GEL168 Lecture 3: Earthquakes
15 Feb 2019
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Reverse fault (60 ) footwall down, hanging wall up. Thrust fault (30 ) footwall down, hanging wall up. Most (90-95%) near plate margins where subduction is occuring. Highest intensity quake in n. a. -new madrid missouri - intraplate - due to movement along a failed rift zone - 8. 1 to 8. 7 magnitude and a 12 in intensity. Earthquakes occur as pressure builds up at a contact zone between two plates. Rocks may bend and deform, releasing the pressure/energy slowly or they may break causing a rapid release of energy and an earthquake. Fault = a crack in the earth"s crust usually sloping hanging wall = overhead side footwall = under foot side. Earthquake position is described using two terms -focus and epicenter. May be surface to 450 miles down. shallow focus=surface to 40 miles deep intermediate focus=40 miles -185 miles in depth deep focus=185 miles to 450 miles deep. Beyond 450 miles rocks behave plastically and bend.
