The Electrical Resistivity Structure of the Aso Caldera, Japan

概要

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An electrical resistivity model of the Aso caldera was constructed using the magnetotelluric (MT) survey data obtained at 200 sites in the caldera area. The modeling reveals the following results : (1) the high-resistivity basement of Cretaceous rocks beneath the caldera floor slants gradually to the center of the caldera ; (2) the low-resistivity layers, of less than 50 ohm-m, are found commonly around the sea level beneath the caldera ; and (3) the majority of these low-resistivity layers are distributed along the ring-like belt surrounding the high-resistivity central cone. The most likely cause of the low-resistivity value at deep layers in the Aso caldera is high water content in high porosity rocks such as tuff and tuff breccia. As the Aso caldera was formed by violent eruptions of pyroclastic flow, these low-resistivity layers are interpreted as the "fall-back" materials in the caldera formation process. Therefore, this modeling result implies that the Aso caldera is the "funnel-shaped type" one formed by the pyroclastic volcanism.
特定非営利活動法人日本火山学会の論文
1998-03-06