Megathrust seismic hazards by reflection mapping

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Most of the world?s great earthquakes are shallow events that occur in association with the tectonic process of subduction. Damage and loss of life result not only from the earthquakes themselves, but from the tsunamis they commonly spawn as well. Regions in the U.S. that will certainly experience such events at some time in the future are Alaska and Cascadia (the coastal region extending from northern California to southern Canada). Estimating the ground motions that can be expected from these earthquakes is obviously a matter of considerable importance. Such estimates depend on the width of the subduction megathrust that produces great earthquakes ? the seismogenic zone; the nearer the landward edge of this zone is to the coast, the longer and stronger the ground motion is likely to be. Deep reflection seismic methods may provide a means of locating the downdip limit of the seismogenic zone. This project will test this method by acquiring marine multichannel (MCS) and wide angle reflection data over a large portion of the Alaska-Aleutian subduction zone. The reflection mapping results can then be compared with the earthquake rupture limit defined by existing earthquake aftershock and geodetic data.