Three-dimensional deformation caused by the Bam, Iran, earthquake and the origin of shallow slip deficit
Our understanding of the earthquake process requires detailed insights into how the tectonic stresses are accumulated and released on seismogenic faults. We derive the full vector displacement field due to the Bam, Iran, earthquake of moment magnitude 6.5 using radar data from the Envisat satellite of the European Space Agency. Analysis of surface deformation indicates that most of the seismic moment release along the 20-km-long strike-slip rupture occurred at a shallow depth of 4–5 km, yet the rupture did not break the surface. The Bam event may therefore represent an end-member case of the 'shallow slip deficit' model, which postulates that coseismic slip in the uppermost crust is systematically less than that at seismogenic depths (4–10 km). The InSAR-derived surface displacement data from the Bam and other large shallow earthquakes suggest that the uppermost section of the seismogenic crust around young and developing faults may undergo a distributed failure in the interseismic period, thereby accumulating little elastic strain.
Additional Information© 2005 Nature Publishing Group. Received 1 October 2004; Accepted 28 January 2005. We thank R. Bürgmann for comments. This work was supported by the National Science Foundation and the Southern California Earthquake Center. Original Envisat ASAR data are copyright of the European Space Agency, acquired under CAT-1 research category. Aftershock locations were provided by M. Tatar, and coordinates of the geologically mapped faults by M. Heydari. P.R. conducted his work at JPL/Caltech, under contract with NASA.
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