Since phreatic eruptions often occur near the surface, it is important to understand the shallow subsurface structure of a volcano to clarify the eruption mechanism. The 2015 phreatic eruption at Owakudani, Hakone Volcano, Japan, was preceded by localized uplift and intensified steam activity. However, the cause of these events is unknown due to a poor understanding of the shallow subsurface structure. We report on a three‐dimensional resistivity structure inferred from dense audio‐frequency magnetotelluric surveys conducted in Owakudani that revealed a ∼100‐m thick conductive layer at the surface underlain by a resistive section, at the edge of which eruptions craters were located. This conductive layer is estimated to be a low‐permeability cap layer, because the inflation source prior to the eruption is located beneath it and the ejecta from the eruption was reported to have originated from a depth of 100 m or less.

中文翻译：

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使用高密度音频大地电磁对日本箱根火山大涌谷2015年火山爆发的源区进行成像

由于潜水爆发通常发生在地表附近，因此重要的是了解火山的浅层地下结构，以阐明喷发机制。在日本箱根火山大涌谷2015年潜水爆发之前，局部隆升和蒸汽活动加剧。但是，由于对浅层地下结构的了解不足，因此这些事件的原因尚不清楚。我们报告了在大涌谷进行的密集的音频大地电磁测量得出的三维电阻率结构，该结构揭示了在地下的一个电阻性剖面下约100 m厚的导电层，该火山岩边缘位于火山口的边缘。估计该导电层是低渗透的覆盖层，