The 1906 Earthquake: Lessons Learned, Lessons Forgotten, and Future Directions
Mary Lou Zoback
The 1906 Mw7.8 earthquake on the N. San Andreas Fault marked the birth of modern earthquake science. For the first time, the effects and impacts of a major seismic event were systematically investigated. Along the entire 300-km-long surface rupture, offsets and other phenomena were documented. In addition, the trace of the San Andreas fault was mapped throughout California. Comprehensive study of seismic intensity showed the strongest shaking occurred in areas of "made land" (fill) and soft sediment, including China Basin and the present day Marina district, two San Francisco neighborhoods again heavily damaged in 1989. Damage to structures showed destruction was closely related to building design and construction -- a painful lesson oft repeated around the world. Based on repeated surveying data and surface offsets, Henry Reid proposed the elastic rebound hypothesis -- that earthquakes represent sudden release of elastic energy along a fault resulting from a cycle of slow strain accumulation produced by relative displacements of neighboring portions of the crust. This hypothesis, developed five decades before the plate tectonics revolution provided an explanation for the large-scale horizontal displacements observed, is still accepted today, with only minor modifications. Looking to the future, a dense array of continuous GPS recorders in N. California, part of EarthScope's Plate Boundary Observatory, can search for fault interactions and determine if the strain rate increases before the next big earthquake, as it may have prior to 1906.
The lecture will be illustrated with slides and is intended for the general audience.
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Last modified: Wed Sep 14 14:39:24 PDT 2005