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EAS 212 The Oceans > Earthquakes > Flashcards

Earthquakes Flashcards

(60 cards)

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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
- Why do we need to understand seismic waves?
- We need to understand in order to build EQ resistant structures.
26
How do the different seismic waves move? (p-wave vs s-wave motion)
27
What do the two types of surface waves look like in motion?
28
Energy released from an earthquake must travel...
- Through the earth
29
– Density of rock will affect the travel time for seismic waves, describe the relationship.
- Waves move fast through high density rocks - Waves move slow through low density rocks
30
What detects ground movement and can be useful in calculating the location of an epicenter?
- Seismograph
31
What does a seismograph do?
- 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
How many seismographs are required to locate an earthquake?
-At least 3 seismographs
33
______ is released during an earthquake
- Energy
34
What happens when waves of energy are transmitted through rock in an earthquake?
- As the waves of energy are transmitted through the rock, this energy with be felt by people at the surface
35
What is magnitude when talking about an earthquake?
– the amount of ground motion related to an earthquake
36
What is intensity when talking about an earthquake?
- effect on humans, and their structures, caused by the energy released by an earthquake
37
Energy released by earthquake will be related to the ________ __ _____ and ____ __ _____ (length x depth).
- Strength of rock and area of break
38
The damage an earthquake causes can be measured in two ways. What are the ways?
1. Magnitude and/or 2. Intensity
39
Explain measuring "Richter magnitude"
- 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
Explain measuring "Moment magnitude"
- 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
What/how does Mercalli Intensity scale measure earthquakes?
- 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
Modified Mercalli Intensity Scale is widely used in ______ and the _______ _______.
- Canada and the United States
43
Intensities in the Mercalli Intensity Scale are reported as ______ _________ ranging from _ (___ ____ _____) to ___ (_______ _____ ______)
- Roman Numerals - I (for ‘not felt’) to XII, for (‘damage nearly total’)
44
The Mercalli Intensity Scale can be used to measure _______ __ _____ __ ___ _____ ___ ________ (useful knowledge for EQ prediction)
-ancient EQ based on old texts and folklore
45
Modern cellphones and laptops have built in ______________ so general population can “tweet” in both ____________ ____ _____________ to seismologists.
-accelerometers - observations and measurements
46
Based on seismicity charts it has become evident that earthquakes originate both at shallow depths (__ _________ ______) and deep in the Earth (_____ _________ ______)
- At spreading ridges - Along subduction zones
47
Describe earthquakes that happen at shallow depths.
-associated with divergent boundaries and transform faults, as well as on continents due to crustal movements
48
Describe earthquakes that happen at deep depths.
- at subduction zones they occur because the brittle lithosphere is forced deep into the asthenosphere (to about 700 km)
49
What are the 3 types of earthquake tectonic plate boundaries? Draw them.
50
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)
- plate margins - Old faults they were once apart of ancient plate boundaries - isostatic rebound
51
What are the 4 things that cause damage in earthquakes?
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
What causes ground motion in earthquakes?
- Ground shaking - Fault movement
53
What happens during earthquake ground failure?
- Landslides - Cracks - Liquefaction
54
Liquefaction at depth can lead to _______ __ ________.
- collapse of surface
55
How do we mitigate earth quake damage?
Avoidance: - Better to build away from earthquake zones Engineering: - Use better construction designs and materials Predicting/giving warnings!
56
What do we use for prediction and forecasting?
- 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
Examples of Induced earth quakes
- Fluid injection & Withdrawal - Hydraulic fracturing - Dams - Engineered earth quakes??
58
The suggestion that fluid injection can case earthquakes was tested and proven in ____ !
- in 1972
59
AN earthquake in a place where oil and gas are produced and in an area where there are no precious earthquakes, is a very _______ ________.
- Very unusual ocurence
60
What are the causes of man made earthquakes?

EAS 212 The Oceans (1 decks)

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