While observing post-seismic relaxation associated with major inter-plate earthquakes is irrefutable, it is rather difficult with intraplate earthquakes. The Mw 7.6 Bhuj earthquake on January 26, 2001 in Western India considered to be an intraplate event and provides a unique opportunity to examine post-earthquake relaxation processes far from plate boundaries. To study the characteristics of transient post-seismic deformation and distribution of strain accumulation rate, five GPS campaigns were made during 2001-2002 and one during 2007, at 14 sites. As the post-seismic relaxation was feeble and not wide spread, it could not be traced from 2001-2002 data. The sixth campaign was intended to facilitate delineation of post-seismic deformation. The displacement at a site in the vicinity of the rupture may contain contributions from at least three processes (i) the plate motion at the site, (ii) contribution from inter-seismic strain accumulation and (iii) contribution from post-seismic relaxation processes due to the earthquake. In order to remove the first two components, we considered the displacement with reference to the site AHMD, which is sufficiently away from the asperity zone. Logarithmic function fits well to six snap shots of position time series of EW and NS components. The best fit is seen at the site DHAM which is closest to the epicenter. Further, the distribution of measure of fit to the NS component portrays that the region of good fit positionally correlates with transect parallel to the rupture zone. It is inferred that the post-seismic relaxation is taking place - mainly in NS direction and the major relaxation (~\ 90%\) occurred with in one year after the earthquake occurrence. Rapidly decaying afterslip and poro-elastic (as also indicated by widespread coseismic liquefaction) mechanisms seem to be responsible for post- seismic relaxation.
AGU Fall Meeting Abstracts
- Pub Date:
- December 2007
- 1207 Transient deformation (6924;