[en] For design or excavation of deep underground tunnels such as for a radioactive waste disposal facility, there is need to assess the mechanical stability of tunnels and any kinds of excavation effect on the rock mass surrounding the tunnels. The three-dimensional in situ stress state is one of the main factors of the assessment. The best way to know the in situ stress clearly is to measure it in the location where a tunnel will be excavated, to minimize the effect of any rock mass heterogeneities. However, obtaining a large number of in situ stress measurement can be difficult, budgetary considerations notwithstanding, because of the large scale of underground structures, such as envisioned for a radioactive waste disposal facility. Therefore we developed a method for determination of in situ stress for arbitrary points from limited results of in situ stress measurement. This report is a summary of the contract work done in the fiscal years from 2004-2006, for the development of a new in situ stress determination method. Initially, we made local scale numerical models of the Tono area. Using these models, we estimated the regional stress state from a limited set of in situ stress measurement results using an inverse analysis. Then we applied the estimated regional stress state to boundary conditions of the same numerical models and calculated local stress at arbitrary points using a forward analysis. The results indicate that the calculated local stress matched the original in situ stress measurement results from the inverse analysis. Furthermore, this approach can be used to explain estimates and in situ stress measurements at other locations independent of the regional stress analyses. (author)