Fast and accurate calculation of seismic wave travel time in 3D TTI media  

三维TTI介质地震波走时的快速精确计算

作　　者：Mao Yuan-Tong Zhao Ai-Hua 毛元彤;赵爱华(中国地震局地球物理研究所,北京100081;中国科学院地质与地球物理研究所,100029;中国科学院大学,北京100049)

机构地区：[1]Institution of Geophysics,China Earthquake Administration,Beijing 100081 [2]Institute of Geology and Geophysics,Chinese Academy of Sciences,Beijing 100029 [3]University of Chinese Academy of Sciences,Beijing 100049

出　　处：《Applied Geophysics》2021年第4期545-556,594,595,共14页应用地球物理（英文版）

基　　金：funded by the National Key R&D Program of China (No. 2020YFA0710600);National Science Foundation of China (No. 41374098);the Special Fund of the Institute of Geophysics,China Earthquake Administration (No. DQJB19B40)

摘　　要：The Tilted tilted transversely isotropic(TTI)media,a kind of anisotropic medium,widely exists within the earth.For faster calculation of travel times in the TTI anisotropic media,we modifi ed a minimum traveltime tree algorithm with high effi ciency by dynamical modifi cation of the secondary wave propagation region during the spread of seismic waves.To manage the wavefront points in the modified version,we used a novel minimum heap sorting technique to reduce the time spent on selecting secondary waves points.In this study,seismic group velocities were obtained from analytical solutions in terms of phase angle,and the corresponding phase angles were determined by binary search rather than approximate equations for weakly anisotropic media.For the most time-consuming part of the secondary wave traveltime calculation,the parallel computation was initially performed using multiple cores and threads.Numerical examples showed that the improved method can calculate seismic travel times and ray paths faster and accurately in a 3D TTI medium.For four cores and eight threads,the computing speed increased by six times when compared to the conventional method.TTI介质(即对称轴倾斜的横向各向同性介质)是地球内部广泛存在的各向异性介质之一。为快速、准确地计算地震波(例如初至波和转换波)在该种介质三维空间中的传播走时和射线路径,本文基于子波传播区域随地震波传播动态调整的最小走时树射线追踪方法,改进了波前点管理的排序方法,并将并行算法应用于射线追踪的子波走时计算中。新方法不再使用基于弱各向异性假设的群速度近似公式,而是以二分法准确地求取给定射线角的地震波群速度;对算法中最为费时的子波传播走时计算部分,进行了多核多线程并行化处理。此外,新方法使用了效率较高的最小堆排序方式管理波前点,可以进一步减小计算量。算例表明,本文方法可快速、精确地计算对称轴任意倾斜的三维TTI介质中的地震波走时和射线路径;和传统算法相比,使用4核8线程计算速度可提高6倍。

关 键 词：TTI media ray tracing minimum traveltime tree algorithm minimum heap sorting parallel computation 

分 类 号：P631.4[天文地球—地质矿产勘探]