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Unformatted text preview: GEOL 0820 Ramsey Natural Disasters Spring, 2011 LECTURE #7: Earthquake Disasters: Monitoring & Mitigation Date: 1 February 2011 I. In the News volcanic eruption in Japan notes II. Introduction what are earthquakes (EQs)? o ground movement caused by the release of seismic energy o seismic energy is usually caused by the brittle failure of rocks under stress important hazards to understand: o kills the most people per year (> 1 million/past century) o commonly strikes without precursors o 1000's of large EQ's every year ~ 20 are > M7.0 account for 90% of the energy released 80% of all the fatalities o recall: most of the fastest growing cities lie on the Pacific Rim and are threatened by large EQ's III. Earthquakes & Faults what is an EQ? o sudden release of stored energy as the result of rapid movement between two blocks (plates) o energy stored because of plate movement and friction release point is the focus or hypocenter energy radiates out in all directions point on the surface directly above the focus is the epicenter fault trace: line where the fault/fracture intersects the surface Page 1/5 Earthquakes in CA/NV during one week fault terminology: o headwall: rock layers above the fault plane o footwall: rock layers below the fault plane o fault types: normal (extensional) due to tensional forces; generally the smallest EQs hanging wall moves down with respect to the footwall...
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