Abstract：In order to choose optimum seismic acquisition parameters for limestone cropping area,we conducted both data acquisition test and frequency spectrum determination for near source seismic waves in the steep limestone structure cropping area in east Sichuan. Acceleration sensors were planted in borehole and on surface to determine the frequency spectra of near-source seismic waves which were generated from different shot conditions (depth,charge and lithology). The frequency spectra were compared with the seismic signals received by seismic geophones so as to check the results .The field test led to the conclusion:①low velocity layer in mountainous region appears as bath surface soil and weathered cropping(IO m or SOj;②downhole 'frequency spectrum and surface frequency spectrum differ greatly due to the influence of low velocity layer lOm thick;③limestone,sandstone and mudstone have very different absorptions to high frequency contents,their absorptions decreasing in the order;④directional一delayed shots play obvious role in decreasing frequency spectrum and seismic wave attenuation;⑤influenced by the low velocity layer,seismic wave varies greatly in their travel time,amplitude,frequency and phase. In order to improve S/N ratio of seismic data in limestone cropping area,we must choose reasonable shot parameters,pay more attention to improving the receiving conditions,and use downhole receiving when it is necessary.
