HR: 11:35h
AN: OS21D-06    [PDF]
TI: Tsunami Hazards From Strike-Slip Earthquakes
AU: * Legg, M R
EM: mrlegg@attglobal.net
AF: Legg Geophysical, 16541 Gothard Street Suite 107, Huntington Beach, CA 92647 United States
AU: Borrero, J C
EM: jborrero@usc.edu
AF: Dept. Civil Engineering, University of Southern California, Los Angeles, CA 90089 United States
AU: Synolakis, C E
EM: costas@usc.edu
AF: Dept. Civil Engineering, University of Southern California, Los Angeles, CA 90089 United States
AB: Strike-slip faulting is often considered unfavorable for tsunami generation during large earthquakes. Although large strike-slip earthquakes triggering landslides and then generating substantial tsunamis are now recognized hazards, many continue to ignore the threat from submarine tectonic displacement during strike-slip earthquakes. Historical data record the occurrence of tsunamis from strike-slip earthquakes, for example, 1906 San Francisco, California, 1994 Mindoro, Philippines, and 1999 Izmit, Turkey. Recognizing that strike-slip fault zones are often curved and comprise numerous en echelon step-overs, we model tsunami generation from realistic strike-slip faulting scenarios. We find that tectonic seafloor uplift, at a restraining bend or"pop-up" structure, provides an efficient mechanism to generate destructive local tsunamis; likewise for subsidence at divergent pull-apart basin structures. Large earthquakes on complex strike-slip fault systems may involve both types of structures. The California Continental Borderland is a high-relief submarine part of the active Pacific-North America transform plate boundary. Natural harbors and bays created by long term vertical motion associated with strike-slip structural irregularities are now sites of burgeoning population and major coastal infrastructure. Significant local tsunamis generated by large strike-slip earthquakes pose a serious, and previously unrecognized threat. We model several restraining bend pop-up structures offshore southern California to quantify the local tsunami hazard. Maximum runup derived in our scenarios ranges from one to several meters, similar to runup observed from the 1994 Mindoro, Philippines, (M=7.1) earthquake. The runup pattern is highly variable, with local extremes along the coast. We only model the static displacement field for the strike-slip earthquake source; dynamic effects of moving large island or submerged banks laterally during strike-slip events remains to be examined. Depending on the size, recurrence of Southern California tsunamis from submarine strike-slip faults is estimated at a few hundred to few thousand years, similar to return periods estimated for large earthquakes on other active faults within the urban area. The combined probability from onshore and offshore hazards may be higher.
DE: 4564 Tsunamis and storm surges
DE: 7223 Seismic hazard assessment and prediction
DE: 8105 Continental margins and sedimentary basins
DE: 8107 Continental neotectonics
DE: 8123 Dynamics, seismotectonics
SC: Ocean Sciences [OS]
MN: 2003 Fall Meeting