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Midterm 2 EAS 212 The Oceans > Earthquakes > Flashcards

Earthquakes Flashcards

1
Q

Earthquake focal depths are…

A
  • Deep
  • Intermediate
  • Shallow
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2
Q

Earthquake Belts are generally parallel plate boundaries but..

A

Some are within plates.

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3
Q

What is an Earthquake?

A

An Earthquake is a shaking or vibration of the ground

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4
Q

Earthquakes represent a release of built-up stress which occurs when rocks being deformed suddenly
break along a _____. The energy arises because friction prevented the ___ ________ _____ on either side of a fault from sliding past one another easily.

A
  • Break along a fault
  • Two opposing rocks
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5
Q

What happens during step one of an earthquake, draw it.

A

-Stress begins
-fault is locked
-elastic deformation begins

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6
Q

What happens during step two of an earthquake, draw it.

A
  • Stress builds
  • deformation continues
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7
Q

What happens during step 3 of an earthquake, draw it.

A
  • Fault slips
  • Stress released
  • Rocks return to undistressed dimension
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8
Q

What was the fault offset of the 1906 San Francisco Earthquake

A
  • Approx. 2.5 meters
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9
Q

There are _ main types of fault movements that initiate earthquakes and the stresses that cause them.

A
  • 3 main types of fault movements
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10
Q

What are the main types of fault movements that initiate earthquakes.

A
  1. Dip-slip
  2. Thrust Faults
  3. Strike-slip faults
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11
Q

What is the stress that causes a dip-slip fault?

A

tensile stress (pull apart or stretch a material, lengthened)

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12
Q

What is the stress that causes a thrust fault?

A

compressive stress (pushes a material-squeezed or shortened)

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13
Q

What is the stress that causes a strike-slip fault?

A

Shearing stress (material is twisted or experiences forces that cause different parts of it to move in different directions or at different speeds)

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14
Q

Label a diagram with
- focus
- epicenter
-seismic waves
-slip

A
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15
Q

The point on a fault at which the first movement or break occurs during an
earthquake is called the _____.

A

The Focus

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16
Q

The point on the Earth’s surface directly
above the focus is called the _________.

A
  • Epicenter
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17
Q

When the blocks slip suddenly at the time of the earthquake, intense vibrations called _______ _____ travel outwards from the focus much as
waves ripple outward from the spot a stone was dropped in a still pond.

A
  • Seismic waves
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18
Q

With sudden displacement and release of ______, the rocks snap back elastically to their previous dimensions. What is this behaviour known as?

A

-Release of stress
- Elastic Rebound

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19
Q

The distance of displacement is known as the ____.

A
  • Slip
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20
Q

Energy released by an earthquake will send
_______ _____ out from the _____.

A
  • Seismic waves
  • Focus
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21
Q

“Body Wave” travels…

A
  • through the interior of the earth
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22
Q

What kind of body waves are compression waves?

A
  • P Waves
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23
Q

What kind of body waves are shear waves that only pass through solid rock (not magma)

A
  • S Waves
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24
Q

What are some features of surface waves?

A
  • Travels along the surface
  • Larger ground displacement than body waves
  • Results in most earthquake damage
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25
Q
  • Why do we need to understand seismic waves?
A
  • We need to understand in order to build EQ resistant structures.
26
Q

How do the different seismic waves move? (p-wave vs s-wave motion)

A
27
Q

What do the two types of surface waves look like in motion?

A
28
Q

Energy released from an earthquake must travel…

A
  • Through the earth
29
Q

– Density of rock will affect the travel time for seismic waves, describe the relationship.

A
  • Waves move fast through high density rocks
  • Waves move slow through low density rocks
30
Q

What detects ground movement and can be useful in calculating the location of an epicenter?

A
  • Seismograph
31
Q

What does a seismograph do?

A
  • Records arrival of different seismic waves
  • Interval of time between the first arrivals of P waves
    and S waves is a function of distance to the epicenter
32
Q

How many seismographs are required to locate an
earthquake?

A

-At least 3 seismographs

33
Q

______ is released during an earthquake

A
  • Energy
34
Q

What happens when waves of energy are transmitted through rock in an earthquake?

A
  • As the waves of energy are transmitted through
    the rock, this energy with be felt by people at
    the surface
35
Q

What is magnitude when talking about an earthquake?

A

– the amount of ground motion related to an earthquake

36
Q

What is intensity when talking about an earthquake?

