Absolute gravity change associated with magma mass movement in the conduit of Asama Volcano (Central Japan), revealed by physical modeling of hydrological gravity disturbances
Absolute gravity change associated with magma mass movement in the conduit of Asama Volcano (Central Japan), revealed by physical modeling of hydrological gravity disturbances
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DOI：
10.1002/2014jb011563
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发表时间：
2015-02
期刊：
影响因子：
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通讯作者：
T. Kazama;S. Okubo;T. Sugano;S. Matsumoto;Wenke Sun;Yoshiyuki Tanaka;E. Koyama
中科院分区：
文献类型：
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作者：
T. Kazama;S. Okubo;T. Sugano;S. Matsumoto;Wenke Sun;Yoshiyuki Tanaka;E. Koyama
利用三维水文模型，从2004年浅间火山（日本中部）水文扰动的绝对重力数据中反演了火山管道中岩浆块运动产生的重力信号。我们使用现实的土壤参数和边界条件改进了先前研究的水文模型，以更好地估计时空陆水分布和随之而来的水文重力扰动。新估算的重力扰动与2004-2009年FG 5重力仪观测到的绝对重力值一致，误差约为2.6 μGal，额外考虑了与排泄区下方倾斜的不透水表面相关的地下水质量过量排泄。从2004年火山喷发期间的绝对重力观测数据中扣除20 μGal振幅的重力扰动后，5 μGal振幅的重力残差与火山喷发同步显著减小，这是因为通道中上升的岩浆块体影响了对安装在浅间火山侧翼的重力仪的向上吸引力。假设导管中的线密度均匀，将剩余重力转换成的岩浆头高度与其他火山观测结果（如气体排放率和地震频率）中的岩浆头时间变化完全一致。通过使用该水文模型和同时获得的真实的气象数据校正水文重力扰动，可以在浅间火山即时监测岩浆团的时空变化，甚至在未来的火山事件爆发之前。
The gravity signal originating from magma mass movement in a volcanic conduit is retrieved from the hydrologically disturbed absolute gravity data obtained at Asama Volcano (Central Japan) in 2004, using a three‐dimensional hydrological model. We improve the hydrological model of the previous study using realistic soil parameters and boundary conditions, to better estimate the spatiotemporal land‐water distributions and the consequent hydrological gravity disturbances. The newly estimated gravity disturbances agree with the absolute gravity values observed by FG5 gravimeters in 2004–2009 within about 2.6 μGal, by additionally accounting for the excess discharge of groundwater mass associated with a sloping impermeable surface below the discharge area. After the gravity disturbance of 20 μGal amplitude is subtracted from the absolute gravity data observed during the 2004 eruptive event, the gravity residual of 5 μGal amplitude shows a significant decrease in synchronization with eruptions, because the ascending magma mass in the conduit affects the upward attraction force to the gravimeters installed on the flank of Asama Volcano. The magma head altitude, to which the residual gravity is converted assuming a homogeneous linear density in the conduit, shows a comprehensive agreement of the time variation in the magma head with those in other volcanic observations, such as gas emission rate and earthquake frequency. By correcting the hydrological gravity disturbances using this hydrological model and simultaneously obtained meteorological data in real time, spatiotemporal variations in the magma mass can be instantaneously monitored at Asama Volcano, even before eruptions during future volcanic events.