Spatial variation of b-value, creep rate, and seismic moment release along Chaman fault system

摘要

The current study analyses the earthquake catalog of Southern Pakistan from 1973 to 2016. The magnitude of completeness (M_c) is 4.9. The b-value and seismic moment release of the Chaman fault system have been calculated and compared with slip rates. The results demonstrate that both seismic moment releases and b-value estimation are consistent with the geodetic slip rates inferred from the InSAR (i.e., lower moment release and higher b-value were estimated on the creep section of the Chaman fault system). The b-value is estimated approximately 1.2 in the northern (i.e., >200 km) and southern (i.e., between 25 and 100 km) portions of Ghazaband fault, which likely depicts the partially creep sections and could not generate large earthquakes. Similarly, the southern Ornach-Nal fault section between 25 and 100 km shows higher b-value (> 1.5), which reflects the creeping nature of the fault. b-value are varied from 0.65 to 1.0 in the region where historic large earthquakes occurred, whereas the b-value is estimated 1.68 for the partial creep section between 110 and 140 km and 2.0 for the creeping section between 210 and 310 km of the Chaman fault.Moreover, b-value of 0.7–1.0 has been found for the central section of both Ornach-Nal and Ghazaband faults. Results reveal that Chaman fault system is likely to host large earthquakes on the section of the faults, which estimate b-value in the range 0.65–1.1 and moderate size earthquakes where b-value is estimated between 1.1 and 1.5. Moreover, faults, which estimate b-value >1.5, are most likely the safe regions from moderate to large earthquakes. In short, estimated b-value clearly depicts the mechanical properties of fault, so that combination of mechanics of fault from geodetic studies and estimated b-value from homogenized earthquake catalog improve the earthquake forecasting models.