Numerical Simulation, Inversion Fitting Of Radon Migration In The Overburden Above Active Fault

As an indicator of information come from the deep earth, radon measurement was applied widely in the active fault investigation. Soil radon measurement can be used to detect the fault location, its strike and dip direction, and can also be used to evaluate qualitatively and half-quantitatively the activity of active faults, this is very important for fracture degree distinguish and engineering seismic evaluation in city district providing an important information. However, this evaluation method had some disadvantages of the uncertainties, with a quite deviation and randomness.Aim at these problems, this dissertation had analyzed in general and systematically the geological characteristics of active faults and the mechanism of radon migration in the overburden above active faults. The geological-physical model of radon migrated in the overburden above active faults was established, and the 2D differential equation for radon migration in overburden had deducted based on the diffusion-convection effect. The numerical resolution of the 2D differential equation was get by the finite difference method, and several main radon concentration distributions in overburden above active faults had been calculated. Based on the 2D section radon concentration contour maps and the profiles crossing the active fault in certain depth, the radon concentration distribution characteristics in the overburden above different kind of active faults, such as steep faults, inclined faults, graben faults and fracture zones, was found out. And the factors influenced the radon concentration distribution characteristics was discussed. All of these had provided the base for radon concentration distribution in the overburden above active faults inversion and interpretation.Based on the results of numerical simulation this dissertation explained the method qualitatively and half-quantitatively to identify the fault location, its strike and dip direction, faults width, buried depth, and provided the foundation for activity evaluation and dynamic monitoring of active faults.The fault parameters, such as fault width, fault depth and the radon concentration in fault, was inversed and fitted from the field measurements of soil radon concentration above the known active faults. And this method had made breakthrough to realize the quantitative inversion for these faults parameters. Compared with other non-seismic methods, the inversed and fitted results on known active faults had shown this inversion and fitting methods has the advantages of high accuracy and precision in active faults detection and evaluation.