Fault Slip rate: Geodetic vs Geologic time scales (Insight from numerical modeling)

Based on the agreement between geodetic and geological plate velocities, interplate fault slip rates are usually considered constant over long periods of time. However, measurements made at different time scales on intracontinental faults suggest that slip rate evolves with time. We examine the slip evolution of a Kazerun fault embedded in an elastic lithosphere loaded by plate motion. Geological and seismic evidence suggests that nearly one half of the convergence between Arbia and Eurasia is accommodated by the crustal deformation in the Zagros. Two competing mechanisms were proposed to describe this accommodation: distributed crustal thickening and localize strain along main faults. The kinematics of Kazerun fault is critical in determining the relative importance of these two mechanisms, in as much as the sliprates predicted by hypotheses of these competing mechanisms are very different. Using a finite element modeling, we construct the elastic-block model with blocks defined by the major strike-slip active faults, and then seek a velocity solution approaching the short and long term kinematics of the Kazerun. The GPS data in the Zagros and neighboring regions are employed as constraint conditions, in successive steps. The inferred average short and long term slip-rate of the Dena and Kazerun is 2.8 mm/yr , 4.8mm/yr and 1.9mm/yr , 2.1mm/yr respectively, with some variation along the fault.