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（Q）的衰减或其逆质量因子（Q）是地球媒体中最基本的参数之一。在区域距离处的衰减的测量传统上使用地震产生的地震波，通常需要对源头有良好的了解或特殊选择的几何形状来取消源效应。基于地震环境噪声相关方法的研究已成为地震学最快速扩展的分支之一。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。最大的挑战是地球的环境噪声场是高度各向异性，不均匀的，并且随时间变化。在这里，我们建议探索从地震环境噪声构建的经验绿色功能（EGF）中提取表面波衰减的方法和程序。我们的方法是将合理的理论理解和实际考虑与真实数据相结合。我们将使用USARRAY和CHINARRAY中的数据作为测试床，其目标是产生该地区的表面波衰减图。理论推导和数值模拟的初步结果表明，即使在不完全弥漫的噪声场的情况下，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幅度，环境场的特定强度，特定的特定强度，其散射器的强度和密度，如果有的话，现场放大因素，以及最重要的是验证。我们提出了两种具有详细配方的方法：线性阵列方法和2D站网络的更通用方法，每种方法都是通过应用程序来开发的，用于数值模拟的数据以及真实的数据。从环境噪声中提取衰减是一个领域的研究问题。特别是，需要创新来解决地球上不均匀，各向异性和时变的环境噪声分布的问题。在这一领域的突破将具有变革性的变革性，以产生一种新的方式来绘制基于传统地震的方法的衰减以及我们对快速扩展的环境噪声地震学的新理解。该方法克服了基于地震的传统方法在绘制表面波衰减（例如地震来源信息以及地震和站点分布）中的一些缺点。衰减图和具有环境噪声的现场因素的新结果对地球内部，地震来源和地震危害的研究具有广泛的影响。