Constraints on absolute magma chamber volume from geodetic measurements: Trapdoor faulting in the Galapagos

当岩浆从地幔中升起时，它在地壳的岩浆房中聚集。当这些岩浆室中的岩浆压力增加时，它会导致地球表面向上凸起，这一过程被称为“膨胀”。膨胀可以用各种各样的仪器测量，包括地面和太空仪器，并且是即将爆发的有用预测器。标准分析方法可用于推导膨胀期间的体积变化，但对总腔体体积不敏感。了解活跃岩浆库的体积对科学家和那些监测火山危险的人来说是非常有用的。总的体积为可能的喷发体积提供了一个上限，并且是对岩浆房演化模型的约束。该项目利用对加拉帕戈斯群岛塞拉内格拉火山的独特观测，对塞拉内格拉火山岩浆库的总量进行了严格的限制。这项研究的广泛影响尤其及时，因为观测表明塞拉内格拉火山爆发和/或地震可能迫在眉睫。自2015年年中以来，这座火山一直在上升，现在比最近一次（2005年）喷发前的高度还要高。该项目还支持研究生研究这个问题。从1992年到2005年的喷发，塞拉内格拉火山上升了近5米，火山口中心的隆起最大。这一数据很好地与一个浅岩状岩浆库相吻合，其顶部深度约为2公里。膨胀被三次活动门断层事件打断，沿火山口内断层系统滑动。最近的一次活动门事件发生在2005年裂缝喷发前3小时。岩浆房对断层的响应取决于岩浆房的体积和岩浆的可压缩性，并在可观测的地表位移中清楚地表达出来。通过限制岩浆和弹性腔体的相对压缩性，研究人员将能够估计出绝对腔体的体积，这可以通过2005年火山喷发的观测得到。这样就可以估算出2005年喷发的岩浆总量的比例，这是预测其他火山的有用参数。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

As magma rises from the Earth's mantle it accumulates in magma chambers in the Earth's crust. As magma pressure in these chambers increases it causes the Earth's surface to bulge upward, a process termed "inflation". Inflation can be measured with a variety of instruments, both ground-based and space based, and is a useful predictor of impending eruptions. Standard analysis methods can be used to derive the change in volume during an inflation episode but are insensitive to the total chamber volume. It would be extremely useful to scientists and those monitoring volcanic hazards to know the volume of active magma chambers. The total volume provides an upper bound on the possible eruptive volume and is a constraint on models of magma chamber evolution. This project uses unique observations at Sierra Negra volcano in the Galapagos to place rigorous bounds on the total volume of Sierra Negra's magma chamber. The Broader Impacts of this study are particularly timely because the observations suggest that an eruption and/or earthquake at Sierra Negra may be imminent. The volcano has been uplifting since mid-2015 and is now higher than it was prior to the most recent (2005) eruption. The project also supports a graduate student to work on this problem.Between 1992 and the 2005 eruption Sierra Negra uplifted by nearly 5 meters, with maximum uplift in the center of the caldera. This data is well fit by a shallow sill-like magma chamber with its top at roughly 2 km depth. Inflation has been punctuated by three trapdoor faulting events, with slip along an intra-caldera fault system. The most recent trapdoor event occurred only 3 hours prior to the 2005 fissure eruption. The response of the magma chamber to the faulting depends on both the volume of the chamber and the compressibility of the magma contained within and is clearly expressed in observable surface displacements. By constraining the relative compressibility of the magma and the elastic chamber, which can be achieved with observations from the 2005 eruption, the researchers will be able to estimate the absolute chamber volume. This will permit estimation of the fraction of total magma that was erupted in 2005, a useful parameter for forecasts at other volcanoes.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.