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Large fractures in the Earth's crust that are associated with movements that produce earthquakes
Mechanism for earthquakes
Rocks on either side of fault are deformed by tectonic forces, bend and store elastic energy, frictional force is overcome
Slippage at the weakest point (the focus) occurs; vibrations occur as the deformed rock "springs back" to its original shape
Point at the depth where the rocks ruptured to produce earthquakes; place where quake waves originate
Primary (P) waves
travel 1.7 times faster than S waves; travel through whole interior; motion is back & forth
Secondary (S) waves
shaking motion at right angles; travels only through solids; slower velocity than P waves; slightly greater amplitude than P waves
location on the surface directly above the focus; located using the difference in velocities of P & S waves
Locating the epicenter
a circle with radius equal to distance to epicenter drawn around each station; point where all 3 circles intersect is epicenter
percent of energy released by earthquakes; originates in a few relatively narrow zones that wind around the globe
Major earthquake zones
Circum-Pacific belt, Mediterranean Sea region to Himalayan complex & oceanic ridge system (underwater mountains)
surface to 70 km; occur along oceanic ridge system; nearly all damaging quakes originate at this depth; not much room so more damage
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