Abstract:

In this paper the AMT method was applied to study the concealed faults of Tan-Lu Fault zone in Suqian, Jiangsu Province. Three AMT profiles had been deployed which included 61 AMT sites and the electrical strike and its dimension were analyzed with these data. By conducting traditional 2-D and advanced 3-D inversion methods, the reliable underground geoelectric models were obtained. The geoelectric strike direction of the sites near the fault derived from GB decomposition is about to N60°E from shallow to deep, which is inferred to be the strike of main fault or branch fault, and is slightly different from that derived from the shallow geological mapping (~N20°E).Then based on the phase tensor analysis result, the dimension data near the fault show 3-D features in some depths. The 3-D inversion method can provide more reliable models of the concealed fault and comprehensively reflect the information of fault tendency, extending depth and other features, so 3-D inversion method is more reliable than the traditional 2-D inversion method.In addition, the location of the fault obtained from the 3-D inversion model matches well with that inferred from radioactive element detection. In conclusion, the geoelectric strike and dimension analysis for electromagnetic data are necessary in the exploration of concealed faults, and the 3-D inversion method can get more reliable resistivity models for concealed faults than the 2-D inversion method.

Key words: audio magnetotelluric sounding method, 3-D inversion, dimensionality analysis, geoelectric strike direction analysis, Tan-Lu Fault zone