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

为了建立伊豆大岛火山顶沟岩浆上升过程的物理模型，在伊豆大岛火山顶沟周围建立了基于局域网的微重力和电磁观测一体化系统。主要研究成果如下：1.建立了一个连接绝对重力观测站和山顶连续微重力观测的混合重力观测网。我们在2005年至2007年期间的首脑会议上没有观察到重大的重力变化。分析了降水对山顶附近重力场季节变化的影响，发现重力场的季节变化可以用一个简单的水扩散模型来模拟.为了检测火山口周围电阻率结构的变化，我们在山顶火山口周围建立了ACTIVE（用于成像火山喷发的受控瞬态电磁阵列）观测系统。通过正演模拟证实了ACTIVE系统能够探测到峰顶附近地下电阻率结构的变化，并进一步发展了电阻率结构三维反演方法.为了监测火山口顶下岩浆的喷发过程，在火山口附近设置了土壤CO2浓度连续观测系统，发现火山喷发速率的增加伴随着CO2浓度的阶段性增加。我们将建立伊豆大岛火山管道中岩浆上升机制的物理模型。

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.