点爆炸震源干扰波理论研究
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摘要
采用地震波的双源传递机理和正压介质模型 ,可以对疏松地质介质中点爆炸震源产生的干扰波进行理论研究。本文提出 ,在疏松激发层中易于产生低频稀疏纵波和低频 SV面波干扰 ,并给出了相应的解析近似解。结果表明 ,对给定的激发层厚度、岩性、有效信号低端频率和波的时域衰减陡度 ,存在一个最小井深 Hmin。当炮孔深度大于 Hmin时 ,增大井深可以更好地压制干扰。如果炮孔深度小于 Hmin,增大井深并不能削弱稀疏纵波 ,反而使这一干扰波更强。当 Hmin大于激发层厚度时 ,则井深增大同样使稀疏纵波干扰更强。结果还表明 ,存在一个由岩性和波的时域衰减陡度决定的临界井深增量Δ H ,当井深增量远小于这一值时 ,井深增量变化并不能显著削弱 SV面波干扰。文中研究结果较好地解释了在井深试验时常常碰到的似是而非的现象。对于提高野外资料采集质量和在处理中压制干扰波提供了一个理论模型近似。
Both the dual source transmission mechanism of seismic wave and the model of positive pressure medium may be used to have theoretical study of noise waves resulting from dynamite point source in loose medium. It is pointed out that there often occur low frequency sparse compressional wave and low frequency SV surface wave in loose shot layer, their approximate analytic solution being offered also. It is also shown that there is a minimum shothole depth for given conditions including thickness and lithology of shot layer, low end frequency of effective signal, and wave attenuation steepness in time domain. If shot hole is deeper than the minimum shothole depth, the increase of shothole depth betters noise suppression. If shot hole is more shallow than the minimum shothole depth, the increase of shothole depth fails to weaken the sparse wave but highlights it. In addition, the increase of shothole depth also enhances sparse wave when the minimum shothole depth is bigger than the thickness of shot layer. It is also indicated that there exists a critical increment ΔH of shothole depth which depends on both lithology and wave attenuation steepness in time domain. If shothole depth increment is much lower than the critical one, the variation of shothole depth increment fails to reduce SV surface wave obviously. The research result explains clearly the specious phenomena that often appear in shothole depth experiments. A theoretical modeling approximation is offered for both improving field data acquisition and suppressing noises in indoor data processing.
Both the dual source transmission mechanism of seismic wave and the model of positive pressure medium may be used to have theoretical study of noise waves resulting from dynamite point source in loose medium. It is pointed out that there often occur low frequency sparse compressional wave and low frequency SV surface wave in loose shot layer, their approximate analytic solution being offered also. It is also shown that there is a minimum shothole depth for given conditions including thickness and lithology of shot layer, low end frequency of effective signal, and wave attenuation steepness in time domain. If shot hole is deeper than the minimum shothole depth, the increase of shothole depth betters noise suppression. If shot hole is more shallow than the minimum shothole depth, the increase of shothole depth fails to weaken the sparse wave but highlights it. In addition, the increase of shothole depth also enhances sparse wave when the minimum shothole depth is bigger than the thickness of shot layer. It is also indicated that there exists a critical increment ΔH of shothole depth which depends on both lithology and wave attenuation steepness in time domain. If shothole depth increment is much lower than the critical one, the variation of shothole depth increment fails to reduce SV surface wave obviously. The research result explains clearly the specious phenomena that often appear in shothole depth experiments. A theoretical modeling approximation is offered for both improving field data acquisition and suppressing noises in indoor data processing.
引文
1 何樵登 .地震勘探原理和方法 ,地质出版社 ,1986
2 Henrych J著 ,熊建国等译 .爆炸动力学及其应用 ,科学出版社 ,1987,16 1～ 2 30
3 Rinehart JS著 ,杨善元译 .固体中的应力瞬变 ,煤炭工业出版社 ,1981,72～ 74 ,149～ 16 1
4 胡德绥 .弹性波动力学 ,地质出版社 ,1989,2 2 8～ 2 2 9
2 Henrych J著 ,熊建国等译 .爆炸动力学及其应用 ,科学出版社 ,1987,16 1～ 2 30
3 Rinehart JS著 ,杨善元译 .固体中的应力瞬变 ,煤炭工业出版社 ,1981,72～ 74 ,149～ 16 1
4 胡德绥 .弹性波动力学 ,地质出版社 ,1989,2 2 8～ 2 2 9
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