著者
並木 敦子 Rivalta Eleonora Woith Heiko Walter Thomas
出版者
日本地球惑星科学連合
雑誌
日本地球惑星科学連合2016年大会
巻号頁・発行日
2016-03-10

Large earthquakes sometimes activate volcanoes both in the near field as well as in the far field. One possible explanation is that shaking may increase the mobility of the volcanic gases stored in magma reservoirs and conduits. Here experimentally and theoretically we investigate how sloshing, the oscillatory motion of fluids contained in a shaking tank, may affect the presence and stability of bubbles and foams, with important implications for magma conduits and reservoirs. We adopt this concept from engineering: severe earthquakes are known to induce sloshing and damage petroleum tanks. Sloshing occurs in a partially filled tank or a fully filled tank with density-stratified fluids. These conditions are met at open summit conduits or at sealed magma reservoirs where a bubbly magma layer overlays a newly injected denser magma layer. We conducted sloshing experiments by shaking a rectangular tank partially filled with liquids, bubbly fluids (foams) and fully filled with density-stratified fluids; i.e., a foam layer overlying a liquid layer. In experiments with foams, we found that foam collapse occurs for oscillations near the resonance frequency of the fluid layer. Low viscosity and large bubble size favor foam collapse during sloshing. In the layered case, the collapsed foam mixes with the underlying liquid layer. Based on scaling considerations, we constrained the conditions for the occurrence of foam collapse in natural magma reservoirs. We find that seismic waves with lower frequencies 0.5 m. Strong ground motion > 0.1 m/s can excite sloshing with sufficient amplitude to collapse a magma foam in an open conduit or a foam overlying basaltic magma in a closed magma reservoir. The gas released from the collapsed foam may in filtrate the rock or diffuse through pores, enhancing heat transfer, or may generate a gas slug to cause a magmatic eruption. The overturn in the magma reservoir provides new nucleation sites which may help to prepare a following/delayed eruption. Mt. Fuji erupted 49 days after the large Hoei earthquake (1707) both dacitic and basaltic magmas. The eruption might have been triggered by magma mixing through sloshing.

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宝永噴火のスロッシング誘発の話なんだけど、揺らす前にマグマだまりの上部に泡が濃集していることが前提だった。地下深部でそれはないだろと感じたが、元禄地震で発生した泡が4年後の宝永地震までに浮き上がっていたかもと思い始めたところ。https://t.co/yKzB6Da3Tk
日本地球惑星科学連合2016年大会/富士宝永噴火は宝永地震に伴うスロッシングで起きたと思うと色々説明できる https://t.co/yKzB6Da3Tk
日本地球惑星科学連合2016年大会/富士宝永噴火は宝永地震に伴うスロッシングで起きたと思うと色々説明できる https://t.co/yKzB6Da3Tk ほう

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