter.
True
True or false: The greater the magnitude of an earthquake, the greater the intensity.
distance from
Using the S-P time from a single seismograph, it is possible to determine the ______ the epicenter.
shear
Walls designed to take horizontal forces from floors and roofs and transmit them to the ground are called ______ walls.
shorter
Wave frequency and period are related. The higher the frequency, the ______ the period.
permeable
What characteristic of faults allows water to carry dissolved metals that are precipitated as ores within the fault zone?
Poorly designed buildings, bridges, and dams
What factor led to the greatest loss of life in the 1971 San Fernando Valley earthquake?
Poor design of buildings and bridges
What factor led to the greatest loss of life in the 1994 Northridge earthquake, despite the lessons learned from the 1971 San Fernando Valley earthquake?
an earthquake occurs
What happens when the stored potential energy in a fault is suddenly released after building up for many years?
A fault where the slip is predominantly horizontal and parallel to the fault plane
What is a strike-slip fault?
The difference in arrival time of S waves and P waves
What is the S-P time?
9.5
What is the largest moment magnitude ever recorded?
3
What is the minimum number of seismograms needed to determine the location of the epicenter of an earthquake?
Acceleration
What is the rate in change of velocity of seismic waves?
Taller and more flexible
What kind of building design is best where the earth foundation is hard rock that transmits high-frequency vibrations?
transform
What kind of fault is shown here (marked with a blue arrow)? (Thin crust; cross section has magma coming up at split; 2 splits offset by horizontal movement in opposite directions (arrow points to that))
normal dip-slip
What kind of fault is shown here? (3 horizontally bedded rock layers offset by angled surface that cuts through them; block on right is above cut and has moved down (extend))
Buildings constructed of stone or brick Short buildings
What types of building are most vulnerable to high-frequency P and S waves close to the epicenter of an earthquake?
An uplifted mound or hill
When a left-lateral strike-slip fault has a right-stepping bend, what kind of topographic feature is likely to form?
flexible
When bracing is incorporated into the earthquake safety design of a building, it is generally constructed of steel because steel is ______. (A 6-story building with braced frames running diagonally across traditional 90° bracing.)
strength; flexibility
When retrofitting bridges, builders add alternating layers of concrete and steel to vertical supports. The concrete provides _____ and the steel provides _____. (Construction of columns wrapped by circular grid of rebar then encased in concrete.)
resonance
When the period of seismic waves is equal to the period of a building, _____ can occur, which can cause catastrophic failure.
Close to the epicenter
Where do high-frequency seismic waves cause the most damage?
A 35-story skyscraper
Which building is likely to have the longest period?
Law of original horizontality
Which law of physical geology can be used to determine that these rocks layers were deformed into folds after they were deposited?
magnitude
_______ is a measure of the the amount of energy released during an earthquake.
inertia
the principle of _____ explains that a stationary object will remain stationary unless acted upon by an external force.
