Stress state of the central part of the Zagros Foreland Folded Belt, Iran

English Abstract:

NW-SE trending of the Zagros Foreland Folded Belt (ZFFB) developed during Mio-Pliocene Arabia-Eurasia convergence. Tectonic convergence is still ongoing and intense seismicity in the ZFFB. Our study area covers the Eastern Zagros (Fars area) with significant set of nearly N-S trending right-lateral strike-slip and several NW-SE trending thrust faults. These lateral fault zones play a major kinematic role by matching the change in shortening state through the study area. Multiple detachment levels (e.g. Hormuz Salt) allow decoupling of deformation between the basement and the cover. Such decoupling of deformation controls the stress conditions between different units within the cover sequence and the brittle crust. In order to reconstruct the paleo and recent stress conditions, we analyzed fault slip and focal mechanism data sets using stress inversion method. Our results show the compressional regimes from Miocene to recent with an anticlockwise change in the direction of main compression stress through time, consistent with variation in Arabia–Eurasia convergent path. Based upon the evidence of pre-syn-folding stage of faulting, it suggests a general NE-SW trending of σ1 axis with no significant change in long term seismicity through the study area. On the other side, the inversion of earthquake focal mechanism shows NNE to N-S compression with a low ratio between differential stresses. It suggest that not only the shortening within the thick sedimentary cover of the Zagros (~12 km) completely decouples from the brittle crust deformation, but our results also mention to a possible non-completely-aligned decoupling due to the obliquity of the shortening directions in the sedimentary cover with respect to the basement.