Generation and study of high-resolution satellite gravity over the Sumatran earthquake region

We have utilized satellite altimetry data to generate the very high-resolution gravity anomaly maps to infer subsurface geological structures in the area of the devastating earthquake (and the corresponding tsunami) that struck the Indian Ocean near Sumatra (Indonesia) on 26 December 2004. In the present study, a high-resolution three-dimensional (3D) gravity image has been generated over a part of the eastern Indian offshore encompassing the Sumatran earthquake region apart from Ninety East Ridge, Andaman subduction zone, etc. Four latitudinal (2°, 3°, 4° and 8.6° N) gravity profiles have been generated across the epicentre (3° N/M w 9.0)/aftershock regions (4° N/M w 5.8 and 8.6° N/M w 6.0 and 6.6). A drastic change of gravity anomaly patterns (∼130 mGal) near the epicentre and the aftershock regions could be observed, which are however slowly diminishing further away from the epicentre. This gravitational difference might have been caused by the differences in plate tectonic processes. Minor/major gravitational differences in other areas may be due to the changes in densities of different lithospheric zones/sedimentary layers. Hence, our study further supports the idea that negative gravity and topography anomalies can be used as a predictor for occurrences of large earthquakes in subduction zones.