Abstract: In urban active fault prospecting, the shallow structures usually display strong lateral inhomogeneity, appearing as the heavy fluctuation of interfaces and considerable variation of layer velocities. In this case, the traditional refraction data processing and interpreting methods based on homogeneous layered structures with level interfaces can't be directly applied to the prospecting. It is very important, therefore, to study the seismic behaviors in these complex structures and to deve~lop a new technique that can be used to process and interpret seismic refraction data obtained from urban areas. In this paper, forward computing of wave field is carried out by using wavefront expanding method in terms of Huygens' principle. Furthermore, in the light of Hagedoorn wavefront refractor imaging principle a new processing method of seismic refraction data and the corresponding interpretation software are developed, in which Hole's original finite-difference codes were modified with Lecomte's five operators for computing seismic travel times. Applying this technique, we successfully process the data from two refraction profiles recently completed in Yixu, Fuzhou City during urban buried fault prospecting. The results show that the shallow structures in the investigation area display three layers, which are sedimentary cover, strongly weathered layer and bedrock, respectively. The buried depth of the upper surface of bedrock ranges from 52m to 58m or so. The variation of P wave velocity in sedimentary cover is considerable.

Key words: complex structures, active fault prospecting, Hagedoorn principle, refractor wavefront imaging, Fuzhou City

摘要： 在城市活断层探测中,浅层结构常常表现为强烈的非均匀性,界面横向强烈起伏,层内速度变化较大,传统的基于平界面均匀层模型的折射资料处理方法不能适用.研究开发能应用于复杂介质结构中折射资料处理的方法就显得十分必要.文中基于惠更斯原理,用波前扩张法对波场作正演计算,根据哈格多恩折射波前成像原理,在lecomte算法和Hole有限差分计算程序的基础上,开发出1种复杂介质结构中折射资料的处理方法与软件,并用此方法处理了福州城市活断层折射探测试验中在义序完成的2条折射剖面资料.结果表明:探测区浅层为3层结构,分别为盖层、强风化层和基岩.基岩顶界面的埋深约为58～52m,盖层P波速度变化较大.

关键词: 复杂介质结构, 活断层探测, 哈格多恩原理, 折射波前成像, 福州