Recurrence Time Distributions of Large Earthquakes in Eastern Iran

Abstract

The eastern part of the Iranian plateau is characterized by large and infrequent earthquakes with recurrence intervals of more than several hundred years. Given that previous observations and paleoseismological studies are insufficient for forecasting large earthquakes, we have developed a physics‐based synthetic seismicity model for the fault system in eastern Iran using the Virtual Quake simulator. The model is independent of the seismic catalogs, however, it is tuned to match available earthquakes records. We show that the modeled seismicity rates and empirical frequency–magnitude distributions are consistent within the uncertainty of the empirical relations. Furthermore, our synthetic catalog agrees with previous paleoseismological investigations. From the resulting catalog, we can obtain the statistical distributions of recurrence times and waiting times for large earthquakes in the region as a whole and for the individual faults. In agreement with previous earthquake simulator studies, we find that the Poisson (time‐independent) distribution best describes the recurrence times of large earthquakes in the region as a whole. Large earthquakes on the individual faults show quasi‐periodic behavior, and for most faults can be well represented by the Weibull distribution. We present the corresponding time‐dependent conditional probabilities for large earthquakes throughout the region and for a few selected individual faults. Long‐term simulations indicate that waiting times for large earthquakes on specific faults are strongly dependent on the fault system configuration. Faults confined by other active faults, or consisting of several segments, host large earthquakes with more distributed recurrence times. Moreover, the obtained long‐term synthetic seismic catalog shows that fault interactions clearly have a major effect on occurrence of large earthquakes, and hence should be taken into account for seismic‐hazard assessment.