The 1707 M8.7 Hoei Earthquake Triggered the Largest Historical Eruption of Mt. Fuji
Abstract
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 Mw8.2 Genroku and the 1707 Mw8.7 Hoei, and Mt. Fuji's explosive (VEI 5) Hoei eruption, which occurred 49 days after the 1707 earthquake. The 1703 earthquake occurred on the Sagami Trough, while the 1707 earthquake spanned the Nankai Trough. 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. In our model, a single vertical dike connects a basaltic magma chamber at a depth of 20 km to an andesitic and dacitic magma chamber at a depth of 8 km and from 8 km to the 1707 eruptive vents. Our results show that the 1703 earthquake increased the normal stress on the dike from 20 km to 8 km and from 8 km to the surface by a maximum of -0.374 MPa and -0.314 MPa, respectively. The 1707 earthquake increased the normal stress on the dike from 20 km to 8 km and from 8 km to the surface by a maximum of -0.346 MPa and -0.986 MPa, respectively. Therefore, both the 1703 and 1707 earthquakes clamped the dike. The 1707 earthquake, however, also decreased the normal stress on the southeastern-most end of the dike at 20 km depth by a maximum of 0.106 MPa, which would have served to partially unclamp it. Both earthquakes produced negative dilatational strain at all magma chamber depths and thus compressed the magma chambers. We conclude that the negative dilatational strain produced by the 1703 earthquake was not sufficient to overcome the clamping of the dike and trigger eruption. We hypothesize instead that the combination of the negative dilatational strain and normal stress change associated with the 1707 earthquake triggered the eruption of Mt. Fuji by permitting opening of the dike at 20 km and ascent of basaltic magma into the 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. We repeated the model for the Mw9.0 11 March 2011 Tohoku-Oki earthquake, which occurred on the Japan trench. We use the USGS finite fault model to model the stress changes. Our results suggest that the Tohoku-Oki earthquake unclamped the dike at all depths by a maximum of 0.105 MPa and imparted positive dilatational strain on all magma chambers. If our model is an accurate representation of the current state of Mt. Fuji's magmatic system, and if our results do describe the qualitative method of eruption triggering for Mt. Fuji (i.e. decreasing normal stress on the dike combined with compression of the magma chambers), then we suggest that the 2011 earthquake will not trigger an eruption of Mt. Fuji. These results indicate a correlation between eruption triggering and the relative orientations of the magmatic system and earthquake fault planes.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2012
- Bibcode:
- 2012AGUFMNH11A1547C
- Keywords:
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- 8168 TECTONOPHYSICS / Stresses: general;
- 4302 NATURAL HAZARDS / Geological;
- 4316 NATURAL HAZARDS / Physical modeling