Short-term seismic crustal deformation of Iran

Shoja Ansari Shoja Ansari,Ahmad Zamani Ahmad Zamani

doi:10.4401/ag-6413

Abstract

<p>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.</p>

Highlights

The Arabian-Eurasian convergent plate boundary zone is one of the largest deformation zones on the Earth [Allen et al 2004]
The rates of deformation in the Arabia-Eurasia collision zone are becoming better constrained through a combination of plate circuit and Global Positioning System (GPS) studies [Allen et al 2004]
Since the negative and positive values of the V12 indicated respectively sinistral and dextral strike-slip motions, we found that the left lateral strike-slip motion only affected the Alborz and eastern Iran, while the right lateral strike-slip motion affected the KopehDagh, Makran and Zagros orogenic belts

Summary

Introduction

The Arabian-Eurasian convergent plate boundary zone is one of the largest deformation zones on the Earth [Allen et al 2004]. The Iranian Plateau is located between the Arabian and Eurasian plates [Sobouti and Arkani-Hamed 1996] and Iran occupies the western part of the Iranian Plateau [Zamani and Hashemi 2000]. Deformation in the Iranian lithosphere is governed by the northern convergence of the Arabian plate relative to the Eurasian plate, lateral heterogeneities in the strength of the lithosphere [Sobouti and Arkani-Hamed 1996] and the disposition of the rigid blocks within the collision zone [Vernant and Chéry 2006]. The result of GPS networks within Iran gives lower estimates of the Arabia-Eurasia convergence rate than earlier, the nonGPS models [DeMets et al 1990, 1994, McClusky et al 2000, Vernant et al 2004, Allen et al 2006]. The primary link of GPS to the earthquake rate estimation, stems from the fact that crustal strain measured at the Earth’s surface eventually manifests itself to some extent in brittle failure; that is, an earthquake [Ward 1998a]

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Conclusion