Permutation entropy variations in seismic noise before and after eruptive activity at Shinmoedake volcano, Kirishima complex, Japan
Permutation entropy variations in seismic noise before and after eruptive activity at Shinmoedake volcano, Kirishima complex, Japan
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DOI：
10.1186/s40623-022-01729-9
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发表时间：
2022-11-30
影响因子：
3
通讯作者：
Ichihara, M.
中科院分区：
文献类型：
--
作者：
Konstantinou, K. I.;Rahmalia, D. A.;Ichihara, M.
排列熵（PE）是一种复杂性度量，它将时间序列编码为符号序列，并可用于在确定性和随机性行为之间进行破译。本研究调查了日本Shinmoedake火山2011年，2017年和2018年三个喷发周期期间地震噪声的PE变化。该火山由一个专门的地震网络和次声麦克风监测，在上述喷发期间不断记录。使用1-7 Hz的频率范围，以推断地震噪声中PE的时间变化，并最大限度地减少任何人为影响。结果表明，每次出疹前PE值均呈下降趋势。通过将这些结果与其他观测结果相结合，我们可以将PE的减少归因于两个原因：第一，火山震颤的发生是一个确定性的信号，第二，在较浅的深度下的新茂岳可以衰减高频地震波，从而导致较少的随机信号的岩浆迁移。PE也表现出一个尖峰样增加之前的三个爆发的发作。在2011年和2017年，这一特征可能与由于含水层和高温岩浆之间的相互作用而导致的气泡增长和崩溃有关。在2018年，含水层大部分已经蒸发;因此，PE值的飙升可能是由于管道内的凝固岩浆破裂而产生的，因为新鲜岩浆正在向上推动。这些结果表明，PE是一个潜在的有用的工具，监测地震噪声在火山，并有助于预测火山爆发与其他广泛使用的方法。
Permutation entropy (PE) is a complexity metric that encodes a time series into sequences of symbols and can be used to decipher between deterministic and stochastic behavior. This study investigates PE variations in seismic noise during three eruption cycles in 2011, 2017, and 2018 at Shinmoedake volcano, Japan. The volcano is monitored by a dedicated seismic network and by infrasound microphones that recorded continuously during the aforementioned eruptions. The frequency range 1-7 Hz was used in order to infer temporal changes of PE in seismic noise and minimize any human contributions. The results showed that PE values decreased before the occurrence of each eruption. By combining these results with other observations we can attribute this decrease in PE to two reasons: first, to the occurrence of volcanic tremor that is a deterministic signal, and second, to magma migration at shallower depth beneath Shinmoedake which can attenuate high-frequency seismic waves and thus result in a less stochastic signal. PE also exhibited a spike-like increase just before the onset of the three eruptions. In 2011 and 2017, this feature was probably associated with bubble growth and collapse due to the interaction between the aquifer and high temperature magma. In 2018 the aquifer had mostly evaporated; hence, the spike in PE values was likely generated by fracturing of solidified magma within the conduit as fresh magma was pushing its way upwards. These results show that PE is a potentially useful tool for monitoring seismic noise at volcanoes and can contribute toward forecasting volcanic eruptions in conjunction with other widely used methodologies.