Abstract

Observations by scuba diving in the heads of Scripps and La Jolla Submarine Canyons have shown that three strong earthquakes (5, 5.8, and 6.3 on the Richter scale) did not trigger failure in marginally stable marine sediments. In situ density measurements compared with laboratory tests of canyon sediments show that fill accumulating under nearshore environmental conditions is near its critical density and will neither expand nor contract when stressed. Sands with these properties cannot be considered to be metastable or expected to fail by spontaneous liquefaction. Movements of sandy sediment from the canyon head into deep water have not been by earthquake-triggered turbidity currents but by other observable mass-movement processes.

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