用地震反射法对玉溪盆地普渡河断裂的探测

Detection of Puduhe fault in Yuxi basin of Yunnan by seismic reflection method

通过在玉溪盆地用地震反射法探测普渡河隐伏断裂的实例,阐述了在覆盖层很厚、人口密集、环境干扰强条件下的地震勘探方法技术.本次勘探针对场地条件使用了大型可控震源和小检波距、长排列、高覆盖次数的观测系统.获得的高信噪比时间剖面清晰地揭示了玉溪盆地内普渡河断裂的产状和规模.勘探结果表明,玉溪盆地覆盖层(N+Q)最大厚度超过820m;基岩面西陡东缓,呈北北东走向的箕状分布;普渡河断裂分两支穿过玉溪盆地西部,主断裂为正断性质,走向约N20°E,倾向东,视倾角75°—80°;断裂规模由南向北逐渐变大,基岩断距在盆地南部的大营街附近为40m,而在盆地北部的九龙池东部,基岩断距增加到280m左右,穿过玉溪盆地西部的普渡河断裂错断了新近系上新统中上部地层.

A scheme is described for seismic prospecting implemented under complicated conditions such as thick overburden, dense population and strong background noise. This is illustrated by detecting Puduhe buried fault located in Yuxi basin using seismic reflection method, in which a spread geometry with a large vibrator, small receiver intervals, long arrangement and high fold number was selected in accordance with the real site conditions. The seismic time sec- tion with higher SNR obtained in this case clearly reveals the attitude and scale of the Puduhe fault. Results show that the maximum overburden of Yuxi basin （N＋Q） is 820 m. The surface of the basement rock changes abruptly in west, while gradually in east, showing a dustpan-like geometry with a strike of NNE -SSW. Puduhe fault is divided into two branches across the western Yuxi ba- sin. The main fault has a strike of N20°E, dipping to east with an apparent an- gle 75°--80°. The fault scale increases gradually from south to north. The throw of the basement is 40 m near Dayingjie town located at the south of the basin, and increases up to 280 m near Jiulongchi town at the north of the basin. The Puduhe fault, crossing western Yuxi basin, dislocated the middle and up- per strata of Pliocene series, Neogene system.