Near-Surface Structure of the Continental United States Using Distant Earthquakes

利用远程地震研究美国大陆的近地表结构

基本信息

批准号：
1735960
负责人：
Miaki Ishii
金额：
$ 6.39万
依托单位：
Harvard University
依托单位国家：
美国
项目类别：
Standard Grant
财政年份：
2017
资助国家：
美国
起止时间：
2017-09-01 至 2018-08-31
项目状态：
已结题

来源：
https://www.nsf.gov/awardsearch/showAward?AWD_ID=1735960&HistoricalAwards=false
关键词：
Near Surface Structure Continental United

项目摘要

This project examines shallowest structure of the United States using a novel approach that utilizes EarthScope USArray seismic data. Depth-dependent estimates of both compressional- and shear-wave speeds will contribute not only to the studies of the subsurface imaging, but also to seismic hazard assessment and earthquake engineering. The new method is non-invasive, such that well drilling or field experiments using explosives are not necessary, and can be applied to any site with a single seismic station or dense arrays. Furthermore, if depth dependence is not sought, easy-to-install and inexpensive instruments can be used, allowing detailed variationsin the soil/crust structure to be revealed at low cost. The near-surface structure obtained from this study can be used as an input model for ground motion simulations, and will contribute to such programs as earthquake early warning that requires shaking predictions at critical locations. This project will also promote multidisciplinary research on the geological study of the continental United States. Since the technique can resolve seismic structure of top few kilometers or less, the lateral variation revealed from this study can be compared to and interpreted with geological provinces observed at the surface. The shallowness of the target also starts to bring together the global seismological analysis (using distant earthquake data) with near-surface critical zone studies, and contribute to our understanding of complex processes that occur at the Earth's surface.The new technique utilizes body-wave polarization to resolve wave speed immediately beneath a seismic station. Seismic wave polarization information has been relatively unexploited compared to other quantities such as travel times, and the essential theoretical framework for relating the polarization information of teleseismic body waves to near-surface wave speeds will be established and tested. Counter-intuitively, the polarization of teleseismic P waves is sensitive to shear-wave speed, while that of S waves is sensitive to both compressional and shear-wave speeds. Moreover, examining the frequency dependence of the polarization data allows a depth-dependent wave speed model of the shallow subsurface to be constructed. The method will be applied to the USArray data to produce the near-surface wave speed model of the continental United States. The spatial variation of the wave speeds, in both vertical and horizontal dimensions, will be studied at different scales through different frequency filters and combination of data from Transportable Array, Reference Network, and Flexible Array. The results will provide better constraints on the crust properties, and can be used to improve crustal corrections used for other types of studies such as global or regional seismic tomography.

该项目使用一种利用Earthscope USArray地震数据的新方法来检查美国的浅层结构。压缩波和剪切波速度的深度依赖性估计不仅会导致地下成像的研究，还会有助于地震危险评估和地震工程。新方法是无创的，因此不需要使用炸药进行井钻或现场实验，并且可以应用于具有单个地震站或密集阵列的任何站点。此外，如果不寻求深度依赖性，则可以使用易于安装和廉价的仪器，从而使土壤/地壳结构以低成本揭示了详细的变化。从这项研究中获得的近表面结构可以用作地面运动模拟的输入模型，并将为需要在关键位置摇晃预测的地震早期警告等程序做出贡献。该项目还将促进有关美国大陆地质研究的多学科研究。由于该技术可以解决前几公里或更少的地震结构，因此可以将这项研究揭示的横向变化与表面观察到的地质省进行比较和解释。目标的浅层还开始将全球地震学分析（使用遥远的地震数据）与近地面关键区域研究汇总在一起，并有助于我们对地球表面上发生的复杂过程的理解。新技术利用体内极化来解决紧邻地震站下方的波浪速度。与其他数量（例如旅行时间）相比，地震波极化信息相对尚未开发，并且将建立和测试将远距离人体波的极化信息与近表面波速度相关联的基本理论框架。违反直觉，伸缩症P波的极化对剪切波敏感，而S波的极化对压缩波和剪切波速度均敏感。此外，检查极化数据的频率依赖性允许构建浅层地下的深度依赖性波速模型。该方法将应用于USARRAY数据，以生成美国大陆的近表面波速度模型。在垂直和水平尺寸中，波速的空间变化将通过不同的频率滤波器研究，以及来自可传输阵列，参考网络和柔性阵列的数据组合。结果将对地壳特性提供更好的约束，并可用于改善用于其他类型研究（例如全球或区域地震层析成像）的地壳校正。