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，或与之相反的品质因数(Q)，是地球上最基本的参数之一--S介质。测量区域距离的衰减传统上使用地震产生的地震波，这通常需要对震源有很好的了解，或者需要特别选择几何图形来抵消震源效应。基于地震环境噪声相关方法的研究已经成为地震学中发展最迅速的分支之一。该方法已被证明在提取地震速度方面是非常有效的。提取幅度信息更具挑战性。最大的挑战是地球？S环境噪声场是高度各向异性的、非均匀的、随时间变化的。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)中提取面波衰减的方法和过程。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。我们将使用来自美国阵列和中国阵列的数据作为试验台，目标是制作该地区的面波衰减图。理论推导和数值模拟的初步结果表明，即使在不完全扩散的噪声场的情况下，我们也不仅可以稳健地恢复走时，还可以恢复射线到达幅度、环境场的S比强度、散射体的强度和密度(如果有的话)、站点放大因子，以及最重要的衰减。我们提出了两种方法，并给出了详细的公式：线阵方法和更一般的二维站网方法，每种方法都是通过对数值模拟数据和实际数据的应用来发展的。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、各向异性和时变的环境噪声分布问题。这一领域的突破将改变绘制地球图的新方法-S衰减，超越传统的基于地震的方法，并改变我们对迅速发展的环境噪声地震学的新理解。这种方法克服了传统的基于地震的方法在绘制面波衰减(如震源信息、地震和台站分布)方面的一些缺点。环境噪声衰减图和场地因子的新结果对研究地球-S内部、震源和地震危害具有广泛的意义。