An intraslab earthquake at a depth of 100 km in the subducting Cocos plate beneath Nevado de Toluca volcano

Seismicity in the subducted Cocos plate below central Mexico, defined by moderate and large earthquakes, ceases well before reaching the active volcanic front. No intraslab earthquake has been reliably located below Nevado de Toluca and Popocatepetl volcanos. Here we report on an M(w)3.3 event at a depth of 98 km, 38 km to the west of Nevado de Toluca. The event provides evidence, for the first time from an earthquake, of subducted slab at a depth of similar to 100 km below the volcano. Recordings of the event also provide evidence of high attenuation of shear waves as they propagate through the mantle-wedge asthenosphere. It is possible that intraslab seismicity beneath active volcanoes in central Mexico at M similar to 3 level is abundant but has not been documented in the past because of poor instrumentation.