Explicit-implicit-integrated 3-D geological modelling approach: A case study of the Xianyan Demolition Volcano (Fujian, China)

Explicit interactive modelling and implicit interpolation modelling are the two classic three-dimensional (3-D) modelling approaches for reconstructing 3-D geological structures from sparse data. The limitations of using a single method appear when performing complex regional modelling containing various types of geological structures. However, due to the complication of spatial geometry computation, the integration and coupling of explicit and implicit modelling approaches and modelling results remain difficult and unresolved. In this paper, we propose an explicit-implicit-integrated 3-D geological modelling approach for the geometric fusion of different types of complex geological structure models. First, suitable methods were chosen to model different types of structures. For example, a Hermite Radial Basis Function (HRBF)-based implicit method was used to model general strata, faults, and folds from geological boundaries and attitudes in a regional geological map; explicit approaches, such as the skinning method and the free-form surface, were used to model local detailed structures, such as Quaternary deposits, monoclinic strata and multi-layer volcanic edifices, from section-constrained data. Finally, the explicit models were resampled and converted to implicit models and were coupled with the implicit models, leading to the integrated regional modelling of various types of geological structures. The validity of the proposed method was tested using the geological map of the Xianyan Demolition Volcano in Fujian. The results demonstrate that the proposed explicit-implicit-integrated 3-D geological modelling approach is efficient and effective, and this approach provides a probable solution for coupling and integrating multiple modelling methods and geological models for an area containing complex geological structures. The 3-D model established using this method can directly reflect the geomorphic features and volcanic passage facies of the Xianyan Demolition Volcano. Moreover, the simulation of radioactive fractures around the center of the volcano can also help to accurately determine the volcano type.