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

火山学的一个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，这些过程通常是隐藏在直接观察之外的。这项提议将开发一个模拟框架，以描绘活火山的内部运作，例如美国夏威夷基拉韦厄的活火山。基拉韦厄火山代表着一个独特的自然实验室：它展示了频繁的喷发，一个密集的仪器监测网络来记录这些喷发，以及悠久的科学研究历史。从2008年到现在，Halemaumau喷口最近的活动是主要的观测目标。岩石从火山口壁落到活跃的熔岩湖上，产生了管道内岩浆和气体的振荡、爆炸和湖高变化，当地传感器网络上记录的振荡地面运动证明了这一点。这种行为的模型必须明确考虑气泡增长、包括分支裂缝在内的复杂管道几何形状以及分层的多相流体流动，以实现地震数据、湖平面波动视频、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纹理数据之间的一致性。通过这项研究获得的关于岩浆流动、气体溶解规律和气泡生长的理论理解应该有助于总体上对活火山的研究，以及在地球科学和工业中产生的涉及气泡流体通过裂隙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。这项建议描述了研究火山活动和解释活动性喷口火山的地震观测的框架。主要应用于夏威夷基拉韦厄火山的短期(数十分钟)动荡事件，与岩石从火山口壁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，爆炸和湖高变化，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定的管道流动模型提供了一种独特的测试，这些模型严重依赖于对岩浆的管道几何形状和流体性质(流变学、多相特征、挥发分含量、溶解规律)的了解，所有这些通常都是直接观察不到的。该项目组将为多相流开发一个数值模拟框架，其时间尺度比通常研究的要短得多，地震波在管道中的气泡岩浆中传播，其中包括深层次的分支堤坝和岩床，正如许多火山所预期的那样。管道-裂缝系统中的压力变化会引起管道和裂缝墙的弹性变形。与固体地球的耦合使得能够预测与岩浆系统的波和共振振荡相关的地震信号。浮力、可压缩性、粘性阻力和非平衡气泡增长和再吸收？所有这些都会随着深度的不同而变化？必须考虑才能预测模式属性。深部分叉堤岸部分控制了振型周期和地面位移。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分含量提供新的约束，并为探测不稳定的喷发过程提供新的框架。

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.