2012 Volume 23 Issue 1 Pages 3-16
The logical model of geologic structure which shows the logical relation between stratigraphic units and boundary surfaces is most important element for three dimensional geologic modeling. Through theoretical examination of the recursive definition for geologic structure formed by an event sequence of sedimentation and erosion, we propose an algorithm to determine the logical model of geologic structure from field survey data. For geologic structures formed by a sequence of event c and c*, it is clear by the definition that the contact surface between the k-th unit and the k+1-th unit is the surface formed by the k-th event. This surface is the depositional surface if the k-th unit is formed by an event c and is the erosion surface if the unit is formed by an event c*. This property leads to an inference rule to determine a sequence of events (v1, v2, c, vn) as follows; (i) event v1 represents all events forming the initial state, (ii) for k = 2, c, n-1, vk = c if the contact surface between the k-th unit and the k+1-th unit is the depositional surface and vk = c* if the contact surface is the erosion surface, (iii) vn= c if the contact surface between the final n-th unit and open space is not eroded and vn = c* if the contact surface is eroded. Based on this property, we define an algorithm to determine a sequence of events for the logical model of geologic structure from field observation on the contact surface. Further, we summarize a flow of data processing to determine 3D model of geologic structure from field survey data. It is expected that this algorithm is useful to prepare consistent data set for 3D geologic modeling.
