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Geology 100 > Earthquakes > Flashcards

Earthquakes Flashcards

(63 cards)

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1
Q

What is an Earthquake?

A

Very strong underground explosion

Earth shaking caused by a rapid release of energy

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2
Q

How destructive are Earthquakes?

A

They destroy buildings and kill people

3.5 million deaths in the last 2,000 years

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3
Q

What causes earthquakes?

A

tectonic stresses that causes rocks to break

Energy moving outward as an expanding sphere of waves

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4
Q

What is seismicty

A

Earthquake activity

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5
Q

What is seismicty due to?

A

motion along a newly formed crustal fracture (fault)

motion on a existing fault

A sudden change in mineral structure

Inflation of a magma chamber

volcanic eruption

giant landslides

meteorite impacts

nuclear detonations

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6
Q

Where do most earthquakes occur?

A

Along faults

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7
Q

What are faults?

A

crustal faults that move rock masses

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8
Q

What is displacement?

A

The amount of movement

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9
Q

What is offset (slip)

A

another term for displacement

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10
Q

How do faults move? (What is stick-slip behavior)

A

move in jumps

quickly stops due to friction

strain will build up again, causing failure

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11
Q

What is stick

A

where friction prevents motion

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12
Q

What is slip

A

friction briefly overwhelmed by motion- violent and quick

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13
Q

What is elasticity

A

A property of materials that results in wave propagation and earthquakes

Bends

the capacity to return to the og configuration after being distorted

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14
Q

What’re the conditions necessary for periodic motion in the form of traveling waves?

A

Elasticity

Source of energy

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15
Q

What is focus?

A

The spot underground where earthquake waves originate

usually works on a fault surface

earthquake waves expand outward thousands of miles from the focus

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16
Q

What is the epicenter

A

land surface directly above the focus

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17
Q

Elastic rebound theory

A

explanation of how energy is spread during earthquakes

Stores a lot of energy in a rock, it acts like a rubber band

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18
Q

What are fault motions

A

result from rocks breaking and stored elastic strain is released

The energy, as waves, generates vibrations

Vibrations cause motions

Foreshocks and aftershocks are ofen

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19
Q

Types of seismic waves?

A

Body Waves

Surface waves

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20
Q

What’re body waves?

A

waves that pass through the Earth’s interior

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21
Q

What’re the two types of body waves?

A

Shear/ Secondary (S) transverse waves

Compressional or Primary (P) longitudinal waves`

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22
Q

Secondary waves

A

travels only through solids: not liquids
can’t feel in water

slower than compressional waves

“Shaking motions”

alternating transverse motion (perpendicular to the pirection of propagation and the raypath)

moves like a wave that crowds do

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23
Q

Compressional or Primary Waves

A

Push-pull (compress and expand) motion

travels through solids, liquids, and gasses

fastest

alternating compression (push pull), directed in the same direction as the wave is propagating (along the raypath)

