Imaging structure and geometry of Alpine slabs by full waveform inversion of teleseismic body waves

远震体波全波形反演高山板块的结构和几何形状成像

• 批准号: 363668812
• 负责人: Professor Dr. Wolfgang Friederich
• 金额: --
• 依托单位: Arbeitsgruppe Geophysik und Geodynamik
• 依托单位国家: 德国
• 项目类别: Priority Programmes
• 财政年份: 2017
• 资助国家: 德国
• 起止时间: 2016-12-31 至 2021-12-31
• 项目状态: 已结题
• 来源: https://gepris.dfg.de/gepris/projekt/363668812?language=en
• 关键词: Imaging; structure; geometry; Alpine; slabs

Seismic body waves from distant earthquakes recorded by the extraordinarily dense and large-aperture AlpArray Seismic Network (AASN) are inverted for the 3D distribution of seismic wave speeds in the lithosphere and sublithospheric mantle beneath the greater Alpine region (activity fields A, B, C and D and research themes 1 and 4). The resulting image is expected to resolve the internal structure and geometry of lithospheric slabs beneath the Alps down to the transition zone. It will give new insights into heavily debated issues such as subduction polarity switches, and provide further detail on possible detachments of the Alpine slabs from the lower crust, on their connection to high-velocity material in the transition zone attributed to Late Cretaceous to Early Paleogene subduction of the Alpine Tethys, and finally on the amount of subducted material accumulated in the transition zone (research theme 1). The 3D image will constitute essential input for geodynamic models of lithospheric deformation and mantle flow as well as plate tectonic reconstructions (research themes 2, 3 and 4).Iterative Gauss-Newton full waveform inversion based on waveform sensitivity kernels and adapted to the teleseismic imaging problem is employed to construct the 3D model of P and S wave speeds beneath the Alpine mountain belt. Numerical simulation of teleseismic wave propagation is performed in a hybrid way where either a 3D spectral element or a 3D discontinuous Galerkin method are used to model wave propagation in the target region. For the rest of the Earth, a fast and efficient solver valid for spherically symmetric earth models is employed. Initial wave speed models are obtained by classical tomographic inversion of automatically determined and quality-ranked travel times of P and S phases. The latter also enter the full waveform inversion as additional constraints to stabilize the inversion against cycle-skipping. Effects of heterogeneities outside the target volume are minimized by inverting linear combinations of the data whose sensitivity is focused on the target region. The approach should permit inversions of body wave records up to periods of a few seconds implying a resolution length of about 20 km.

通过对大阿尔卑斯地区岩石圈和岩石圈下地幔中地震波速度的三维分布（活动场A、B、C和D以及研究主题1和4），反演了由非常密集和大孔径的AlpArray地震网络（AALPINE）记录的远距离地震的地震体波。由此产生的图像预计将解决内部结构和几何形状的岩石圈板下阿尔卑斯山的过渡区。它将为俯冲极性转换等备受争议的问题提供新的见解，并进一步详细说明阿尔卑斯板块可能从下地壳中分离出来，它们与晚白垩世至早第三纪阿尔卑斯特提斯俯冲过渡带中的高速物质的联系，以及最后在过渡带中积累的俯冲物质的数量（研究主题1）。三维图像将构成岩石圈变形和地幔流动以及板块构造重建的地球动力学模型的重要输入（研究主题2、3和4）。采用基于波形灵敏度核的迭代高斯-牛顿全波形反演方法，并适应于地震成像问题，建立了阿尔卑斯山带下的三维P波和S波速度模型。数值模拟中的混合方式，其中无论是一个三维谱元素或三维间断伽辽金方法被用来模拟波在目标区域的传播。对于地球的其他部分，采用了一种适用于球对称地球模型的快速有效的求解器。初始波速模型通过自动确定和质量排序的P和S相位走时的经典层析反演获得。后者还进入全波形反演作为附加约束，以稳定反演，防止周期跳跃。通过将其灵敏度集中在目标区域上的数据的线性组合反转，使目标体积外部的非均匀性的影响最小化。该方法应允许反演体波记录的几秒钟的时间意味着约20公里的分辨率长度。