Earthquakes Flashcards
Most earthquakes occur along what plate boundary?
Most earthquakes occur along active plate boundaries
Seismic Energy
Energy that radiates from fault movement via earthquakes
elastic rebound theory
The deformation that results from application of a stress
Strain
The deformation that results from application of a stress.
The release of seismic energy is explained by what theory
Elastic Rebound Theory
Brittle Deformation
A style of strain in which an object suddenly breaks, fractures, or otherwise fails in a different way than ductile deformation.
Focus
Initiation point of an earthquake or fault movement.
The place where the initial offsetting rupture takes place between the fault blocks is called the focus.
The earthquake focus, also called hypocenter, is the initial point of rupture and displacement of the rock moves from the hypocenter along the fault surface.
Offset
Amount of movement during a faulting event.
seismic stress causes continuous, gradual displacement between the fault blocks called…….
Fault Creep
After an initial earthquake, continuous application of stress in the crust causes elastic energy to begin to build again during a period of inactivity along the fault. The accumulating elastic strain may be periodically released to produce small earthquakes on or near the main fault called____
Foreshocks
Foreshock
An earthquake that sometimes occurs before the larger mainshock.
The main release of energy during the major earthquake is known as the_________
Mainshock
Mainshock
Largest earthquake in an earthquake sequence.
Focus is also known as
Hypocenter
epicenter
The epicenter is the location on the Earth’s surface vertically above the focus. This is the location that most news reports give because it is the center of the area where people are affected
The location at the surface directly above the focus of an earthquake, typically associated with strong damage.
amplitude
Height or depth of a wave from the middle point.
Magnitude
A measure of earthquake strength. Scales include Richter and Moment.
Wave amplitude indicates the ________ or height of earthquake motion.
Wave amplitude indicates the magnitude or height of earthquake motion.
Wavelength
The distance between any two repeating portions of a wave (e.g., two successive wave crests).
_________is the number of repetitions of the motion over a period of time, cycles per time unit.
Wave frequency
When waves combine in sync, they produce _____________, where the influence of one wave adds to and magnifies the other.
When waves combine in sync, they produce CONSTRUCTIVE INTERFERENCE, where the influence of one wave adds to and magnifies the other.
If waves are out of sync, they produce __________, which diminishes the amplitudes of both waves.
If waves are out of sync, they produce DESTRUCTIVE INTERFERENCE, which diminishes the amplitudes of both waves.
If two combined waves have the same amplitude and frequency but are one-half wavelength out of sync, the resulting destructive interference can _____________
If two combined waves have the same amplitude and frequency but are one-half wavelength out of sync, the resulting destructive interference can ELIMINATE EACH WAVE.
These processes of wave amplitude, frequency, period, and constructive and destructive interference determine the _____ and ______ of earthquakes.
These processes of wave amplitude, frequency, period, and constructive and destructive interference determine the MAGNITUDE and INTENSITY of earthquakes.
What type of inference?
Constructive Interference
What constructive waves look like
What type of interference
Destructive
If two combined waves have the same amplitude and frequency but are one-half wavelength out of sync, the resulting destructive interference can ___________.
if two combined waves have the same amplitude and frequency but are one-half wavelength out of sync, the resulting destructive interference can ELIMINATE EACH WAVE
Seismic waves
are the physical expression of energy released by the elastic rebound of rock within displaced fault blocks and are felt as an earthquake
Seismic waves occur as what two kinds of waves?
Seismic waves occur as body waves and surface waves
Body Waves
Seismic waves that travel through the Earth, mainly P waves and S waves.
Body waves pass underground through the Earth’s interior body and are the first seismic waves to propagate out from the focus.
Body waves include which waves?
Body waves include primary (P) waves and secondary (S) waves
___________ are the fastest body waves and move through rock via compression, very much like sound waves move through air.
P waves are the fastest body waves and move through rock via compression, very much like sound waves move through air.
Rock particles move forward and back during passage of the ______ waves, enabling them to travel through solids, liquids, plasma, and gases
Rock particles move forward and back during passage of the P waves, enabling them to travel through solids, liquids, plasma, and gases
S waves
Second-fastest seismic wave that has a sheer motion
Because ___ waves are restricted to lateral movement they can only travel through solids but not liquids, plasma or gases
S Waves
P-waves are compressional or shear
Compressional
S waves are compressional or shear.
Shear
During an earthquake what do body waves do?
During an earthquake, body waves pass through the Earth and into the mantle as a sub-spherical wave front. Considering a point on a wave front, the path followed by a specific point on the spreading wave front is called a seismic ray and a seismic ray reaches a specific seismograph located at one of thousands of seismic monitoring stations scattered over the Earth. Density increases with depth in the Earth, and since seismic velocity increases with density, a process called refraction causes earthquake rays to curve away from the vertical and bend back toward the surface, passing through different bodies of rock along the way.
