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# Machine - GEOL 114 The Earth's Dynamic Interior Lecture...

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GEOL 114 The Earth's Dynamic Interior Lecture Notes (Copyright © 2006 by Jeffrey S. Barker) Lab 4. The Earthquake Machine Purpose: to demonstrate the Elastic Rebound theory of earthquake occurrence, and the complexity caused by the interaction of different fault segments. Background: Following the 1906 San Francisco earthquake, Harry Fielding Reid proposed a radical new theory for what causes earthquakes. Reid's Elastic Rebound theory suggests that stress (force/area) is constantly building up in the region where an earthquake is going to occur. When that stress reaches the frictional strength of the fault, the fault slips, causing an earthquake and relieving the stress. The stress slowly builds up again until another earthquake occurs. Analyzing earthquake recurrence, we find that reality is a bit more complicated than this. Earthquakes occur on fault segments, so only a portion of a fault will slip in a given earthquake. The apparatus shown below is designed to illustrate some of these physical principles. The regional force is applied by turning a reel which pulls on a string. Clicks of the reel's ratchet may be considered increments of time (e.g. a year). The string stretches a spring. As with all springs, the force applied is proportional to the length of the spring. Stress is force divided by the area of the fault (or wood block in this case). Since the area is constant, the length of the spring is also proportional to the stress applied to the fault. The frictional

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Machine - GEOL 114 The Earth's Dynamic Interior Lecture...

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