基于二维电测深数据作三维反演的基岩探测

Bedrock detection based on two-dimensional electrical sounding datafor three-dimensional inversion

在城市基岩面探测时,受到城市交通、电磁等严重干扰的制约,常选用直流电测深作为主要物探方法。二维电测深剖面沿测线排列电极,采集视电阻率数据后进行二维反演,用所获得剖面方向上的二维电阻率断面图像推断地质体的位置及产状。但由于复杂的实际情况并非适合二维反演条件(走向无限延展并与测线正交),二维反演会产生较大误差。为此,可试用测区多剖面二维电测深数据作三维反演,获得测区三维电阻率立体图像,推断地质体分布的空间形态。在山东某市地质调查中,布设点距50 m、线距为100 m电测深测网,采集二维对称四极测深数据。对该测区二维电极排列建立三维反演数据格式后,进行三维电阻率反演,获得测区三维电阻率图像,推断的基岩面与钻探验证基本一致。

In the detection of urban bedrock surfaces,due to the severe urban traffic and electromagnetic interference,direct current sounding is often used as the main geophysical method.The two-dimensional electrical sounding profile arranges electrodes along the survey line,collects the apparent resistivity data and performs two-dimensional inversion,and uses the obtained two-dimensional resistivity cross-sectional image in the direction of the profile to infer the location and attitude of the geological body.However,due to the complicated actual situation,it is not suitable for the two-dimensional inversion conditions(infinitely extending and orthogonal to the survey line),and the two-dimensional inversion will produce large errors.In view of such a situation,three-dimensional inversion of multi-section two-dimensional electric sounding data of the survey area can be used to obtain three-dimensional resistivity stereo images of the survey area,and the spatial form of geological body distribution can be inferred.In a geological survey of a city in Shandong Province,an electrical sounding network with a distance of 50m and a line spacing of 100m was set up to collect two-dimensional symmetrical quadrupole sounding data.After establishing a three-dimensional inversion data format for the two-dimensional electrode arrangement in the survey area,a three-dimensional resistivity inversion was performed to obtain a three-dimensional resistivity image of the survey area.The inferred bedrock surface is basically the same as the drilling verification.