Abstract：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 resuiting 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 waveiattenuation 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.
