Spatial and temporal changes of b-value, fractal analysis and stress tensor inversion in the Sistan and Makran zones, Eastern and Southeastern Iran

The Sistan and Makran zones have always been seismically active based on all available geological, geophysical, tectonic and earthquake data. We have assessed the seismic activity in these two zones utilizing available earthquake catalogs. The focal depth, frequency and magnitude of earthquakes are greater in the Makran zone than those in the Sistan. A decrease in the ratio of b -value to time after 2018 in both zones indicates an increase in stress, suggesting the potential occurrence of a significant earthquake in the future. Furthermore, the spatial variation of the b -value demonstrates that the western part of Makran has experienced less stress than the eastern part. While in the Sistan Suture Zone, the middle part has undergone more stress than the north and south. The bvalues obtained for the Sistan and Makran are 0.535 +/- 0.05 and 0.606 +/- 0.06, and the fractal dimensions for these zones are 1.66 +/- 0.03 and 1.78 +/- 0.05, respectively. The results of stress tensor inversion depict that faulting in the Sistan Suture Zone are of strike -slip and inverse types, and the direction of maximum horizontal stress is NE -SW. A variety of faults can be observed throughout the Makran zone, including normal, strike -slip, and inverse faults. The maximum horizontal stress direction changes from NE -SW in the western part to almost EW in the middle part, and by moving eastward the E -W direction changes to NE -SW. This is due to the imposed stresses from the Arabia -Eurasia collision zone in the west, the India -Eurasia collision zone in the east and the northward Makran subduction.