中国地震局地球物理研究所, 北京 100081
基金项目: 国家自然科学基金项目（41374098），中国地震局地球物理研究所基本科研业务费专项基金项目（DQJB19B40）资助
详细信息
作者简介: 赵爱华, 男, 研究员, 2001年在中国科学院地质与地球物理研究所获理学博士学位, 主要从事复杂介质射线追踪方法及其应用研究.E-mail: ahzhao@cea-igp.ac.cn
中图分类号: P315;P631 收稿日期:2020-09-11
修回日期:2021-05-20
上线日期:2021-07-10
An interpolation-based method for accurately calculating hypocentral loci for earthquake location on sparse grids
ZHAO AiHuaInstitute of Geophysics, China Earthquake Administration, Beijing 100081, China
MSC: P315;P631
--> Received Date: 11 September 2020
Revised Date: 20 May 2021
Available Online: 10 July 2021
摘要
摘要:区域和全球地震定位越来越多地基于更接近实际的横向非均匀速度模型.速度模型主要来自于地震体波层析成像结果，分辨率不是很高.这样，模型宜于以稀疏网格剖分以减少计算时间和计算机内存需求.当剖分的模型单元较大时，基于射线追踪技术计算复杂介质地震定位中震源轨迹的方法——选取震源轨迹所经过单元节点（位于单元中心，称为震源轨迹节点）为轨迹参考点，利用最小走时树射线追踪方法计算绝对残差场中连接轨迹参考点的射线路径作为震源轨迹——计算结果误差较大，难以满足精定位需要.针对该问题，本文对其进行了改进：不将震源轨迹节点作为轨迹参考点，而是基于插值技术计算每个轨迹节点其法线点对（即该节点与其周围残差正负极性不同的相邻节点组成的点对中梯度绝对值最大的那对）间残差为零的点作为震源轨迹参考点.算例表明：和原方法相比，改进方法计算的震源轨迹更为精细，计算精度提高数十（线性插值）至数百倍（非线性插值），而计算效率基本保持在同一数量级，使利用震源轨迹进行直观、快速和高精度的区域或全球地震事件定位成为可能；壳幔界面反射纵波（PmP）对震源的约束和直达纵波（Pg）相似；同一台站PmP-Pg波到时差约束的震源轨迹对震源深度有很好的约束.
关键词: 地震定位/
稀疏网格/
震源轨迹/
射线追踪/
插值
Abstract:Regional and global earthquake location is increasingly based on more realistic models including lateral velocity heterogeneity. Most of such models are derived from seismic body-wave tomographic results. They have large scales and low resolutions, and therefore are usually discretized with sparse grids due to computational time and memory. When elements of a complex velocity model are large, it is difficult to accurately calculate hypocentral loci, which are useful for robust and visual earthquake location. To solve the problem, I modify a ray tracing-based method in which nodes at the centers of the model elements traversed by a hypocentral locus, referred to as focal locus nodes (FLNs), are selected as focal locus reference points (FLRPs); ray paths through the FLRPs in the field of absolute residual are calculated with a minimum traveltime tree algorithm to represent the true hypocentral locus. In the modified version, FLRPs are not assigned to be FLNs but to be zero-residual points obtained by interpolation, between the normal node pairs of FLNs. As for a FLN, its normal node pair is the one with maximum absolute gradient among all the pairs consisting of it and its adjacent nodes differing from it in the residual polarity (positive, zero, or negative). Numerical examples show that compared with the original method, the modified one can more accurately calculate hypocentral loci and the accuracy is improved by tens to hundreds times while the calculation efficiency almost remains the same order of magnitude. This makes it possible to visually, quickly and accurately locate regional and global events using their hypocentral loci. As for an earthquake in the crust, its compressional waves reflected (PmP) from the crust-mantle boundary are similar in constraining the hypocenter to the direct compressional waves (Pg); hypocentral loci constrained with differential times between PmP and Pg waves at the same stations provide good constraint on the hypocentral depth.
Key words:Earthquake location/
Sparse grids/
Hypocentral locus/
Ray tracing/
Interpolation
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http://www.geophy.cn/data/article/export-pdf?id=d3dc27e1-fa6a-4167-916b-0ad297acc735
