150Lec22-1

150Lec22-1 - Lecture #22: Subduction Zone Earthquakes...

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Lecture #22: Subduction Zone Earthquakes (Abbott, pp. 65-69, 117-120, 133-137, 163-166) The seven most intense earthquakes from 1906-2006 were associated with subduction zones (Table 6.1, p. 133). The 2011 Japanese earthquake was also associated with a subduction zone. As mentioned before, subduction occurs at convergent boundaries involving ocean-ocean or ocean-continent plates . In subduction zones, earthquakes may occur anywhere from the surface to depths of hundreds of kilometers (Figure 3.10, p. 57). At and near the surface, earthquakes result as the plate bends from subduction (p. 65). Intense earthquakes may also occur at greater depths as the brittle subducting plate passes underneath the brittle overlying plate (p. 65; Figure 3.10, p. 57). Below 100 kilometers, the mantle is too hot and ductile (plastic) to produce earthquakes with subducting plates and any earthquakes occur within any surviving brittle subducting plates (p. 65). Fortunately, the energy released by severe earthquakes at depths of 100 kilometers or more largely dissipates before it reaches the surface (p. 65, 67). In some subduction zones, brittle subducting plates may reach depths of more than 700 kilometers (p. 65). At greater depths, the subducting plates become too ductile for earthquakes and dissolve into the mantle. In contrast, the foci of continent-continent convergence zones (which involve no subduction) rarely exceed depths of 70 kilometers, and the foci of transform faults are even more shallow. Chile (1960)
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150Lec22-1 - Lecture #22: Subduction Zone Earthquakes...

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