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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.

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Figure 1: Coseismic deformation caused by the Bam earthquake as imaged by the Envisat ASAR data.
Figure 2: Displacements along a profile A–A′ perpendicular to the Bam earthquake rupture (Fig. 1).
Figure 3: Distribution of seismic potency averaged along the fault length L.


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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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Correspondence to Yuri Fialko.

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Supplementary information

Supplementary Figure 1

Shaded relief map of the epicentral area of the Bam earthquake. (JPG 41 kb)

Supplementary Figure 2

Slip distribution from the inversion of the Envisat ASAR data for the layered elastic half-space model. (JPG 24 kb)

Supplementary Figure 3

Sub-sampled ASAR data used in the inversion; best-fitting models; and residuals after subtracting the best-fitting models from the data. (JPG 80 kb)

Supplementary Legends

Legends for Supplementary Figs 1-3. (DOC 19 kb)

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Fialko, Y., Sandwell, D., Simons, M. et al. Three-dimensional deformation caused by the Bam, Iran, earthquake and the origin of shallow slip deficit. Nature 435, 295–299 (2005).

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