No evidence of unusually large postseismic deformation in Andaman region immediately after 2004 Sumatra-Andaman earthquake

摘要

Static offsets due to the 26 December 2004 Sumatra-Andaman earthquake have been reported from the campaign mode GPS measurements in the Andaman-Nicobar region. However, these measurements contain contributions from postseismic deformation that must have occurred in the 16-25 days period between the earthquake and the measurements. We analyse these and tide gauge measurements of coseismic deformation, a longer time series of postseismic deformation from GPS measurements at Port Blair in the South Andaman and aftershocks, to suggest that postseismic displacement not larger than 7 cm occurred in the 16-25 days following the earthquake in the South Andaman and probably elsewhere in the Andaman Nicobar region. Earlier, this contribution was estimated to be as large as 1 m in the Andaman region, which implied that the magnitude of the earthquake based on these campaign mode measurements should be decreased. We suggest an Mw for this earthquake as 9.23.