Refraction
Waves that change direction due to changing speeds, typically caused by a change in density of the medium
seismic velocity increases with ____
seismic velocity increases with density
__________ are produced when body waves from the focus strike the Earth’s surface.
SURFACE WAVES are produced when body waves from the focus strike the Earth’s surface.
because of their complex horizontal and vertical movement, ________ waves are responsible for most of the damage caused by an earthquake.
because of their complex horizontal and vertical movement, SURFACE WAVES are responsible for most of the damage caused by an earthquake.
Raleigh Waves
Surface waves take the form of rolling waves called Raleigh Waves
-Raleigh waves cause rock particles to move in a direction opposite to that of water particles in ocean waves.
Surface waves take the form of side to side waves called _________
Love waves
Which travels slower surface waves or body waves?
Surface waves
because of their complex horizontal and vertical movement, _______ waves are responsible for most of the damage caused by an earthquake
because of their complex horizontal and vertical movement, SURFACE waves are responsible for most of the damage caused by an earthquake
Love Waves
Surface waves that have a side-to-side motion.
______waves produce predominantly horizontal ground shaking and, ironically from their name, are the most destructive.
LOVE waves produce predominantly horizontal ground shaking and, ironically from their name, are the most destructive.
______ waves produce an elliptical motion with longitudinal dilation and compression like ocean waves
Rayleigh waves produce an elliptical motion with longitudinal dilation and compression, like ocean waves.
Description how induced seismicity happens
Earthquakes known as induced seismicity occur near natural gas extraction sites because of human activity. Injection of waste fluids in the ground, commonly a byproduct of an extraction process for natural gas known as fracking, can increase the outward pressure that liquid in the pores of a rock exerts, known as pore pressure. The increase in pore pressure decreases the frictional forces that keep rocks from sliding past each other, essentially lubricating fault planes. This effect is causing earthquakes to occur near injection sites, in a human induced activity known as induced seismicity.
induced seismicity
Earthquakes that occur due to human activity.
What is the focus of an earthquake?
Where the actual rupture of rock occurs in the subsurface producing the earthquake
The focus is where the actual rupture of rock begins that releases energy that travels outward as seismic waves
Which seismic wave type travels the fastest?
P-waves
P-waves travel fastest, then S-waves, and finally surface waves, which include Love and Rayleigh waves.
Two types of surface waves
Love waves (side to side) and Raleigh Waves (rolling)
Which seismic wave type is most damaging?
Surface (Love and Rayleigh) waves are the most dangerous, with the ironically-named Love waves causing the most damage.
What attributes do p-waves have?
Compressive
High Frequency
Low Amplitude
Fastest waves
Attributes of S-Waves
Secondary waves Shear Low Frequency High Amplitude 2nd fastest wave
Which waves are the second fastest?
S-Waves
Which waves are similar to sound waves?
P-Waves
Waves that can pass through solid, liquid, and gas
P-waves
S waves can pass through…
Solids
Places the following waves in the order in which they arrive at a seismic station (1 being first to arrive). (S, P, and Surface)
- P-waves
- S-waves
- Surface waves
What kind of wave?
P Wave
What type of wave?
S wave
What type of wave?
Love Wave
What type of wave>
Rayleigh wave
If we compare two earthquakes from the same location and one is magnitude 5.0 and makes a wave 1 mm high and the other is magnitude 6.0. what is the height of the wave from the bigger quake?
10
If we compare two earthquakes from the same location and one is magnitude 5.0 and the other is magnitude 6.0. how many times more energy is released from the second bigger quake?
32
You are in the kitchen of your house when an earthquake strikes. The shaking causes the dishes to rattle and a bowl falls off the counter and shatters on the floor. Afterwards the pictures on the walls are askew and when you open the fridge some items fall out. But there is no permanent damage to the walls or windows.
How would this quake rate on the Mercalli Intensity scale?
V
Discussing the Loma Prieta earthquake. Select all the earthquake hazards that resulted from this quake according to the video.
Landslides
Liquefaction
Fire
Building collapse
Loma Prieta earthquake
Why was the damage greater in the Marina district of San Francisco than in Santa Cruz?
It was built on unstable ground that amplified ground shaking
According to the video on the Alaska Earthquake, how long did the shaking last?
4.5 minutes
Discussing the 1964 Alaska earthquake. Select all the earthquake hazards that resulted from this quake and were mentioned or seen the video.
Landslides Tsunami Liquefaction Land elevation changes Building collapse
What is a seismic hazard?
