Continued Post Seismic Deformation of Andaman Islands

The December 2004 Sumatra-Andaman earthquake was the second largest (Mw 9.3) and second deadliest (280,000 casualties) earthquake ever recorded. It was also unusual in that it combined a normal 'fast' rupture with a more unusual slow fault slip event. This unique occurrence presents an important opportunity to examine two questions with potentially wide-ranging implications for global earthquake studies: (1) what processes and rheologies re-equilibrate stress following great earthquakes in island arc settings? And (2) What Earth properties control the speed of rupture in great earthquakes? The boundary between the Indian and Andaman tectonic plates is almost entirely submarine, but the Andaman-Nicobar Island group enables a revealing look at post seismic deformation in the segment that ruptured principally as a slow earthquake and hence generated relatively little ground shaking. We are continuing to capture post seismic deformation after the Sumatra-Andaman earthquake by operating a network of 14 Global Positioning System (GPS) sites in the Andaman-Nicobar Islands. The network currently consists of 4 continuous and 10 campaign sites. These 'ground- truth' geodetic data (from a locale where data acquisition is notoriously difficult), which could be combined with satellite measurements of gravity and shoreline changes to examine key scientific questions about the deformation and stress cycle on a subduction thrust that exhibited unusual slow slip behavior during one of the largest earthquakes of the past century, will be presented. Data up to Oct 2008 will be used in the analysis.