The Mosha Fault and Seismicity of South Central Alborz Range, Iran

Field investigation of the western part of the Mosha Fault in several structural sections in the south central Alborz Range showed that the fault has a high angle of dip to the north. Study of the kinematics of the Mosha Fault in this area, based on S–C fabric and microstructures, demonstrates that it is a deepseated semi-ductile thrust. The Mosha Fault is associated with a large hangingwall anticline, cored by Precambrian rocks, and series of footwall synclines, formed of late Tertiary rocks. This geometry, together with several low angle short-cut thrusts in the fault footwall, implies that the Mosha Fault is an inverted normal fault which has been reactivated since the late Tertiary. In the study area, the reverse fault mechanism was associated with the rapid uplift and igneous activity in the central Alborz Range during the late Tertiary.