**Abstract**

Identification of the fault plane of earthquakes can be a critical contribution of seismology to regional tectonic studies and assessment of expected deformation and damage patterns. A fundamental ambiguity in the representation of an earthquake with a focal mechanism is to recognize the causative fault plane accommodating the slip during the event among the two nodal planes. The Coulomb static stress has been commonly used to determine the stress distribution induced by an event. However, for the first time in this research, the Coulomb regional stress was resolved on nodal planes to realize the optimally oriented plane for failure having maximum Coulomb stress on which the regional stress triggers an event. The method has been conducted for the April 5th, 2017 Sefidsang earthquake in NE Iran. The results reveal that the earthquake-triggering fault is a northeast-dipping listric fault with dextral reverse movement. The identified structural aspects subjected to active deformation in the area have crucial implications for seismic hazard assessment of the region and potential future failure areas.

**Keywords:** Coulomb stress change, causative fault geometry, active tectonics, earthquake, aftershock distributions
