Physics-based probabilistic seismic hazard analysis: the case of Tehran Basin in Iran

Seismic hazard estimation relies on Ground Motion Prediction Equations (GMPEs) giving the expected motion level as a function of several parameters characterizing the source and the sites of interest. However, in regions like Greater Tehran metropolitan area located in the Alborz seismotectonic province, northern Iran records of moderate to large earthquakes at short distances from the faults are still few and most local and regional GMPEs are poorly constrained at short ranges. In other words, data may only partially account for the rupture process, seismic wave propagation, and three-dimensional complex configurations (i.e., Tehran Basin in this case). Here, to investigate the capabilities of physics-based methods, two sets of 3-D numerical simulations of possible earthquakes scenarios in Tehran region along two predominate sources are carried out through the finite difference approach for low frequency motions. Then the stochastic finite fault method is used for quantifying ground motion values at higher frequencies. At last, the combined broadband simulation results are used in a probabilistic seismic hazard analysis. The seismic hazard results show the combined effects of the site and basin, and give a high-resolution representation of the hazard in the near field of active earthquake faults in the Tehran Basin, particularly over long periods. This representation is anticipated to be more accurate than those based simply on empirical GMPEs. It should be noted that effects of other less important surrounding faults are not included in the hazard analysis due to lack of sufficient data and computational limitations.