Variations of the Seismic B-value along the Bitlis-Zagros Belt in Iraq and its Surroundings

The study aims to investigate the temporal and spatial variations of b-value and its relationship to focal depth and faulting style along the Bitlis-Zagros Belt in Iraq and its surroundings. The earthquake source in this study was extracted from the earthquake catalogue, which updated by the Seismological Laboratory of the University of Basrah for the period from 1 January 1980 to 31 December 2019, that includes 7066 earthquakes that occurred between the latitudes 31o–38o N and longitudes 41ͦ–49o E. The source of fault plane solutions is the Global Centroid Moment Tensor Catalogue. To study the temporal and spatial variations of the b-value, the earthquake catalogue was divided into several time windows (decade, year and month) into different study zones. Dependence of b-value on the focal depth was studied in each selected zone and the dependence on faulting style was also studied for the entire study area. The regression analysis method was used to calculate the b-value. It is relatively stable and does exhibit neither substantial long-term changes nor changes much over the study region. A significant statistical decrease of b-value between 0 and 35 km depth can be observed. The strike-slip, normal and reverse faulting earthquakes have low, intermediate and high b-value, respectively. The high b-value for the reverse focal mechanism in Bitlis-Zagros Belt that compared with the normal focal mechanism and the strike-slip mechanism can be explained by the higher ratio between large and small earthquakes.