Slip Distribution of the 2001 West India Earthquake

We used the orientation and size of the fault determined from our aftershock results to carry out an inversion of teleseismic data for the slip distribution of the 2001 West India earthquake. Previous inversions for this earthquake have been done by but these solutions did not use the constraints on the fault geometry that are now available. Choosing the correct fault plane from the two nodal planes of the focal mechanism and limiting the mainshock source area to the size of the aftershock region affects the slip distribution. We used 19 teleseismic P waveforms which were well distributed in azimuth in a finite-fault inversion on a grid of 80 subfaults. Since the observed waveforms look similar at all azimuths, we decided that there was not much time resolution and used only one time window. The results of the inversion for the various rupture velocities tested, did not show significant differences. We show the results for a rupture velocity of 2.9 km per sec. The results of the inversion show that the largest area of slip is close to hypocenter. This asperity is about 10 km x 20 km with a maximum slip of about 10 meters. The area of large slip in the region of the hypocenter corresponds closely to the area of most severe damage in the villages east of Bhuj. This area probably experienced very strong shaking from the rupture of the asperity. Bhuj, is located more than 30 km west from the closest portion of the fault and probably experience somewhat lower levels of ground motions, as seen in the intensity distribution. The character of the slip distribution appears different from other shallow earthquakes of equal size. The area of the fault is small for a Mw7.7 event. Comparing the slip distribution of the 2001 West India earthquake to the similarly sized (Mw7.7) 1999 Taiwan earthquake. The Taiwan earthquake is spread out over a larger area and shows a more complicated slip distribution. These difference can also be seen in the teleseismic waveforms. The India event has a more compact waveform with a large amplitude pulse at the beginning. The smaller source size means the 2001 West India earthquake had a higher static stress drop. This implies that the nearfield ground motions were higher, although with shorter durations, compared to the 1999 Chichi Taiwan earthquake.