9316528 Kanamori This research is to study the characteristics of tsunami- producing earthquakes to determine the role of sediment subduction at plate margins and the resulting influence on the mechanism of subduction-zone earthquakes. Detailed investigations of the 1992 Nicaragua earthquake and other subduction-zone earthquakes will be done to determine the source characteristics and spectra in relation to the sediment structure near the epicenter of the respective events. In addition to traditional seismic analysis, the research will involve use of a newly recognized long-period phase, the W phase, which arrives between the P and S waves. The traditional tsunami warning system is based on the location and the magnitude of the earthquake. Unfortunately, because of past instrumental limitations, the traditional system uses 20-second surface-wave magnitude for warning purposes. However, for slow earthquakes such as the Nicaragua event, the 20-second surface-wave magnitude does not represent the true size of the earthquake. At periods longer than 100 seconds, the tsunami potential would have been better recognized. This research is a component of the National Earthquake Hazard Reduction Program. ***
