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Geology: Earthquakes
Chapter 11 Strayer
26
Geology
Undergraduate 1
05/26/2009

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Term
Earthquake
Definition
Vibration on earth produced by a rapid release of energy from ruptured rocks that have undergone stress beyond their limit. Mostly occur along existing faults when fictional fault surfaces are overcome. First figure out by H.F. Reid.
Term
Focus
Definition
Source of energy causing an earthquake. The weakest point along a fault where stress is released.
Term
Faults
Definition
Large fractures in the earth's crust. Movements of these build up stress/energy and cause earthquakes when released/relieved
Term
Elastic rebound
Definition
As rocks bend, they store energy. The "springing back" of rocks to their original shape causing an earthquake.
Term
Foreshocks
Definition
Small earthquakes that often, but NOT always, precede a major earthquake by days or even years.
Term
Aftershock
Definition
Adjustments that take place after a major earthquake that generate smaller earthquakes.
Term
Surface wave/ L-waves or long waves
Definition
Seismic wave that travels along OUTER LAYER of earth. Waves that cause the greatest destruction, have highest amplitude and lowest speed.
Term
Body waves
Definition
Seismic waves which travel through Earth's INTERIOR. Has subdivision of p - and s-waves
Term
Primary waves (p-waves)
Definition
Body waves which COMPRESS or PULL rock in direction the waver is traveling. Travels through solid, liquid, and gas.
Term
Secondary waves (s-waves)
Definition
Body waves which "shakes" the particles in the rock. Can only travel through SOLIDS. Will NOT transmit through liquid.
Term
Epicenter
Definition
Location on Earth's surface directly above the focus of an earthquake. Located through process of triangulation.
Term
Triangulation
Definition
Process of locating the epicenter of an earthquake by using the distances measured from THREE seismic stations.
Term
circum-Pacific belt
Definition
Location of the principal earthquake epicenter zones. Where the greatest energy is released.
Term
Modified Mercalli Intensity Scale
Definition
Scale that uses damages to building in California to estimate the intensity of ground shaking for a local earthquake.
Term
Magnitude
Definition
Estimation of the amount of ENERGY released at the source of the earthquake based on seismic records.
Term
Richter scale
Definition
First seismic scale using seismic records to estimate the relative sizes of earthquakes. Magnitude of an earthquake is estimated by measuring the amplitude (maximum displacement) of the largest seismic wave recorded.
Term
Moment magnitude
Definition
A calculation of average displacement of the fault, the area of the fault surface, and the sheer strength of the faulted rock. Used to estimate the size of moderate and large earthquakes.
Term
Tsunami wave
Definition
A secondary effect of an earthquake that is a surface affecting the ocean.
Term
San Andreas
Definition
Most studied fault in the world.
Term
fault creep
Definition
Slow, gradual displacement along fault. Occurs relatively smoothly and has little noticeable seismic activity.
Term
Seismology
Definition
Study of earthquakes. Dates back to almost 2000 years ago in China which an ancient Chinese seismograph.
Term
Seismograph
Definition
Instrument that records seismic waves. Must have a mass freely suspended to record any vibration usually on a rotating drum or magnetic tape. Since movement of Earth happens both vertically and horizontally, more than one type of this is needed. Produces seismograms.
Term
Rayleigh Way
Definition
Surface wave that acts like an ocean wave moving along the surface of the Earth.
Term
Love Wave
Definition
Surface wave similar to S-Wave, but moves PARALLEL to Earth's surface. Create a side-to-side motion along surface that is particular damaging to structures.
Term
Liquefaction
Definition
Occurs when unconsolidated materials (such as moist soil) are saturated with water. The vibration caused by earthquakes causes the water to rise up so the surface layer loses cohesiveness. Can cause underground objects such as storage tanks to float to the surface.
Term
Seiches
Definition
Destructive force caused by seismic vibrations. It is the rhythmic sloshing of waves in lakes, reservoirs, and enclosed basins.
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