基于起伏界面走时校正的三维最短路径射线追踪方法  

Three-dimensional shortest path ray tracing method with traveltime correction for undulating interfaces

作　　者：秦泽光 赵爱华[1] 徐涛[2] 姚时 QIN ZeGuang;ZHAO AiHua;XU Tao;YAO Shi(Institute of Geophysics,China Earthquake Administration,Beijing 100081,China;Key Laboratory of Deep Petroleum Intelligent Exploration and Development,Institute of Geology and Geophysics,Chinese Academy of Sciences,Beijing 100029,China;University of the Chinese Academy of Sciences,Beijing 100049,China)

机构地区：[1]中国地震局地球物理研究所,北京100081 [2]中国科学院地质与地球物理研究所,深层油气理论与智能勘探开发重点实验室,北京100029 [3]中国科学院大学,北京100049

出　　处：《地球物理学报》2025年第2期578-594,共17页Chinese Journal of Geophysics

基　　金：国家重点研发计划项目(2020YFA0710601);国家自然科学基金项目(41374098,41974065)资助

摘　　要：最短路径射线追踪方法来源于图理论,可以获得最小走时路径,是初至波和反射波走时成像的重要正演模拟方法之一.最短路径法通常以规则网格离散速度模型,规则网格难以精确表征起伏地表和地下弯曲界面,因而计算的走时精度不是很高.减小网格尺寸可以减小计算误差,但同时会增加计算时间,对于三维模型尤其如此.为此,本文针对三维模型提出一种基于规则网格的走时校正方法:当地震射线传播至或起始于边界节点(近似表征界面的模型节点)时,将走时校正为射线传播至或起始于边界节点所对应界面节点(模型节点网格线与界面的交点)的走时.应用走时校正技术后可以基本消除由界面近似引起的反射波走时误差,并且可改善射线路径分布.数值模型计算结果表明:走时校正方法所用计算时间基本保持在和常规算法相同的量级,但走时校正方法可提高反射波的走时精度约1~2个数量级.The shortest path ray tracing method,which originates from the graph theory,gives minimum traveltime rays from the source to receivers and plays an important role in seismic tomography with first-break or reflection traveltime.It is usually based on a regular grid spanning the model,and the accuracy of calculated traveltime is not high because of the rough characterization of the undulating surface and underground curved interfaces on the regular grid.Refining the grid reduces errors of calculated traveltime but greatly increases the computational time,especially for 3D models.To solve the contradiction between accuracy and efficiency of the shortest path method,we introduce regular grid based traveltime correction technique for three-dimensional models:when a seismic ray starts from or arrives at one of boundary model nodes with which interfaces are approximately characterized,its traveltime is modified to that of the ray starting from or arriving at the interface node(intersection points of the model-node grid and the interfaces)responding to the boundary model node.The travel time correction technique can basically eliminate the reflection wave travel time error resulting from the interface approximation.The improvement on the traveltime accuracy also betters the ray path distribution.Numerical tests show that application of the traveltime correction technique to calculating reflection traveltime increases the accuracy by about 1~2 orders of magnitude while the computation time remains the basically same order as that of the conventional algorithm.

关 键 词：射线追踪 最短路径算法 规则网格 起伏界面 走时校正 

分 类 号：P315[天文地球—地震学]