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

大地测量对绝对岩浆房体积的限制：加拉帕戈斯群岛的活板门断层

• 批准号: 1829763
• 负责人: Paul Segall
• 金额: $ 11.94万
• 依托单位: Stanford University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2018
• 资助国家: 美国
• 起止时间: 2018-08-15 至 2021-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1829763&HistoricalAwards=false
• 关键词: Constraints; absolute; magma; chamber; volume

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.

当岩浆从地幔上升时，它会聚集在地壳的岩浆室中。当这些洞穴中的岩浆压力增加时，它会导致地球表面向上膨胀，这一过程被称为“膨胀”。通货膨胀可以用各种工具来衡量，既有地面的，也有空间的，是即将爆发的有用的预测指标。标准分析方法可以用来得出充气期间的体积变化，但对总腔体积不敏感。对于科学家和那些监测火山灾害的人来说，了解活动岩浆室的体积将是极其有用的。总体积为可能的喷发量提供了上限，并限制了岩浆室演化模型。该项目利用对加拉帕戈斯山脉内格拉火山的独特观测，对内格拉山脉岩浆室的总体积设定了严格的界限。这项研究的更广泛影响特别及时，因为观察表明，内格拉山脉可能即将发生喷发和/或地震。这座火山自2015年年中以来一直在上升，现在比最近一次(2005年)喷发之前的水平要高。该项目还支持一名研究生研究这一问题。1992年至2005年内格拉火山喷发之间，内格拉山脉上升了近5米，其中最大的上升位于火山口的中心。这一数据很好地符合一个浅的岩浆室，它的顶部大约有2公里深。通货膨胀被三次陷门断层事件打断，并沿着火山口内断层系统滑动。最近一次活板门事件发生在2005年裂缝喷发前3小时。岩浆房对断层作用的响应取决于岩浆室的体积和所含岩浆的可压缩性，并以可见的地表位移清楚地表达出来。通过限制岩浆和弹性洞穴的相对可压缩性，研究人员将能够估计绝对洞穴体积。这将允许估计2005年喷发的岩浆总数的比例，这是预测其他火山的有用参数。这一奖项反映了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。