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.

断层扫描是一种强大的地震技术，用于限制地球内部的三维（3-D）结构[例如Romanowicz，2003; Thurber和Ritsema，2005年]。 3-D地震结构的模型在广泛学科的地球科学家研究中占据了基础。（身体或表面波）的旅行时间是断层扫描中最流行的数据类型。旅行时间可在地震目录中使用，或者可以以相对简单的方式进行测量。此外，旅行时间可能与速度异质性以线性方式有关，从而简化了层析成像逆问题。数百万的旅行时间构成现代数据集。但是，层析成像模型是否解释了波传播的其他属性，简化的波浪理论如何损害模型的准确性？这些是我们在研究中正在解决的问题。我们正在分析3-D光谱元素方法（SEM）波模拟[Komatitsch和Tromp，1999; Komatitsch等人，2002年]为了研究如何使用传统上不在层析成像倒置中不使用的观察力来改善3-D地震模型。（1）体波振幅已证明[Ritsema等，2002; Komatitsch等人，2002年]，可以通过模型S20RT的地幔中的剪切速度异质性来解释SS/S幅度比的模式（但不是幅度）。我们正在研究这些体波振幅比是否可以用于约束地幔中剪切速度的（侧）梯度的（我们怀疑它被层析成像模型低估了。体浪行进时间在20-100 MHz之间。虽然预计在理论上可以进行这种变化[Dahlen等，2000]，但我们正在使用SEM模拟来研究该信号是否可用于约束地幔中异质性的幅度和频谱。 -Scale“异质性我们正在分析SEM波形，以进行新的分辨率测试，以探讨“小规模”（即200 km）结构是否会产生可观察到的行进时间或波形变化。我们对限制冰岛的地幔结构特别感兴趣，冰岛是一个覆盖异常地幔上升流的地区。BOADER的影响：研究正在支持对地球物理学学生进行地震学数据分析和高级科学计算的培训。该研究增强了P.I.与全球波传播理论和地球动力学方面的专家的合作。