桂南陇瑞洼地浅层岩溶自然电场特征剖析

岩溶洼地地下水渗透流在一定的渗透压力作用下，通过洼地土层过滤后沿碳酸盐岩溶蚀裂隙网络或孔隙下渗补给岩溶管道或地下河等深层岩溶水，便会产生离子导电岩土层的自然极化现象和自然电场，这种自然电场的研究方法可用于洼地浅层岩溶水的探测。研究结果表明，陇瑞洼地浅层岩溶发育带产生的自然电场实测值的平面等值线在洼地中心部位上出现了场幅值-60～-80 mV、带宽约40 m的带状异常，异常带由北至南呈似“S”状分布；自然电位梯度实测值的平面等值线在岩溶发育带顶部在地面投影中心线附近出现由负值向正值过度的“零值”异常带，“零值”异常带平面分布位置的变化指示了洼地浅层岩溶发育的平面差异与变化。以第18测线为例，陇瑞洼地浅层岩溶自然电位在剖面上分布满足位函数分布特征，即自然电位在浅层岩溶带顶部（615/18测点附近）取得极小值，在极小值的两侧由于逐渐远离岩溶发育带自然电位幅值逐渐减弱，直至趋近于零；自然电场梯度在浅层岩溶带顶部（615/18测点）附近出现由负值向正值过度的“零点”异常，呈似中心对称曲线。水文地质监测钻孔在不同深度揭露了浅层溶洞、溶隙和断层破碎带，从而验证了自然电场法探测岩溶洼地浅层岩溶水资源的有效性。 

Analysis of the characteristicsof self-potential anomalous in shallow karst area of Longrui valley,southern Guangxi,China

Under the influence of osmotic pressure, the seepage water flow filtered by depressions soil in karst valley, gradually infiltrate downward and finally discharge to karst conduits or underground river through upper karst erosion networks or karst fissures. In this process, the spontaneous polarization phenomenon or self-potential field will form by the ionic conductive materials. Therefore, the study on self-potential can be applied to explore shallow groundwater in karst valley. The study results showed that the self-potentials banded anomalies ranging from -60～-80 mv with about 40 m wide and extending from north to south with "S" shape have been observed just near the center of Longrui karst valley. On the plane view, the self-potential gradient contours present "zero" value anomalies varying from negative to positive near the top of the karst zones. The spatialdistribution of the "zero" value anomalous zones indicates the surface differences and changes of shallow karst development. Taking Line 18 as an example, the self-potentials caused by shallow karst seepage water in Longrui valley follow the potential function distribution, namely the self-potentials have reached the minimum and accordingly self-potential gradients vary from negative to positive with the shape of central symmetry which shows the "zero" value just near the top of the shallow karst zones(station 615). The self-potentials on either side of the minimum gradually weaken until go to zero due to the stations moving away from the karst zone. Shallow caves, dissolved-fissures and fault fractures were exposed at different depths by the hydrogeologic monitoring borehole. Thus it means that the self-potential can be used as an effective geophysical method for detecting shallow karst water.