转换波勘探中的低速带效应

主要讨论了3个问题:①低速带表层的纵横波速度比对多分量记录矢量性的影响;②多分量记录上折射波的类型;③形成转换折射波的条件。理论分析表明,在转换波勘探中,当低速带表层的纵横波速度比较大时多分量记录表现为标量波场,当纵横波速度比不是很大时则表现为矢量波场;模型分析表明,垂直方向记录上的折射纵波主要是下行和上行纵波,水平方向记录的转换折射横波主要是下行纵波和上行横波。文章还分析了低速带底层介质和下伏基岩不同纵横波速度对转换折射横波振幅的影响,认为形成转换折射横波的条件是低速带底层横波速度远远小于下伏介质的横波速度。

Effects on low velocity zone in converted wave exploration

Three questions are discussed: ①In the overlay of low velocity zone, the velocity ratios between P and S have an effect on the vector of multicomponent record for scalar. ②Which type is the refraction wave in multicomponent records.③What is the advantageous condition to form the converted refraction wave. Theoretical analysis indicates that, in the converted wave exploration, multicomponent records is scalar wave field when velocity ratio of P-wave to SV wave is big enough, otherwise it is vector wave field when the ratio is small enough. Analysis to model indicates the refraction P-wave on the vertical component comes mainly from down P-wave and up P-wave and the conversion refraction S-wave on the horizontal component comes mainly from down P-wave and up S-wave field. By the effect analysis to amplitude to different velocity value of P-wave and S-wave in the bottom of low velocity zone and bedrock, the advantageous condition to form conversion refraction S is that S-wave velocity in the bottom of low velocity zone is much smaller than that of the bedrock.