Article ID | Journal | Published Year | Pages | File Type |
---|---|---|---|---|
4695232 | Tectonophysics | 2006 | 15 Pages |
Abstract
To understand the generation mechanism of the Bam earthquake (Mw 6.6), we studied three-dimensional VP, VS and Poisson's ratio (Ï) structures in the Bam area by using the seismic tomography method. We inverted accurate arrival times of 19490 P waves and 19015 S waves from 2396 aftershocks recorded by a temporal high-sensitivity seismic network. The 3-D velocity structure of the seismogenic region was well resolved to a depth of 14Â km with significant velocity variations of up to 5%. The general pattern of aftershock distribution was relocated by using the 3-D structure to delineate a source fault for a length of approximately 20Â km along a line 4.5Â km west of the known geological Bam fault; this source fault dips steeply westward and strikes a nearly north-south line. The main shallow cluster of aftershocks south of the city of Bam is distributed just under the minor surface ruptures in the desert. The 3-D velocity structure shows a thick layer of high VS and low Ï (minimum: 0.20) at a depth range of 2-6Â km. The deeper layer, with a thickness of about 2Â km, appears to have a low VS and high Ï (maximum: 0.28) from 6Â km depth beneath Bam to a depth of 9Â km south of the city. The inferred increase of Poisson's ratio from 2 to 10Â km in depth may be associated with a change from rigid and SiO2-rich rock to more mafic rock, including the probable existence of fluids. The main seismic gap of aftershock distribution at the depth range of 2 to 7Â km coincides well with the large slip zone in the shallow thick layer of high VS and low Ï. The large slip propagating mainly in the shallow rigid layer may be one of the main reasons why the Bam area suffered heavy damage.
Related Topics
Physical Sciences and Engineering
Earth and Planetary Sciences
Earth-Surface Processes
Authors
Hossein Sadeghi, S.M. Fatemi Aghda, Sadaomi Suzuki, Takeshi Nakamura,