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GEOG 2110L (50)


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GEOG 2110L
David Stanley

EARTHQUAKES * Asharp release of energy resulting in a series of elastic waves propagated through the Earth at the moment of rupture along a fault. The rupture is initiated where stress along the fault exceeds the elastic limit of the rock so that sudden movement occurs. They are also associated with volcanic activity. * seismic waves: pulses of energy generated by an earthquake, that pass through the Earth as shock waves * transmission speed & direction can vary according to the Tº and density of the various layers within the planet ** Types of seismic waves: P wave (primary seismic wave): a type of seismic wave, propagated like a sound wave, in which the material involved in the wave motion is alternately compressed & expanded * S wave (secondary or shear seismic wave): a seismic wave in which particles vibrate at right angles to the direction in which the wave travels * a shear or ‘shake’ wave which moves material at right angles to its direction of movement; cannot pass through liquid material L wave (surface wave): a seismic wave that travels along Earth’s surface, but not through the Earth, and at slower velocities than either P or S waves How to measure earthquakes: Magnitude vs Intensity * Magnitude: amount of shaking… numerical * seismograph or seismmeter: an instrument that measures seismic waves & Earth vibrations * uses the Moment Magnitude Scale (formerly the Richter Scale), which reflects the amount of energy released by an earthquake and considers the amount of fault slippage, the size of the area that ruptured, and the nature of the materials that faulted in estimating the magnitude of an earthquake * Intensity: the size and damage of an earthquake measured by its impact on the human landscape structures and activities). Uses the modified mercalli scale ** Some major quakes: 1812 New Madrid, MO 1886 Charleston, SC (6.7) 1906 San Francisco, Ca (8.25) 1964 Alaska (8.6) 1976 Tangshan, China (7.6) 1989 Loma Prieta, Ca (7.1) 1994 Northridge, CA (6.8) 2002 Denali,Alaska (7.9) 2004 Sumatra, Indonesia (9.3) 2010 Haiti (7.0) 2010 Maule, Chile (8.8) 2011 coast of Japan (9.1) Distribution: * Circum-Pacific belt: around the Pacific Ocean, at subduction zones ** 80% of shallow earthquakes (<63 mi depth) occur in this belt * Trans-Eurasian belt: Mediterranean Sea area eastward thru SWAsia, the Himalayas, to SEAsia & China * mid-oceanic ridges * intraplate earthquakes: such as those in Georgia or Missouri; not well understood * earthquakes may be classified as shallow (<63 mi depth
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