ABSTRACT
The current tectonic activity in Asia is attributed to the underthrusting of the Indian plate beneath the Eurasian plate; stresses are being generated and released through earthquakes of various magnitudes. Drastic variations in satellite-derived surface temperature and geoid or gravity data have been utilized as predictors of seismic behaviour over land and ocean lithospheres. A sharp change in the surface temperature patterns (around 6°C–7°C) could be observed near the Bhuj region just before the occurrences of these mild tremors. A gravity anomaly of 37 mGal has been observed near the Island Belt Fault earthquake epicentre. The Indian Ocean has experienced two major plate reorganizations from the late Jurassic to the present. At most subduction zones, like the one near the Andaman, seismicity involves very large earthquakes characterized by a thrust-faulting mechanism, expressing the overriding of the subducting oceanic plate by another plate. Variations in the gravity field, using satellite altimetry–based geoid or gravity, have been utilized as a predictor of seismic behaviour. Profiles generated over the epicentre and the aftershock regions over the Andaman subduction zone show a drastic change (~130 mGal) in the gravity patterns. Also, a temporal geoid has been studied over the Andaman swarm region using Gravity Recovery and Climate Experiment time-variant data for such studies. Drastic changes in geoid could be observed during the pre-occurrence and Swarm occurrence phases. Four case studies with thermal and gravity precursors are discussed, two over land and two over ocean, with the study areas mainly in the Bhuj–Kachchh for land and the Andaman subduction zone in the Bay of Bengal for oceans.
