Mantle Earthquakes: Deep Quakes Beneath the Moho in the Wyoming Craton

Abstract Deep continental mantle earthquakes that occur below the Moho remain enigmatic because they occur in ductile rock, where earthquakes are not expected. Here, we report seven well-located earthquakes beneath the Moho in central Wyoming, including six previously unreported events, identified using USArray data through deep-learning detection followed by manual review. The mantle earthquakes occurred in regions spatially separated from crustal seismicity. Unlike crustal earthquakes, these mantle earthquakes tend to exhibit simple waveforms generated from the source beneath Moho, without complex multiples or reverberations. Associated faults are favorably oriented to the regional stress and exhibit rupture characteristics similar to those of intraplate crustal earthquakes. The estimated temperature at the hypocenters ranges between 550°C and 900°C, indicating rupture in or near the ductile regime. Two pairs of mantle events formed closely spaced doublets, suggesting episodic stress release at local stress concentrations. These findings are consistent with thermal runaway as a viable rupture mechanism for mantle earthquakes, which may allow failure under ductile conditions. Continued monitoring and investigation of mantle earthquakes in the Wyoming Craton will help better understand earthquake nucleation in the ductile regime.