Dynamic triggering and criticality: earthquake interactions during unrest at Sierra Negra volcano, Galapagos Islands

对许多地震断层系统和火山的观测告诉我们，大地震引起的应力的微小变化可能引发其他大地震或火山爆发。在最近的一个例子中，这些相互作用支撑了2016年意大利中部的一系列大破坏性地震。目前缺乏对某些断层和火山对小应力变化的敏感性以及这些相互作用的性质的了解，这是阻碍我们预测未来大地震和火山爆发的能力的一些关键未知因素。利用许多重复触发事件的高质量数据来研究这些相互作用的机会是有价值的，但极其罕见。由于新岩浆在浅层的到来，加拉帕戈斯群岛的Sierra Negra火山目前显示出相当大的动荡迹象。2018年1月的新观察表明，动荡使火山特别容易受到远程地震触发的影响。与数千公里外的大地震相关的微小低频震动正在火山中引发小的高频地震。美洲太平洋沿岸沿着发生大地震的频率很高，因此触发事件频繁，初步分析表明，迅速部署高分辨率地震网络可能会在明年记录到数十次触发事件。Sierra Negra正在展示一个极好的，但短期的，“天然实验室”来研究地震-地震和地震-火山临界触发。该项目将在Sierra Negra部署一个高密度的地震仪网络，为期12个月，以记录火山发生的地震活动。这些数据将使我们能够确定地震触发的时间、地点和方式，并提供有关控制“临界应力”地质系统响应的因素的重要新信息。此外，这些数据将使我们能够跟踪火山动荡的演变，以及与部署期间发生的任何喷发活动相关的地震信号。

Observations across many earthquake fault systems and volcanoes tell us that the small changes in stress due to large earthquakes can trigger other large earthquakes or volcanic eruptions. In a recent example, these interactions underpinned the sequence of large destructive earthquakes in central Italy in 2016. The lack of current understanding of the susceptibility of certain faults and volcanoes to small stress changes and the nature of these interactions are some of the key unknowns hampering our ability to forecast future large earthquakes and eruptions. Opportunities to study these interactions, with high quality data over many repeated triggering events, are valuable, but extremely rare.Sierra Negra volcano in the Galapagos Islands is currently showing considerable signs of unrest, due to the arrival of new magma at shallow levels. New observations in January 2018 show that the unrest has made the volcano particularly and unusually susceptible to remote earthquake triggering. The tiny low frequency shaking associated with large earthquakes many 1000s of kilometres away is triggering small high frequency earthquakes in the volcano. The high rate of large earthquakes along the Pacific coast of the Americas provides frequent triggering events, and preliminary analysis suggests that rapid deployment of a high resolution seismic network might expect to record many tens of triggering episodes in the next year. Sierra Negra is presenting a superb, but short-term, 'natural laboratory' to study earthquake-earthquake and earthquake-volcano critical triggering.This project will deploy a high-density network of seismometers at Sierra Negra for 12 months for record the seismic activity taking place at the volcano. These data will allow us to determine when, where, and how earthquake triggering is taking place, and provide important new information about the factors that control the response of 'critically-stressed' geological systems. In addition, the data will allow us to follow the evolution of volcanic unrest, and the seismic signals associated with any eruptive activity that occurs during deployment.