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首页> 外文期刊>Journal of Volcanology and Geothermal Research >Fluid dynamics inside a 'wet' volcano inferred from the complex frequencies of long-period (LP) events: An example from Papandayan volcano, West Java, Indonesia, during the 2011 seismic unrest
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Fluid dynamics inside a 'wet' volcano inferred from the complex frequencies of long-period (LP) events: An example from Papandayan volcano, West Java, Indonesia, during the 2011 seismic unrest

机译：从长周期（LP）事件的复杂频率推断出“湿”火山内部的流体动力学：以印度尼西亚西爪哇省的帕潘达延火山为例，该地震发生于2011年地震动荡期间

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We present results of our study aimed at understanding the dynamics of fluids inside a "wet" volcano through the analysis of swarms of long-period (LP) events accompanying the 2011 seismic unrest at Papandayan volcano, West Java, Indonesia. Prior to this unrest, we measured an extremely high percentage (100%) of CO2 in the ground at the summit crater, however with a very low value of SO2 flux (similar to 6 tons/day). Increase in volcanic activity was also observed from the records of a tiltmeter. A long-term inflation was followed by an abrupt deflation that took place concurrently with the swarms of LP events. Thereafter, swarms of local-tectonic (LT) and volcano-tectonic (VT) earthquakes started. We focus here on analyzing the LP events in the following manner. First, we estimate the source location of LP events by applying a 3-D non-linear hypocenter localization algorithm which includes topography. We then study the waveforms and spectral characteristics of LP events recorded at different stations and investigate whether or not these characteristics are due to source effects. Subsequently, we compute the oscillation frequencies (f) and the decay characteristics (Q factor) in the complex frequency domain of the coda part of the LP events by using the Sompi method which is based on a homogeneous auto-regressive (AR) equation. The rectangular fluid-filled crack model is used to estimate the physical processes related to the observed temporal variations in the complex frequencies. We divide the swarms of LP events into two intervals. The first interval occurred between June and July 2011 (48 LP events), while the second interval extended from September to October 2011 (36 LP events). The frequencies of LP events observed during these intervals range between 1.1 and 6.2 Hz while the Q factors are widely scattered between 20 and 400. We estimate the compositions of fluids inside the crack during both intervals as either water foam (mixtures of water and H2O gas/steam) or misty gas (mixtures of water droplets and H2O gas/steam). We finally suggest that if an eruption were to have taken place following the 2011 unrest it would have been in phreatic style rather than magmatic style. The results of our study therefore contribute to the effort in the prediction of the behavior of future eruptions, and to volcanic hazards assessment and therefore to volcanic risk mitigation. (C) 2014 Elsevier B.V. All rights reserved.
机译：我们目前的研究结果旨在通过分析2011年印度尼西亚西爪哇省帕潘达延火山发生的地震动乱后伴随的长周期（LP）事件群的分析来了解“湿”火山中的流体动力学。在发生这种动荡之前，我们在山顶火山口测出的地面中的二氧化碳含量非常高（100％），但二氧化硫通量却非常低（约6吨/天）。从倾斜仪的记录还可以观察到火山活动的增加。长期的通货紧随其后的是突然的通货紧缩，这与LP事件蜂拥而至。此后，大量的局部构造（LT）和火山构造（VT）地震开始了。我们在这里集中于通过以下方式分析LP事件。首先，我们通过应用包含地形的3-D非线性震源定位算法来估计LP事件的源位置。然后，我们研究在不同台站记录的LP事件的波形和频谱特征，并研究这些特征是否是源效应造成的。随后，我们使用基于均匀自回归（AR）方程的Sompi方法，计算LP事件尾声部分的复频域中的振荡频率（f）和衰减特性（Q因子）。矩形的充满流体的裂缝模型用于估计与复杂频率中观察到的时间变化有关的物理过程。我们将LP事件群分为两个间隔。第一个间隔发生在2011年6月至2011年7月之间（48个LP事件），而第二个间隔从2011年9月扩展到2011年10月（36个LP事件）。在这些时间间隔内观察到的LP事件的频率范围为1.1至6.2 Hz，而Q因子则广泛分布在20至400之间。我们估计在两个时间间隔内裂缝内部的流体成分均为水泡沫（水和H2O气体的混合物） /蒸汽）或有雾的气体（水滴和H2O气体/蒸汽的混合物）。我们最后建议，如果要在2011年动乱后发生喷发，那将是潜水式而不是岩浆式。因此，我们的研究结果有助于预测未来喷发的行为，并有助于评估火山爆发的危害，从而有助于减轻火山爆发的风险。 （C）2014 Elsevier B.V.保留所有权利。

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