Numerical Simulation And Analysis Of Magnetotelluric Sounding For Concealed Fault Zone

The detection of concealed fault play an important role in geothermalresources investigation, the distribution of deep deposit, the occurrence ofgroundwater, the site selection of large engineering sense. Magnetotelluricsounding method (MT) due to its own characteristics in underground deep faultstructure and fracture zone play an important role in exploration. Through theestablishment of different fault fracture zone model, analysis of magnetotelluricmethod to model the response characteristics of the two polarization modes, canprovide certain help for actual data interpretation.This paper established the normal fault, reverse fault and low resistancelayer model, based on the finite element method, using the two-dimensionalmagnetotelluric forward simulation to get the magnetotelluric method fordifferent response characteristics of the fault model:(1) impedance phaserelative to the apparent resistivity is affected by low resistance layer is small, theelectrical structure of the underground rock better reflect the overall form.(2)when the fault slip is bigger, can according to the two polarization modes in thehigh frequency part is a significant phenomenon of "reverse" to distinguishbetween normal fault and reverse fault; When the fault slip smaller or low resistance layer is thick, from the profile of two polarization modes are difficultto distinguish between normal fault and reverse fault.By forward modeling, the model of fracture zone by magnetotelluricresponse characteristics are:(1) when the fracture zone resistivity is lower thanthe first layer medium resistivity, apparent resistivity and impedance phaseprofile curve is relatively steep in fracture zone, a depressed form;When thefracture zone resistivity is greater than the first layer medium resistivity,apparent resistivity and impedance phase profile of concave shape disappeared,in the fault fracture zone curve slow.(2) model, the fault dip Angle of30°,45°,60°, the apparent resistivity section obtained in low resistance fault fracturezone in place have obvious concave shape, the fracture zone reflect Angle is notclear, the impedance phase of broken belt Angle reflect relatively well.(3) lowresistance fault fracture zone width of forward modeling analysis shows that thefracture zone gradually widened, the apparent resistivity curve and impedancephase curve steepened gradually in fracture zone position.A workspace is carried out in the end, through magnetotelluric soundingwork, based on the analysis of the basis of summarizing the magnetotelluricresponse characteristics of fault model, deduce the workspace sounding profilein the three places of the fault location, and consistent with the actual geologicaldata, this model has certain practical significance.