Theoretical and Observational Studies of Surface Wave Attenuation From Ambient Noise

环境噪声表面波衰减的理论和观测研究

• 批准号: 1215824
• 负责人: Xiaodong Song
• 金额: $ 34.31万
• 依托单位: University of Illinois at Urbana-Champaign
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2012
• 资助国家: 美国
• 起止时间: 2012-07-01 至 2016-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1215824&HistoricalAwards=false
• 关键词: Theoretical; Observational; Studies; Surface; Wave

Attenuation, or its inverse, quality factor (Q), is one of the most fundamental parameters of the Earth?s media. Measurement of attenuation at regional distances traditionally uses seismic waves generated by earthquakes, which generally requires either a good knowledge of the source or a special choice of geometries to cancel out source effects. Research based on seismic ambient noise correlation methodology has emerged as one of most rapidly expanding branches of seismology. The approach has been demonstrated to be highly effective at extracting seismic velocities. Extracting amplitude information is more challenging. The greatest challenge is that the Earth?s ambient noise field is highly anisotropic, non-uniform, and variable with time. Here, we propose to explore the methodologies and procedures for extracting surface wave attenuation from empirical Green functions (EGFs) constructed from seismic ambient noise. Our approaches are to combine sound theoretical understanding and practical considerations with real data. We will use data from the USArray and ChinArray as testing beds with the goal to produce surface wave attenuation maps of the regions. Preliminary results from theoretical derivations and numerical simulations show that even in the case of incompletely diffuse noise fields, we can robustly recover not only travel times, but also ray arrival amplitudes, the ambient field?s specific intensity, the strength and density of its scatterers if any, site amplification factors, and most importantly attenuation. We propose two approaches with detailed formulations: linear array methods and more general methods for 2D station networks, each to be developed through applications to numerically simulated data, and to real data. Extraction of attenuation from ambient noise is a frontier research problem. In particular, innovations are required to address the issue of non-uniform, anisotropic, and time-variable ambient noise distribution on Earth. Breakthroughs in this area will be transformative in producing a new way for mapping the Earth?s attenuation beyond traditional earthquake based methods and in our new understanding of the rapidly expanding ambient noise seismology. The approach overcomes some of the disadvantages of traditional earthquake-based method in mapping surface wave attenuation (such as earthquake source information and earthquake and station distribution). New results from attenuation maps and site factors with ambient noise have broad implications for studies of Earth?s interior, earthquake sources, and earthquake hazards.

衰减，或其反比，质量因子(Q)，是地球最基本的参数之一。媒体。测量区域距离上的衰减通常使用地震产生的地震波，这通常需要对震源有很好的了解，或者特别选择几何形状来抵消震源的影响。基于地震环境噪声相关方法的研究已成为地震学中发展最为迅速的分支之一。该方法已被证明在提取地震速度方面非常有效。提取振幅信息更具挑战性。最大的挑战是地球？环境噪声场具有高度的各向异性、非均匀性和随时间变化的特点。在这里，我们建议探索从地震环境噪声构造的经验格林函数（egf）中提取表面波衰减的方法和步骤。我们的方法是将良好的理论认识和实际考虑与实际数据相结合。我们将使用来自USArray和ChinArray的数据作为测试平台，目的是生成该区域的表面波衰减图。理论推导和数值模拟的初步结果表明，即使在不完全漫射噪声场的情况下，我们不仅可以稳健地恢复行进时间，而且还可以恢复射线到达振幅，环境场？S比强度，散射体的强度和密度（如果有的话），场地放大因素，最重要的是衰减。我们提出了两种详细的方法：线性阵列方法和二维台站网络的更一般的方法，每一种方法都将通过应用于数值模拟数据和实际数据来发展。从环境噪声中提取衰减是一个前沿研究问题。特别是，需要创新来解决地球上非均匀、各向异性和时变环境噪声分布的问题。这一领域的突破将带来革命性的变化，产生一种绘制地球地图的新方法？S衰减超越了传统的基于地震的方法，并在我们对快速扩展的环境噪声地震学的新认识。该方法克服了传统基于地震的地表波衰减制图方法的一些缺点（如震源信息和地震台站分布）。含环境噪声的衰减图和场地因子的新结果对地球的研究具有广泛的意义。S内部、震源、地震危险。