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Exam 2 Flashcards

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1
Q

What is an earthquake ?

A

A sudden release of energy in the earth’s crust or upper
mantle, usually caused by movement along a fault plane or by volcanic activity and resulting in the generation of seismic waves

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2
Q

What are seismic waves ?

A

Are the waves of energy caused by the sudden breaking of rock within the earth or an explosion. They are the energy that travels through the earth and is recorded on seismographs

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3
Q

What is the earthquakes rupture patch ?

A

Rupture starts at the focus
Slip/motion moves outward mostly along the plane from the initiation point (focus)
Epicenter is point on the Earth’s surface directly above the focus
During a MAJOR ‘quake, slip may be 2-20 m (7-70 ft)
Rupture area may be 1000 km2 (400 mi2) or more

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4
Q

How are earthquakes measured ?

A

The amount of energy released (magnitude)

The effects of ground motion on people and structures (intensity)

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5
Q

Explain the modified Mercalli scale

A

Descriptive scale of earthquake effect intensity
Distinguished by use of Roman numerals
I. Not felt
II. Felt by persons at rest
III. Hanging objects swing; vibration like passing light trucks
IV. Vibration like passing of heavy trucks
V. Felt outdoors; awakes sleepers; unstable objects move
VI. Felt by all; glassware broken; books off shelves
VII. Hard to stand; noticed in cars; damages some masonry
VIII. Collapses some masonry; moves some frame housing
IX. General panic; foundation damage; cracks in ground
X. Most structures destroyed; landslides; water thrown
XI. Rails greatly bent; underground pipes out of service
XII. Damage nearly total
Usually displayed as intensity maps
Two different styles: contoured and colored
Usually based on written records`

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6
Q

Explain the Richter magnitude scale

A

A base-10 logarithmic scale, which defines magnitude as the logarithm of the ratio of the amplitude of the seismic waves to an arbitrary, minor amplitude

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7
Q

Explain the moment magnitude scale. Equation ?

A

Seismologists have more recently developed a standard magnitude scale that is completely independent of the type of instrument
Moment = rock rigidity x fault area that slipped x slip distance

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8
Q

What is a foreshock ? What is a aftershock ?

A

Foreshocks and aftershocks are smaller earthquakes that occur shortly (usually up to days to weeks to months ) before and after a major earthquake

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9
Q

Why is an aftershock especially dangerous ?

A

You think it might be over than the afterschock hits you

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10
Q

How is friction important in faulting ?

A

Friction along the fault slows, prevents and arrests motion

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11
Q

What is stress ?

A

Something an object feels

Force/unit area

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12
Q

What is strain ?

A

Any change in shape or volume of a material

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13
Q

What is deformation ?

A

Includes strain and translation along dislocations

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14
Q

Define fault

A

A fracture or system of fractures along which movement has occurred parallel to the fracture surface in association with a loss of cohesion

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15
Q

What is a footwall ?

A

The bottom of the fault

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16
Q

What is a hangwall ?

A

The top of the fault

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17
Q

What are the different types of faults and how does each move ?

A

Dip slip
Normal fault- hanging wall block moved down relative to footwall
(stretches and thins crust, common along divergent margins and extending intraplate areas)

Reverse or thrust fault- hanging wall block moved up relative to footwall
(shortens and thickens out, common along convergent margins and relatively nearby areas)

Strike slip
Left lateral strike-slip fault- rocks across the fault from you moved to the left
Right lateral strike-slip fault- rocks across the fault from you moved to the right
Blocks of rocks move past each other
Conservative (no to little extension or shortening)
Many are transform faults along plate boundaries like the San Andreas fault

Oblique slip
Oblique slip fault- hanging wall moved in both strike slip and dip slip directions relative to
footwall

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18
Q

What is compressional stress ?

A

Rock is squeeze by stresses pushing toward each other

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19
Q

What is shear stress ?

A

Parts of solid are pushed past each other in a sliding fashion parallel to the surface along which they contact each other

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20
Q

What types of faults occur at convergent boundaries ?

A

Mostly reverse/ thrust faults

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21
Q

What is the associated earthquake depth ? Explain

A

A range including deep at convergent

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22
Q

What types of faults occur at divergent boundaries ?

A

Normal faults and transform faults

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23
Q

What is the associated earthquake depth ?

