Probabilistic Analysis of Strong Ground Motion and Tsunami Hazards in Southeast Asia

The December 2004 Sumatra-Andaman earthquake emphasized the need for a consistent and comprehensive assessment of tsunami hazard. We have developed a method for Probabilistic Tsunami Hazard Analysis (PTHA) based on the traditional Probabilistic Seismic Hazard Analysis (PSHA) and therefore completely consistent with standard seismic practice. In lieu of attenuation relations, it uses the summation of finitedifference Green’s functions that have been pre-computed for individual subfaults, which enables us to rapidly construct scenario tsunami waveforms from an aggregate of subfaults that comprise a single large event. For every fault system, it is then possible to integrate over sets of thousands of events within a certain magnitude range that represents a fully probabilistic distribution. Because of the enclosed nature of ports and harbors, effects of resonance need to be addressed as well, which is why we have extended this method to not only analyze exceedance levels of maximum wave height, but also of spectral amplitudes. As in PSHA, these spectral amplitudes can be matched with the spectral response of harbors, and thus allow a comprehensive probabilistic analysis of tsunami hazard in ports and harbors.