Interrogation of global seismic models with 3D wave simulations

通过 3D 波模拟询问全球地震模型

• 批准号: 0609763
• 负责人: Jeroen Ritsema
• 金额: $ 17.41万
• 依托单位: Regents of the University of Michigan - Ann Arbor
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2006
• 资助国家: 美国
• 起止时间: 2006-06-15 至 2010-05-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0609763&HistoricalAwards=false
• 关键词: Interrogation; global; seismic; models; 3D

Tomography is a powerful seismic technique for constraining the three-dimensional (3-D) structure of the Earth's interior [e.g., Romanowicz, 2003; Thurber and Ritsema, 2005]. Models of 3-D seismic structure take a central place in the research of Earth scientists from a wide range of disciplines.The traveltime (of a body- or surface wave) is the most popular data type in tomography. Traveltimes are available in seismological catalogs, or they can be measured in a relatively straightforward manner. Moreover, traveltimes can be related to velocity heterogeneity in a linear fashion, simplifying the tomographic inverse problem. Millions of traveltimes constitute modern data sets. However, do tomographic models explain other attributes of wave propagation and how do simplified wave theories compromise model accuracy? These are the questions we are addressing in our research.We are analyzing 3-D Spectral-Element Method (SEM) wave simulations [Komatitsch and Tromp, 1999; Komatitsch et al., 2002] to investigate how 3-D seismic models can be improved using observables that are traditionally not used in tomographic inversions.(1) Body wave amplitudesWe have demonstrated [Ritsema et al., 2002; Komatitsch et al., 2002] that the pattern (but not the amplitude) of SS/S amplitude ratios can be explained by shear velocity heterogeneity in the mantle for model S20RTS. We are investigating whether these body wave amplitude ratios can be used to constrain the (lateral) gradients of shear velocity in the mantle, which we suspect to be underestimated by tomographic models.(2) Frequency-dependent body wave traveltimesWe are observing a systematic variation of body wave traveltimes between 20-100 mHz. While such a variation is expected on theoretical grounds [Dahlen et al., 2000], we are using SEM simulations to investigate whether this signal can be used to constrain the amplitude and spectrum of heterogeneity in the mantle.(3) Resolution of "small-scale" heterogeneityWe are analyzing SEM waveforms to conduct new resolution tests that explore whether "small-scale" (i.e., 200 km) structures produce observable traveltime or waveform variations. We are particularly interested in constraining the mantle structure of Iceland, a region overlying an anomalous mantle upwelling.Broader Impact: The research is supporting the training of a Geophysics student in seismological data analysis and advanced scientific computing. The research enhances the P.I.'s collaboration with specialists in global wave propagation theories and geodynamics.

层析成像是用于约束地球内部的三维（3-D）结构的强大地震技术[例如，Romanowicz，2003; Thurber and Ritsema，2005]。三维地震结构模型在各个学科的地球科学家的研究中占有中心地位。走时（体波或面波）是层析成像中最常用的数据类型。走时可以在地震目录中找到，也可以用相对简单的方式测量。此外，走时可以以线性方式与速度不均匀性相关，从而简化层析成像逆问题。数以百万计的旅行时间构成了现代数据集。然而，层析成像模型是否解释了波传播的其他属性？简化的波动理论如何影响模型的准确性？这些是我们在研究中要解决的问题。我们正在分析3-D谱元法（SEM）波浪模拟[Komatitsch和Tromp，1999; Komatitsch等人，2002]研究如何使用传统上不用于层析反演的可观测量来改进3-D地震模型。(1)体波振幅我们已经证明[Ritsema等人，2002; Komatitsch等人，2002]的模式（但不是振幅）的SS/S振幅比可以解释为剪切速度在地幔中的不均匀性模型S20 RTS。我们正在研究这些体波振幅比是否可以用来约束地幔中的剪切速度（横向）梯度，我们怀疑被低估的层析成像模型。(2)频率相关的体波旅行时间我们正在观察体波旅行时间在20-100 mHz之间的系统变化。虽然这种变化在理论上是预期的[Dahlen等人，2000]，我们正在使用SEM模拟来研究该信号是否可以用于限制地幔中不均匀性的幅度和频谱。(3)“小尺度”不均匀性的分辨率我们正在分析SEM波形，以进行新的分辨率测试，探索“小尺度”（即， 200公里）的结构产生可观察到的走时或波形变化。我们特别感兴趣的是约束冰岛的地幔结构，一个覆盖在异常地幔上涌的地区。更广泛的影响：这项研究正在支持地震数据分析和先进的科学计算的地球物理学学生的培训。该研究增强了P.I.与全球波传播理论和地球动力学专家的合作。