Active tectonics and late Cenozoic strain distribution in central and eastern Iran

Abstract

Right‐lateral shear between central Iran and Afghanistan is accommodated on N–S right‐lateral strike‐slip faults surrounding the aseismic Dasht‐e‐Lut. North of ∼34°N, the right‐lateral shear is accommodated on left‐lateral faults that rotate clockwise about vertical axes. Little is known of the late Tertiary and younger offsets and slip rates on the active fault systems, results that are important for understanding the regional tectonics. We use observations from satellite imagery to identify displaced geological and geomorphological markers, which we use in conjunction with the overall morphology and orientation of the active fault systems to estimate the total cumulative right‐lateral shear. Estimates of cumulative fault movements from offset features and inferred vertical axis rotation of fault‐bounded blocks suggest that the late Cenozoic strain is concentrated toward the eastern margin of Iran, along the Sistan shear zone, where bedrock offsets of at least 70 km are observed across the active faults. The geomorphology of the Deh Shir, Anar, and Great Kavir strike‐slip faults in central Iran suggest that although little shortening is accommodated across this region, they might still be active, and hence capable of producing earthquakes. Present‐day activity on these faults in central Iran would not be expected from distributions of instrumental and historical earthquakes. Although speculative, the late Tertiary strain distribution described in this paper is consistent with what we know of the present‐day rates of shear in eastern Iran and provides a framework to which later, more detailed, work can be added.