EES 150 Exam 2 Flashcards
What’s an earthquake?
A shaking of Earth’s crust due to a release of energy
What do earthquakes create?
Seismic waves
What can cause an earthquakes?
.Volcanic activity
.Meteorite impact
.Underwater landslides
.Nuclear bomb explosions
What is the most frequent cause of earthquakes?
Movement along faults
Do earthquakes or buildings kill people?
Buildings
How do the earthquakes in Japan differ from Haiti?
Some of them are deeper
What produces a tsunami?
The offset of the ocean floor displaced water
Why does Japan experience a lot of earthquakes?
A subduction zone
What caused many people to die in Japan?
Tsunami and powerful earthquake
What caused many people to die in Haiti?
Poor building codes and a large earthquake
Why does Haiti experience a lot of earthquakes?
Because it’s along a transform plate boundary in the Caribbean.
What’s stress?
A force applied to a rock
What’s strain?
The response to the stress
What’s brittle deformation?
When a rock breaks
What’s ductile deformation?
When a rock bends/ change shape
What’s evidence of brittle deformation?
A fault
What is evidence of ductile deformation?
A fold
When do earthquakes occur?
When rocks in the Earth’s crust behave in a brittle fashion, break and move relative to each other
What are 2 types of stresses of rocks?
Uniform pressure
Differential pressure
What the 3 types of differential stress?
Compression
Extension
Shear
What plate boundary causes compression?
Convergent
What plate boundary causes extension?
Divergent
What plate boundary causes shear?
Transform
What terms do geologist use to describe rock layers and fault orientation?
Strike and dip
What’s a strike?
The line formed by the intersection of the inclined plane with a horizontal one
What’s a dip?
The direction of inclination
What’s the difference between a strike-slip fault & a dip-slip fault?
Strike-slip fault: Moves back and forth
Dip-slip faulty: Moves up and down
How do you interpret dip-slip faults?
- Determine which side went up
2. Determine which side is the hanging wall
How can you classify faults?
By the relative movement along them
What’s an oblique fault?
A fault that involves both kinds of movement
What’s elastic rebound?
A pre-earthquake strain and/ or an earthquake strain
How does a pre-earthquake strain describe movement along a fault?
A gradual strain in space and time
How does a pre-earthquake strain describe movement along a fault?
An abrupt strain in space and time
Are shallow faults locked or transitioned and caused by what
lock and earthquakes
Are deeper faults locked or transitioned and caused by what
Transition and tremor and slip
What’s a faults hypocenter (focus)?
The exact location of the earthquake
What’s the faults
epicenter?
The location directly above on the surface
What are primary waves?
Compressional earthquake waves that travel the fastest
How do P waves travel?
They compress and expand as they move back and forth
Can S waves move through liquid? Why?
No, because liquids don’t move up and down relative to each other
How do S-waves travel?
They move up and down relative to each other and shear at right angles
What’s used to record earthquakes?
Seismographs
What are seismograms generated by?
Earthquakes, although from nuclear testing
When do you measure the S waves?
Before the amplitude increases
How many seismograms are needed to determine the epicenter?
3
When is a station the closet?
When the distance between the P and S wave isn’t far
What 3 components are used to measure all directions?
.E-W
.N-S
.Vertical
How do waves travel within the Earth?
More rapidly at depth where material is more dense
What’s a S-wave shadow zone?
S-waves being detected to only 103 degrees on either side of the earthquakes
What’s a P-wave shadow zone?
A refraction at the core-mantle and inner core/ outer core
What do seismic tomographs show?
Cool, subducted lithospheric plates
What’s the difference between cool and warm areas?
.Cool- high velocity
.Warm-low velocity
How many people generally are killed by earthquakes each year?
Thousands
What are some factors that influence whether an earthquake will kill large numbers of people?
Buildings
Tectonic plates
What’s the difference between Japan’s and Haiti’s tectonic setting?
Japan: Continental-Oceanic convergent boundary
Haiti: Continental-Continental transform boundary
Are large earthquakes frequent occurrences?
No
What effect(s) does stress have on rocks?
Breaking or bending/ changing a rocks formation
What can strain be?
Change in size, shapes, or volume
What’s a fold?
A structure caused by ductile deformation
What’s a fault?
A structure caused by brittle deformation
What’s differential stress?
