Iterative de-convolution of the local waveforms: Characterization of the seismic sources in Kachchh, India

Abstract

The deviatoric and double couple (DC) constrained moment tensor inversions of multiple point sources (10–20 s) for regional (or local) earthquakes, developed by Zahradnik et al. (2005), has been applied on the data of nine significant Bhuj aftershocks of M w4.4– M w5.6 recorded at three-component 5–15 accelerograph and 5–11 seismograph stations (epicentral distances < 130 km). The deviatoric moment tensor solutions of events on the north Wagad fault (NWF) in the 15–29 km depth range reveal a systematic depth-wise variation in the faulting patterns. At shallow depth (~ 15 km), they suggest a left lateral strike-slip movement with a minor reverse component along a south dipping plane (~ 61°), whereas, at 18–22 km depth range they change to pure reverse movement on a preferred south dipping plane (10–54°) and finally they change to the normal movement with minor strike-slip (S-S) component at deeper (25–29 km) depth range. The deviatoric MT solution of one event on the south Wagad fault (SWF) suggests a reverse movement with a minor S-S component on a 35° southeast dipping plane at 24 km depth. The deviatoric MT solutions for two events on the Gedi fault reveal a reverse movement with a minor left-lateral strike-slip component on an E–W trending and south dipping (40–61°) plane at 3–4 km depth. Whereas, one event on the Island belt fault (IBF) suggests a right lateral strike slip movement with a normal component on an almost vertical (~ 79°) plane at 29 km depth. The deviatoric moment tensor solutions of all the nine events show a larger (94–99%) double-couple (DC) component at shallow (3–15 km) depth range suggesting domination of brittle failure in the upper crust beneath the Kachchh region. However, the deeper events show larger non-DC (i.e. compensated linear vector dipole, CLVD) component suggesting increase in deviation from the double-couple (DC) solution in the lower crust (15–30 km depth range). This increase in non-DC component could be attributed to the source complexity in the lower crust. Further, the increase in normal component on NWF as well as IBF in the 25–30 km depth range can be explained in terms of presence of aqueous fluid in the lower crust as revealed by the tomographic studies.