Graphing method is a traditional method for three-point problem. At present, there is no complete calculation method to solve three-point problem by elementary geometry. Based on the principle of three-point method, a few formulas derived from the knowledge of geometry and trigonometric function are proposed to calculate dip angle, dip, and strike of fault surface. The formulas used to calculate the dip angle of fault surface are the algebraic expressions, within which the horizontal distance and height difference between three known points are used as parameters. The formulas used to calculate dip or strike of fault surface are algebraic expressions that include parameters such as the horizontal distance and height difference as well as the azimuth of the line between the three known points. These new formulas are easy to programme. The steps to obstain the occurrence of buried active fault surface by using the three-point method are presented as follows. First, the spatial location data of the three known points on the fault surface is obtained from improved composite drilling geological section. Secondly, based on the height relationship of the three known points, the formulas are chosen to calculate the dip angle and the auxiliary angle of the fault surface. Thirdly, based on the spatial location relationship of the three known points, the formulas are chosen to calculate the dip and strike of the fault surface. Taking the Kouma fault as an example, the dip angle, dip, and strike of the Kouma fault surface are obtained by using these new formulas. In the prospecting trench, the dip angle, dip, and strike of the Kouma fault surface are measured by using geological compass. Both results of the dip angle, dip, and strike are quite consistent. © 2022, Science Press. All right reserved.
