Abstract
A two-dimensional (2-D) structural transition from a flat valley floor to a mountain slope, with a presumed reverse fault at its base, was investigated by the audio-magnetotelluric sounding method. By calling on previously available geological information, it was possible to reformulate the problem so that only two basic questions remained to be answered: (1) does the structure effectively involve a fault, and (2) if so what is the dip angle of this fault? Since the soundings away from the mountain furnished the 1-D valley structure, it was possible to construct a 2-D model in which the only specified parameter was the unknown dip angle. Even the absence of a fault could be simulated in the model by giving this parameter a definite value. The model responses were computed numerically by the technique of finite differences and compared with the measured response curves, yielding quite clear answers in favor of a reverse fault dipping at an angle of less than 30° under the mountain. It was also possible to secure some information concerning details of the valley structure.
