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for schools > earthquakes > earthquake cycle |
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The earthquake cycle (5) |
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The idea of the earthquake cycle was developed by Harry Fielding Reid to explain his observations of the San Francisco earthquake of 1906. The earthquake caused an average of four to five meters surface slip along 450 kilometers of the San Andreas Fault (another strike-slip fault). Reid examined precise survey data of the area taken in the 1880s and again immediately after the earthquake. For the first time, these observations revealed the surface deformation caused by an earthquake. The survey data revealed that points on the southwest side of the San Andreas Fault had moved to the northwest compared with points on the other side of the fault. Reid also found that the points close to the fault had moved much more than those further away. When he used the survey data to extrapolate the surface slip, his calculations matched the distance the ground had broken apart at the fault. Reid also compared further survey data of California from the 1860s and 1880s. He found that the Farallon lighthouse, located a long way to the southwest of the fault, had moved north-west over a 20-year period. These observations led Reid to propose his elastic rebound theory of the earthquake cycle.
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Harry Reid |
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