A Re-Evaluation of Earthquake Hazards Within the California Coastal Zone: Lessons from the Loma Prieta Earthquakeby Richard J. McCarthy, California Seismic Safety Commission, Sacramento, United States,
Robert G. Bea, California Seismic Safety Commission, Sacramento, United States,
James E. Slosson, California Seismic Safety Commission, Sacramento, United States,
Abstract: The 7.1 magnitude Loma Prieta earthquake occurred on October 17, 1989, had a duration of 15 seconds, and took 62 lives. Among the lessons learned from this earthquake with regard to offshore platforms are the fact that earthquakes characterized by substantial thrust fault motions can be expected to generate intense vertical motions that can be equal to or greater than the horizontal motions. These vertical motions can have important effects on the heavily loaded, cantilever or long-span decks of platforms that may have been designed for less intense vertical motions. Accumulations of softer and weaker soils can be expected to modify, and in some cases amplify the motions associated with stronger soils. Soft soils associated with the edges of sedimentary basins can also be expected to further modify the motions. If the soils are granular, of low density, and relatively freely draining, then liquefaction can be induced in portions of the sea floor. If a structure is technically obsolete, poorly constructed, or has been allowed to deteriorate, then it is very likely that the structure will not perform acceptably in an intense earthquake.
Subject Headings: Earthquakes | Offshore platforms | Coastal management | Coastal environment | Ground motion | Offshore construction | Load and resistance factor design | Earthquake resistant structures | Soft soils | North America | California | United States
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