Constraints On The Rupture Mechanism Of The 2001 Bhuj Earthquake From Satellite Imagery

We use satellite imagery collected by Landsat, ASTER, and IRS-1D in the years before and after the January 26, 2001 Bhuj earthquake, India, to identify coseismic changes in the topography. In this approach, we search for changes in the distribution of submergence during the seasonal monsoon flooding that covers the low lying portions of the region in the southernmost Rann of Kachchh. It appears that about 15 km WNW of the reported USGS epicenter, ponding in an area of about 80 km² occurred in the ensuing monsoon period whereas prior to 2001, namely in 1999 and 2000, the submergence occurred further north of this region. The observed changes in the distribution of submerged areas during the monsoon are consistent with a zone of uplift near approximately 23.45° latitude. It appears that this uplift also shifted the southern limit of the adjacent salt region to the north. We suggest that the inferred uplift puts additional constraints on the location of the rupture. A rupture model with slip on a 40x20km² rupture, extending from a depth of about 37 km to 10 km is consistent with the models suggested previously from teleseismic waveform inversions and the aftershock distribution. The dislocation model predicts subsidence in the north which coincides with the low lying salt flat region between the Pachham and Khadir islands. This apparent corelation between the earthquake induced subsidence and the low lying area suggests that similar large earthquakes in this region occurred in the past.