Something that could cause harm during or after an earthquake
What is seismic risk?
the chances that people may be killed, injured or sustain economic losses due to earthquake
the chances that people may be killed, injured or sustain economic losses due to earthquake
Question options:
types of man-made structures opinions of local citizens the strength of building materials The hazards in an area population density
types of man-made structures
the strength of building materials
The hazards in an area
population density
How far was the seafloor uplifted during the Japan quake in 2011?
10 Meters
Why did over 96% of citizens escape the tsunami during the 2011 Japan Quake?
Due to effective emergency education
What alerted many citizens of Chile to move to higher ground in the 2010 Tsunami?
Strong ground shaking
How much was the seafloor uplifted during the 2010 Chile quake?
2-3 meters
What was the length of the rupture in the Great Alaskan Earthquake of 1964?
800 km
What factors contributed to the increased devastation in the 1964 Alaska quake?
The seafloor uplifted up to 9 meters in some areas while dropping in others.
Splay faults caused uplift close to shore where there was less time to evacuate
Landslides caused surges up to 50 meters high
What was the date of the earthquake that caused the Ghost Forests?
1/26/1700
Place the following events that formed a ghost forest in order from beginning to end.
- as stress builds, the land along the coast is uplifted.
- A great earthquake occurs dropping the coast below sea level and creating a tsunami
- The trees along the coast die in a salty marsh.
- The trees are raised above sea level creating a ghost forest.
What two plates were involved in the March 2011 Earthquake
Pacific Plate
Okhotsk Plate
What types of studies have been used to determine the risk of tsunami along the Japanese Coast?
Field studies of sand layers along the coast.
High precision GPS monitoring.
Studies of historical records of earthquakes and tsunamis going back as far as 869 A.D.
What happened during the Tohoku Earthquake
Seafloor was uplifted by 10 meters near the plate boundary
about 20,000 people were killed or missing
The fault moved by as much as 60 meters
The tsunami inundation height reached 20 meters and run-up height reached 40 meters
GPS stations moved towards the fault by as much as 5 meters
Which of the following was the type of early warning system in place during the Tohoku earthquake?
A network of GPS stations and computers that broadcast a warning 66 seconds before strong shaking arrived.
A network of animals in zoos that warned of the quake by making loud noises
A dense network of broadband seismometers and computers that broadcast a warning 14 seconds before strong shaking arrived
There was only the earthquake itself as a warning
A dense network of broadband seismometers and computers that broadcast a warning 14 seconds before strong shaking arrived
Which technologies have been added to the early warning system in Japan since the 2011 Earthquake?
A system of seafloor seismometers and pressure gauges called S-Net.
an integrated GPS and seismic data network called GEONET
What contributed to the low fatalities outside of the Tsunami zone?
strong earthquake engineering practices
an early warning system
Strong building codes and construction practices
Centuries of experience with earthquakes
The Loma Prieta earthquake was named after…
the location of the epicenter
The location below the surface where the earthquake happened is called the
Focus
The location on the surface above where the earthquake happened is called the
the epicenter
True or False
the epicenter is always on the fault
False
How much fault surface is ruptured in a magnitude 6 earthquake?
100 square km
True or False
The offset along a fault from an earthquake will always reach the surface of the Earth.
False
The fault motion of large earthquakes is similar to…
a) a piece of taffy pulling apart
b) a zipper unzipping
c) a balloon popping
d) a hammer breaking a brick
b) a zipper unzipping
The epicenter is located by noting the time of arrival of seismic waves at seismic stations surrounding the earthquake. How quickly does this determination typically occur?
Within minutes
Which of the following would be considered to be an “earthquake prediction”?
a) A magnitude 7-8 quake will occur on the San Jacinto fault in California on July 8th 2033
b) A magnitude 4 to 5 quake will occur in California in summer 2025
c) An earthquake will occur on October 5th
d) A magnitude 7 or greater quake will occur in 2022
a) A magnitude 7-8 quake will occur on the San Jacinto fault in California on July 8th 2033
What is the current ability of seismologists to predict earthquakes?
Seismologists cannot predict the date, location and magnitude of an earthquake
Scientists expected an earthquake to occur on the San Andreas Fault around 1988. When did it actually happen?
2004
When the earthquake finally did occur, was a warning issued before it happened? (San Andreas 2004)
No, no warning was issued
What happened to the scientists that failed to predict the Earthquake in 2009?
They were convicted of manslaughter but later released
In the video, an analogy is used. A fault is similar to what?
A stick
What happens to the rocks along a fault as the tectonic plates on either side move?
They bend and store elastic energy
When does the rock along the fault begin to slip?
When the strength of the rock is exceeded
What happens to the shape of the crust after the earthquake occurs?
