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.

该项目采用一种利用 EarthScope USArray 地震数据的新颖方法来检查美国最浅的结构。压缩波速和剪切波速的深度相关估计不仅有助于地下成像的研究，而且有助于地震危险评估和地震工程。新方法是非侵入性的，不需要使用炸药进行钻井或现场实验，并且可以应用于任何具有单个地震台或密集阵列的地点。此外，如果不寻求深度依赖性，则可以使用易于安装且廉价的仪器，从而能够以低成本揭示土壤/地壳结构的详细变化。从这项研究中获得的近地表结构可以用作地面运动模拟的输入模型，并将有助于诸如需要在关键位置进行震动预测的地震预警等项目。该项目还将促进美国大陆地质研究的多学科研究。由于该技术可以解析顶部几公里或更小的地震结构，因此本研究揭示的横向变化可以与在地表观察到的地质区域进行比较和解释。目标的浅度也开始将全球地震学分析（使用遥远的地震数据）与近地表临界区研究结合起来，并有助于我们理解地球表面发生的复杂过程。新技术利用体波偏振来解析地震台正下方的波速。与走时等其他量相比，地震波偏振信息相对未被开发，将建立和测试将远震体波偏振信息与近地表波速联系起来的基本理论框架。与直觉相反，远震 P 波的偏振对剪切波速度敏感，而 S 波的偏振对压缩波和剪切波速度都敏感。此外，检查偏振数据的频率依赖性可以构建浅层地下的与深度相关的波速模型。该方法将应用于 USArray 数据，以生成美国大陆的近地表波速模型。将通过不同频率滤波器以及组合来自可移动阵列、参考网络和柔性阵列的数据，在不同尺度上研究波速在垂直和水平维度上的空间变化。结果将为地壳特性提供更好的约束，并可用于改进用于其他类型研究（例如全球或区域地震层析成像）的地壳校正。