Lecture 20 Mar 17 2008 Earths interior

Lecture 20 Mar 17 - Magnitude 7.4 earthquake Turkey 1999 17,118 people died We like to describe the size of earthquakes Maximum amplitude of ground

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Magnitude 7.4 earthquake, Turkey, 1999. 17,118 people died.
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We like to describe the size of earthquakes. Maximum amplitude of ground shaking is used to assign a magnitude given in numbers from 1-10 (Richter scale). The human perception of the ground shaking is described in the qualitative Mercalli intensity scale given in values from I to XII. Magnitude 6.9 earthquake in Armenia in caused 25,000 deaths 15,000 injuries 517,000 homeless
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The magnitude depends on the amplitude of ground movement caused by seismic waves. The scale is logarithmic. Two earthquakes that differ in size of ground motion by a factor of 10 and energy release by a factor of 32 differ in magnitude by 1.
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The intensity is the most useful information about where the greatest damage to structures, and therefore impact on human life, is concentrated.
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P waves are analogous to sound waves in air -- they are compressional waves. They travel in a series of compressions and expansions. Particles of matter are pushed and pulled in the direction of the path of travel of the wave. P waves travel at about 6 km/s (3.7 mi/s), about 14 times the speed of sound waves in air. Slip on a fault in the direction of wave propagation would set up P waves.
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S waves are shear waves because they push material at right angles to their path of travel. Liquids and gases do not
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This note was uploaded on 04/11/2008 for the course EVSC 280 taught by Professor Herman during the Spring '08 term at UVA.

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Lecture 20 Mar 17 - Magnitude 7.4 earthquake Turkey 1999 17,118 people died We like to describe the size of earthquakes Maximum amplitude of ground

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