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，或其倒数，品质因数（Q），是地球最基本的参数之一？s媒体。在区域距离上测量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，或者需要特殊选择的几何形状来抵消震源效应。基于地震环境噪声相关方法的研究已成为地震学发展最快的分支之一。该方法已被证明是非常有效的提取地震速度。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的，非均匀的，并随时间变化。在这里，我们建议探索的方法和程序，提取面波衰减的经验绿色函数（EGFs）构造地震环境噪声。我们的方法是将联合收割机合理的理论理解和实际考虑与真实的数据相结合。我们将使用来自USAray和ChinArray的数据作为测试床，目的是制作该地区的面波衰减图。从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，我们可以鲁棒地恢复不仅旅行时间，但射线到达幅度，环境场？的比强度，其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，详细的配方：线性阵列方法和更一般的方法，二维站网络，每个开发通过应用程序的数值模拟数据，和真实的数据。从背景噪声中提取衰减量是一个前沿研究问题。特别是，需要创新来解决地球上不均匀、各向异性和时变环境噪声分布的问题。这一领域的突破性进展将产生一种新的绘制地球地图的方式？的衰减超出了传统的地震为基础的方法和我们的新的理解迅速扩大的环境噪声地震学。该方法克服了传统的基于地震的方法在绘制面波衰减图（如震源信息和地震与台站分布）方面的一些缺点。新的结果，从衰减地图和现场因素与环境噪声有广泛的影响，研究地球？的内部，地震震源和地震灾害。