Studying post-seismic deformation 2010 Mw 6.5 Rigan earthquake in SW Iran using InSAR

Document Type : Research Article

Authors

Department of Earth Sciences, Institute for Advanced Studies in Basic Sciences, Zanjan, Iran

Abstract

On 20 December 2010, an earthquake with Mw 6.5 occurred in Rigan, a small town in the desert south of Bam city. The earthquake epicenter was in a low population area so, luckily, it caused only few casualties. Five days later 76 aftershocks reported by Iranian Seismological Center (ISC). On 27 January 2011, another earthquake (Mw 6.2) stroke an area at ~ 20 km southwest of the first earthquake. Bam earthquake Mw 6.6 occurred in 2003 with 40,000 victims is one of the deadliest earthquakes in Iran which is located in shear zones at southeast Iran. Considering the active faults distribution of the region and aftershocks of the 2010 Rigan earthquake encouraged us to better investigate and model the post-seismic deformation related to the 2010 earthquake. Post-seismic syudying provides information about rheology of the surrounding region and improves our knowledge about the strain release after the earthquake. In this study, COSMO-SkyMed (from Italian Space Agency, ASI) images spanning the temporal interval between 27 January 2011 and 15 July 2011 are used to investigate the post-seismic deformation following both earthquakes. We applied the Small Baseline Subset (SBAS) algorithm for images to obtain the post-seismic mean velocity map and the relative deformation time series. 109 interferograms, post-seismic mean velocity map and the relative deformation time series obtained Mean velocity map shows that displacements of post-seismic phase are right lateral strike slip same as co-seismic mechanism. Time series analysis reveals a clear post-seismic signal exponentially increasing with time until reaching the rate of more than 8 mm/year which indicates the end of post-seismic phase and following inter-seismic phase, starts with steady stress accumulation. Later, we modeled the post seismic signal considering a dislocation on a finite fault in an elastic and homogeneous half-space that are the assumptions for the Okada (1985) model. Post-seismic results modeled by adopting a two-step approach: (1) a non-linear inversion performed to constrain the fault geometry parameters and considering a uniform slip, then (2) a linear inversion performed to retrieve the slip distribution on the fault plane previously obtained. The fault plane is split into 1×1 km patches along strike and down-dip. Determining fault parameters and slip distribution by Okada model, indicates that the slip is concentrated in downdip of the coseismic depth with 1.2 m slip and also at the edges of the coseismic asperity. This slip distribution indicates that “afterslip” is the mechanism for post-seismic deformation of the Rigan earthquake. 

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References

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Iranian Journal of Geophysics
Volume 12, Issue 2
November 2018
Pages 96-108

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