Stress where there’s more forces pressed on the sides of the rock, compressing the rock
What are 2 kinds of dip-slip faults?
Normal and reverse
What’s the difference between a normal and reverse dip-slip fault?
Normal: has a zone of omission and hanging wall moves down
Reverse: has of zone of repetition and hanging wall moves up
What’s the difference between the hanging wall and foot wall?
Hanging wall is on the right
Footwall is on the left
What kind of differential stress causes reverse dip-slip faults?
Compression
What kind of differential stress causes normal dip-slip faults?
Extension
What are two kinds of strike-slip faults?
Right and left lateral
What differential stress causes strike-slip faults movement?
Shear
How can movement along strike-slip faults cause compression?
When a left-stepping right-lateral strike-slip fault results in compression and uplifting
How can movement along strike-slip faults cause extension?
When a right-stepping right-lateral strike-slip fault results in rifting and the formation of basins
What’s an episodic tremor and slip?
A seismic phenomenon observed in subduction zones that’s a non-earthquake seismic rumbling, tremor, and slow slip along the plate interface
How can you tell the difference between an earthquake and tremor & slip?
By the speed and focus.
Tremor and Slips have a slow slip
Earthquakes have a fast slip
How does a fault move due to elastic rebound?
It moves fast
How does episodic tremor and slip differ from our classic view of fault movement?
It moves slower and take days
What kind of waves are generated from earthquakes?
P,S, and Surface waves
What are secondary waves (S-waves)?
Shear earthquake waves at right angles to the wave direction that travel slower than P-waves
What are surface waves and how do they travel?
Slow earthquake waves whose effect lessens with depth. Slow and on the surface
Why does a seismograph have 3 components?
To measure all direction of ground movement.
How can we use P & S wave travel times to calculate the distance to the earthquake?
By finding a point where the waves intercept each other at 3 different locations
What’s the S-wave shadow zone?
A zone where S-waves can only be detected 103 degrees to either side of earthquakes and creates a liquid layer
How do earthquakes help us understand Earth’s interior?
By how waves are refracted as they encounter boundaries between 2 types of material and traveling more rapidly at depth where material is more dense
What’s the P-wave shadow zone?
A zone where P-waves extend from 103-143 degrees away from the earthquake
Where are P-waves refracted?
The core-mantle and the inner/outer core, suggesting the presence of the solid inner core
What’s a seismic tomograph?
A 3-D image of Earth’s sub-surface characteristics in an effort to understand deep geological structure by gathering P and S waves travel time measurements.
How does seismic tomograph help us understand the nature of the mantle?
That the in cool areas of the mantle there’s high velocity and warm areas in the mantle there’s low velocity
What’s the difference between warm in cool areas in the mantle?
Cool areas: Mantle plumes
Warm areas: Subduction zones
How does the effects of ground motion vary?
By local geology, distance from earthquake, and local building codes
What’s sediment liquefaction?
When the sediment or soil is saturated with water
What areas are vulnerable to sediment liquefaction?
Areas with loose sediment and near bodies of water
What’s a fault scarp?
Changes in ground level are caused by movement along faults during earthquakes where one side is taller than the other
How are landslides & avalanches associated with earthquakes?
They can be set off by earthquake waves in areas of steep slopes
How are tsunamis associated with earthquakes?
If land slides into the ocean, the displaced water will form a tsunami wave
What are some secondary dangers of earthquakes?
Damaged roads Fire Broken levees Broken pipelines Power grid problems
What’s the difference between magnitude and intensity?
Magnitude does not vary by location
Intensity does
What’s magnitude?
A measurement of some parameter of an earthquake
What’s intensity?
Is how it affects people
What’s the Richter scale?
A magnitude scale based on amplitude of earthquake waves
How is the Richter scale calculated?
By the distance between S & P waves and amplitude
what factors are considered when calculation the magnitude of an earthquake based on “seismic moment”?
Area of fault rupture
Amount of displacement
Force needed to cause rocks to displace
What is the Moment Magnitude Scale?
A magnitude Scale based on “Seismic moment”
What are the advantages of using the moment magnitude scale?
It’s more accurate for large earthquakes which gives a larger number
What’s the Mercalli scale?
A scale that describes earthquake intensity
How is the Mercalli scale used?
It has a chart that has 3 column; intensity, shaking, and description/damage
What causes Mercalli intensity to vary?
