THE 26 DECEMBER 2004 EARTHQUAKE IN INDONESIA - FUTURE EARTHQUAKES AND TSUNAMIS IN THE SUMATRA-ANDAMAN MEGATHRUST REGION

Tsunami Society International Future major earthquakes in the Sumatra-Andaman megathrust region can be expected to generate destructive tsunamis that will result in great losses of life and property in countries bordering the Andaman Sea Basin, Sumatra and the Indian Ocean. Megathrust earthquakes with moment magnitutes of Mw=9 or more, similar to the Mw=9.2+ of 26 December 2004, at convergent tectonic plate boundaries closer to the oceanic trench west of Sumatra, can be expected to generate very destuctive tsunamis, along populated coastal areas of Indonesia, but also to other countries bordering the Indian Ocean. In spite of the better understanding of the risks and of the protective measures that have been implemented since 2004, the destructiveness of future events is expected to be significant in the Andaman Sea basin, coastal areas of Sumatra and countries bordering the Indian Ocean. In order to estimate the recurrence frequency of future tsunami-generating earthquakes in the Sumatra-Andaman megathrust region similar to the 2004 event, the present study examines briefly existing geodynamic processes in the north and west of the Island of Sumatra, as well as past and recent tsunami generating earthquakes in the vicinity of the Andaman Sea Basin, including the Andaman and Nicobar groups of islands. Specifically examined is the Andaman fault system, recently prolonged through the Sumatra zone (the Sumatra fault), which has been reactivated due to the lateral escape of the Sumatra forearc sliver plate, and as a result of the oblique convergence and subduction with the Indo-Australian plate to the south. The present study reviews and analyzes the active mechanisms for different tectonic zones in this Sumatra-Andaman megathrust region, and provides an assessment of the potential for future destructive tsunamis, based mainly on the recent historic record, on active tectonic forces, and on evaluation of recurrence frequency.