Postseismic relaxation due to Bhuj earthquake on J

Authors: C D Reddy P S Sunil Roland Bürgmann D V Chandrasekhar Teruyuki Kato

Publish Date: 2012/04/17

Volume: 65, Issue: 2, Pages: 1119-1134

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Abstract

Earthquakes cause static stress perturbations in the nearby crust and mantle Obeying rheological laws this stress relaxes in a time frame of months to years with the spatial extent of few km to hundreds of km While postseismic relaxation associated with major interplate earthquakes is well established there have been few opportunities to explore its occurrence following intraplate earthquakes The M w 76 Bhuj earthquake on January 26 2001 in western India is considered to be an intraplate event and provided a unique opportunity to examine postearthquake relaxation processes sufficiently away from plate boundaries To study the characteristics of transient postseismic deformation six Global Positioning System campaigns were made at 14 sites The postseismic transients were delineated after removing plate motions from the position time series Postseismic deformation has been observed at all the sites in the study area During 2001–2007 the site closest to the epicenter exhibited postseismic deformation of about 30 and 25 mm in the north and east components respectively Time series of the NS and EW components of the postseismic transients can be fitted to both logarithmic and exponential functions Close to the epicenter the logarithmic function fits well to the initial transient and an exponential function fits well to the later phases The remaining sites located east and west of the epicentral region exhibited significantly diminished north–south relaxation Rapidly decaying afterslip and poroelastic mechanisms seem to be responsible for postseismic relaxation in the vicinity of epicenter during the initial period subsequent to the Bhuj earthquake Postseismic relaxation by viscoelastic flow below the seismogenic zone seems to affect displacements across the entire Bhuj region This paper presents the characteristics of postseismic transients and deformation processes in the scenario of the highly heterogeneous crust in the Bhuj regionWe thank Kaoru Miyashita for providing GPS receivers and active participation in GPS campaigns We acknowledge the efforts of M Ponraj S Amirtharaj BD Kadam K Vijay Kumar Y Aoki and T Iinuma in collecting the GPS data We also thank Bob King for all his support in using GAMIT/GLOBK software The maps in this paper were generated using the Generic Mapping Tools GMT software by Paul Wessel and Walter H F Smith

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