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快慢横波到时差是地震物理预报的重要线索之一.长期以来由于快慢横波到时差的较大离散,横波观测到时差变化与地震发生过程中应力变化之间无法建立能被绝大多数观测结果证实的物理联系.快慢横波测量离散既可能来自观测台站下方地层结构和介质的各向异性差异,也可能来自数据处理过程.本文利用新西兰南岛北部KHZ台站从2013年1月到2017年1月的单台近震数据,在观测台站底部介质物性和结构基本稳定的前提下,基于横波偏振矢量分析和可视化方法对横波数据进行处理,对横波处理过程中引起快慢横波倒时差测量离散的频率滤波、距离归一化因素进行了逐一的对比,并对台站下方介质各向异性分层可能引起的多次分裂所表现出来的“假离散”现象进行了分析,由此给出了改正横波测量离散的方法.用“有效震源距”作为到时差归一化路径长度得到的横波归一化到时差随震源距变化的关系图清晰地展示出7.8级地震前后应力变化的空间范围和影响程度,是较大地震前后观测地区存在应力积累的明确标识.给出了确定横波分裂界面深度的方法,得到了新西兰南岛北部KHZ台站下3个横波分裂界面深度.
One of the important clues to the physical prediction of seismic wave is the fast-slow shear-wave time-lapse.For a long time, due to the large discrepancy of the time-lapse between the fast shear and the slow shear wave, the time-lapse observed by the shear wave can not be established between the changes of stress during the earthquake and can be confirmed by most observations Of the physical contact between the fast and slow shear wave measurements scattered either from the observation station below the anisotropy of the formation structure and medium anisotropy may also be derived from the data processing.This paper utilizes the KHZ station in the northern South Island of New Zealand from January 2013 to January 2017 On the premise that the physical properties and the structure of the media at the bottom of the observation station are basically stable, the shear wave data are processed based on the analysis of the shear wave polarization vector and the visualization method. The shear wave velocity difference is measured during the shear wave processing Frequency filtering and distance normalization factors are analyzed one by one, and the phenomenon of “False Discrepancy ” manifested by multiple splits caused by the anisotropy of the medium below the station is analyzed. A method to correct the discretization of shear wave measurement is given by using the “effective seismic source distance” as the normalized shear wave length to the time difference The relationship between the time difference and the variation of the seismic source distance clearly shows the spatial extent and influence degree of the stress changes before and after the MS7.8 earthquake and is a clear indication of the stress accumulation in the observed area before and after the large earthquake.The method of determining the depth of shear wave interface , The depth of the three shear-wave splitting interfaces at KHZ station in the northern part of South Island of New Zealand was obtained.