Sonographs of submarine sediment failure caused by the 1980 earthquake off northern California |
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Authors: | Michael E. Field Robert K. Hall |
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Affiliation: | (1) U.S. Geological Survey, 345 Middlefield Rd., 94025 Menlo Park, CA |
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Abstract: | In 1980, a large earthquake caused extensive sediment failure on the shallow continental shelf off the Klamath River in northern California. Side-scan sonography was used to complement detailed geophysical profiling in identifying specific features and resolving modes of failure. The features include a nearly flat failure terrace mantled with sand boils, collapse craters and sediment flows, and bounded on the seaward side by a meandering continuous toe ridge. Seaward of the terrace lies a compression zone delineated by small pressure ridges. Our findings indicate a temporal progression of failure from lique-faction of shallow subsurface sand to lateral spread of intact blocks to sediment collapse and flow. |
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