Two-decade seismicity of the SE Alborz region, Iran: Relocation of earthquake hypocenters using cross-correlation based time corrections

Abstract

Located on the foothills of Alborz mountains, in northern Iran, the city of Tehran is surrounded by many active faults that have caused destructive earthquakes in the past. Two earthquakes magnitudes 4.1 and 3.6 occurred on 13 th August 2015, known as Javadabad earthquakes, affected the SE Alborz region near Tehran. In this study, we relocated 780 events with magnitude 2.0 and larger that occurred during 1996-2015, which provides an enhanced image of seismicity in the region. We manually re-picked 6845 P-wave and 4675 S-waves arrival times on 41 seismic stations encompassing the SE Alborz regions. We then used our arrival times to relocate the earthquakes using a probabilistic method. Then we focus on improving the picked arrival times by cross-correlating the waveforms of P-and S-waves for event pairs with similar waveforms. The differential times of event pairs for all observations were weighted based on the quality of correlations. We computed more than 220,000 and 140,000 differential times for P-and S-wave records, respectively, and selected pairs of waveforms with coefficients of 0.7 or higher. Finally, in order to minimize the effect of inaccurate velocity structure, we applied the double-difference location method.