Pattern recognition of major asperities using local recurrence time in Alborz Mountains, Northern Iran

Abstract

In this study, seismic data recorded during the period 01/01/1996 to 09/01/2009 has been used to evaluate the seismic hazard potential along the Alborz region, Northern Iran. The technique of mapping local recurrence time, TL, is used to map major asperities, which are considered as the areas with maximum hazard. We calculated TL from a and b values which are in turn derived from the frequency–magnitude relation constants within a radius of 30 km about every corner point of a 10-km spacing grid. Since b value is inversely related to applied stress, the areas with lowest b values and/or shortest TL are interpreted to locate the asperities or the areas of maximum seismic hazard. To test this method, we computed TL map using seismic catalogues before and after the 2004 Baladeh earthquake of Mw 6.2. The local recurrence time map before the earthquake shows anomalously short TL in the epicentral region of the Baladeh earthquake a decade before its occurrence. The TL map after the earthquake indicates that this large event has redistributed the applied stress in the Alborz region. The microseismicity of the region after the Baladeh earthquake, however, suggests that there are two anomalies in TL map positioned in Alborz. The places where these anomalies are observed can be considered as the areas with maximum seismic hazard for future large earthquake in the Alborz region.