Present-day deformation in NE Iran and the South Caspian constraint by Global Positioning System measurements
Abstract
The continental collision between Arabia, the Eurasia and distribution of earthquake epicenters show that most of the deformation is accommodated within the political borders of Iran. In recent years, constraints from GPS, seismology and geological estimates of fault slip-rate have allowed considerable advances in understanding the rates and kinematics of faulting across many parts of Iran. However, until now, only little is known on the present-day distribution of strain across the eastern and northeastern parts of the country, such that it has been difficult to assess the rates of faulting, the related earthquake hazard, and the relationship between the active faults and the overall tectonic motions. This area is one of the most densely populated regions of Iran with almost 6.5 million habitants and a significant number of historical earthquakes like the Qumis 856 A.D earthquake with 200.000 victims. But while eastern Alborz and Kopeh Dagh are clearly regions of active faulting, a lack of instrumental earthquakes is presently observed, making this area particularly interesting for hazard assessment studies. The sparse GPS measurements in NE Iran provide only limited constraints on the applicability of different kinematic scenarios that have been proposed to explain the role of the observed faults. Here, we present a velocity field, composed from 47 GPS stations (20 campaign and 27 permanent), recording over up to 11 years, and covering the entire NE of Iran. This new GPS velocity field helps to investigate how northward directed Arabia-Eurasia shortening is accommodated at the northern boundary of the deforming zone. A regional deformation field for NE Iran has been estimated from the GPS measurements. It shows how the incoming ~7 mm/yr of NS shortening between Central Iran and Eurasia is accommodated in Alborz, Binalud and Kopeh Dagh. The shortening rate decreases toward the east and dies out at the Afghanistan border. The deformation pattern is contrasted along the mountain range from Kopeh Dagh to Alborz. East of 57°E, the present-day tectonic is accommodated on thrust faults in eastern Kopeh Dagh, Binalud, Siah Kuh and Kuh-e-Surkh. West of 57°E, the pattern is different. Most of the shortening is absorbed by 6-7mm/yr of right-lateral strike-slip motion along the Ashkabad Fault and 4-6 mm/yr of left-lateral strike-slip motion on the Astaneh-Shahroud Fault system.Further west, in central Alborz, the left-lateral displacement is accommodated in a smoother, more distributed way than in eastern Alborz where it is absorbed in narrow zones and sharply on individual faults. In eastern Alborz, some GPS fault slip-rates are slightly higher than their geologic slip-rate, leading us to look carefully on the hazard assessment of this range. Maximum cumulated left-lateral slip rate (6mm/yr) is located in a zone around latitude 56°E where no geological estimations of individual fault slip-rates are available. The remaining key question is to localize the left-lateral movement on the different individual faults in eastern Alborz between 53°E and 57°E. Ongoing work using a combined geodetic (GPS + InSAR) and tectonic approach could constrain the seismic potential in this region in a significant way.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2012
- Bibcode:
- 2012AGUFM.G52A..08M
- Keywords:
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- 1242 GEODESY AND GRAVITY / Seismic cycle related deformations