Data_Sheet_1_Coupling Between Magmatic Degassing and Volcanic Tremor in Basaltic Volcanism.docx

Magmatic degassing, typically measured as SO2 flux, plays a fundamental role in controlling volcanic eruption style and is one of the key parameters used by volcano observatories to assess volcanic unrest and detect eruption precursors. Volcanic tremor, the integrated amplitude of seismic energy release over a range of frequencies, is also a key parameter in volcano monitoring. A connection between volcanic degassing and tremor has been inferred through correlations between the signals which are often, but not always, observed during periods of unrest or eruption. However, data are often equivocal and our understanding of the physical processes, which couple degassing with tremor are still evolving. New insights into degassing-tremor coupling can be made by investigation of the long-term relationship between degassing and tremor, focusing on the frequency-dependence of tremor and passive degassing behavior. In this study, we examine how long-term SO2 emission rates and volcanic tremor on Mt. Etna, track rapid variability in eruptive dynamics. Correlations between SO2 flux and tremor are explored in both quiescent and eruptive periods, comparing the two parameters at both long and short time-scales (< < 1 day) for ∼2 years. Our analysis reveals that over ∼month-long timescales passive degassing of SO2 and tremor tend to be well-correlated, but these correlations are lost over shorter timescales. This reflects a coupling process between passive degassing and tremor, produced by a combination of gas flow through permeable magma and the convective flow of magma within the conduit. Short-term correlations are lost because variations in the continuous degassing process are relatively small compared with the overall degassing rate and fall below measurement noise. During eruptive periods strong correlations are observed between degassing and tremor, with a significant contribution of higher frequency signal in tremor, controlled by eruptive style. These observations suggest that in syn-eruptive periods the tremor source is dominated by the coupling between the eruption column and the ground through infrasonic waves, rather than conduit processes. Our results demonstrate the importance of high quality long-term observations and offer new insights into the physical mechanisms which couple degassing and volcanic tremor at active volcanoes.

岩浆排气，通常以二氧化硫（SO2）通量衡量，在控制火山爆发风格中扮演着根本的角色，是火山观测站评估火山不稳定状态和检测爆发前兆的关键参数之一。火山微震，即在不同频率范围内地震能量释放的积分振幅，也是火山监测中的关键参数。通过分析在不安定或爆发期间通常（但并非总是）观察到的信号之间的相关性，推测出火山排气与微震之间存在关联。然而，数据往往含糊不清，我们对将排气与微震耦合的物理过程的理解仍在不断演进。通过对排气与微震之间长期关系的调查，关注微震的频率依赖性和被动排气行为，可以揭示排气-微震耦合的新见解。在本研究中，我们探讨了埃特纳火山长期SO2排放速率和火山微震如何追踪爆发动力学中的快速变化。在宁静期和爆发期，我们探索了SO2通量与微震之间的相关性，对比了这两个参数在长（< < 1天）和短时间尺度（约2年）上的表现。我们的分析揭示，在约一个月的时间尺度上，被动排气和微震通常具有良好的相关性，但在更短的时间尺度上，这些相关性则消失。这反映了被动排气与微震之间的耦合过程，由气体通过多孔岩浆流动和岩浆管道内的对流流动共同产生。短期相关性消失的原因是，与总体排气速率相比，连续排气过程中的变化相对较小，且低于测量噪声。在爆发期间，排气与微震之间观察到强烈的关联，微震中的高频信号对爆发风格有显著贡献。这些观察表明，在爆发同期，微震的来源主要是由通过次声波将爆发柱与地面耦合的机制所主导，而非管道过程。我们的结果证明了高质量长期观测的重要性，并为活跃火山中排气与火山微震耦合的物理机制提供了新的见解。