HR: 1340h
AN: OS23D-1351    [Abstracts]
TI: Tsunami Hazard Based on Empirical Data From Tsunamigenic Earthquakes
AU: * Nishenko, S
EM: spn3@pge.com
AF: Pacific Gas and Electric Co., Geosciences Dept. 245 Market Street Mail Code N4C , San Francisco, CA 94105 United States
AU: Plafker, G
EM: gplafker@usgs.gov
AF: Plafker Geohazard Consultants, 235 Highland Terrace , Woodside, CA 94062 United States
AU: Page, W
EM: wdp7@pge.com
AF: Pacific Gas and Electric Co., Geosciences Dept. 245 Market Street Mail Code N4C , San Francisco, CA 94105 United States
AB: Published and unpublished data on tsunami runup, coseismic vertical displacement, and seismologic data for 35 large tsunamigenic earthquakes with maximum runups $>$1 m are evaluated to develop an empirical relationship between tsunami runup and earthquake magnitude. For most tsunamigenic earthquakes, the associated tsunamis are primarily generated by large-scale vertical coseismic displacement of the seafloor. In some events, however, the highest runups from local waves are associated with earthquake-triggered submarine landslides. Analysis of worldwide data supports the hypothesis that large submarine slides that occur as a secondary effect of earthquake shaking are more common than has been generally recognized. For tectonic tsunamis, both average fault slip and maximum regional tsunami runup correlate with earthquake size as measured by seismic moment or earthquake magnitude. Maximum runup heights increase linearly from about 1 m to 15 m in the magnitude range 7.2 to 9.5 for tectonic tsunamis that are not complicated by unusual bathymetry or irregular configurations of the coast (Runup (m) = 4.99 Mw $-$ 34.6). Tsunamis generated by earthquake-triggered submarine landslides tend to be more local in distribution, and as much as 4 times higher, than comparable magnitude tectonic tsunamis. Maximum runup heights for landslide-generated waves increase linearly from about 12 m to 52 m in the magnitude range 7.1 to 9.2 (Runup (m) = 20.28 Mw $-$ 130.78). Most, if not all, tsunamis associated with strike-slip faulting earthquakes are probably landslide-generated because strike-slip displacements are inherently very inefficient generators of tectonic tsunamis at all magnitudes. Factors that control the susceptibility of earthquake triggered submarine landsliding include: magnitude and type of faulting; the frequency of shaking by large earthquakes; the geology and topography of the submarine slope; the availability of thick sediment accumulation, such as deltas and glacial margins; and the presence of high fluid pressures, clathrates, gas, and liquefiable sediment in the bottom strata.
DE: 4564 Tsunamis and storm surges
SC: Ocean Sciences [OS]
MN: 2004 AGU Fall Meeting