The November 12,2017 Kermanshah earthquake is the greatest seismic event (Mw 7.3) in the folded Zagros belt presenting both dynamic and kinematic significance. The present study focuses on the kinematic compatibility of this major event with the regional stress regime prevailing in the Zagros. We have combined geological information on the mechanical behavior of the basement and sedimentary cover with kinematic data obtained from focal mechanism of earthquakes have occurred in North Zagros. The inversion analysis of the fault slip data with well know depths and locating indicate that seismic deformation in the upper brittle crust in consistent with a homogenous regional transpressional tectonic regime under an under an andersonian stress condition, despite the presence of several decoupling/ decollement main shock (Mw 7,3) which occurred on a near horizontal basement detachment cannot be explained by the regional tectonic regime. Our study shows that the main thrust earthquake and other similar smaller event resulted from ship on decollement/decoupling surfaces at different depths controlled by a secondary non-andersonian stress regime different from the regional tectonic regime. In fact, the Main Resent Fault plays the role of “Backstop” agaist underthrusting of the Arabian upper crust beneath the Central Iranian micro- continent. It produces a “Piston effect” due which shortening of the upper most part of the Zagros basement along with the overlaying sedimentary cover occurs through slipping on sub-horizontal detachment horizons that usually cannot be reactivated under tectonic stress with a horizontal maximum stress axis (σ_1).