Shallow crustal model of the DehDasht in Zagros, Iran, using Rayleigh wave tomography

Abstract

Surface wave tomography is considered an efficient method to reveal the physical properties of subsurface geological structures, particularly beneath geologically complex areas where conventional active seismic methods are problematic. The salt-rich DehDasht structural basin, in the SW of Iran, is an example of this area, which is characterized by high seismicity. Despite the complex geology and the great thickness of evaporitic deposits in this region, surface wave tomography can retrieve high-resolution images by applying a dense network of stations. Therefore, >11,000 micro-earthquakes (M ≤ 3.0) recorded by 116 broadband stations in 9 months were processed to detect geological structures and a crustal model beneath the DehDasht region. After selecting strict data selection criteria, the observed dispersion curves of Rayleigh waves were then measured using the multiple filter analysis method, and the 2D tomography was done for periods of 0.3 to 5.0 s. A non-linear iterative damped least-squares inversion procedure was then applied to each local dispersion curve to obtain the 1D VS model of the uppermost 5 km, and the results were inserted into the original cells to construct a quasi-3D VS model. Although our resulted VS model has high correlations with known geological units and tectonic features of the study area, we validated it by inverting the observed gravity data independently and consequently recovering the location of the anomalies at the basin and/or around faults, anticlines, and synclines. Generally, the observed low-and high-velocity anomalies are associated with the sedimentary materials.