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Geology 100 > Earthquakes > Flashcards

Earthquakes Flashcards

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
Q

What’re love waves

A

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

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26
Q

What’re rayleigh waves

A

P-waves intersecting the surface

move like ripples on a pond

Particle motion consists of elliptical motions

most destructive, turbulence

the slowest

27
Q

What’re surface waves

A

Waves that travel along Earth’s surface

28
Q

What is seismology

A

The study of earthquake waves
how long it last
the vertical movements
the horizontal movements

reveals the size and location of earthquakes

29
Q

What is seismographs

A

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
Q

How do you determine the distance of station to epicenter?

A

(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
Q

What does seismograph measures?

A

Wave arrival times

magnitude of ground motion

32
Q

How to locate and epicenter?

A

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
Q

What is seismograph operation?

A

Waves arrive in a sequence
P-waves arrives first
S-waves arrive second

34
Q

What’re the two means of describing earthquakes?

A

Intensity

Magnitude

35
Q

What is intensity

A

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
Q

What is the magnitude?

A

the amount of energy released

37
Q

What’re the magnitude scales

A

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
Q

What is the mercalli intensity scale

A

measures the intensity of shaking and damage at a specific location

depends on distance to earthquake and strength of earthquake

39
Q

What is the richter magnitude scale

A

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
Q

log 10

A

1

41
Q

log 100

A

2

42
Q

log 1000

A

3

43
Q

log 10000

A

4

44
Q

log 100000

A

5

45
Q

log 1000000

A

6

46
Q

log 10000000

A

7

47
Q

log 100000000

A

8

48
Q

log 1000000000

A

9

49
Q

What is the seismic moment?

A

(the amount of slip) x (length of rupture) x (depth of rupture) x (rock strength)

50
Q

Richter magnitude, Energy

A

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
Q

Richter magnitude, Amplitude

A

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
Q

Earthquake order

A

1st ground shaking and displacement

2nd earthquake waves arrive in diff sequences

  1. p-waves first to come
    create a rapid up and down movement
  2. s-waves around next
    produce back and forth motion
    stronger than p-waves
    cause extensive damage
  3. 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
Q

how do landslides and avalanches happen

A

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
Q

What is liquefaction

A

waves liquefy H2O-filled sediments

high pore pressure reducing forces grains apart reducing friction

Water-saturated sediments turn into a mobile fluid

55
Q

How do liquified sediments flow

A

like a slurry

56
Q

What does sand become through liquefaction

A

quicksand

57
Q

What does clay become through liquefaction

A

quickclay

58
Q

What’re trunamis

A

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
Q

How frequent are tsunamis

A

1 every year

94 in the last 100 years

51,000 victims

are inevitable

60
Q

Wind waves

A

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
Q

What is tsunami behavior

A

low wave height
long wavelength

frictional drag when water shallows
-waves grow in height, reaching 10-15m or more

62
Q

What does tsunami destruction depend on

A

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
Q

Tsunami prediction

A

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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