Fault-kinematic and stress state investigation using focal mechanism solution along the Mosha fault, Alborz Mountain: implication for changing stress tectonic regime

Investigation of historical and instrumental seismicity and fault kinematics of major faults are used to deduce the stress state in the northeast of Greater Tehran. In the present study, we have identified the Mw 5.1 earthquake and its related aftershocks in northeast Tehran that occurred on May 7, 2020. In this regard, after combining the waveforms of seismograms recorded in the seismic stations of Tehran and neighbouring provinces, the location, magnitude, and exact time of occurrence of the main shock and its six aftershocks have been calculated. Then, using three methods, including waveform modelling, P wave polarity and the ratio of P and S wave amplitudes, the focal mechanism of the fault causing seismic events is estimated. Fault kinematic study and the epicenter of the seismic event and related aftershocks suggest that the Mosha fault could be responsible for the event. Furthermore, the regional tectonic stress field has been calculated by focal mechanism inversion. Comparisons between stress field orientations and stress ratio provide new information on the local stress field. The variation of the stress ratio in the lower and upper crust is considerably high, demonstrating an inhomogeneity of deformation related to the Mosha fault.