Ground deformation in the two years since the 2003 Bam, Iran earthquake

Eric Fielding(1) , Gareth Funning(2) , Morteza Talebian(3) , Paul Lundgren(1) , Li Zhenhong(4) , Roland B├╝rgmann(2) , and Tim Wright(5)

(1) Jet Propulsion Laboratory, Caltech, 4800 Oak Grove Drive, Pasadena, California 91109, United States
(2) University of California, Berkeley, McCone Hall, Berkeley, California 94720, United States
(3) Geological Survey of Iran, P.O. Box 13185-1494, Tehran, Iran
(4) University College London, Gower Street, London, WC1E 6BT, United Kingdom
(5) University of Oxford, Parks Road, Oxford OX1 3PR, United Kingdom

Abstract

The December 2003 Mw 6.6 earthquake that devastated Bam, Iran involved several meters of slip on a previously unknown fault beneath the city. The outstanding surface conditions for InSAR and frequent coverage by Envisat ASAR provide an opportunity to map the ground deformation and study the time history in the two years since the earthquake. Envisat ASAR beam I2 data has been acquired about a dozen times on each of three tracks over the Bam area to date and the flat desert allows excellent coherence with long baselines, so we can form a time series of the post-seismic deformation by connecting all the scenes. Envisat ASAR WS data has also been acquired on two tracks for several months after the Bam earthquake, and has been used to make WS-WS interferograms by the Polibari and Polimi groups. The post-seismic surface deformation associated with the 2003 earthquake rupture is one order of magnitude smaller than the co-seismic deformation, so the signal is much closer to the noise due to atmospheric variations. For the descending, day-time, track over Bam we are exploring the use of MERIS water vapor measurements to derive an atmospheric correction for the InSAR data to better separate the ground deformation signal. Unfortunately, optical instruments including MERIS and MODIS can only measure water vapor during the day, so the ascending tracks cannot be corrected. Preliminary analysis shows that most of the ground deformation happened in the first six months after the earthquake, which is similar to the short decay time of post-seismic deformation observed after the September 2004 Parkfield, California earthquake. The distribution of deformation indicates at least two different processes were involved, at different depths in the crust.

 

 

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