Short-term seismic crustal deformation of Iran

Abstract

In this paper the short-term seismic deformation of Iran is determined by the earthquake moment tensor summation. The study areas include the Alborz, Kopeh-Dagh, eastern Iran, Makran and Zagros orogenic belts. The spatial distribution and focal mechanisms of the earthquakes delineate the deformation zones. The mean directions of the P and T axes are determined by the equal area projection of the seismic moment tensors. The orientations of the P-axes are dominantly correlated with the NE crustal motion of Iran relative to Eurasia. The average strain rates are calculated in all of the regions. The maximum shear strain and dilatation rates are defined by the eigenvalues of the average strain rate tensors. The dilatation rate indicates that not only the dominant compression but also the subsidiary tension affects the Alborz and Makran orogenic belts. The velocity tensor components discriminate the vertical thickening and thinning of the crust in some regions of Iran. The seismic deformation rates, which are determined by the velocity tensors, are smaller than the geodetic deformation rates. In the high seismic deformation zones, such as the eastern Iran and Alborz, the geodetic deformation rate is comparable with the seismic deformation rate. Our results indicate that the NW Zagros and Kopeh-Dagh have the lowest seismic deformation rates. The seismic shortening rate increases from NW to SE in the Zagros orogenic belt. The seismic deformation orientations are different from the P-axes, probably due to the lateral translation. The maximum percentage of the seismic deformation in the study areas is related to the eastern Iran and the minimum one is related to the Makran orgenic belt. The average shape tensors indicate that the focal mechanisms in the Kopeh-Dagh have the highest internal similarity. The eastern Iran has the largest seismic moment rate, while the central Zagros has the lowest one.