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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
what are body waves vs surface waves
body: travel through interior of earth surface: travel in rock layers just below surface
26
what are the types of body waves
p (primary waves) and s (secondary waves)
27
waves in order of fastest to slowest (when it'll reach seismograph) | which wave will have greatest velocity
p, s, surface | p
28
movement of p waves | particle motion
push (compress) rock and pull (stretch) rock stretch occurs after the compression has passed through them | parallel to direction wave is traveling
29
what kinds of material can P waves travel through? why?
entire interior * gas, liq, solid resist stresses that change volume * so when compressed they spring back when stress removed
30
movement of s waves | particle motion
shear waves | perpendicular (right angle) to the direction of wave
31
what kinds of material can S waves pass through? Why?
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
31
what do s and p waves change
p: volume s: shape
32
what are the 2 types of surface waves? | movements of each
love: Side to side rayleigh: rolling ocean waves
33
TF: displacement varies along segments of faults that behave differently
true
33
amplitude | what seismic wave has the highest? lowest? medium?
height of wave/groundshaking | surface, p, s
34
what wave creates greater ground shaking? | why
surface | retain max amplitude longer
35
what's the zone of greatest seismic activity | what kind of faults are there
circum-Pacific belt | megathrust and thrust
36
what is the earthquake cycle
basically elastic rebound (long periods of stick, short period of slip)
37
what's another zone of strong seismic activity | what kind of faults lie here
alpine-himalayan belt | thrust and strike
38
3rd seismic activity zone what kind of actitvity and plate boundary
mid-atlantic ridge weak divergent
39
why are eqs at certain places
near place where convergent plates collide or transform boundaries grind
40
what are the factors that keep a fault from slipping
cohesion, friction, normal force
41
how do you know when an eq is farther away (more distance from epicenter)
longer time lag btw p and s waves
42
does the arrival time of the p wave indicate anything abt the distance from epicenter
no, p-s interval, not possible to find arrival time of p wave
42
how do you find the epicenter
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
what are the two measurements describing the size of an eq | define those pls
magnitude: measure of energy released at source of eq based on seismograph data intensity: measure of ground shaking based on damage
43
modified mercalli intensity scale
roman numerals CA buildings as its standard
44
What was the drawback of the modified mercalli intensity scale? why? | how do we put this in place today
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
how do you indentify s and surface wave diagrams?
s waves have double amplitude (curve at top and bottom) but surface waves just have curves at surface and straight down
46
Richter Magnitude scale when was it developed | what kind of numbers
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
How do magnitude and intensity scales differ?
magnitude doesn't change at different stations, intensity does
48
how do you measure the magnitute on richter scale
1. plot amplitude of largest seismic wave (right) 2. plot p-s interval (left) 3. connect dots and read magnitude (middle)
49
what does an increase in 1M on the richter scale mean?
10x amplitude/groundshaking 32x energy released
50
what does an increase of 2M mean? 3M | how many microns are in 0M, 1M, 2M, 3M, 4M
100x amplitude/groundshaking (10^2) 1000x amplitude/groundshaking (10^3) | 1, 10, 100, 1000 (1mm), 10000 (10mm)
51
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?
32x (32^1) 1024 (32^2) **32,768 (32^3)**
52
why is the moment magnitude scale used instead of richter?
richter is saturated for major eqs (can't distinguish over 5.0)
53
Moment magnitude -symbol
Mw
54
how is the moment magnitude scale calculated?
avg amount of slip on fault, area on fault that slipped, strength of faulted rock
55
moment magnitude - how is it like the richter scale - who created it - what numbers
* 1 increase in magnitute (Mw) = 32x energy released * Hiro Kanamori * Newtons
56
TF: Earthquakes groundshaking is greatest at the epicenter then weakens
false, epicenter to 50 km has the same groundshaking
57
why is non-ductile reinforced concrete bad? | how does the material that structures are built relate to amplitude
more deaths, more likely to collapse | softer materials amplify vibrations more than bedrock=more damage
58
what are four factors that influence how much destruction an eq can cause on structures
1. magnitude 2. duration 3. material that structures rest on 4. material that structures are made of (codes)
59
liquefaction | what happens to pipes and stuctural buildings
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
Ground shaking causes
Fire Liquefaction Landslides
61
What causes permanent displacement of land
Subsistence and uplift Fault rupture Tsunami
62
Tsunamis are caused by
Displacement along a mega thrust fault
63
Tsunamis formation
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
Rupture length vs width
Rupture width is the flap that moves up creating the bulge but the length is the how long the tsunami covers
65
When do seismic waves travel faster What 2 waves helped us see us in earth
More rigid material (not ductile) P and s
66
What are dip slip faults
Movement is parallel to the dip of the fault surface (pulled apart)
67
What is the hanging wall vs foot wall
Hanging: rock surface above fault (on top of slide) Foot: rock surface below fault (under slide looks like a shoe kinda)
68
Fault scarp
Low long cliff from Displacement (below hanging wall)
69
What are normal slip faults
Hanging wall goes down (butt goes down slide) that stretches crust Tensional forces (arrows outwards)
70
Reverse dip slip faults
Hanging wall goes up (butt up slide) and has compressional forces (arrows in) and shortens crust
71
Thrust faults What happens to strata Common where
Type of reverse Low angle (less than 45) Old over young Subduction zone
72
Strike slip Types
Displacement is horizontal and parallel to the fault surface Left lateral and right lateral
73
How do you distinguish btw left and eight lateral
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
Some Strike slip faults are
Transform faults
75
fault creep
gradual displacemeny w/ little shaking
76
major, moderate, shallow eq
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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