Abstract

The 8 September 2017 Mw 8.2 Tehuantepec, Mexico earthquake was the second largest normal‐faulting earthquake to occur in a shallow subduction environment since 1976 (GCMT catalog), and the earthquake sequence featured an extremely long‐lasting and productive aftershock activity that deviated from typical intraslab earthquakes. Here we relocated the early aftershocks within 5 days following the mainshock and investigated the source process of the mainshock using back‐projection and finite fault inversion methods. Our results showed that the earthquake rupture propagated along a ∼150‐km‐long, NW‐striking normal fault. After rupturing approximately 100 km, it triggered activity on a ∼40‐km‐long fault located ∼50 km to the northeast. We employed a stochastic branching model to isolate the background seismicity rate, and compared this rate to those of five other earthquakes of similar magnitudes. The results indicated that the background seismicity of the Mexico event occurred at a much higher rate than those of the other five representative earthquakes. Considering that the rupture planes showed similar dip angles and strikes to those of the outer‐rise normal faults, we suggest that the ruptures of the Mw 8.2 earthquake are possibly the reactivation of hydrated outer‐rise normal faults in the subducting slab.