Conduit Evolution during the 1992 Eruptive Sequence at Mt. Spurr, Alaska

岩浆通过浅层管道向上运移在火山活动中起着重要作用，因为岩浆在上升过程中所经历的物理变化可能决定最终喷发的风格和强度。然而，人们对火山导管的形状、它们在喷发过程中的演变以及导管形状对岩浆上升速度的影响知之甚少。本文拟通过对1992年美国阿拉斯加州斯珀尔火山喷发过程中导管的演化进行分析，利用单个地震来确定不同喷发序列阶段导管周围的应力场。这项工作将补充和测试已经完成的关于斯珀尔火山喷发序列的众多地震和岩石学研究的结果。我们特别感兴趣的是确定导管在(1)导致第一次爆炸事件的十个月活动期间的应力状态，(2)喷发期间[1992年6月至9月]，以及(3)喷发后时期。对这三个时间段的评估将使我们能够评估喷发活动之前岩浆上升的条件，检查管道对个别喷发的反应，并检验1992年11月和12月的地震群实际上是由于在浅层形成了固化塞而“失败”的喷发的假设。因此，我们的研究结果将有助于深入了解1992年斯珀尔火山的喷发，并有助于建立岩浆迁移事件应力场响应的一般模型。此外，我们将把我们的结果与附近伊利亚姆纳火山岩脉位的应力场研究结果进行比较，希望能揭示促进或阻碍侵入岩浆向地表传播的条件，从而改善对火山地区未来地震危机的解释。

EAR-0229655CashmanThe upward migration of magma through shallow conduits plays an important role in volcanic activity, as the physical changes that magma undergoes during ascent may determine the style and intensity of the resulting eruption. However, little is known about the shapes of volcanic conduits, their evolution through the course of an eruption, or the effect of conduit shape on rates of magma ascent. We propose to analyze conduit evolution during the 1992 eruptions of Mt. Spurr, Alaska, by using individual earthquakes to determine the stress field around the conduit for different phases of the eruptive sequence. This work will both complement and test results from the numerous seismic and petrologic studies already completed on the Spurr eruptive sequence. We are particularly interested in determining the stress state of the conduit during (1) the ten months of activity leading up to the first explosive event, (2) the intra-eruptive period [June - September 1992], and (3) the post-eruptive period. Evaluation of these three time periods will allow us to evaluate conditions of magma ascent prior to eruptive activity, examine the response of the conduit to individual eruptions, and test the hypothesis that seismic swarms in November and December of 1992 were actually eruptions that "failed" because a solidified plug had formed at shallow levels. Our results will thus both provide insight into the 1992 eruptions at Mt. Spurr and aid development of a general model of stress field response to episodes of magma migration. Additionally, we will compare our results with those from a stress field study of dike emplacement at nearby Iliamna Volcano with the hope of shedding light on conditions that either promote or hinder propagation of intruding magma to the surface, thus improving interpretations of future seismic crises in volcanic regions.