AbstractThe Zagros Fold and Thrust Belt (ZFTB) in southern Iran is a seismically active tectonic zone, where SW-vergent thrust faults and NW-SE- and NE-SW-oriented strike-slip fault systems accommodate for crustal shortening, resulting from the active Arabia-Eurasia collision. The majority of earthquakes in Iran occur within the ZFTB, posing a major hazard for the society. The April 9th, 2013, Kaki Earthquake (Mw = 6.3) in the southern part of the ZFTB took place along a fault that was previously unknown, regarding its surface expression, geometry and kinematics. We have used surface-subsurface distributions and focal mechanism solutions of the Kaki Earthquake aftershocks to characterize the fault system responsible for the quake. Our results indicate that it was a NE-vergent thrust fault with a minor dextral component that slipped ∼7 to 17 km at depth, causing the Kaki Earthquake. There were no surface ruptures, although some surface fissures developed in fluvial terraces during the main shock. We interpret this fault as a blind backthrust, which likely represents a reactivated Mesozoic basement fault, emanating from the Zagros detachment surface. An upper shallow décollement zone within the Miocene Gachsaran Salt facilitated its upward propagation on the back-limb of an overturned syncline.
Seismicity and the State of Stress in the Dezful Embayment, Zagros Fold and Thrust Belt