Distance from epicenter
What’s a shake map?
A map that uses color to denote mercalli intensity
What causes tsunamis to form?
Earthquakes, volcanic activity, and landslides
Which is more likely to cause massive numbers of deaths, an earthquakes or tsunami?
Tsunami
What caused the 2004 Banda Aceh tsunami?
An earthquake
How is the Banda Aceh tsunami related to plate tectonics?
It happened along a subduction zone, dragged the overriding plate with it, and then rebounded back
What’s the DART system?
A system that tracks tsunamis by monitoring water pressure on the ocean floor.
What are 2 ways volcanoes and tsunamis are linked?
- Tsunamis may be caused by volcanic eruptions- lava may displace seawater
- Volcanic islands are prone to underwater landslides
How did the eruption of Krakatau cause a tsunami?
By the collapse of the volcano into its magma chamber
Why are the shores of volcanic islands especially prone to landslides?
Because lava cools quickly when it meets cold seawater, leading to the buildup of steep slopes and eventually collapse
How does the shores of volcanic islands trigger tsunamis?
By the collapse of the lava deltas in the sea
What tsunami threat exists for the Atlantic?
The eruption of the volcano of Cumbre Vieja
What is the geologic explanation for the tsunami threat for the Atlantic?
Waves as high as 13m high on the eastern US coast
Why is Hawaii especially threatened by tsunamis?
Because it’s surround by the “ring of fire” and threated from all directions
How doe tsunami waves interact with islands (as opposed to wind-generated waves)?
Wind-blown waves have short wavelengths & generally affect only of side of an island and ripples to many islands until the waves stop on their own
How does the shape of the ocean basin and water depth affect the movement of the tsunami wave?
The waves do not travel outward in all directions equally
Why does the west coast of the US have a lot of earthquakes?
Because it’s near subduction zones, transform faults, and mid-ocean ridges
How did the San Andreas fault form?
By the subduction of an oceanic plate over several 10’s of million of years. (Farallon plate)
What caused the Good Friday earthquake in Alaska?
Vertical displacement associated with a subduction zone
Why are there earthquakes along the Cascadia subduction zone?
Because of the subduction of the Juan de Fuca at around 4.5 cm/yr
How do we know there was a very large earthquake in Cascadia in 1700?
By the subsidence of land killing of coastal trees , rupture zone, fire pits, and tree ring dating
Why do we think the earthquake in Cascadia was a magnitude 9?
Eyewitness accounts of intensity from the oral records of First people
Why do we compare the Cascadia earthquake with the one in Chile?
Related to subduction and the largest recorded earthquakes
What part of Kentucky is given a high seismic risk and why?
Western Kentucky and because of large earthquakes that happened in 1811-1812
What were the effects of the 1811-1812 New Madrid earthquake?
Ground displacement, new lakes, cliffs formed, waterfalls formed in streams, and sand blows
What are some ways the magnitudes of the New Madrid earthquakes were calculated and why do they give different results?
- Fault-rupture length estimates from aftershock location give smaller moment magnitudes: 7.3-7.7
- Soft, water-saturated sediment of ground amplifies shaking: 7.0 to 7.5
Why do earthquakes occur in the New Madrid area?
Because of “Reelfoot Rift”
What’s the reelfoot rift?
A buried ancient failed rift valley that formed ~ 600 million years ago
How did the reelfoot rift probably form?
By aulacogen( failed rifts, often form as continents break apart)
What’s a shake map?
A map that uses color to denote Mercalli intensity
What are some reason building collapse during earthquakes?
Soft first floors and hollow core brick construction
Does the Mercalli intensity vary with distance from epicenter?
Yes
How does the time of day influence the death rate when an earthquake occurs?
Some people may start their day and go to work at certain times and some people stay at home at certain times
How does paleoseismology help us understand earthquake risk?
It’s the study of ancient earthquakes to help understand earthquake frequency and plan for the future
What’s resonance?
Is when the building period and the earthquake wave period match and combine, increasing shaking
What happens to earthquake waves when they pass through loose sediments?
They travel more slowly
What are some ways to decrease the effects of resonance?
Change of shape & height of building. Move weights to lower floors and building materials.
What are some engineering techniques to help buildings withstand earthquakes?
Interior walls especially shear walls, flexible bracing frames, base isolation (shock absorbers), small frame construction, not too tall, modern construction
