Imaging the complex geometry of a magma reservoir using FEM-based linear inverse modeling of InSAR data: application to Rabaul Caldera, Papua New Guinea
Imaging the complex geometry of a magma reservoir using FEM-based linear inverse modeling of InSAR data: application to Rabaul Caldera, Papua New Guinea
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DOI：
10.1093/gji/ggx119
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发表时间：
2017-06-01
影响因子：
2.8
通讯作者：
Molist, Joan Marti
中科院分区：
文献类型：
--
作者：
Ronchin, Erika;Masterlark, Timothy;Molist, Joan Marti
我们测试了一个创新的反演方案，使用绿色的功能，从一系列的压力源嵌入在有限元法（FEM）模型的图像，而不假设先验的几何形状，复合和复杂的形状的火山变形源。我们反演干涉合成孔径雷达（干涉合成孔径雷达）数据估计的压力和形状的拉包尔火山口，巴布亚新几内亚的岩浆库。结果图像的扩展浅岩浆系统负责的一个广泛和长期的2007年2月至2010年12月之间的火山口沉降。弹性有限元解被集成到正则化的线性反演的干涉合成孔径雷达数据的火山表面位移，以获得3-D图像的变形源。绿色函数矩阵是从一个库的前向线的视线位移解决方案的一个网格的立方基本变形源。通过从公共网格域中移除相应的立方单元并模拟流体质量通量注入腔体中来顺序地生成每个源，这导致流体填充腔体的加压和体积变化。使用单个网格生成所有FEM模型避免了非线性反演和重新划分可变几何域的计算昂贵的过程。除了生成绿色函数库的3-D网格的配置之外，在不假设先验源几何形状的情况下，大地测量数据将岩浆储层的几何形状指示为源阵列内的压力（或岩浆通量）的3-D分布。对拉包尔破火山口的干涉合成孔径雷达数据进行反演，结果表明，在破火山口的两个相对面下，形成了一个无定形的浅岩浆系统，该系统由相互连通的源分布。成像岩浆系统两侧的边缘区域可能是东侧正在进行的Tavurvur火山喷发安山岩产品和西侧过去Vulcan火山喷发更进化物质的补给水库。源的相互连接和空间分布对应于文献中描述的火山产品的岩相学和火山口特有的单次和双次喷发的动力学。对变形源在空间和时间上的复杂几何形状进行成像的能力可以提高我们监测活火山的能力，扩大我们对活火山系统动态的理解，并改善对火山爆发的预测。
We test an innovative inversion scheme using Green's functions from an array of pressure sources embedded in finite-element method (FEM) models to image, without assuming an a-priori geometry, the composite and complex shape of a volcano deformation source. We invert interferometric synthetic aperture radar (InSAR) data to estimate the pressurization and shape of the magma reservoir of Rabaul caldera, Papua New Guinea. The results image the extended shallow magmatic system responsible for a broad and long-term subsidence of the caldera between 2007 February and 2010 December. Elastic FEM solutions are integrated into the regularized linear inversion of InSAR data of volcano surface displacements in order to obtain a 3-D image of the source of deformation. The Green's function matrix is constructed from a library of forward line-of-sight displacement solutions for a grid of cubic elementary deformation sources. Each source is sequentially generated by removing the corresponding cubic elements from a common meshed domain and simulating the injection of a fluid mass flux into the cavity, which results in a pressurization and volumetric change of the fluid-filled cavity. The use of a single mesh for the generation of all FEM models avoids the computationally expensive process of non-linear inversion and remeshing a variable geometry domain. Without assuming an a-priori source geometry other than the configuration of the 3-D grid that generates the library of Green's functions, the geodetic data dictate the geometry of the magma reservoir as a 3-D distribution of pressure (or flux of magma) within the source array. The inversion of InSAR data of Rabaul caldera shows a distribution of interconnected sources forming an amorphous, shallow magmatic system elongated under two opposite sides of the caldera. The marginal areas at the sides of the imaged magmatic system are the possible feeding reservoirs of the ongoing Tavurvur volcano eruption of andesitic products on the east side and of the past Vulcan volcano eruptions of more evolved materials on the west side. The interconnection and spatial distributions of sources correspond to the petrography of the volcanic products described in the literature and to the dynamics of the single and twin eruptions that characterize the caldera. The ability to image the complex geometry of deformation sources in both space and time can improve our ability to monitor active volcanoes, widen our understanding of the dynamics of active volcanic systems and improve the predictions of eruptions.