[en] The authors analyzed dissolved constituents of 35 wells to investigate ground water movement in the Iwakura area, Kyoto city. The results were as follows: (1) The chemical composition of well waters was of SO₄^2-+Cl^--K⁺+Na⁺ and HCO₃^-- Ca²⁺-Mg²⁺ types. (2) The higher concentration of dissolved major inorganic constituents was detected in the area enclosed by contour lines between 110 and 130 meters, particularly an eastern part of the Nagatani stream. (3) The pattern of NH₄⁺-N and PO₄^3--P distributions was similar to that of major inorganic constituents, but the pattern of NO₃^--N distribution was completely similar to that of NH₄⁺-N and PO₄^3--P, and NO₂^--N was not present in almost all well waters. (4) The dissolved oxygen estimated on basis of dissolved argon was considerably unsaturated in well waters of eastern part of the Nagatani stream. (5) The dissolved nitrogen of a great number of wells was considerably unsaturated, and denitrification was found in a small number of wells. (6) By using simultaneous measurement of dissolved argon, the effective velosity of ground water ranged from 1.7 to 3.0 meters per day, corresponding to different hydraulic gradients. (author)

[en] Precipitation samples are collected at the six localities in the southwestern Japan weekly or monthly over a long period of time (1978-1989) in order to estimate chemical weathering rates and amount of weathered materials through chemical composition in natural waters. Major chemical composition is determined for the precipitation samples. Together with the data available in the literature, the following characteristics are recognized : 1) Most pH values fall in the narrow range of 4.4 to 5.4, 2) Systematic variations in pH values are observed among the precipitation samples of different geologic environments, 3) pH values become almost constant from 1984 to 1989, 4) NO₃^- concentrations gradually decrease to an almost constant value with time, and 5) ΔSO₄^2- concentrations gradually have a tendency to decrease from 1978 to 1985. The mechanism of phenomena described above is also presented. (author)

[en] A large-scale landslide took place at a southeastern slope of Mt. Jizuki, Nagano Prefecture, on July 26, 1985. It has been said that landslide is closely related to the hydrological and hydrogeochemical nature of groundwater involved. To investigate the weathering mechanism and the origin of groundwater, we collected and analyzed water samples from the large-scale landslide area. The following facts can be pointed out: (1) weather-rock interaction is remarkably active in the landslide area, (2) most of the waters from the landslide area are in equilibrium with Na-montmorillonite (3) immediately after the landslide occurred bicarbonate and sodium ions are dominant, but sulfate and sodium ions become dominant with time, and (4) groundwater passing through horizontally drilled holes dose not effectively drain off to stabilize a slope in the landslide area. And our hypothesis on the mechanism for the formation of sodium sulfate type water is also presented. (author)

[en] The landslide at the Otobaru area, Beppu City, occurred twice in 1943 and 1969. A part of this area, even now, is affected considerably by thermal activities. Variations in chemical and isotopic compositions of waters from the Otobaru area and its vicinity were investigated from 1977 to 1983 and 1986 to 1987. The results are as follows: (1) electric conductivity data suggest that the two kinds of low-concentration water and high-concentration water exist in the landslide area, (2) the existence-of two groundwater aquifer in the landslide area and its vicinity is inferred from tritium data, (3) variations chemical composition of waters from the horizontal borehole are accompanied by the rise and decline of water table, (4) the waters from the landslide area and its vicinity are in equilibrium with montmorillonite, (5) the most waters under 10^-1 atm. of P_co2 are saturated or supersaturated with calcite, and (6) there is no detectable contribution of geothermal water to the waters from the landslide and its vicinity. And our hypothesis on the mechanism for the formation of calcium sulfate type water is also presented. (author)

[en] We have continued the measurement of gamma-ray at 4 tunnels for crustal movement observation. We have also continued the measurement of chemical composition (or electrical conductivity) and temperature of the groundwater at 7 wells which are hot or mineral springs. The observation tunnels and wells are mainly located near Yamasaki, Shikano and Yoshioka faults. The observation periods range from 7 months to 14 years. In 1990, there were 2 neighboring earthquake activities whose magnitudes are greater than 5. There were also 2 typhoon landings accompanied with heavy rainfall and rapid change in atmospheric pressure. Although there were several typhoon-related changes in the gamma-ray intensity, the electrical conductivity or the water temperature at several observation tunnels or wells, we detected only one clear earthquake-related (coseismic) change in electrical conductivity of the groundwater at one observation well. As there clearly exist some sensitive observation stations to neighboring earthquakes, it seems important to investigate the conditions of such observation stations. (author)