近场地震快慢横波到时差测量离散辨析和改正

发布时间：2018-06-07 06:15

本文选题：横波分裂 + 到时差离散　；参考：《科学通报》2017年Z2期

【摘要】：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.
[Abstract]:Fast and slow shear wave to moveout is one of the important clues in seismic physical prediction. For a long time, due to the large dispersion between fast and slow shear wave and time difference, the physical relation between the observed time difference and the stress change during earthquake can not be established by most of the observed results. The dispersion of fast and slow shear wave measurements may be due either to anisotropic differences in formation structure and medium beneath the observation station or to the data processing process. In this paper, based on the near seismic data from January 2013 to January 2017 at KHZ station in the northern South Island of New Zealand, the physical properties and structure of the media at the bottom of the station are basically stable. The S-wave data are processed based on S-wave polarization vector analysis and visualization method. The frequency filtering and the normalized distance factor are compared one by one, which results in the discrete measurement of fast and slow S-wave inversion moveout in the process of S-wave processing. The phenomenon of "pseudo-dispersion", which may be caused by multiple splitting caused by anisotropic stratification of medium beneath the station, is analyzed, and a method to correct the measurement discretization of shear waves is given. Using "effective focal distance" as the length of normalized path to the time difference, the relationship diagram between the normalized S-wave and the time-difference with the focal distance shows clearly the spatial range and influence degree of the stress change before and after the M7.8 earthquake. It is a clear indicator of stress accumulation in observed areas before and after large earthquakes. The method of determining the depth of the shear wave splitting interface is given and the depth of the three shear wave splitting interfaces under the KHZ station in the northern South Island of New Zealand is obtained.
【作者单位】：北京大学地球与空间科学学院;
【基金】：国家自然科学基金(41674053)资助
【分类号】：P631.4

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