1. A method of analyzing a three-dimensional (3D) geological structure, comprising: estimating a density value and a resistivity value on common coordinates L, M, and N to calculate a density model D data (L,M,N) and a resistivity model R data (L,M,N) on a same 3D grid (L×M×N), thus obtaining physical property models; normalizing the physical property models, thus obtaining normalized physical property models ND data (L,M,N) and NR data (L,M,N) which are then represented in a scatter plot of physical properties; converting distribution positions of the ND data (L,M,N) and NR data (L,M,N) on the scatter plot of physical properties into type angle (TA) using a four-quadrant inverse tangent and into type intensity (TI) using a distance from an origin; determining a minimum of TI values, which classifies two or more classes on a scatter plot of the TA and TI values, to be a threshold; and analyzing the 3D geological structure based on a local extreme point and/or points in the scatter plot for the TA and TI using the threshold, wherein analyzing the 3D geological structure is performed by determining a rock type, and a structure depending on physical properties and geological positions of the classes.