The concept of geological disposal of HLW in Japan is based on a multibarrier system which combines a stable geological environment with an engineered barrier system. However, special consideration is given to the long-term stability of the geological environment, taking into account the fact that Japan is located in a tectonically active zone. Development of research/prediction technologies for geotectonic events has been carried out to evaluate the long-term stability of geological environment in any given site. This paper describes an overview of geotectonic events in Japan from the point of view of the long-term stability of geological environment. Moreover, the current status of research/prediction technologies developed by JNC is summarized.

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  This paper reviews the present state of researches on tectonic uplift and denudation, and shows perspective goals and direction of future researches from the viewpoint of geological disposal of HLW in Japan. Detailed history of tectonics and denudation in geologic time scale, including the rates, temporal and spatial distributions and processes, reconstructed from geologic and geomorphologic evidences will enable us to make the geological predictions. Improvements of the analytic methods for the geological histories, e.g. identification of the tectonic and denudational imprints and age determinations, are indispensable for the accurate prediction.
  Developments of the tools and methodologies for assessments of the degree and extension of influences by the tectonic uplift, subsidence and denudation on the geological environments such as ground water flows are also fundamental problem in the study field of the geological disposal of HLW.
  Collaboration of scientific researches using the geological and geomorphological methods and applied technology, such as numerical simulations of ground water flows, is important in improving the safety and accuracy of the geological disposal of HLW.

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  This article provides the preliminary results of literature and field survey in terms of the long-term stability in and around the Horonobe area. The Horonobe area is situated in the Tenpoku Basin, and is dominated by the Neogene to Quaternary sedimentary sequences. Based on the time-staratigraphy and sedimentary analysis, depositional area has migrated from east to west in the basin. The distribution of hypocenters for micro-earthquake, geologic structures, and the Quaternary sediments indicate that present-day activity has been localized with the western part of the Horonobe area. In addition, the seismic reflection profiles of the Horonobe area show the growth structures of the fold-and-thrust belt of central Hokkaido suggesting that the ongoing-tectonics (neotectonics) in the study area has begun in three to two million years ago.
  The Horonobe area has widespread distribution of the marine terrace deposits, which are correlated to the marine oxygen isotope stages (MIS) 9 through 5c. The elevation of these marine-terrace surfaces on axial part is higher than that of on limb in the Sarobetsu Anticline at the western part of the Horonobe area. The former shoreline of MIS 1 proceeded ca. 14 km away from that of MIS 7 although there is no great difference in global-scale sea-level in each stage. The active folds are distributed in area to be changed into land in MIS 1. In order to assess the long-term stability of geological environments in the test-field Horonobe area it is important to consider the faulting and folding effects to the uplifting, subsidence, migration of former shoreline and so on.

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  Because of the high denudation rates in Japan, the landform and geological characters will be largely changed in the geological time-scale. These changes are major controlling factors on the hydrogeology, and affect the hydrological and chemical conditions of the groundwater. Estimation of these effects on geological environments by the denudation is one of the important problems for the safety of geological disposal of HLW in Japan.
  Development of the methodology to predict the long-term (10^4-5 year order) denudation rates is the first priority for solving this problem. Statistical analyses of the denudation rates and patterns in the geologic and geomorphic records are the basis for the prediction.
  The relationship of uplift rates and denudation rates of the marine terraces was analyzed as a case study. Denudation rates were calculated from the volume of dissected valleys on the marine terraces by using a 50-m DEM. Time-dependency of the denudation rates was also examined from the geomorphologic data of terraces, hills and mountains in the various landform development stages.
  Percentages of the denuded volume to a total uplifted volume of the land is 10-20 % in the first 125 kilo years since the emergence, come to several tens of % in next 100 ky and amount to 100 % in the equilibrium stage, ca. 0.5 to one million years after the emergence.

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  The effects of volcanism on the geological environments include a dynamic destruction and subsidence of basement rocks, caused by the intrusion and eruption of magma. To ensure the long-term stability of geological disposal system, a possibility of renewed volcanism at the site might be examined based on the geotectonic data of the deep underground using geophysical and geochemical approaches. This paper describes an overview of geophysical approaches for detecting magmas and/or high temperature fluids related to volcanism within the crust and uppermost mantle. Moreover, we present the images of the seismic velocity and electrical resistivity structure beneath the Onikobe-Narugo volcanic region and the southern Kii Peninsula, carried out in JNC's R&D program.

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  In Japan they have extensively measured the crustal heat flow (conductive heat flux) since 1957 to make clear the heat flow distribution around Japan. On the other hand, they have not revealed the distribution of the total heat flux yet which consists of the conductive term and the advective term, and is required for investigation of heat transfer at volcano zones and so forth.
  Authors calculated the total heat fluxes and fluid flow velocities from data of wells in all over Japan to find out that in northeastern part of Japan the total heat flux is higher at Pacific side than the side of the Sea of Japan, that in southwestern part of Japan the total heat flux is lower around the Inland Sea, that the high total heat flux zones are almost confined to the vicinities of Quaternary volcanoes, that the total heat fluxes not lower than 1W/m² seem to owe their growth possibly to the fast ascending fluid flows which are generated locally in the fluid convection systems by heat sources and so forth.
  Authors also carried out the sensitivity study of heat transfer and temperature distribution near Unzen Volcano located in Shimabara Peninsula using a three-dimensional non-steady non-isothermal fluid flow model and compared the simulation results of total heat fluxes with estimation from data of wells near the volcano.

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  Though the Tono uranium deposit, central Japan, has been subjected to uplift and associated denudation since its formation at about 10 million years ago, most of the uranium has been preserved in the deposit. Uplift and denudation might result in a change of groundwater flow and the formation of oxidized zone in the shallow subsurface. Such changes of the geological environment would affect the chemistry and migration behaviour of uranium. The description of long-term uranium preservation process throughout the uplift and denudation history can contribute to enhancing the confidence in the demonstration of long-term safety of a geological disposal system.
  As part of the study on how geological phenomena affect the geological environment, the amount of uplift/subsidence and vertical displacement rate were estimated from the presently observed strata thicknesses, in consideration of global sea-level change and erosion during formation of unconformities.
  As a result, the quantitative estimation of uplift is about 340m and was the greatest between the sedimentation of the Seto Group, which was completed at about 1.5 million years ago, and the present. The average vertical displacement rate during this period is estimated to have been in a range between 0.2 and 0.3mm/year.
  It is pointed out that the quantitative estimate of uplift would be affected by the estimations of sea-level during the deposition and amount of erosion during the unconformities. The accuracy of the estimated duration of the displacement affects the quantitative estimation of the vertical displacement rate. Alternative estimates of the vertical displacement rate after the Mizunami Group sedimentation, based on the known age data, would vary over an order of magnitude (about 10 times difference).

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  Long-term migration behavior of rare earth elements (REE) as a chemical analogue of Am and Cm, together with U and Th, was investigated based upon chemical analyses of Andosol and Loam in Kanto area, central Japan. Basaltic glass has been weathered to clay minerals and iron oxyhydroxides in Andosol and Loam. The order of mobility of the elements during the chemical weathering of Andosol is alkali, alkali earth elements > REE > U, Th. The release rate of these elements is smaller in Loam underlying Andosol than in Andosol. Maximum release rate of REE, U and Th from the basaltic glass in Andosol during 3000 years is estimated to be ca. 50%, 30% and 30%, respectively. However, REE, U and Th released from the basaltic glass migrated downward and accumulated in Loam, suggesting that REE, U and Th were not removed from Andosol + Loam system for a long period.

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