Long term fault slip rates, distributed deformation rates and forecast of seismicity in the Iranian Plateau

Abstract

In this paper, the long-term crustal flow of the Iranian Plateau is computed using a kinematic finite-element model (NeoKinema software). Based on the iterated weighted least squares method, the models are fitted to the newest data set of Iran including updated fault traces, geologic fault offset rates, geodetic benchmark velocities, principal stress directions, and velocity boundary conditions. We are successful to find the best kinematic model, in which geological slip rates, geodetic velocities, and interpolated stress directions are fitted at levels of 0.35, 1.0, and 1.0 datum standard deviation, respectively. The best fitted model, for the first time, provides long-term fault slip rates, velocity, and anelastic strain rate field in the Iranian Plateau from all available kinematic data. In order to verify the model, the estimates of fault slip rates are compared to slip rates from merely analyzing geodetic benchmark velocities or paleoseismological studies or published geological rates which have not been used in the model. Our estimated rates are all in the range of geodetic rates and are even more consistent with geological rates than previous GPS-based estimates. Using the selected model, long-term average seismicity maps and long-term moment rates are produced on the basis of the SHIFT hypothesis and previous global calibrations. Our kinematic model also provides a new constraint on ratio of seismic deformation to total deformation for different seismic zones of Iran. The resulting slip rates and the proposed seismic fraction of deformation provide the necessary input data for future time-dependent hazard studies in Iran. Moreover, spatial distribution and total number of strong (M > 6) and major (M > 7) earthquakes, which dominate the seismic hazard, are all compatible with the regional seismic catalog.