2D Magnetotelluric forward modelling for deep buried water-rich fault and its application

Abstract

Water inrush is a common geological disaster during the tunnel construction in the broken zone of deep buried water-rich faults. In order to improve the exploring accuracy of this water-rich faults, we first design four water-rich fault models with different inclined angle (22.5°, 45°, 67.5° and 90°) in 2D Magnetotelluric (MT) forward modelling using the finite element method. The simulation results show that the contour lines of apparent resistivity and impedance phase in these four models have a sparse concave feature, which increases with the inclined angle of the water-rich fault. However, the lateral resolution for the inclined fault in TM mode is better than that of TE model. We finally arranged two MT exploring lines in rocky mountainous area of southwest China to detect the deep buried water-rich fault. The inversion results show four significant low resistivity zones in the two MT measured lines. Combine with the geological data, we found that each two low resistivity areas are coherence with the fracture fault zone. Moreover, considering the forward modelling of the faults, we infer that two fracture faults spread in our study area. One fault F1 is northwest tilt with the inclined angle ~60°, and the other fault F2 is southeast tilt with the inclined angle ~80°. All these were also confirmed by the drilling data. The detections of two tilt water rich faults can effectively avoid potential hazards at this area and the forward numerical simulation can provide abundant theoretical reference for the field measured data.