Combined approach to estimate the depth of the magma surface in a shallow conduit at Aso volcano, Japan
Combined approach to estimate the depth of the magma surface in a shallow conduit at Aso volcano, Japan
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DOI：
10.1186/s40623-021-01523-z
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发表时间：
2021-10-18
影响因子：
3
通讯作者：
Yokoo, Akihiko
中科院分区：
文献类型：
--
作者：
Ishii, Kyoka;Yokoo, Akihiko
开放式火山提供了执行各种观察方法的机会，可用于研究浅层管道系统。管道浅部的岩浆-空气界面的深度可以作为露天火山火山活动的指标。尽管有许多方法用于估计深度，但由于其他未知参数，大多数方法都无法将深度限制在较窄的范围内。为了更准确地约束深度，我们结合了两种常用的估计岩浆-空气界面深度的方法。他们考虑了爆炸的地震信号和次声信号之间的声共振频率和到达时间延迟。两种方法都有相同的未知参数：岩浆-空气界面的深度和喷口内的声速。因此，这些未知数受到限制，以便可以同时解释观察到的谐振频率和时间延迟。我们使用2015年在日本阿苏火山附近记录的Strombolian爆炸的地震声学数据。估计深度和声速分别为40-200 m和300-680 m/s。深度范围比之前仅使用到达时间延迟的研究要窄。然而，只有少量观测数据可用于估计，因为其余数据无法提供真实的深度或声速。特别是，观察到的时间延迟数据的广泛分布无法通过我们的简单假设来解释。通过考虑更复杂的爆炸环境，例如分布在管道内熔岩池整个表面的爆炸源位置，大部分观测数据都可以用于估计。这表明控制观察到的时间延迟的因素并不像通常预期的那么简单。图文摘要
Open-vent volcanoes provide opportunities to perform various methods of observation that can be used to study shallow plumbing systems. The depth of the magma-air interface in the shallow portion of the conduit can be used as an indicator of the volcanic activity of open-vent volcanoes. Although there are many methods used to estimate the depth, most of them cannot constrain the depth to a narrow range due to other unknown parameters. To constrain the depth more accurately, we combine two methods commonly used for estimating the depth of the magma-air interface. They consider the acoustic resonant frequency and the time delay of arrivals between the seismic and infrasound signals of explosions. Both methods have the same unknown parameters: the depth of the magma-air interface and the sound velocity inside the vent. Therefore, these unknowns are constrained so that both the observed resonant frequency and time delay can be explained simultaneously. We use seismo-acoustic data of Strombolian explosions recorded in the vicinity of Aso volcano, Japan, in 2015. The estimated depths and the sound velocities are 40-200 m and 300-680 m/s, respectively. The depth range is narrower than that of a previous study using only the time delay of arrivals. However, only a small amount of the observed data can be used for the estimation, as the rest of the data cannot provide realistic depths or sound velocities. In particular, a wide distribution of the observed time delay data cannot be explained by our simple assumptions. By considering a more complicated environment of explosions, such as source positions of explosions distributed across the whole surface of a lava pond in the conduit, most of the observed data can be used for estimation. This suggests that the factor controlling the observed time delay is not as simple as generally expected. Graphic abstract