GeologyFinal

GeologyFinal - Earthquakes 12/13/2007 6:03:00 PM Stress v....

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Earthquakes 13/12/2007 19:03:00 Stress v. Strain Stress: the local force per unit area that causes rocks to deform Strain: the relative amount of deformation, expressed as the percentage of  distortion Elastic rebound theory: A theory of fault movement and EQ generation holding that faults remained  locked while strain energy accumulates in the rock formations on both sides,  temporarily deforming them until a sudden slip along the fault releases the  energy Fault slip The distance of the displacement between two blocks that occurs during an  EQ when elastic rebound causes the blocks on either side of a fault to spring  back to their undeformed state.  Focus Point at which the slip begins Epicenter The geographic point on the earth’s surface directly above the focus. Aftershock Smaller shocks that occur as a consequence of a previous earthquake of  larger magnitude.  Follow the main EQ in sequences, and their foci are distributed in and around  the rupture plane of the main shock. Number and sizes depend on the main shock’s magnitude.  Foreshock Small EQ that occur near, but before a main shock.  One of more foreshocks have preceded many large earthquakes P waves Primary waves
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Compressional waves o Push and pull particles in the direction of their path and travel Fastest out of all waves Go through solids, liquids, and gaseous materials S waves Secondary/stadium Shear waves o Push material at right angles to their path of travel  Only exist in rocks- NOT in liquids or gases Surface-wave motion Most destructive o Two types: Rolling, elliptical motion that dies down with depth beneath the  surface (picture p. 303) Ground shakes sideways, with no vertical motion Richter magnitude scale The maximum amplitude of the ground shaking and the P-S wave interval,  indicated on the seismographic record, is used to assign a Richter magnitude  to an EQ Now, instead of the Richter scale, seismologists prefer… Moment magnitude o The product of the area and the average slip across the fault break o It increases by about one unit for every 10-fold increase in the area of  faulting  o Can be measured more accurately than richter
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Which occur more often? Large or small earthquakes? Small
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This note was uploaded on 04/17/2008 for the course GEOL 101 taught by Professor Notgoingtotell.. during the Fall '08 term at Beloit.

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GeologyFinal - Earthquakes 12/13/2007 6:03:00 PM Stress v....

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