Collaborative Research: CMG Research: Statistical Seismic Imaging

研究方向：统计地震成像。Levander， W.W. Symes， S. minkoff结晶壳和浅层近地表（100m深）环境都是复杂的、力学不均匀的区域，其力学性质的空间分布往往与相对光滑的层状沉积柱明显不同。勘探地震学是目前最重要的地下勘探手段之一：用于沉积柱中的石油勘探，用于浅层地下的岩土工程/环境目的，以及用于了解结晶地壳中的构造过程。反射地震学是石油工业发展起来的，用于勘探沉积柱，即介质是层状的，能量优势是单一分散的，尺度是二分的。它在近地表环境和地壳深部的应用都非常成功，但也存在着石油勘探中不常见的问题。近表面受到化学和机械风化过程的影响，产生高度不均匀的非分层介质。由于压实、化学变化和水的存在与否，机械性能在几个波长内会发生数量级的变化。结晶地壳虽然在力学性质上缺乏数量级的变化，但其地震速度和密度非均质在空间上具有复杂的自仿射（分形）分布。对于在地壳中较长的传播路径，波场往往落在强散射区，在这种情况下，线性成像系统将产生平庸或无意义的结果。该研究项目为复杂介质的互补成像范式迈出了第一步，该范式被称为统计地震成像，其中地下的统计特性是利用地震波场的统计特性绘制的。由于这是一个非常大的主题，建议的范围将限于几个领域的努力。研究将探索(1)亚波长尺度非均质性与宏观尺度传播效应（有效力学特性、速度、衰减、色散等）之间的有效模型；(2)多重反射和折射的区分程度及其对传统地震成像的影响；(3)强散射起始点的识别。该研究涉及高水平的软件开发和计算工作，包括三维地震模拟和材料属性和统计的非线性反演。没有一个单一学科拥有在统计地震成像方面取得重大进展的工具：需要地球物理学、应用数学和高性能计算方面的专业知识。主要研究人员在这些领域具有专业知识。这项研究有可能改善对社会具有重要意义的环境/岩土工程调查，以及对地壳结构和构造的更基础的研究。

Collaborative Research: CMG Research: Statistical Seismic ImagingA. Levander, W.W. Symes, S. MinkoffBoth the crystalline crust and the shallow near surface ( 100m depth) environment are complex, mechanically heterogeneous regions, often having spatial distributions of mechanical properties that are distinctly different from the relatively smoothly layered sedimentary column. Exploration seismology is currently one of the most important means of exploring the subsurface: for petroleum in the sedimentary column, for geotechnical/environmental purposes in the shallow subsurface, and for understanding of tectonic processes in the crystalline crust. Reflection seismology was developed by the petroleum industry to explore the sedimentary column, i.e., the medium is layered, the preponderance of energy is singly scattered, and scales are dichotomous. Its applications in both the near-surface environment and the deep crust have been very successful but also present problems not usually encountered in petroleum exploration. The near surface is subjected to chemical and mechanical weathering processes that produce a highly heterogeneous, nonlayered medium. Mechanical properties can vary by an order of magnitude within a few wavelengths due to compaction, chemical alteration, and the presence or absence of water. The crystalline crust, although lacking order of magnitude changes in mechanical properties, has a spatially complex, often self-affine (fractal) distribution of seismic velocity and density heterogeneities. For the relatively long path propagation in the crust, the wavefield often falls in a strong scattering regime in which linear imaging systems will produce mediocre or nonsensical results.This research program makes first steps toward a complementary imaging paradigm for complex media, termed statistical seismic imaging, in which statistical properties of the subsurface are mapped using statistical properties of the seismic wavefield. As this is an extremely large topic, the proposal scope will be limited to a few areas of endeavor. The investigations will explore (1) effective models relating subwavelength scale heterogeneity to macro-scale propagation effects (effective mechanical properties, velocity, attenuation, dispersion, etc), (2) the extent to which multiple reflection and refraction can be differentiated and their effects on traditional seismic imaging, and (3) the identification of the onset of strong scattering. The research involves a high level of software development and computational effort, including 3D seismic simulation and nonlinear inversion for material properties and statistics. No single discipline possesses the tools to make significant progress on statistical seismic imaging: expertise in geophysics, applied math, and high performance computing are needed. The principal investigators have expertise in these areas. The research has the potential of improving societally important environmental/geotechnical investigations as well as more fundamental research on the structure and tectonics of the Earth's crust.