Taking the excavation blasting of bed rock mass in Sania Project as the background, six blasting experiments have been done at the bottom of weak weathering granite in Sanxia dam and the 36 sets of seismic waveform at different positions away from the explosion sources are measured. Through the analyses of both frequency and statistics, it is found that vibration frequency varies inversely as both the charge weight and distance away from the explosion source and that the duration of seismic waves varies directly as the charge weight and inversely as the distance. The attenuation law of seismic waves is determined by applying the neural network theory. Meanwhile,the microcracking zone boundaries of rock mass in blasting are mersured using the computer tomography (CT) and their corresponding critical vibration velocities of rock particles are also calculated which are 13.8～16.6 cm/s.%以三峡工程坝基岩体开挖爆破为背景，在弱风化花岗岩底板内进行了6次现场爆破试验，测量出距爆源不等距离处的36组地震波形。通过频域与统计分析发现，岩石质点振动主频率与药量、距离成反比关系；地震波作用时间与爆破药量成正比关系，而与距离成反比关系。应用神经网络理论建立的基于爆破地震效应先验知识的网络模型（PKFN）能很好地描述爆破地震波的衰减规律，其计算平均相对误差仅为3.5 % 。用地震层析成象方法（CT）较准确地测定出了岩体爆破松裂区边界，并结合PKFN模型得到了三峡工程坝基岩体的临界质点振动速度范围13.8 ～ 16.6 cm/s。
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