U.S. GEOLOGICAL SURVEY EARTHQUAKE AND NATIONAL OCEANIC AND ATMOSPHERIC ADMINISTRATION TSUNAMI HAZARD ASSESSMENTS FOR THE REGION AFFECTED BY THE 2004 SUMATRA EARTHQUAKE

The December 26, 2004 M 9.0 Sumatra earthquake occurred along one of the most active plate tectonic margins in the world that accommodates about 50 mm/yr of oblique north-westward convergence between the Eurasia/Burma and India/Australia plates. Modeling studies show that slip in this great subduction earthquake probably increased hazard on some adjacent faults including portions of the 1900-km-long Sumatran fault and along adjacent segments of the subduction zone that ruptured in historic great earthquakes. Earthquakes along crustal faults cause high shaking hazards, while great earthquakes along the subduction zone cause tsunami hazard and more moderate shaking hazards. The U.S. Geological Survey has been involved in assessing earthquake hazards across southeast Asia during the early 1980's (SEASEE), mid 1990's (GSHAP), and in the early 2000's (Indonesia and Malaysian Peninsula). Currently, the USGS and NOAA are funded by USAID to contribute to the development of an Indian Ocean tsunami warning system. The USGS will increase recording and processing of real-time seismic data in order to improve the speed and accuracy of earthquake locations, magnitudes, and other relevant parameters; install GPS-based geodetic monitoring systems; install and upgrade local seismic stations; map vulnerability and seismic hazard in Indonesia, Singapore, Malaysia, and Thailand. Seismic hazard shaking maps will be developed for use in reconstruction of structures destroyed by the 2004 earthquake and in planning for future events. NOAA will focus on supporting the development of a Tsunami Warning System in the Indian Ocean, including a tsunami forecast system that will integrate real-time deep-ocean tsunami measurements with numerical models to forecast tsunami inundation and impact on coastal communities. An important USGS contribution to this effort will be the identification and specification of potential tsunami sources, to be used by NOAA in the development of a pre-computed database of tsunami generation and propagation solutions; these are required to initialize models that forecast community-specific inundation. Once completed, these forecast models can also be exploited to develop community-specific inundation maps to help guide hazard mitigation efforts and emergency management planning.