Volcanic eruptions in high resolution

火山地震学关注的是火山喷发前后的时间。虽然火山生命周期中最重要的部分是喷发本身，但在喷发的大爆炸阶段很少测到地震。这是因为在火山喷发产生广泛的地震噪声时，测量地震的技术难度很大。在这里，研究人员通过使用现代地震探测技术来解决这个问题，以记录大规模爆炸性喷发期间的地震活动。他们用对2008年奥克莫克火山喷发的初步分析来说明新的方法；没有任何警告地喷发的火山口位于阿拉斯加阿留申群岛东部。多种技术使探测到的事件数增加了4倍。在喷发过程中，事件发生率变化很大，其原因尚不清楚。地震似乎记录了一段与爆炸历史相关但又不同的应力和破坏历史。为了更好地控制喷发期间的地震率，研究小组使用尖端软件重新分析了记录的数据。训练后的算法能够在噪声中识别出新的地震事件。新的活动目录用于更好地了解火山地下管道系统。同样的方法也适用于阿留申群岛、冰岛和俄罗斯的其他火山，这些火山表现出类似的大规模喷发。这项对比研究允许评估在大规模喷发期间，火山地震活动是否可以用来限制地下岩浆循环。该项目为一名研究生和本科生提供支持和培训，特别是来自科学界代表性不足的群体。其结果改进了火山危险评估，有助于减轻当地人口和空中交通的风险。研究人员建议通过利用一种无监督的、全局训练的检测算法来改善Okmok的共同喷发地震记录。地震率和喷发周期之间的关系仍不清楚。不仅在喷发开始时地震速率明显增加，而且在喷发结束时似乎有一次地震活动爆发。喷发中期的地震活动增加可能与喷发重组有关，但与主要的羽流形成事件没有明显的联系。这可能是因为地震对固体地壳中的应力敏感，而不是管道中的喷发过程。利用新的记录，研究人员识别并确定了地震的一致震级。已知震级的新地震允许对整个喷发过程中的地震率进行自我一致的测量。它可以用来评估地震是否标志着最不开放、压力最大的时间和地点。在该项目的第二阶段，同样的方法也被应用于其他类似的大规模喷发，这些喷发拥有足够的公开地震数据。这些喷发是：格里姆斯沃顿火山、卡萨托奇火山和谢维卢克火山。该团队打算与一名本科生一起探索纳布罗的数据集，尽管它不太具有可比性。这些比较研究改善了对地震作为火山开放或关闭状态指标的有效性的评估。预期结果将有助于了解加压和开启之间的快速波动在重大爆炸性喷发中是否常见。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

Volcano seismology has focused on the times before and after eruptions. Although the most important part of a volcano’s lifecycle is the eruption itself, few earthquakes have been measured during the large, explosive phase of an eruption. This lack is because of the technical difficulties of measuring earthquakes while the eruption is producing a wide range of seismic noise. Here the researchers address this problem by using modern techniques of earthquake detection to chronicle the seismicity during a large-scale, explosive eruption. They illustrate the new approach with a preliminary analysis of the 2008 eruption of Mount Okmok; the volcano caldera, which exploded without warning, is located in the eastern Aleutian Islands of Alaska. Multiple techniques increase the number of detected events by factor of 4. Event rate varies in a non-trivial way during the eruption which cause is still unclear. Earthquakes appear to be recording a history of stress and failure that is related to, but distinct from the history of explosions. To better constrain earthquake rate during the eruption, the team re-analyzes recorded data using cutting-edge software. The trained algorithm is capable of identifying new seismic events among the noise. The new event catalog is used to better understand the volcano subterranean plumbing system. The same approach is applied to other volcanos in the Aleutians, Iceland, and Russia, which exhibit similar large eruptions. The comparative study allows evaluating whether volcano seismicity can be used to constrain subterranean magma cycle during large eruptions. The project provides support and training for one graduate student and undergraduate students, notably from underrepresented groups in science. Its outcomes improve volcanic hazard assessment, helping mitigating risks for local population and air traffic. The researchers propose to improve the co-eruptive seismic record of Okmok by utilizing an unsupervised, globally trained detection algorithm. The relationship between earthquake rate and the eruption cycle is still unclear. Not only is there an obvious increase in the earthquake rate at the eruption initiation, but there also appears to be a seismicity burst at the end of the eruption. Seismicity increases in the middle of the eruption may be associated with eruption reorganization but is not clearly associated with major plume-forming events. This may be a result of earthquakes’ sensitivity to the stresses in the solid crust rather than the eruptive processes in the conduit. Using the new record, the researchers identify and determine consistent magnitudes for the earthquakes. The new earthquakes at known magnitudes allow a self-consistent measure of earthquake rate throughout the eruption. It can be used to evaluate whether the earthquakes are marking the least open, most pressurized times and places. In the project second phase, the same methods are applied to other similarly large eruptions that have sufficient, publicly available seismic data. Those eruptions are: Grimsvotn, Kasatochi and Sheveluch. The team intends to explore the dataset of Nabro with an undergraduate, although it is not quite comparable. These comparative studies improve assessing the utility of earthquakes as an indicator of opened or closed volcano state. The expected outcomes will help understanding whether rapid fluctuations between pressurization and opening are common in major explosive eruptions.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.