Lecture 12 Earthquake_Geology and Effect on people

Lecture 12 Earthquake_Geology and Effect on people -...

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9/25/2011 1 Lecture 12 Earthquakes Chapter 5 Part 1: Geology Part 2: Earthquake and people Outline What earthquakes are Where earthquakes occur How fault ruptures generate earthquakes How we measure and study earthquakes What earthquake hazards are How scientists attempt to predict earthquakes How people mitigate earthquake hazards Earthquakes Defined Trembling, shaking, or vibration of Earth. Tectonic movements within lithosphere causes earthquakes and most occur along preexisting faults. Movements generate seismic waves that travel outward in all directions from fault. Seismic waves originate at focus and migrate outward; epicenter marks projection of focus directly to surface. Figure 5-2 Movement on Faults Causes Earthquakes
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9/25/2011 2 Where Earthquakes Occur Transform Boundaries Motions along transform plate boundaries cause many large earthquakes globally Transform plate boundaries are complex San Andreas fault zone is a system of many connected faults that allow plates to move past each other Main San Andreas fault cuts to basal crust and extends from a divergent plate boundary in the Gulf of California northward to near Cape Mendocino, where it merges with an offshore transform fault. Figure 5-3 The San Andreas Fault Zone Large fault system = transform plate boundary. Where Earthquakes Occur Convergent Boundaries Largest earthquakes on record occurred along subduction zones, where one plate slips beneath another Reverse/thrust faults are common Figure 5-4a The Largest Earthquakes Occur at Convergent Plate Boundaries Figure 5-4c Tsunami generated from May 1960 Chilean quake of 9.5 magnitude was also devastating to Japan. Where Earthquakes Occur Divergent Boundaries Pulling apart or extension of the lithosphere and normal faulting along these oceanic divergent plate boundaries causes many shallow, small-to-moderate-size earthquakes along MORs Pull-apart basins or rifts are also common on land with some quakes larger than those at the MORs Figure 5-5a Earthquakes at Divergent Plate Boundaries Earthquakes are common in the East African rift zone, where normal faulting marks new divergent plate boundaries.
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9/25/2011 3 Where Earthquakes Occur Not all along Boundaries: Intraplate Locations Central Mississippi Valley experiences many small- to-moderate-size intraplate earthquakes. Map shows epicenters of earthquakes recorded since 1974. Figure 5-7 Earthquakes in the Mississippi Valley Elastic Rebound Theory Figure 5-8 The Elastic Rebound Theory Explains Fault Rupture and Earthquake Generation Sudden release of elastic strain that built up along a fault releases seismic energy, causing earthquakes (right). Theory developed from
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Lecture 12 Earthquake_Geology and Effect on people -...

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