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DISP Earth Science > Earthquakes > Flashcards

Earthquakes Flashcards

1
Q

What are the possible results of brittle failure in the Earth’s crust?

A

earthquakes, joints, faults

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2
Q

What is an earthquake’s focus?

A

the place where energy is released (on the fracture, etc.)

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3
Q

What is an earthquake’s epicentre?

A

the place on the Earth’s surface directly above where the energy is released

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4
Q

What happens when the stress on the crust exceeds elastic reound?

A

stored energy is released suddenly, resulting in brittle failure - if it fractures, earthquake

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5
Q

What parts of an earthquake can be felt/seen?

A

ground motion, landslides, scarps, after shocks, tsunamis

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6
Q

What part of an earthquake causes the most damage?

A

indirect results of ground motion - falling debris, landslides…

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7
Q

Why are landslides so dangerous?

A

cut off area from outside world - cut utilities, dam rivers, break roads

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8
Q

How do the intensities of after shocks compare to the actual earthquake, and why do they cause damage?

A

less intense; hit things that were damaged by main earthquake

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9
Q

What is a scarp?

A

fault surface where it intersects the earth

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10
Q

How is earthquake intensity measured?

A

Mercalli Intensity Scale - by asking people what they felt

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11
Q

Why is measuring earthquakes with intensity bad?

A

intensity is independent of amount of energy released ;
varies based on the time and place;
hard to measure if no one was present;
can’t compare between earthquakes

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12
Q

What is used instead of intensity to measure earthquake strength?

A

magnitude - the energy released

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13
Q

What scale is used to measure magnitude?

A

Richter scale

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14
Q

What type of scale is the Richter scale?

A

exponential - each magnitude quake produces 10 times more ground motion than the magnitude - 1

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15
Q

What does measuring magnitude allow one to do that couldn’t be done by measuring intensity?

A

comparison of earthquake

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16
Q

What are the 3 notable magnitudes on the Richter scale?

A

M1: just able to record;
M5: damage begins
M8.5: maximum magnitude

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17
Q

What does the energy relassed (magnitude) of an earthquake really represeent?

A

the potential destructive power of an earthquake

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18
Q

What decides the actual destruction caused by an earthquake?

A

where the energy was released

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19
Q

What does a seismometer do?

A

generates a seismograph

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20
Q

How does a simple seismometer work?

A

earth moves while pen (fixed by spring) does not, so pen draws wiggly lines to represent ground motion

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21
Q

Where do seismometers work best?

A

in places without competing energy (traffic, people, etc.)

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22
Q

What does a typical seismograph look like?

A

small oscillations for P wave;
larger oscillations for S-wave;
huge oscillations for Surface-wave;
decreases except for spikes (aftershocks)

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23
Q

What effect does fault size (amount of sliding/fault surface area) have on earthquake size?

A

bigger faults make bigger earthquakes (based on magnitude) - pretty linear with magnitude

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24
Q

What effect does earthquake size (magnitude) have on the length of time the earthquake lasts?

A

bigger earthquakes last a longer time

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25
Q

Why do higher energy earthquakes cause so much damage?

A

double wammy - more ground shaking that lasts longer

26
Q

How are earthquakes distributed in energy?

A

not evenly - many very small ones; not many high magnitude ones

27
Q

How frequently do earthquakes that just start causing damage occur?

A

M5 - every 9 hours

28
Q

What are two ways in which earthquake energy travels?

A

body waves and surface waves

29
Q

What are body waves?

A

pass through interior of earth; travel in straight line from source

30
Q

What are the types of body waves?

A

P-waves (compression waves) and S-waves (shear waves)

31
Q

What are the characterisitcs of P-waves?

A

compressional and fast (4-7 km/sec)

32
Q

What kind of particle oscillation do compressional waves cause?

A

particle oscillation in direction of wave oscillation

33
Q

How fast do P-waves travel and why is it a range?

A

4-7 km/s; varies as a funciton of the material

34
Q

In what sorts of materials do waves travel faster?

A

denser materials

35
Q

What are the characteristics of S-waves?

A

shear, slow (2-5 km/sec), and do not travel through liquids

36
Q

What kind of particle oscillation do shear waves cause?

A

particle oscillation perpendicular to wave propagation direction

37
Q

How fast do S-waves travel and why is it a range?

A

2-5 km/sec; varies as a function of the material

38
Q

How do we know the earth’s core is at least partly liquid?

A

S-waves do not travel through liquid, so earthquakes on one side of the core leave an “S-wave shadow” on the other side of the core where no S-waves arrive but P-waves do

39
Q

How are earthquakes located?

A

measure difference in time between arrival of P-wave and S-wave to tell distance; do this at 3 stations and triangulate

40
Q

What does the difference in arrival time between S and P waves tell you?

A

the distance of the earthquake (the farther it is, the longer the time difference)

41
Q

What does the difference in arrival time between S and P waves NOT tell you?

A

the direction of the earthquake

42
Q

Why are 3 stations required to locate earthquakes?

A

each station can only find distance of earthquake to it - must triangulate (see point where radius of earthquake distances from each sttion all meet)

43
Q

What are surface waves?

A

waves that travel along earth’s surface

44
Q

How are surface waves created?

A

when body waves intersect the surface of the earth - their energy disperses along it

45
Q

What are some types of surface waves?

A

Love waves and Rayleigh waves

46
Q

What are the general characteristics of surface waves?

A

disrupt surface; complex wave set; slowest

47
Q

What kind of movements are generated by Love waves

A

side to side horizontal motion of surface

48
Q

What surface waves are the fastest?

A

Love waves

49
Q

What kind of movements are caused by Rayleigh waves?

A

rolling motion at surface; largest waves

50
Q

What surface waves are the slowest?

A

Rayleigh waves

51
Q

What surface waves cause most of the felt motion in an earthquake?

A

Rayleigh waves

52
Q

How are earthquakes distributed geographically?

A

unevenly in depth, intensity, and geography

53
Q

What characteristics of earthquakes are we good at predicting?

A

where and how big

54
Q

What characteristic(s) of earthquakes are we bad at predicting?

A

when

55
Q

Why can we predict where earthquakes happen?

A

earthquakes are unevenly distributed geographically and are most likely to happen where they’ve already occurred; (also some geological features)

56
Q

Why can we predict how big earthquakes will be?

A

magnitudes often match those of previous earthquakes in a certain area

57
Q

Why can’t we say when earthquakes will occur?

A

earthquakes are unevenly distributed in time

58
Q

What often marks fracturing associated with magma movement?

A

earthquakes

59
Q

What may accompany eruption/large movements of magma that accompany eruption?

A

“harmonic” earthquakes

60
Q

How can earthquakes be used to map out distribution of magma under volcanos?

A

earthquakes often mark fracturing associated with magma; S-waves don’t travel through liquids - put seismometers around volcanos before eruption and observe earthquakes

DISP Earth Science (7 decks)

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