Seismotectonic characteristics of the 2017 Sefid Sang (Mw 6) earthquake

Seismotectonic characteristics of the 2017 Sefid Sang (Mw 6) earthquake

The 5th April 2017 Sefid Sang earthquake rise an opportunity to study the deformation pattern in the SE of the Kopeh Dagh Mountains. Multiple event relocation of the Sefid Sang main shock and its 59 aftershocks shows unidirectional rupture directivity from NW to SE. The focal mechanisms for the mainshock and the two largest aftershocks reveal a mainly reverse mechanism (with average strikes of ~300 and ~70 for fault planes) with a small strike-slip component. The optimal model based on InSAR data indicates a NE- dipping reverse fault, which is consistent with the NE-dipping fault plane of the focal mechanism and the aftershock pattern. To characterize the regional stress state, we performed an extensive field measurement of fault kinematics in the study area. Separate inversion of both geological and seismological fault slip data indicates a similar transpressional stress regime (NNE-oriented compression) for the study area. These results indicate the change in the kinematics of deformation from strike-slip faulting along the main NNW-striking faults (e.g., Bakharden-Quchan fault system) to reverse faulting at their WNW-striking terminations (e.g., Neyshabur fault and southern termination of the Hezar Masjed fault systems).

The 5th April 2017 Sefid Sang earthquake rise an opportunity to study the deformation pattern in the SE of the Kopeh Dagh Mountains. Multiple event relocation of the Sefid Sang main shock and its 59 aftershocks shows unidirectional rupture directivity from NW to SE. The focal mechanisms for the mainshock and the two largest aftershocks reveal a mainly reverse mechanism (with average strikes of ~300 and ~70 for fault planes) with a small strike-slip component. The optimal model based on InSAR data indicates a NE- dipping reverse fault, which is consistent with the NE-dipping fault plane of the focal mechanism and the aftershock pattern. To characterize the regional stress state, we performed an extensive field measurement of fault kinematics in the study area. Separate inversion of both geological and seismological fault slip data indicates a similar transpressional stress regime (NNE-oriented compression) for the study area. These results indicate the change in the kinematics of deformation from strike-slip faulting along the main NNW-striking faults (e.g., Bakharden-Quchan fault system) to reverse faulting at their WNW-striking terminations (e.g., Neyshabur fault and southern termination of the Hezar Masjed fault systems).