MICROSEISMICITY AND SEISMIC STRUCTURE IN CHAHARMAHALE- BAKHTIARY REGION (HIGH ZAGROS, IRAN)

From 2002 April 17 to 2002 June 11, a dense seismological network of 29 stations was installed in the Chahar-Mahale-Bakhtiari province. The data of this temporary network was deployed to investigate mechanism of the deformation around north segment of the Kazerun fault system in the High Zagros that is considered as the internal transition zone in the Zagros. Microearthquake study in this region reveals that convergence between Arabian plate and Central Iran is accommodated by the partitioning. Main Zagros Thrust didn't show any seismic activity during this field study. The zone of the strike slip faults transfers right- lateral motion between Main Recent Fault and Dena fault. Dena fault is the north segment of the Kazerun fault system that separates different deformation regimes in High Zagros region. The events deeper than 16 km have not seen in this study and superficial events are located near strike-slip faults. Seismic structure of the upper crust in this region includes 8 km thick layer over a 6 km thick layer. Receiver function analysis reveals thickening of the crust to ~60 km in south-east of the Main Zagros Thrust. Any variation in depth of the Moho is not observed across Dena Fault which suggests this is a pure strike-slip fault. Higher seismic velocity and the events with shallower depth in compare with central Zagros suggest that the sedimentary layer in this part of the High Zagros is different from that in the Central Zagros and it is more brittle.