Collaborative Research: Waves in Volcanic Conduit-crack Systems and Very Long Period Seismicity at Kilauea Volcano, Hawaii

合作研究：夏威夷基拉韦厄火山的火山管道裂缝系统中的波浪和甚长周期地震活动

• 批准号: 1624431
• 负责人: Eric Dunham
• 金额: $ 5.29万
• 依托单位: Stanford University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2016
• 资助国家: 美国
• 起止时间: 2016-10-01 至 2018-09-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1624431&HistoricalAwards=false
• 关键词: Collaborative; Research; Waves; Volcanic; Conduit

An overarching goal of volcanology is to characterize eruptive activity and link this to the physical processes governing magma ascent and eruption, which are generally hidden from direct observation. This proposal will develop a modeling framework to image the inner workings of active volcanoes, such as at Kilauea, Hawaii, USA. Kilauea represents a unique natural laboratory: it exhibits frequent eruptions, a dense instrumental monitoring network to record these eruptions, and a long history of scientific study. Recent activity at the Halemaumau vent, from 2008 to the present day, is the primary observational target. Rock falls from the crater walls onto the active lava lake generate oscillations of the magma and gas within the conduit, explosions, and lake height variations, as evidenced through oscillatory ground motion recorded on the local sensor network. Models for this behavior must explicitly consider bubble growth, complex conduit geometry that includes branching cracks, and stratified, multiphase fluid flow to achieve consistency between seismic data, video of lake level fluctuations, chemical data that constrain gas contents, and textural data that constrain near-surface magma density and bubble content. Theoretical understandings of magma flow, gas solubility laws, and bubble growth gained as a result of this study should benefit the study of active volcanoes generally, as well as diverse applications arising in Earth science and industry that involve flow of bubbly fluids through networks of cracks. Both the modeling tools and results could ultimately be used to monitor active volcanoes, understand their dynamics, and inform eruption forecasts. This proposal describes a framework for the study of volcanic activity and interpretation of seismic observations at active, open vent volcanoes. The primary application is to short term (tens of minutes) unrest episodes at Kilauea volcano, Hawaii, associated with rock falls from the crater walls onto the active lava lake surface, which induce oscillations of the magma and gas within the conduit, explosions, and lake height variations, as evidenced through oscillatory ground motion recorded on nearby seismometers and tilt meters. These natural experiments provide a unique test for unsteady conduit flow models, which depend critically on knowing conduit geometry and fluid properties of magma (rheology, multiphase character, volatile content, solubility law), all of which are generally hidden from direct observation. The project team will develop a numerical modeling framework for multiphase flow, at much shorter timescales than typically studied, with seismic wave propagation through bubbly magma in conduits that include branching dikes and sills at depth, as is expected at many volcanoes. Pressure changes in the conduit-crack system cause elastic deformations of the conduit and crack walls. Coupling to the solid Earth enables prediction of seismic signals associated with waves and resonant oscillations of the magmatic system. Buoyancy, compressibility, viscous drag, and non-equilibrium bubble growth and resorption ? all of which vary with depth ? must be accounted for to predict mode properties. Branching dikes/sills at depth partially control mode periods and ground displacement. Observable periods and decay rates of seismic signals are thus linked directly to the evolving depth distribution of gas, conduit architecture, and viscous drag. Inversion of these signals will provide new constraints on the shallow magmatic system and total volatile content at Kilauea, and a new framework for probing unsteady eruptive processes.

火山学的首要目标是描述喷发活动的特征，并将其与控制岩浆上升和喷发的物理过程联系起来，而这些过程通常无法直接观察到。该提案将开发一个建模框架来描绘活火山的内部运作情况，例如美国夏威夷基拉韦厄火山。基拉韦厄火山代表了一个独特的自然实验室：它经常喷发、记录这些喷发的密集仪器监测网络以及悠久的科学研究历史。从 2008 年至今，Halemaumau 喷口最近的活动是主要观测目标。岩石从火山口壁掉落到活跃的熔岩湖上，会产生管道内岩浆和气体的振荡、爆炸和湖的高度变化，正如本地传感器网络上记录的振荡地面运动所证明的那样。这种行为的模型必须明确考虑气泡生长、包括分支裂缝的复杂管道几何形状以及分层多相流体流动，以实现地震数据、湖面波动视频、限制气体含量的化学数据以及限制近地表岩浆密度和气泡含量的结构数据之间的一致性。通过这项研究获得的对岩浆流动、气体溶解度定律和气泡生长的理论理解应该有利于对活火山的研究，以及地球科学和工业中涉及气泡流体通过裂缝网络流动的各种应用。建模工具和结果最终都可以用于监测活火山、了解其动态并为喷发预测提供信息。该提案描述了一个研究火山活动和解释活火山地震观测的框架。主要应用是夏威夷基拉韦厄火山的短期（数十分钟）动荡事件，该事件与岩石从火山口壁掉落到活跃的熔岩湖表面有关，这会引起管道内岩浆和气体的振荡、爆炸和湖泊高度变化，正如附近地震仪和倾斜仪记录的振荡地面运动所证明的那样。这些自然实验为非稳态管道流模型提供了独特的测试，这主要取决于了解管道几何形状和岩浆的流体特性（流变性、多相特征、挥发物含量、溶解度定律），所有这些通常都无法直接观察。该项目团队将开发一个多相流数值模拟框架，其时间尺度比通常研究的时间尺度要短得多，地震波通过管道中的气泡岩浆传播，这些管道包括深度的分支岩脉和基台，正如许多火山所预期的那样。管道-裂缝系统中的压力变化导致管道和裂缝壁的弹性变形。与固体地球的耦合可以预测与岩浆系统的波和共振相关的地震信号。浮力、压缩性、粘性阻力和非平衡气泡生长和吸收 ?所有这些都随深度而变化？必须考虑到预测模式属性。深度处的分支堤坝/窗台部分控制模态周期和地面位移。因此，地震信号的可观测周期和衰减率与气体、管道结构和粘性阻力的演变深度分布直接相关。这些信号的反演将为基拉韦厄浅层岩浆系统和总挥发物含量提供新的约束，并为探测不稳定喷发过程提供新的框架。