Collaborative Research: A New 3-D Velocity and Structural Model of the Northern Basins in the Los Angeles Region for Improved Ground Motion Estimates

合作研究：洛杉矶地区北部盆地的新 3D 速度和结构模型，用于改进地震动估计

• 批准号: 2105320
• 负责人: Patricia Persaud
• 金额: $ 20.46万
• 依托单位: Louisiana State University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2021
• 资助国家: 美国
• 起止时间: 2021-07-15 至 2023-03-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2105320&HistoricalAwards=false
• 关键词: Collaborative; Research; New; Velocity; Structural

The next large earthquake on the southern San Andreas fault is expected to produce strong ground shaking hundreds of kilometers to the north, in Los Angeles, California. This will occur because the geologic structures beneath the Earth’s surface act as a wave guide channeling earthquake waves into downtown Los Angeles. It has been shown that the ground motions one can expect could be a factor of four larger than what earthquake hazard models predict. This difference may significantly increase damages resulting from earthquakes. It should also be accounted for when planning for earthquake resilience in the greater Los Angeles area. The inaccurate estimates for ground shaking result from incomplete Earth models which do not properly represent the geologic structures that channel seismic energy. Here, the researchers build a more detailed Earth model of the region. They use recordings from a new style of seismic field experiment carried out between 2017 and 2020; it consisted of laying out more than 700 modern instruments along 10 lines across the study area. This dense geometry allows the team to image better than ever before the subterranean structures channeling earthquake energy. The researchers carry out a full suite of analyses of the dense dataset. They refine and update models for regional seismic velocity. They simulate expected ground motions accounting for the new findings. The new Earth models are made available to the scientific community by updating the Southern California Earthquake Center community velocity models; this is done using a newly developed platform for embedding high-resolution models into larger-scale regional models. Results of the study improve seismic hazard assessment in the Los Angeles area. This collaborative project also supports a female early-career scientist from an underrepresented group, and graduate and undergraduate students at Louisiana State University and the California Institute of Technology. The researchers use receiver functions to construct profiles of the structure along each of the lines, using several teleseismic events that were recorded. The three-dimensional (3-D) shear wave velocities for the basins will be obtained from surface wave analysis based on ambient noise correlation between the nodes and broadband stations that were deployed as part of the survey, and the Southern California Seismic Network stations in the region. They combine the profiles and 3-D shear wave velocity estimates by using the gravity data across the basins. They produce attenuation (QS and QP) models from ambient noise and local earthquakes. The expected result will be a 3-D Earth model for the basins with a well-defined basement interface and shear wave velocities down through the sedimentary layers obtained at a higher resolution than existing models. As a further step, the team will simulate earthquake ground motions with the new model and compare strong motions to those predicted from noise correlations. The unique geometry of the survey allows the team to try more advanced methods including level-set inversion, autocorrelation methods, and possibly full waveform inversion. This advances the application of some of these methodologies for the first time to this particular type of data set. The full suite of methodologies developed here will be applicable other major cities around the world that are located on sedimentary basins such as San Francisco, Seattle, Mexico City and Lima.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

圣安德烈亚斯断层南部的下一次大地震预计将在加州洛杉矶以北数百公里处产生强烈的地面震动。这将会发生，因为地球表面下的地质结构起到了波导作用，将地震波引导到洛杉矶市中心。已经表明，人们可以预期的地面运动可能是地震危险模型预测的四倍。这种差异可能会显著增加地震造成的损失。在规划大洛杉矶地区的地震复原力时，也应该考虑到这一点。对地面震动的不准确估计是由不完整的地球模型造成的，这些模型不能正确地表示输送地震能量的地质结构。在这里，研究人员建立了一个更详细的该地区的地球模型。他们使用了2017至2020年间进行的一种新型地震现场实验的录音；该实验包括在研究区域的10条线上铺设700多台现代仪器。这种密集的几何结构使研究小组比以往任何时候都能更好地成像地下结构输送地震能量。研究人员对密集的数据集进行了一整套分析。他们改进和更新了区域地震速度的模型。他们模拟了预期的地面运动，解释了新的发现。新的地球模型通过更新南加州地震中心社区速度模型向科学界提供；这是使用一个新开发的平台来实现的，该平台用于将高分辨率模型嵌入更大规模的区域模型。这项研究的结果改善了洛杉矶地区的地震危险性评估。这一合作项目还支持一名来自代表性不足群体的早期职业女性科学家，以及路易斯安那州立大学和加州理工学院的研究生和本科生。研究人员使用接收器功能，利用记录的几个远震事件，沿着每条线构建结构的轮廓。盆地的三维(3-D)剪切波速度将通过面波分析获得，面波分析基于作为调查一部分部署的节点和宽带站与该地区的南加州地震台网之间的环境噪声相关性。他们利用盆地的重力数据，将剖面和三维剪切波速度估计结合在一起。他们从环境噪声和当地地震中产生衰减(QS和QP)模型。预期的结果将是一个盆地的三维地球模型，该模型具有明确的基底界面和向下穿过沉积层的剪切波速度，其分辨率高于现有模型。作为进一步的步骤，研究小组将用新模型模拟地震地面运动，并将强运动与根据噪声相关性预测的运动进行比较。测量的独特几何结构使团队可以尝试更高级的方法，包括水平集反演、自相关方法，以及可能的全波形反演。这推动了这些方法中的一些方法首次应用于这种特定类型的数据集。这里开发的全套方法将适用于位于旧金山、西雅图、墨西哥城和利马等沉积盆地上的世界其他主要城市。该奖项反映了NSF的法定使命，并已通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

项目成果

Effect of Merging Multiscale Models on Seismic Wavefield Predictions Near the Southern San Andreas Fault

• DOI: 10.1029/2021jb021915
• 发表时间: 2021-09
• 期刊: Journal of Geophysical Research: Solid Earth
• 作者: R. Ajala;P. Persaud

Urban Basin Structure Imaging Based on Dense Arrays and Bayesian Array‐Based Coherent Receiver Functions

基于密集阵列和贝叶斯阵列的城市盆地结构成像——基于相干接收函数

• DOI: 10.1029/2021jb022279
• 发表时间: 2021
• 期刊: Journal of Geophysical Research: Solid Earth
• 作者: Wang, Xin;Zhan, Zhongwen;Zhong, Minyan;Persaud, Patricia;Clayton, Robert W.
• 通讯作者: Clayton, Robert W.

Ground-Motion Evaluation of Hybrid Seismic Velocity Models

混合地震速度模型的地震动评估

• DOI: 10.1785/0320220022
• 发表时间: 2022
• 期刊: The Seismic Record
• 作者: Ajala, Rasheed;Persaud, Patricia
• 通讯作者: Persaud, Patricia