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GEO LECTURE > Earthquakes > Flashcards

Earthquakes Flashcards

1
Q

What is an earthquake?

A

ground shaking caused by release of stored energy from the sudden and rapid slippage of rocks along faults

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2
Q

What is a fault?

describe its relation to plate boundaries and locked faults

A

fractures along crust where movement occurs
* doesn’t have to be on a plate boundary, but most are
* most are locked bc of confining pressure causing them to be squeezed shut

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3
Q

What is the hypocenter?

is it above or below surface?

aka

A

location of where slippage starts and waves radiate to surrounding rock like ripples

below (abajo)

focus

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4
Q

Epicenter

A

the point on surface directly above hypocenter

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5
Q

Do earthquakes create energy?

A

No, they release STORED energy

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6
Q

What are seismic waves?

A

energy that causes the material that transmits them to shake

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7
Q

rupture plane

every point that slips…

A

portion of fault that slips

produces seismic waves

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8
Q

where do faults form along

A

the boundaries btw different tectonic plates

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9
Q

Elastic Rebound

A
  1. Bending of crustal rock due to differential stress
    * plate movement along a locked fault (movement isn’t gradual, gets stuck, and then slips rapidly)
    * gets stuck due to frictional resistance from slipping
    * since the plates still want to move, but are at a locked fault, the rock bends which increases the stress and stores elastic energy
    * over tens to hundreds of years
  2. the stress eventually overbears the frictional resistance, so slippage occurs creating an earthquake
    * seconds to minutes
  3. like a rubberband, the stored elastic energy is released/ stress relieved causing the crustal rock to return to its original shape but in a different location (no longer bent)
    * after EQ
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10
Q

are all faults on plate boundaries

A

All plate boundaries are faults but not all faults are on plate boundaries

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11
Q

What are the sources of most large eqs

A

transfrom and convergent plate boundaries

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12
Q

who proposed elastic rebound

A

reid

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13
Q

What kind of eq are at mid ocean ridges
What kind of faults

A

Shallow (crust and lithosphere is thin)
Normal at rift
Strike slip at transform

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14
Q

where do deep and intermediate earthquakes occur?

A

where subduction occurs

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15
Q

the collision of India and Eursia results in what severity of eqs

A

intermediate to shallow

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16
Q

what kinds of faults do compressional forces associated with c vs. c convergence create?

A

reverse and thrust faults

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17
Q

what fault does o vs c convergence create?

A

megathrust faults

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18
Q

what fault do transform plate boundaries produce?

A

strike slip faults

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19
Q

most transform faults are not

A

straight nor continuous, they branch off

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20
Q

what fault produces the largest and most destructive eqs

A

megathrust

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21
Q

how does slippage travel along the fault surface?

A

each section that slips strains another, causing it to slip

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22
Q

Seismographs

aka

A

instruments that detect and record seismic waves

seismometers

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23
Q

how do seismographs work

since you are dealing with small numbers, you must ___ ground motion

A

weight remains stationary during eq bc of inertia while the support and drum moves

amplify

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24
Q

seismograms

what kinds of waves do they depict

A

recordings from seismographs/seismometers

body and surface

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25
Q

what are body waves vs surface waves

A

body: travel through interior of earth
surface: travel in rock layers just below surface

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26
Q

what are the types of body waves

A

p (primary waves) and s (secondary waves)

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27
Q

waves in order of fastest to slowest (when it’ll reach seismograph)

which wave will have greatest velocity

A

p, s, surface

p

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28
Q

movement of p waves

particle motion

A

push (compress) rock and pull (stretch) rock
stretch occurs after the compression has passed through them

parallel to direction wave is traveling

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29
Q

what kinds of material can P waves travel through? why?

A

entire interior
* gas, liq, solid resist stresses that change volume
* so when compressed they spring back when stress removed

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30
Q

movement of s waves

particle motion

A

shear waves

perpendicular (right angle) to the direction of wave

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31
Q

what kinds of material can S waves pass through? Why?

A

only solids
* gases and liqs don’t resist stresses that change their shape, so they don’t return to og shape when stress removed, thus it doesn’t transmit them

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31
Q

what do s and p waves change

A

p: volume
s: shape

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32
Q

what are the 2 types of surface waves?

movements of each

A

love: Side to side
rayleigh: rolling ocean waves

33
Q

TF: displacement varies along segments of faults that behave differently

A

true

33
Q

amplitude

what seismic wave has the highest? lowest? medium?

A

height of wave/groundshaking

surface, p, s

34
Q

what wave creates greater ground shaking?

why

A

surface

retain max amplitude longer

35
Q

what’s the zone of greatest seismic activity

what kind of faults are there

A

circum-Pacific belt

megathrust and thrust

36
Q

what is the earthquake cycle

A

basically elastic rebound (long periods of stick, short period of slip)

37
Q

what’s another zone of strong seismic activity

what kind of faults lie here

A

alpine-himalayan belt

thrust and strike

38
Q

3rd seismic activity zone
what kind of actitvity and plate boundary

A

mid-atlantic ridge
weak
divergent

39
Q

why are eqs at certain places

A

near place where convergent plates collide or transform boundaries grind

40
Q

what are the factors that keep a fault from slipping

A

cohesion, friction, normal force

41
Q

how do you know when an eq is farther away (more distance from epicenter)

A

longer time lag btw p and s waves

42
Q

does the arrival time of the p wave indicate anything abt the distance from epicenter

A

no, p-s interval, not possible to find arrival time of p wave

42
Q

how do you find the epicenter

A
  1. find p-s interval
  2. use time-travel graph to draw vertical line representing the P-S interval, and slide till lines (p at bottom, s at top) match with ticks
  3. read the distance
    (do this for 3 stations)
  4. use triangulation: each circle’s radius should equal the distance btw that station and the epicenter, where circles intersect is the epicenter
42
Q

what are the two measurements describing the size of an eq

define those pls

A

magnitude: measure of energy released at source of eq based on seismograph data
intensity: measure of ground shaking based on damage

43
Q

modified mercalli intensity scale

A

roman numerals
CA buildings as its standard

44
Q

What was the drawback of the modified mercalli intensity scale? why?

how do we put this in place today

A

destruction doesn’t always equal severity
buildings might be super strong or super weak, populated or abandoned

we ask did you feel it? did things fall off shelves

45
Q

how do you indentify s and surface wave diagrams?

