The 1707 M_w8.7 Hoei earthquake triggered the largest historical eruption of Mt. Fuji

Studies in magma-tectonics point to a spatiotemporal correlation between earthquakes and volcanic eruptions. Here, we examine the correlation between two great Japanese earthquakes, the 1703 M_w 8.2 Genroku and 1707 M _w 8.7 Hoei, and Mt. Fuji's explosive (VEI 5) Hoei eruption, 49 days after the 1707 earthquake. We model the static stress changes and dilatational strain imparted on the Mt. Fuji magmatic system due to each earthquake to determine if these mechanisms enhanced the potential for eruption. Our results show that both earthquakes clamped the dike from 8 km to the surface and compressed magma chambers at 8 km and 20 km depths. The 1707 earthquake decreased the normal stress on the dike at 20 km, the proposed depth of a basaltic magma chamber, by 1.06 bars (0.106 MPa). We hypothesize that the stress change and strain generated by the 1707 earthquake triggered the eruption of Mt. Fuji by permitting opening of the dike and ascent of basaltic magma from 20 km into andesitic and dacitic magma chambers located at 8 km depth. The injection of basaltic magma into the more evolved magmatic system induced magma mixing and a Plinian eruption ensued.