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Abstract

The Shahrud fault lies in the western Alborz and in the southeast of the sinistral strike-slip Rudbar fault (1990 7.3 Mw Rudbar-Manjil). The surface trace of the Shahrud fault is depicted on the active faults map of Iran as a continuous twisted curve of 65 km in length. Shahrud fault lies in the north of Qazvin and is accounted for a potential source of future destructive earthquakes. 698 local earthquakes have carefully relocated and focal mechanisms were determined for two events. According to the focal mechanisms of earthquakes that occurred in the area between the Rudbar and Shahrud faults, sinistral kinematics is suggested for the western part of the Shahrud fault. The remote sensing analysis of satellite imageries complemented by field measurements allows for revising the fault map of the area. Also, earthquake-related features such as thermal and travertine springs as well as landslides are aligned along the main fault traces of the area indicating the tectonic activity of these deep-seated structures. The kinematics investigation based on seismological and geological data indicates that the Shahrud Valley is affected by a complex fault network comprising a variety of faults with different orientations. The seismicity extended over the area and fault kinematics measured along the fault zones indicate that the Shahrud fault zone is not a simple S-dipping ”thrust fault”, but, is a simplified geological interpretation of an intersection zone produced by kinematic and structural interactions of distinct E-W, NNE- and NW-striking fault trends at the southern flank of the Shahrud Valley.