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常规陆上VSP(Vertical Seismic Profiling)勘探普遍采用纵波震源激发,三分量检波器接收,主要利用的是纵波和转换横波信息。已有的研究表明,炸药震源在井下激发、可控震源在地面垂向振动,均会产生较强的纯纵波和一定强度的纯横波;泊松比差别较大的分界面有利于形成较强的透射转换横波。本文通过对激发形成的纯横波和下行转换形成的横波进行对比分析,认为纯横波的主频往往低于纯纵波的主频,而下行转换横波的主频通常接近纵波的主频。本文分别对两个陆上纵波源零偏和非零偏VSP资料进行分析,结果表明这些资料中普遍存在纯横波,只是横波的强弱存在不同程度的变化。利用纵波源零偏VSP资料,可以获得横波速度信。最后对VSP纵波和横波联合应用前景进行了分析,应该充分利用纵波源VSP资料中的横波信息。
Conventional VSP (Vertical Seismic Profiling) exploration generally uses longitudinal wave source excitation, three-component detector to receive, the main use of the longitudinal wave and the conversion of shear wave information. Previous studies have shown that explosives source excitation in the underground, vibrator vibrating vertically on the ground, will have a strong pure longitudinal wave and pure shear wave of a certain intensity; Poisson ratio of the larger differences in the interface is conducive to the formation of strong Transmitted transversal shear waves. In this paper, by contrasting the shear waves formed by the pure shear wave and the downward transition, it is considered that the fundamental frequency of the pure shear wave is often lower than that of the pure longitudinal wave, while the dominant frequency of the downsampling shear wave is usually close to the fundamental frequency of the longitudinal wave. In this paper, the VSP data of two longitudinal P-wave sources are analyzed respectively. The results show that pure S-waves are common in these data, but the intensity of the S-wave changes to some extent. By using the VSP data of longitudinal wave source, the S-wave velocity signal can be obtained. Finally, the prospect of combined application of VSP and S-wave is analyzed, and the S-wave information in VSP data should be fully utilized.