A
  • effect on humans, and their structures, caused by the energy released
    by an earthquake
37
Q

Energy released by
earthquake will be
related to the ________
__ _____ and ____ __
_____ (length x depth).

A
  • Strength of rock and area of break
38
Q

The damage an earthquake causes can be measured in
two ways. What are the ways?

A
  1. Magnitude and/or 2. Intensity
39
Q

Explain measuring “Richter magnitude”

A
  • measures the amount of ground displacement or shaking it produces at the epicentre.
  • The scale is logarithmic (means that an earthquake of
    magnitude 5 causes ten times as much ground movement as one of magnitude 4)
40
Q

Explain measuring “Moment magnitude”

A
  • measures what
    happened at the earthquake source NOT how much the ground shakes at a distant point
  • takes into account the area of break on the fault surface, the displacement along the fault, and the strength of the rock.
41
Q

What/how does Mercalli Intensity scale measure earthquakes?

A
  • Measures the impact of an earthquake event on humans and surface features

-Many local factors are considered such as local geology, construction practices, and distance to the epicenter

42
Q

Modified Mercalli Intensity Scale is widely used in ______ and the _______ _______.

A
  • Canada and the United States
43
Q

Intensities in the Mercalli Intensity Scale are reported as ______ _________ ranging
from _ (___ ____ _____) to ___ (_______ _____ ______)

A
  • Roman Numerals
  • I (for ‘not felt’) to XII, for (‘damage nearly total’)
44
Q

The Mercalli Intensity Scale can be used to measure _______ __ _____ __ ___ _____ ___ ________ (useful knowledge for EQ prediction)

A

-ancient EQ based on old texts and folklore

45
Q

Modern cellphones and laptops have built in ______________ so general population can “tweet” in both ____________ ____ _____________ to seismologists.

A

-accelerometers

  • observations and measurements
46
Q

Based on seismicity charts it has become evident that earthquakes originate both at shallow depths (__ _________ ______) and deep in the Earth (_____ _________ ______)

A
  • At spreading ridges
  • Along subduction zones
47
Q

Describe earthquakes that happen at shallow depths.

A

-associated with divergent boundaries and transform faults, as well as on continents due to crustal movements

48
Q

Describe earthquakes that happen at deep depths.

A
  • at subduction zones they occur because the
    brittle lithosphere is forced deep into the
    asthenosphere (to about 700 km)
49
Q

What are the 3 types of earthquake tectonic plate boundaries? Draw them.

A
50
Q

Some earthquakes are unusual in that they are not associated with _____ _______. They often occur on
___ ______ that were once part of______ ______ ___________ (e.g., the South Carolina earthquake in
1886). Others may arise as a result of _________ _______ (e.g., those occasionally in eastern Canada in the Ottawa to Montreal region)

A
  • plate margins
  • Old faults they were once apart of ancient plate boundaries
  • isostatic rebound
51
Q

What are the 4 things that cause damage in earthquakes?

A

Earthquakes damage
1. Ground motion
2. Ground failure
3. Fire
4. Tsunamis

( also remember Mitigating EQ damage
Man induced EQ
EQ risk in Canada)

52
Q

What causes ground motion in earthquakes?

A
  • Ground shaking
  • Fault movement
53
Q

What happens during earthquake ground failure?

A
  • Landslides
  • Cracks
  • Liquefaction
54
Q

Liquefaction at depth can lead to _______ __ ________.

A
  • collapse of surface
55
Q

How do we mitigate earth quake damage?

A

Avoidance:
- Better to build away from earthquake
zones

Engineering:
- Use better construction designs and materials

Predicting/giving warnings!

56
Q

What do we use for prediction and forecasting?

A
  • Geological field work (find ancient EQ example. japan)
  • Seismic gaps(highlight the major gaps we know of)
  • Precursors
  • Prediction (date, place, and magnitude
    of next big one)
  • Forecasting (Forecast chance of given size EQ, along a given fault, or in given time interval)
  • Watching animal behaviour
57
Q

Examples of Induced earth quakes

A
  • Fluid injection & Withdrawal
  • Hydraulic fracturing
  • Dams
  • Engineered earth quakes??
58
Q

The suggestion that fluid injection can case
earthquakes was tested and proven in ____ !

A
  • in 1972
59
Q

AN earthquake in a place where oil and gas are produced and in an area where there are no precious earthquakes, is a very _______ ________.

A
  • Very unusual ocurence
60
Q

What are the causes of man made earthquakes?

A

Midterm 2 EAS 212 The Oceans (3 decks)

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