AFTERSHOCK PROBABILISTIC SEISMIC HAZARD ANALYSIS OF THE SARPOL-E ZAHAB EARTHQUAKE OF NOVEMBER12,2017

Aftershock seismic hazard analysis plays an essential role in search, rescue, evaluation and repair of damaged structures and reoccupation after a severe mainshock. For this sake, several methods have been developed over the past years. During recent years, two practical methods have been proposed, one by Wiemer et al. (2002) and one by Yeo and Cornell (2005) known as APSHA1. In this paper, we have derived the seismicity parameters (a and b), the modified Omori law parameters (a, p, k) and also their temporal changes for the Sarpol-e Zahab earthquake of November 12, 2017 which struck the western Kermanshah province and led to a great financial loss and fatalities. The affected region also experienced numerous aftershocks which some of them were strong and caused various problems. Implementing the obtained parameters in both aforementioned methods, aftershocks hazard maps were developed for 33% exceedance probability within three short time periods (second 15, 30 and 60 days after the mainshock) and one long time period (days 60 to 270) after the mainshock. In order to improve the accuracy of the results, utilizing the available aftershocks’ local data, a simple local attenuation relation appropriate for aftershocks was developed. Finally, the computed maps have been compared with the real recorded accelerations in the region. It was observed that the seismicity parameters and the Omori law parameters varied over time. This is demonstrated that in our case, the method proposed by Yeo and Cornell (2005) matches the reality better. Moreover, within the long time period, a conspicuous underestimation in the Tazeh Abad station is observed. However, in both methods, the considered long time period, possesses hazard values remarkably higher than the short time periods which can be due to the long length of the considered time period and neglecting the temporal variation of the seismicity parameters.

Keywords:

Aftershocks , Seismic hazard analysis , Omori law , Hazard maps , Sarpol-e Zahab earthquake