Probabilistic seismic hazard assessment for 8 densely-populated cities of Iran

In this study, we used the recent comprehensive earthquake catalogue of Mousavi-Bafrouei and Babaie Mahani (2020), including historical and instrumental earthquakes until the end of 2018, to calculate Probabilistic Seismic Hazard Assessment (PSHA) at eight metropolitans with a population of more than 1 million. These metropolitans include Ahvaz, Isfahan, Karaj, Mashhad, Qom, Shiraz, Tabriz, and Tehran. Our approach was implemented using a MATLAB code that was compiled for the purpose of this study. The historical seismicity within a 300-km radius was considered around each city, and the seismicity parameters were obtained in each case. We provided the hazard curve and uniform hazard spectrum for peak ground acceleration (PGA) and pseudo-response spectral acceleration (PSA) at periods of 0.04, 0.1, 0.2, 0.3, 1.0, and 3.0 sec for the return periods of 50, 475, and 2475 years, respectively. For hazard calculations, we used four ground motion prediction equations with equal weights; Boor et al. (2014), Idriss (2014), Kale et al. (2015), and Farajpour et al. (2019). Our PSHA results show that the highest hazard occurs in the cities of Shiraz and Tabriz, whereas the lowest hazard level happens in the city of Isfahan. Specifically, the largest PGA values at the bedrock ( = 760 m/sec) condition and for the return periods of 50, 475, and 2475 years are 77 cm/sec2 (Shiraz and Tabriz), 203 cm/sec2 (Shiraz and Tabriz), and 535 cm/sec2 (Tabriz), respectively. On the other hand, the smallest PGA values for the same return periods occur for the city of Isfahan at 29 cm/sec2, 77 cm/sec2, and 125 cm/sec2. We also compared our results with other PSHA studies obtained by other researchers, including Mousavi Befrouei et al. (2014), Salahshour et al. (2018), and Shahbazi and Mansouri (2019). In general, we found that our results show lower values in terms of ground motion amplitudes. For example, Mousavi-Bafrouei et al. (1393) obtained higher values by up to ~30% than those obtained in this study. This difference is probably due to the inclusion of different datasets for source characterization and calculation of seismicity parameters. In the approach used in this study and the works of Salahshour et al. (2018) and Shahbazi and Mansouri (2019), historical seismicity is the only source of information for the determination of seismic sources and their parameters, which resulted in similar ground motion values. However, Mousavi Befroui et al. (2014) used geological, geophysical, and seismotectonic evidence along with historical seismicity for source characterization.