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

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，这些过程通常是隐藏的，无法直接观察。该提案将开发一个建模框架，以成像活火山的内部运作，如在基拉韦厄，夏威夷，美国。基拉韦厄代表了一个独特的天然实验室：它展示了频繁的喷发，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年至今，Halemaumau喷口最近的活动是主要的观测目标。罗克瀑布从火山口的墙壁到活跃的熔岩湖上产生的岩浆和气体的振荡导管，爆炸，和湖的高度变化，证明了通过振荡地面运动记录在本地传感器网络。这种行为的模型必须明确考虑气泡的生长，复杂的管道几何形状，包括分支裂缝，分层，多相流体流动，以实现地震数据之间的一致性，湖平面波动的视频，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。作为这项研究的结果，获得的岩浆流动，气体溶解度的法律和气泡生长的理论认识，应有利于活火山的研究，以及在地球科学和工业中产生的各种应用，涉及流动的气泡流体通过网络的裂缝。建模工具和结果最终都可以用于监测活火山，了解它们的动态，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在活的开放喷口火山进行的地震观测的框架。主要的应用是短期（几十分钟）动荡发作在基拉韦厄火山，夏威夷，与罗克瀑布从火山口壁到活跃的熔岩湖表面，这引起的岩浆和气体的振荡导管，爆炸，和湖的高度变化，证明了通过振荡地面运动记录在附近的地震仪和倾斜仪。这些自然实验提供了一个独特的测试不稳定管道流动模型，这主要取决于知道管道的几何形状和流体性质的岩浆（流变学，多相特征，挥发物含量，溶解度定律），所有这些通常是隐藏的直接观察。该项目团队将开发一个多相流的数值建模框架，其时间尺度比通常研究的要短得多，地震波通过管道中的气泡岩浆传播，管道包括分支堤坝和深度的岩床，正如许多火山所预期的那样。裂缝系统中的压力变化引起管道和裂缝壁的弹性变形。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联的地震信号。浮力、压缩性、粘性阻力和非平衡气泡生长和再吸收？所有这些都随深度而变化必须考虑到预测模式属性。深度处的支堤/底坎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直接与气体、管道结构和粘性阻力的演变深度分布有关。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.