Interferometric Displacement and Damage Assessment for the 2003 Bam Earthquake

We demonstrate that interferometric observations of the Mw6.6 Bam (Iran) earthquake on December 26, 2003 acquired by Envisat-ASAR can not only map surface displacements and constrain fault models, but can also be used for damage mapping using the coherence magnitude. The Bam earthquake was the deadliest earthquake in 2003. An estimated 30000 people were killed and 85% of the buildings in the area were damaged or destroyed. Using interferometric displacement maps derived from Envisat-ASAR data on ascending and descending tracks we derive the approximate 3-dimensional displacement field by fitting a simple displacement model to the observations. The interferometric coherence in the city of Bam decreases markedly in a coseismic interferogram with respect to the coherence in an interferogram before the event. We define a coherence change index as the ratio of the coherence values to map damage levels in Bam and validate them using high-resolution imagery acquired by IKONOS after the earthquake. We find a close agreement between our damage maps and those derived from optical images after the earthquake. This suggests that coherence-based damage maps might be used for rapid damage mapping where interferometric data can be made available shortly after a damaging earthquake.