Abstract Long-period signal (LPs, 0.2–2 s) and very long-period signal (VLP, 2–100 s) observed in the shallow volcanic plumbing system are typically repetitive and time-invariant in their location and source mechanism, offering in-situ probes of hot fluid transport over the eruption cycles. While the amplitude and activity of volcanic-tectonic earthquakes and LP events have been commonly used to infer overpressure within their source region, one missing link is an observable that may permit inference on the change in the permeability of the conduit plug/wall, which can regulate the degree of pressurization, affect the mechanical strength of the surrounding rock, and consequently the likelihood of an upcoming eruption. Here we show that during the 2011–2016 eruption cycle at Aso volcano in Japan, long-period tremor events, a VLP of ~15 s period, with opposite waveform polarity can be systematically detected and categorized as pressurization and depressurization events in the same crack-like conduit. We suggest that, depending on the strength of the surrounding rock and the permeability of the crack-like conduit wall/plug, pressurization due to magmatic heat and vaporization is more likely to occur when a less permeable conduit plug/wall can effectively keep the gas inside the crack-like conduit. On the other hand, depressurization is prone to occur if the conduit wall/plug permeability is sufficiently high to allow gas to escape from the conduit. Considering the amplitude of LPT proportional to the conduit overpressure, contrasting energetics of these diverse LPT events allows us to define whether the conduit is prone to pressurization or depressurization, providing a framework to infer how the permeability of the conduit wall/plug may evolve over an eruption cycle.

中文翻译：

---

通过日本阿苏火山下的各种长期震动对管道渗透率进行实时和原位评估

摘要 在浅层火山管道系统中观察到的长周期信号（LPs，0.2-2 s）和超长周期信号（VLP，2-100 s）在其位置和来源机制上通常具有重复性和时不变性，提供了- 喷发周期中热流体传输的原位探针。虽然火山构造地震和 LP 事件的振幅和活动通常被用来推断其源区内的超压，但一个缺失的环节是一个可观测的，它可能允许推断导管塞/壁渗透性的变化，这可以调节加压程度，影响围岩的机械强度，从而影响即将喷发的可能性。在这里，我们展示了在 2011-2016 年日本阿苏火山的喷发周期中，长周期的震颤事件，~15 s 周期的 VLP，可以系统地检测到波形极性相反的情况，并将其归类为同一裂纹状管道中的加压和减压事件。我们认为，根据围岩的强度和裂缝状导管壁/塞的渗透性，当渗透性较低的导管塞/壁可以有效地保持气体时，更容易发生岩浆热和汽化导致的加压。裂缝状的导管内。另一方面，如果导管壁/塞渗透性足够高以允许气体从导管逸出，则容易发生减压。考虑到 LPT 的幅度与管道超压成正比，这些不同 LPT 事件的对比能量使我们能够定义管道是否易于加压或减压，