Kinematic and Geomorphic Constraints on Right-Lateral Strike-Slip Motion along the Damghan Fault, Eastern Alborz

The Damghan Fault, situated along the southern margin of the Eastern Alborz Mountains, defines a major tectonic boundary between Central Iran and the Alborz structural domain. Quaternary fault activity has produced diverse morphotectonic expressions, especially evident in the alluvial fans north of Damghan. This study examines fault kinematics and associated deformation patterns within Quaternary deposits using a combination of high-resolution remote sensing, geomorphic mapping, and field investigations. Although previously interpreted as a left-lateral strike-slip fault with an extensional component, our findings indicate a dominant right-lateral strike-slip mechanism accompanied by compressional deformation. This transition has resulted in uplift of the northern block in the eastern segment and uplift of the southern block in the western segment. The right-lateral component becomes more pronounced eastward, with stream offsets exceeding 90 meters in Holocene deposits. Estimated slip rates vary from ~ 9 mm/year in the west to ~ 3 mm/year in the east, with Siyah Kuh representing a transitional zone in both slip rate and structural behavior. These integrated geomorphic and seismic observations suggest that the Damghan Fault is actively propagating eastward as part of a broader regional shift from compressional to strike-slip tectonics. The concentration of deformation in the eastern segment highlights this zone as a likely locus of future seismic hazard.