Seismicity and return period investigation of destructive earthquake in Makran subduction zone

Abstract This work uses the frequency-magnitude relation for the earthquakes to analyze seismicity and return period for the earthquakes in Makran subduction and its adjacent region. The data for seismicity analysis and return period range from 1934 to 2022, with moment magnitude and depth ranging from 4.0 to 8.1 and 0 to 115 km. The b-values for eastern and western Makran are obtained by the maximum likelihood technique of 0.7 ± 0.04 and 0.764 ± 0.04, respectively. The temporal decrease of the b-value of the eastern and western vicinities of Makran suggests that stress levels in both regions are increasing, indicating potential big earthquakes may occur subsequentially. Similarly, the spatial variation of the b-value also suggests that stress in both areas is increasing. Notably, the change in the b-value is inversely proportional to the stress level in the region. If the stress level increases, the b-value decreases, and vice versa. The earthquake return periods with magnitude 5 and 5.5 vary from 1 to 2.7 and 2 to 8 years, and magnitude 6 and 6.5 vary from 5 to 30 and 10 to 60 years, respectively. The earthquake return periods with magnitude 7 and 7.5 vary from 20 to 120 and 50 to 300 years, and magnitude 8 and 8.5 range from 100 to 600 and 200 to 1200 years, respectively. The finding demonstrates that both the eastern and western vicinities of the Makran fault zone have high tectonic stress, and significant big earthquakes may occur in the future.