Flashcards in Exam 2 Deck (55)
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1
What is an earthquake ?
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
2
What are seismic waves ?
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
3
What is the earthquakes rupture patch ?
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
4
How are earthquakes measured ?
The amount of energy released (magnitude)
The effects of ground motion on people and structures (intensity)
5
Explain the modified Mercalli scale
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`
6
Explain the Richter magnitude scale
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
7
Explain the moment magnitude scale. Equation ?
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
8
What is a foreshock ? What is a aftershock ?
Foreshocks and aftershocks are smaller earthquakes that occur shortly (usually up to days to weeks to months ) before and after a major earthquake
9
Why is an aftershock especially dangerous ?
You think it might be over than the afterschock hits you
10
How is friction important in faulting ?
Friction along the fault slows, prevents and arrests motion
11
What is stress ?
Something an object feels
Force/unit area
12
What is strain ?
Any change in shape or volume of a material
13
What is deformation ?
Includes strain and translation along dislocations
14
Define fault
A fracture or system of fractures along which movement has occurred parallel to the fracture surface in association with a loss of cohesion
15
What is a footwall ?
The bottom of the fault
16
What is a hangwall ?
The top of the fault
17
What are the different types of faults and how does each move ?
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
18
What is compressional stress ?
Rock is squeeze by stresses pushing toward each other
19
What is shear stress ?
Parts of solid are pushed past each other in a sliding fashion parallel to the surface along which they contact each other
20
What types of faults occur at convergent boundaries ?
Mostly reverse/ thrust faults
21
What is the associated earthquake depth ? Explain
A range including deep at convergent
22
What types of faults occur at divergent boundaries ?
Normal faults and transform faults
23
What is the associated earthquake depth ?
Shallow at divergent
24
Describe a transform plate boundary
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
