Numerical Analysis of Geological Structure and Fracture System in the Kurikoma Geothermal Area Part 2:3-Dimensional Experiment

Abstract

A numerical experiment with three-dimensional Virtual Basement Displacement Method based on elasto-plastic finite element method was applied to an analysis of geologic structure and fracture systems in northern part of the Kurikoma geothermal area. In addition, a comparison between results of two- and three-dimensional experiment for the same area was made. The result of two-dimension al experiment is described in Mizugaki (1991). The result of three-dimensional experiment shows that the basement rocks and Miocene pyroclastic rocks are highly strained at major geothermal fields, such as Uenotai, Kawarage, Doroyu and Arayu, whereas small strain values are calculated for strata at minor geothermal fields. Principal stress distribution in this experiment has no dominated direction. In practice strain causes fracturing in rocks, and highly strained zones can be interpreted in highly fractured zones. Therefore this result suggests that the highly fractured zones are formed in rocks at major geothermal fields. This three-dimensional experiment reproduces the fracture systems in geothermal fields better than two-dimensional experiment.