EOSC 114 Chapter Notes - Chapter 2: Accretionary Wedge, Echo Sounding, Seismic Wave
23 Nov 2017
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Document Summary
Scale of earthquake magnitude is logarithmic: earthquakes with magnitude <0 means original number"s value is 0-1. Seismogram: instrument that records ground motion: framework fixed to earth supports suspended pendulum attached to a pen, paper firmly attached to the framework just below pen, when ground moves, pen stays put & paper moves relative to it. Majority of earthquakes occur at margins of earth"s tectonic plates. Earthquake patterns are useful to identify where catastrophic results are most likely. Earth"s lithosphere is composed of 9 major plates & many minor plates. 2 types of plates: oceanic: fast (cm/a), young (<200 ma), dense (destroyed at subduction zones, continental: slow (mm-cm/a), older, less dense (not subducted) 2 forces drive earthquakes: gravity: pulls on denser portions of plates that are diving under others, heat: heat within earth causes convection cells to cycle within mantle. Plate motion varies from 0-15 cm per year. The largest earthquakes occur at subduction zones (creates tsunamis)
