Study of magma ascent mechanism in conduit based on continuous microgravity and electromagnetic observation

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In order to construct a physical model of magma ascent process in the summit conduit of Izu-oshima volcano, we established a LAN-based integrated system for microgravity and electromagnetic observation around the summit area. We obtained the following results as shown below.1.We established a hybrid gravity observation network connecting absolute gravity measurement stations and a continuous microgravity observation at the summit. We observed no significant gravity changes at the summit during the period from 2005 to 2007. Analyzing the effect of precipitation on the seasonal gravity variations observed around the summit, we found that the seasonal variations could be modeled by a simple hydraulic diffusion of rainfall.2. To detect changes in the electrical resistivity structure around the crater, we established the ACTIVE (Array of Controlled Transient-electromagnetics for Imaging Volcanic Edifice) observation system around the summit crater. We confirmed by a forward simulation that the ACTIVE system could detect changes in the subsurface resistivity structure around the summit, and further developed a method of 3-D inversion of resistivity structure.3. In order to monitor the degassing of magma accumulating beneath the summit caldera, we installed a continuous soil CO2 concentration observation system near the summit crater, and found that episodic increases in CO2 concentration were accompanied by the increased rates of volcano inflation.Based on the results of integrated monitoring of magma ascent, accumulation and degassing, we will construct a physical model of magma ascent mechanism in the conduit of Izu-Oshima volcano.