It returns to its original shape but offset
What type of fault is present at the Grand Tetons and Jackson hole?
Reverse Fault
Events in the order in which they occur along a fault experiencing elastic rebound.
- Rocks along the fault bend as stress accumulates
- The stress exceeds the strength of the rocks and an earthquake begins
- Tectonic plates move on either side of a locked fault segment
- The rocks snap back to their original shape, releasing elastic energy in the form of seismic waves
- The rocks on either side of the fault lock back together but in an offset position
What happens when the earthquake waves reach the seismograph?
The ground and drum move back and forth but the heavy mass does not move with the ground due to inertia
Wave that Passes directly through the mantle (P wave type)
P Waves
What wave Passes through the mantle bouncing once off the surface. (P wave type)
PP waves
What wave Passes through the mantle and outer core but not the inner core (P wave type)
PKP waves
What wave Passes through the mantle, outer core and the inner core (P wave type)
PKIKP waves
What waves are Diffracted around the core
Pdiff Waves
At what distance (in degrees) from the epicenter does the P wave shadow zone start?
103 degrees
At what distance (in degrees) from the epicenter does the P wave shadow zone end?
142 degrees
Which wave Passes directly through the mantle (s wave)
S wave
Which Passes directly through the mantle (S waves)
SS waves
Which wave Passes through the mantle bouncing twice (s wave)
SSS waves
Which wave Diffracted around the core? (s wave)
Diffracted around the core
Sometimes a wave bounces off the Inner core. What letter is used to indicate that?
i (lower case)
Sometimes a p wave bounces off the surface directly above the hypocenter. What letter is used to indicate that?
p (lower case)
Sometimes an s wave bounces off the surface directly above the hypocenter. What letter is used to indicate that?
s (lower case)
So what would you call a p wave that bounced off the outer core?
PKP
What is the lowest moment magnitude that people are able to feel?
2.5
What are the 3 directions of seismographs
north-south (x axis), east-west (y axis), and up-down (z axis).
Epicenter
The location at the surface directly above the focus of an earthquake, typically associated with strong damage.
Surface Waves
Seismic waves that only move along the surface, mainly R waves and L waves.
Focus
Initiation point of an earthquake or fault movement
Tomography
A process of using 3D seismic arrays to get subsurface images
seismic anomalies
Areas that have an unpredicted change in seismic data, indicating a change in properties.
According to the Ritcher scale one unit shakes the ground how much harder?
Ten-Fold
Moment Magnitude
A magnitude scale based on calculation of the energy released in an earthquake.
Modified Mercalli Intensity Scale (MMI)
A qualitative earthquake scale, from I-XII, of the degree of shaking in an earthquake.
Resonance
An amplification of earthquake waves due to a structure of buildings or structures
Liquefaction
Process of saturated sediments becoming internally weak (like quicksand) and destabilizing foundations.
The shaking breaks the cohesion between grains of sediment, creating a slurry of particles suspended in water. Buildings settle or tilt in the liquified sediment, which looks very much like quicksand in the movies
The shaking breaks the cohesion between grains of sediment, creating a slurry of particles suspended in water. Buildings settle or tilt in the liquified sediment, which looks very much like quicksand in the movies
are waves generated in lakes by earthquakes.
subsidence
The act of the land surface down-warping, typically referred to when discussing sedimentation or with rapid groundwater removal.
Which building type is most likely to collapse in an earthquake?
Unreinforced masonry
Unreinforced masonry undergoes brittle failure from intense shaking and is the most likely to collapse. Steel and wood can deform elastically, allowing them to bend before breaking. Base isolators can prevent resonance, further reducing damage.
What is required for liquefaction to occur in an earthquake?
Liquefaction results from shaking saturated unconsolidated sediments.
Ritcher scale is determined…
is determined from the maximum amplitude of the pen tracing on the seismogram recording.
the actual energy released for each magnitude unit is
32
Modified Mercalli Intensity Scale by severity
I - Not Felt II -Weak III - Weak IV -Light VI - Moderate VII- Strong VIII- Very Strong VIIII - Severe IX - Violent X - Extreme
Surface Waves
Seismic waves that only move along the surface, mainly R waves and L waves
Body waves
Seismic waves that travel through the Earth, mainly P waves and S waves
Seismic Gap
A seismic gap is a section of a fault that has produced earthquakes in the past but is now quiet. For some seismic gaps, no earthquakes have been observed historically, but it is believed that the fault segment is capable of producing earthquakes on some other basis, such as plate-motion information or strain measurements.
Earthquake intensity
describe the severity of an earthquake’s effects on the Earth’s surface, humans, and buildings at different locations in the area of the epicenter