A

s waves have double amplitude (curve at top and bottom) but surface waves just have curves at surface and straight down

46
Q

Richter Magnitude scale

when was it developed

what kind of numbers

A

based on fact that seismic waves weaken w/distance from source, so the amplitudes decrease (when comparing seismograms from a station closer and farther from source) mL

1935

logarithmic

47
Q

How do magnitude and intensity scales differ?

A

magnitude doesn’t change at different stations, intensity does

48
Q

how do you measure the magnitute on richter scale

A
  1. plot amplitude of largest seismic wave (right)
  2. plot p-s interval (left)
  3. connect dots and read magnitude (middle)
49
Q

what does an increase in 1M on the richter scale mean?

A

10x amplitude/groundshaking
32x energy released

50
Q

what does an increase of 2M mean? 3M

how many microns are in 0M, 1M, 2M, 3M, 4M

A

100x amplitude/groundshaking (10^2)
1000x amplitude/groundshaking (10^3)

1, 10, 100, 1000 (1mm), 10000 (10mm)

51
Q

energy released from an increase in 1M, 2M, 3M

How many M5 earthquakes would it take to release the same amount of energy as a M8 earthquake?

A

32x (32^1)
1024 (32^2)
32,768 (32^3)

52
Q

why is the moment magnitude scale used instead of richter?

A

richter is saturated for major eqs (can’t distinguish over 5.0)

53
Q

Moment magnitude
-symbol

A

Mw

54
Q

how is the moment magnitude scale calculated?

A

avg amount of slip on fault, area on fault that slipped, strength of faulted rock

55
Q

moment magnitude
- how is it like the richter scale
- who created it
- what numbers

A
  • 1 increase in magnitute (Mw) = 32x energy released
  • Hiro Kanamori
  • Newtons
56
Q

TF: Earthquakes groundshaking is greatest at the epicenter then weakens

A

false, epicenter to 50 km has the same groundshaking

57
Q

why is non-ductile reinforced concrete bad?

how does the material that structures are built relate to amplitude

A

more deaths, more likely to collapse

softer materials amplify vibrations more than bedrock=more damage

58
Q

what are four factors that influence how much destruction an eq can cause on structures

A
  1. magnitude
  2. duration
  3. material that structures rest on
  4. material that structures are made of (codes)
59
Q

liquefaction

what happens to pipes and stuctural buildings

A

loosely saturated material (sand particles) squeeze together causing water and upper sandy layers to move up (raises water table), while the ground lowers due to compacting sand

pipes rise up, buildings sink down

60
Q

Ground shaking causes

A

Fire
Liquefaction
Landslides

61
Q

What causes permanent displacement of land

A

Subsistence and uplift
Fault rupture
Tsunami

62
Q

Tsunamis are caused by

A

Displacement along a mega thrust fault

63
Q

Tsunamis formation

A
  1. Subducting oceanic plate causes the overriding plate to bend due to locked fault which stores elastic energy
  2. Overcomes frictional resistance so it slides up the fault (rupture)
  3. Bulge splits in two directions bc of gravity into tsunamis but is undetectable until it feels bottom and slows and gets taller (water recedes before tsunami on some sides of rupture length )
64
Q

Rupture length vs width

A

Rupture width is the flap that moves up creating the bulge but the length is the how long the tsunami covers

65
Q

When do seismic waves travel faster
What 2 waves helped us see us in earth

A

More rigid material (not ductile)
P and s

66
Q

What are dip slip faults

A

Movement is parallel to the dip of the fault surface (pulled apart)

67
Q

What is the hanging wall vs foot wall

A

Hanging: rock surface above fault (on top of slide)
Foot: rock surface below fault (under slide looks like a shoe kinda)

68
Q

Fault scarp

A

Low long cliff from Displacement (below hanging wall)

69
Q

What are normal slip faults

A

Hanging wall goes down (butt goes down slide) that stretches crust

Tensional forces (arrows outwards)

70
Q

Reverse dip slip faults

A

Hanging wall goes up (butt up slide) and has compressional forces (arrows in) and shortens crust

71
Q

Thrust faults
What happens to strata
Common where

A

Type of reverse
Low angle (less than 45)
Old over young
Subduction zone

72
Q

Strike slip
Types

A

Displacement is horizontal and parallel to the fault surface

Left lateral and right lateral

73
Q

How do you distinguish btw left and eight lateral

A

Belly button rule: face fault line ———, see if things are displaced to the left or to the right, will get the same answer no matter what side you’re on

74
Q

Some Strike slip faults are

A

Transform faults

75
Q

fault creep

A

gradual displacemeny w/ little shaking

76
Q

major, moderate, shallow eq

A

major along segmenets that have been locked for long time and store elastic energy
moderate: cloesly spaced intervals
creeping

GEO LECTURE (19 decks)

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