Source models of long-period seismic events at Galeras volcano, Colombia
Source models of long-period seismic events at Galeras volcano, Colombia
复制标题
哥伦比亚加莱拉斯火山长周期地震事件的震源模型
DOI：
10.1093/gji/ggab325
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发表时间：
2021
影响因子：
2.8
通讯作者：
Taguchi Kimiko
中科院分区：
文献类型：
--
作者：
Torres Roberto;Kumagai Hiroyuki;Taguchi Kimiko
在哥伦比亚的Galeras火山，在从喷发圆顶形成到火山爆发的过渡期间，反复发生了长周期（LP）地震事件。自1989年以来，两种类型的LP事件已被观察到：一个由持久的，衰减的谐波振荡（NLP事件）和其他的非谐波振荡的功能（BLP事件）的特点。NLP事件归因于岩浆中充满尘埃气体的裂缝堵塞喷发管道的共振。1992-2010年期间，Galeras发生了16次NLP事件，每次NLP事件的频率和质量因子都具有系统的时间变化。我们和以前的估计在三个NLP事件的裂纹模型参数表明，类似的时间变化裂纹的几何形状和流体性质可以解释的裂纹内的灰分含量的增加和裂纹体积的减少。我们发现，NLP事件，伴随着低SO2通量，与BLP事件，这是伴随着高SO2排放量的直接相关。从我们的观察和分析结果，我们推断，BLP事件产生的共振开放裂缝的最上部的岩浆塞，对应于凝灰岩脉，有效地转移火山气体。在充分脱气和致密化之后，岩浆塞有效地密封了管道。更深岩浆中不断增长的超压然后通过沿通道边缘的剪切断裂沿着释放。更深的气泡状岩浆侵入剪切断裂，使岩浆减压并碎裂，产生尘埃气体并触发产生NLP事件的裂缝共振。因此，我们的研究结果表明，岩浆岩栓的性质的演变控制的发生在Galeras的BLP和NLP事件。虽然NLP事件并不总是发生在爆炸性喷发之前，但它们表明在浅管道中正在建立重要的超压。
Long-period (LP) seismic events have occurred repeatedly at Galeras volcano, Colombia, during the transition from effusive dome formation to explosive Vulcanian eruptions. Since 1989, two types of LP events have been observed there: one characterized by long-lasting, decaying harmonic oscillations (NLP events) and the other by non-harmonic oscillatory features (BLP events). NLP events are attributed to resonances of a dusty gas-filled crack in the magma plugging the eruptive conduit. Sixteen episodes of NLP events occurred at Galeras during 1992–2010, each characterized by systematic temporal variations in the frequencies and quality factors of NLP events. Our and previous estimates of crack model parameters during three of those NLP episodes indicate that the similar temporal variations in crack geometry and fluid properties can be explained by an increase in the ash content within the crack and a decrease in crack volume. We found that NLP events, associated with low SO2fluxes, are anticorrelated with BLP events, which are accompanied by high SO2emissions. From our observations and analytical results, we inferred that BLP events are generated by resonances of open cracks in the uppermost magma plug, corresponding to tuffisite veins, that efficiently transfer volcanic gases. After sufficient degassing and densification, the magma plug effectively seals the conduit. The growing overpressure in the deeper magma is then released through a shear fracture along the conduit margin. The intrusion of deeper, vesiculated magma into the shear fracture depressurizes and fragments the magma, producing a dusty gas and triggering the crack resonances that generate NLP events. Our results thus indicate that the evolution of the properties of the magma plug controls the occurrences of BLP and NLP events at Galeras. Although NLP events do not always precede explosive eruptions, they indicate that an important overpressure is building in the shallow conduit.