Evidence of strain accumulation in the Andaman region for the giant 2004 Sumatra Andaman earthquake

Abstract

We report results of Global Positioning System (GPS) and tide gauge data from the Andaman region that pertain to the period before the 26 December 2004 Sumatra–Andaman earthquake (M_w 9.2). In the preceding 40 years, seismicity in the frontal arc region was generally very low, implying locking of the main thrust zone. The campaign mode GPS data support strain accumulation in the region, corresponding to a slip deficit rate of about 3  cm/year. However, the tide‐gauge data of the preceding three years from the earthquake indicate land subsidence at a rate of about 3.3  cm/year, whereas uplift was expected in the period prior to the earthquake, as the region experienced coseismic subsidence during the earthquake.