Study These Flashcards
A

Shallow at divergent

24
Q

Describe a transform plate boundary

Study These Flashcards
A

Strike-slip faults that cut through the entire lithosphere

25
What types of faults occur at transform boundaries ?
Strike-slip fault
26
What is their depth ? Give an example
Shallow foci | San Andreas fault
27
What is a triple junction ?
Location where three tectonic plates come together
28
Can earthquakes occur within a plate ?
Yes
29
What is the most common type of fault in the Basin and Range province ?
Mountain chains and flat arid valleys or basins
30
Define earthquake focus and epicenter
Focus is in the center of the earth and the epicenter is point on the Earth’s surface directly above the focus
31
Explain elastic rebound theory
The energy which is released (which was stored as strain in the rock) is converted to seismic waves which radiate from the earthquake focus
32
What is a P wave and how does it move ?
Compressive waves that do not produce much damage Push-pull fashion or compressional motion Travels faster
33
What is an S wave and how does it move ?
Shear waves that deform the ground perpendicular to their direction of travel Travels slower
34
What is an Love wave and how does it move ?
Fastest surface wave and moves the ground from side-to-side | Horizontal motion
35
What is a Rayleigh wave and how does it move ?
Rolls along the ground just like a wave rolls across a lake or an ocean Moves ground up and down and side-to-side in the same direction
36
With what types of material is ground shaking high and low ?
Ground shaking is minimal on bedrock and high on mud
37
How do you locate an earthquake ?
Use an equation or a nomogram to find the distance associated with the difference in P and S wave arrival times Use that distance as the radius of a circle centered on the location of the seismometer and draw a circle Location of epicenter is at the intersection of the circles
38
What are the active and Quaternary fault classes ?
Active – faults that moved in the last 10,000 years Quaternary faults - active faults and potentially active faults that have been recognized at the surface and which have evidence of movement during the Quaternary time period
39
What are three types of primary damage from earthquake ?
Strong ground shaking, surface faulting and subsidence/uplift
40
What are three types of primary earthquake damage ? Explain each
Ground motion- results from the movement of seismic waves through the earth, especially near the surface Faulting and ground rupture- where a fault breaks the surface buildings can be split, roads disrupted, and anything that lies on or across the fault broken apart
41
What are three types of secondary earthquake damage ?
Liquefaction Triggered events Tsunamis/seiches
42
Explain liquefaction
Earthquake motion/intense shaking can cause a water-saturated near-surface layer of sand or mud to change rapidly from a solid to a liquid
43
What should you do to protect yourself during an earthquake, if you are indoors ? Outdoors ?
If you are inside: Drop, cover and hold on. Move as little as possible. Stay away from windows to avoid being injured by shattered glass. Stay indoors until the shaking stops and you are sure it is safe to exit. Then, use stairs in case there are aftershocks, power outages or other damage. Building facades and signs commonly fall. Be aware that fire alarms and sprinkler systems frequently go off in buildings during an earthquake, even if there is no fire. If you are outside: Find a clear spot (away from buildings, power lines, trees, streetlights) and drop to the ground. Stay there until the shaking stops. If you are in a vehicle, pull over to a clear location and stop. Avoid bridges, overpasses and power lines if possible. Stay inside with your seatbelt fastened until the shaking stops. Then, drive carefully, avoiding bridges and ramps that may have been damaged. If a power line falls on your vehicle, do not get out. Wait for assistance. If you are in a mountainous area or near unstable slopes or cliffs, be alert for falling rocks and other debris. Landslides are often triggered by Earthquakes.
44
What are somethings you can do to prepare for an earthquake ?
Make sure your home is securely anchored to its foundation. Bolt and brace water heaters and gas appliances to wall studs. Bolt bookcases, china cabinets and other tall furniture to wall studs. Non-structural damage costs most of the human injuries in earthquake resistance structures Hang heavy items, such as pictures and mirrors, away from beds, couches and anywhere people sleep or sit. Brace overhead light fixtures. Install strong latches or bolts on cabinets. Large or heavy items should be closest to the floor. Learn how to shut off the gas valves in your home and keep a wrench handy for that purpose. Learn about your area’s seismic building standards and land use codes before you begin new construction. Keep and maintain an emergency supplies kit in an easy-to-access location.
45
What is a tsunami ?
A series of ocean waves that sends surges of water, sometimes reaching heights of over 100 ft (30.5 meters), onto land
46
What causes a tsunami ?
Earthquakes (as in example to right) Landslides Volcanic eruptions (OK, and meteorite impacts)
47
How many waves make up a tsunami ?
A series of waves
48
At what speeds do tsunami travel ?
500 miles
49
Why are some tsunami waves slower near shore ?
Friction of the shore
50
In what direction does a tsunami travel from its source ?
Travels in all directions
51
What are three factors that determine how devastating a tsunami will be ?
1. Direct action (primary damage) causes most damage •a. depends on wave height if triggered by an earthquake depends on earthquake magnitude. if triggered by a landslide, depends on amount of material that slid •b. depends on local offshore topography because that can effect wave height and where the wave breaks –wave trap - energy of a long section of the wave can be concentrated on a particular part of the shoreline as a result of the shoreline or sea floor topography configuration. Harbor focusing •c. varies with orientation of coast relative to the orientation of the incoming wave. If wave is normal to coast, more damage is done than if it sweeps past parallel to the coast line 2. Tides 3. Proximity to causing fault, landslide or volcanic collapse
52
What is a runup ?
The deep-water wave amplitude divided by the run-up height
53
What is a tsunami inundation ?
The result of a tsunami traveling a long distance inland, a horizontal measurement
54
How does a tsunami system warning system works ?
``` DART buoys (Deep-ocean Assessment and Reporting of Tsunamis) Each DART® station consists of a surface buoy and seafloor bottom pressure recording (BPR) package that detects pressure changes caused by tsunamis. The surface buoy receives transmitted information from the BPR via an acoustic link and then transmits data to a satellite, which retransmits the data to ground stations for immediate. The commercial satellite phone network is used for communication between 31 of the buoys ```
55
What are three important aspects of mitigation ?
Evacuation Building restrictions Education

Geology (4 decks)

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