起伏地表下高精度三维地震波走时层析成像方法及其应用研究

Seismic imaging is an effective way to understand the Earth's internal structure and dynamic process. With the development of seismic detection and its technology, intensive observations become more and more, making the imaging of the internal structure of the Earth towards three-dimension and high accuracy, so as to get better imagings of the real Earth. Undulating surface is an important factor which affects the precision of the fine imaging of the three-dimensional structure. How to evaluate and eliminate the influence of surface topography, and make full use of the intensive data to reconstruct the three-dimensional structure of the study area has become the key content in seismic imaging study. The applicant made a useful and beneficial attempt in two-dimensional seismic imaging with surface topography, which may provide references and technical reserves to three-dimensional high resolution seismic imaging. In this project, we intend to develop a high accurate three-dimensional finite-difference tomography scheme that can match the complex terrain perfectly. By applying the method to theoretical models and three-dimensional wide-angle seismic data collected in eastern Kunlun orogeny belt, to verify its feasibility and validity, and to quantitatively evaluate the influence of the surface topography made on the crust and mantle structure imaging, which serves as methodological basis and practical model for the imaging of the fine three-dimensional structure of the crust and mantle.

地震学成像是认识地球内部精细结构和动力学过程的有效手段。近年来，随着地震探测的深入和探测技术的发展，地震资料不断积累，要求地球内部结构成像向三维和更高精度方向发展，以使成像结果更加逼近真实地球结构。起伏地表是影响三维结构地震学成像精度的重要因素。如何评估和消除起伏地表影响、并充分利用已有观测资料重建地球内部三维结构已成为高精度地震成像研究的关键内容。申请者前期在二维起伏地表地震成像方面所做的有益探索为三维高精度地震成像研究提供了借鉴依据与技术储备。本项目拟发展起伏地表下三维地震波走时精确计算和高精度层析成像新方法，通过将新方法应用于理论模型数据和东昆仑造山带三维主动源宽角地震数据，验证方法的可行性和有效性，并定量评判起伏地表对壳幔结构成像质量的影响，为壳幔精细结构三维成像研究提供方法基础与实践依据。

为了精细的描述地球内部结构和动力学过程，地球内部结构成像向三维和高精度发展。走时层析成像是重建地下速度结构的主要工具。然而，传统的走时成像方法受三维复杂地表地形、各向异性复杂介质组成及反演时所使用震相单一等的限制成像精度较低，难以满足地壳精细结构重建的需要。针对上述问题，本项目发展了一整套直接对起伏地表进行高精度走时计算和层析成像的方法，并在实际资料的处理中取得了良好的应用效果。. 具体的方法研究主要包括：提出了三维复杂地质模型贴体网格建模新方法，使用偏微分方程的方法生成高质量的贴体网格，实现了对复杂地质模型的精确描述；将笛卡尔坐标系地震波传播理论推广到普适性的曲线坐标系，建立了三维曲线坐标系下刻画地震波运动学特征的程函方程；发展了曲线坐标系程函方程的因式分解快速扫描求解方法，实现了起伏地表各向同性和各向异性介质模型中地震波走时的精确计算；在起伏地表走时计算的基础上，推导了起伏地表模型伴随状态公式，采用分区多步的思想，发展了适用于起伏地表的多震相（初至波和反射波）联合伴随走时层析方法，有效提高了速度结构成像的分辨率。. 本项目研究成果丰富，已发表及拟发表SCI论文共计10篇，项目负责人获得优秀青年基金资助，培养硕士1人，在读博士生1人，在读硕士生3人，成效显著。