Deformation and Seismicity Accompanying Effusive Silicic Eruptions

伴随硅质喷发的变形和地震活动

• 批准号: 0710844
• 负责人: Paul Segall
• 金额: --
• 依托单位: Stanford University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2007
• 资助国家: 美国
• 起止时间: 2007-07-01 至 2010-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0710844&HistoricalAwards=false
• 关键词: Deformation; Seismicity; Accompanying; Effusive; Silicic

Arc volcanoes erupt both explosively and effusively, and while effusive eruptions are less hazardous they are more amenable to study. Furthermore, many important physical and chemical processes are common to both styles of activity. As magma ascends the decrease in pressure results in exsolution of volatile constituents, which has the dual effect of increasing melt viscosity and promoting crystal growth. Considerable progress has been made in the past decade in modeling these processes, yet surprisingly little attention has been given to coupling the resultant tractions on the boundary of volcanic conduits to stress and deformation in the surrounding elastic medium. At the same time commonly used volcano deformation models remain highly idealized, and these idealizations are particularly inadequate in the case of erupting volcanoes. The goal of the proposed research is to more fully understand the driving forces and associated deformation and seismicity of effusive dome-building eruptions, with particular emphasis on the current eruption at Mount St. Helens. The proposed work involves the development of coupled magma flow and deformation models, and the analysis of both near-conduit and broader scale deformation and seismic data at Mount St. Helens in order to better constrain these models.The recent and largely unexpected reawakening of Mount St. Helens demonstrates serious limitations in our understanding of the processes that drive volcanic eruptions. The ongoing eruption has raised a number of first-order questions including: How did St. Helens begin erupting with so little precursory activity? Seismicity associated with the current eruption is limited to the upper few kilometers, yet magma is clearly rising from the mid-crust. In contrast, seismic swarms in preceding decades extended from 2 to 9 km depth. Were the earlier swarms associated with magma transport? If not, what other processes could explain the seismicity? What processes control the dramatic transient tilt signals in the near field of the extruding dome at Mt. St. Helens? What constraints do they place on the mechanics of dome extrusion? Following the onset of the eruption PBO and the USGS rushed to deploy GPS instruments on the volcano. If we are to take advantage of improved monitoring data then it is imperative that we begin to consider more realistic deformation sources which take into account the physical properties of magma movement from depth and its effect on the surrounding medium.We propose to develop both quasi-analytic and Finite Element Method (FEM) models that relate physical-chemical processes in the magma chamber and conduit system to surface deformation and seismicity. Predictions of the coupled chamber/conduit models will be compared to observed time-dependent deformation and effusive flux to better constrain parameters such as magma chamber volume and recharge rate at Mt. St. Helens. Various models of swarm seismogenesis will be investigated and compared to observations based on Dieterich's seismicity rate theory [Dieterich, Jour. Geopys. Res, 1994]. One promising model involves cyclic increase in stress due to crystallization-driven gas exsolution and pressurization interrupted by periods of gas escape. Dramatic near vent tilt cycles will be analyzed to constrain the source of these transient deformations. Finally, we will examine thermal models to test the hypothesis that the first erupted 2004 lavas were residual magmas from the 1980's dome-forming eruptions.

弧火山既爆发又喷发，虽然喷发的危险性较小，但它们更适合研究。 此外，许多重要的物理和化学过程是共同的两种类型的活动。 当岩浆上升时，压力的降低导致挥发分的出溶，这具有增加熔体粘度和促进晶体生长的双重作用。 在过去的十年中，在模拟这些过程中已经取得了相当大的进展，但令人惊讶的是，很少有人注意到耦合的火山管道的边界上的应力和变形在周围的弹性介质中产生的牵引力。 与此同时，常用的火山变形模型仍然高度理想化，这些理想化在火山爆发的情况下尤其不足。 拟议研究的目标是更充分地了解喷发式圆顶建筑喷发的驱动力和相关变形和地震活动，特别强调目前圣海伦斯火山的喷发。 拟议的工作涉及耦合岩浆流动和变形模型的发展，以及近导管和更广泛的规模变形和地震数据在圣海伦斯山的分析，以更好地约束这些models.The最近和很大程度上意想不到的复活圣海伦斯山表明，在我们的理解驱动火山爆发的过程中存在严重的局限性。 正在进行的火山爆发提出了一些一级问题，包括：圣海伦斯是如何开始喷发的，而火山活动如此之少？ 与这次喷发有关的地震活动仅限于火山上部几公里，但岩浆显然是从中地壳上升。 相比之下，前几十年的震群从2公里深延伸到9公里深。 早期的蜂群与岩浆运输有关吗？ 如果不是，还有什么其他过程可以解释地震活动？ 是什么过程控制了近场的突出圆顶在山戏剧性的瞬态倾斜信号。圣海伦？ 它们对圆顶挤出的力学有什么限制？ 火山爆发后，PBO和美国地质勘探局迅速在火山上部署了GPS仪器。 如果我们要利用改进的监测数据，那么我们开始必须考虑更现实的变形源，考虑到岩浆运动的物理性质，从深度和它对周围medium.We的影响，建议开发准分析和有限元方法（FEM）模型的物理化学过程中的岩浆房和管道系统的表面变形和地震活动。 耦合室/管道模型的预测将进行比较，观察到的随时间变化的变形和溢出通量，以更好地约束参数，如岩浆房的体积和补给率在山。圣海伦。 将研究震群成因的各种模型，并与基于迪特里希的地震活动率理论的观测结果进行比较[迪特里希，Jour. Geopys Res，1994年]。 一个有前途的模型涉及由于结晶驱动的气体出溶和加压中断的气体逃逸期间的应力周期性增加。 将分析剧烈的近喷口倾斜周期，以限制这些瞬态变形的来源。 最后，我们将研究热模型来检验假设，即2004年第一次喷发的熔岩是20世纪80年代形成圆顶的火山喷发的残余岩浆。