Particle motion is parallel to the direction of propagation

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24
Q

What are the types of surface waves

A

Love waves

Rayleigh waves

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25
What're love waves
S-waves intersecting the surface move like a writing snake violent, destructive waves that push the rock sideways Transverse horizontal motion, perpendicular to the direction slower than S waves
26
What're rayleigh waves
P-waves intersecting the surface move like ripples on a pond Particle motion consists of elliptical motions most destructive, turbulence the slowest
27
What're surface waves
Waves that travel along Earth's surface
28
What is seismology
The study of earthquake waves how long it last the vertical movements the horizontal movements reveals the size and location of earthquakes
29
What is seismographs
instruments that record seismicity they detect earthquakes anywhere on earth drum always rotating Weight stays still preserves a record of wave arrivals 1st wave causes frame to sink (pen goes up) next vibration causes opposite motion
30
How do you determine the distance of station to epicenter?
(arrival time of )S - P(arrival time of) s=S waves p=P waves The arrival time increases based off how far they are from the epicenter
31
What does seismograph measures?
Wave arrival times | magnitude of ground motion
32
How to locate and epicenter?
data from 3 stations a circle is drawn around each station the radius is equal to the distance to the epicenter circles around 3 or more stations will intersect the point of the intersection is the epicenter
33
What is seismograph operation?
Waves arrive in a sequence P-waves arrives first S-waves arrive second
34
What're the two means of describing earthquakes?
Intensity | Magnitude
35
What is intensity
The degree of shaking based on damage Mercalli intensity scale diminishes with distance damage occurs in zones roman numeral assigned to diff levels of damage
36
What is the magnitude?
the amount of energy released
37
What're the magnitude scales
richter magnitude scale seismic moment magnitude scale scales are logarithmic increases 1 unit= 10 fold- increase in ground motion increases of 1 unit = 33- fold increase in energy
38
What is the mercalli intensity scale
measures the intensity of shaking and damage at a specific location depends on distance to earthquake and strength of earthquake
39
What is the richter magnitude scale
richter assigned each earthquake a number as a measure of its size depends on the amplitude (size) of the ground movement caused by seismic waves
40
log 10
1
41
log 100
2
42
log 1000
3
43
log 10000
4
44
log 100000
5
45
log 1000000
6
46
log 10000000
7
47
log 100000000
8
48
log 1000000000
9
49
What is the seismic moment?
(the amount of slip) x (length of rupture) x (depth of rupture) x (rock strength)
50
Richter magnitude, Energy
The increased energy released as seismic waves with increasing magnitude of an earthquake is a factor of 33!!!! for each magnitude unit Ex. 2-4=2 33^2= 33 x 33 =1089
51
Richter magnitude, Amplitude
Two earthquakes that differ in size of ground motion by a factor of 10, differ in magnitude by 1 richter unit Mg 2 is 10 times stronger than Mg 1 Ex. 4-2 10^2 = 100 Mg 4 is 100 times stronger than Mg 2
52
Earthquake order
1st ground shaking and displacement 2nd earthquake waves arrive in diff sequences 3. p-waves first to come create a rapid up and down movement 4. s-waves around next produce back and forth motion stronger than p-waves cause extensive damage 5. surface waves can come after s-waves - love waves firsts - ground moves like a snake - r-waves are the last to arrive - last longer than others - extensive damage
53
how do landslides and avalanches happen
shaking causes slopes to fail ancient slope failures follow earthquakes in uplands an earthquake started the landslide that uncorked Mt. St. Helens on May 18,1980
54
What is liquefaction
waves liquefy H2O-filled sediments high pore pressure reducing forces grains apart reducing friction Water-saturated sediments turn into a mobile fluid
55
How do liquified sediments flow
like a slurry
56
What does sand become through liquefaction
quicksand
57
What does clay become through liquefaction
quickclay
58
What're trunamis
waves generated by a disturbance in the sea or lake generated by abrupt changes in water level Ocean floor is unevenly uplifted or downdropped during an earthquake motion on a fold on the ocean floor harbor waves Normal faulting drops the seabed; thrusting raises it -displaces the volume of overlying water giant mound (trough) forms on sea surface (enormous- 10,000mi^2 area) -mound collapses creating waves that race rapidly away wavelengths 10s-100s of meters wave height and length unaffected by windspeed wave velocity 100s of kph -jetliner speed water comes ashore
59
How frequent are tsunamis
1 every year 94 in the last 100 years 51,000 victims are inevitable
60
Wind waves
wind driven waves that contain a small volume of water and do not submerge higher areas influence the upper 100m wavelengths 10s-100s of meters wave height and length affected by windspeed wave velocity maximum 10s of kph waves break in shallow water and expand all stored energy
61
What is tsunami behavior
low wave height long wavelength frictional drag when water shallows -waves grow in height, reaching 10-15m or more
62
What does tsunami destruction depend on
offshore bathymetry -increase amplitude but limit wave energy quick deep-to-shallow transition is the deadlies condition waves have maximum energy heights are modest water pours into land as a sheet broad, low land allows for maximum damage steep rise of land- less damage
63
Tsunami prediction
scientific modeling predicts tsunami behavior detection is expanding detectors placed on ocean floor senses pressure increase from changes in sea thickness

Geology 100 (3 decks)

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