Co-Seismic Surface Displacement Induced by the Bam Earthquake, Iran (۲۶/۱۲/۲۰۰۳, M=۶.۶): Insights from InSAR, GPS, SPOT۵ Analyses and Levelling

Co-seismic surface deformation measurements in the vicinity of a ruptured fault provide constraints on detailed fault geometry and slip distribution at depth. Together with seismological data, they give unique insights on the mechanical behaviour of a seismic fault. Three different satellite and ground geodetic measurements of Bam earthquake (Mw ۶.۶, December ۲۶, ۲۰۰۳) induced surface deformation are presented. Envisat ASAR interferometry provides precise and dense information. However, due to this strike-slip fault orientation, sub-pixel correlation technique applied to Spot-۵ images makes more explicit the horizontal component of surface deformation. We complete these oblique and horizontal estimations of deformation with a levelling profile along the main road crossing the rupture from west to east. This geodetic data allows us to propose a dislocation model at depth. The slip vector, on a quasi-vertical fault, slightly dipping towards east, has a strike-slip component as high as ۲m, while the dip-slip component appears to be small. We suggest that rupture may have been initiated at depth on the Bam fault and propagated towards surface along this new fault branch. In addition to co-seismic deformation, InSAR analysis and levelling data reveal the presence of a high-rate subsiding zone south-east of Bam city. The phenomenon is likely due to heavy water withdrawal for cultivation purpose or water supply to the Bam and Baravat inhabitants. Ultimately, we present a work in progress involving GPS and InSAR which aims to map post-seismic deformation in the vicinity of Bam. However, technical problems in GPS campaigns and atmospheric artifacts in InSAR acquisitions did not enable us to show any evidence of such a deformation so far.

Keywords:

SAR Interferometry , Levelling , Sub-pixel correlation offsets , Dislocation model at depth , GPS