典型岩溶富水构造的多极距联合剖面曲线正演模拟研究

Research on forward simulation of multi-electrode spacing combined profile curves of typical karst water-rich structrues

基于点电源电场微分方程以及电场满足的边界条件出发,结合目前高密度电法找水时常用的点线布设方式,对岩溶区常见的隐伏断层破碎带和溶洞两类低阻富水构造的多极距联合剖面曲线进行了二维正演模拟。模拟结果表明:联合剖面曲线对地下隐伏低阻体反应灵敏,曲线存在良好的分异性。对溶洞低阻富水构造来说,溶洞富水构造埋深约为1/2~2/3倍极距时,正交点异常最明显,随着联合剖面极距继续增大,同步低趋势逐渐显现;地下低阻溶洞空间范围越大,联合剖面曲线分异性越好,正交点异常越明显。对断层破碎带低阻富水构造来说,随着联合剖面极距的增大,正交点向断裂破碎带倾斜方向略为移动,但并不明显,正交点位置主要受浅部低阻的影响,随着极距的逐渐增大,同步低趋势逐渐显现,正交点左侧在断层倾斜方向上越来越多的测点呈现同步低异常,但曲线较平缓,而正交点右侧的曲线较陡,视电阻率在断层顶板的正上方处出现极小值。当联合剖面曲线正交点异常较明显时,随极距的增大正交点处视电阻率值逐渐降低,当联合剖面曲线异常形态以同步低为主时,随极距的增大正交点处视电阻率值趋于稳定。联合剖面曲线左右两支形态对于水平对称模型是对称的,对于倾斜模型是非对称的,倾斜低阻构造的倾向与联合剖面曲线正交点附近较陡一侧的曲线倾向一致。模拟结果可应用到岩溶地区高密度电法的多极距联合剖面曲线资料解释中。

Based on differential equation of a point source and the boundary conditions of electric field,and combined the popular high density electrode layout for exploring groundwater at present,we conduct 2 Dforward simulation of multi-electrode spacing combined profile curve for two common and water-rich structures with low resistance in karst area such as buried fault zone and karst cave.The simulation results show that the combined profile curves are sensitive to underground hidden low resistivity structrues,and the curves are well differentiated.For the water-rich cave,the orthogonal point is the most prominent when the depth of water-rich cave is about 1/2-2/3 times the electrode space;as the distance of the electrode continues to increase,the synchronous low trend gradually appears.The larger the space range of the underground low-resistance cave is,the better the curve differentiation of the combined profile is,and the more obvious abnormal of the orthogonal point presents.For the water-rich fault zone,when the electrode space increases,the orthogonal point slightly moves to the dip direction of the fault,but is not obvious.The position of the orthogonal point is mainly affected by the low resistivity in the shallow part.With the increase of the electrode space,the downward low resistivity zone play a considerable role,for which more and more measuring points present as low synchronization in the dip direction on the left side of the orthogonal point with smaller slope curve while larger slope curve from the right side of the orthogonal point,the apparent resistivity reaches the minimum value at the top of the fault.The apparent resistivity decreases gradually with the increase of the electrode space when the orthogonal points of combined profile curve are obvious,whereas the apparent resistivity tends to be stable with the increase of the electrode space when the abnormal shape of combined profile curve shows as low synchronization.Branches of combined profile curve on both sides are symmetrical to the horizontal symmetry model while asymmetric to the tilt model,and the inclination of low resistance body is consistent with the inclination of the steep side of the orthogonal point nearby.The simulation results can be applied to the interpretation of multi-electrode spacing combined profile curve in karst area.