Many thermal springs are known in Okiura district along the Aseishigawa River, a tributary of the Iwaki-gawa River which flows down the Tsugaru Plain, Aomori Prefecture. In this district, three faults F1-F3 of N-S direction and one fault F4 of NE-SW direction are recognized geologically. The western part of the F2 fault consist of the Okiura basalt member and the Itadome Formation both of Miocene age, and the eastern part of the fault consist of the Aoni Formation of Pliocene age; these rocks and terrace deposits are covered by volcanic ash. In a block between the F2 fault and the F3 fault, many naturally issuing thermal springs of high temper-ature are scattered, and high ground temperature is obtained by shallow drilling. Ground temperature is comparatively low at eastern part of the F2 fault and western part of the F3 fault, especially at the latter. The F3 fault is a distinct boundary of chemical composition of thermal waters; the waters in eastern part of the fault belong to Cl>SO4 type and dissolve 0.95-1.82 g/kg of substances, but the waters in western part of the fault belong to SO4>HCO3 type and dissolve 0.25-0.35 g/kg of substances. The F3 fault is considered to form a barrier of flowing of thermal water. It is assumed that the block between the F2 fault and the F3 fault is a pass zone of thermal water and especially the F2 fault is an excellent pass, then relatively high temperature and slightly high thermal water level are obtained by drilling near the F2 fault.
The Tanigawa Hot Spring is characterized by a Ca-a-SO-C1 type water of meteoric origin. The Ca2+ and Na+ concentrations of thermal waters are almost equivalent to SO4 2-a and Cl- concentrations, respec-tively. The hot springs are classified into two groups, one of which is high in Ca/Na ratio and discharged in the downstream area of the Tanigawa, and the other is low in Ca/Na ratio and discharged in the upstream area. The Ca/Na ratio of the former is three times larger than the latter. The K/Cl and Li/Cl ratios are common between these two thermal waters. Based on these chemical and isotopical characters, it is esti-mated that an original thermal water is diluted with shallow ground water in various proportion in each area, and also that the both original thermal waters are the same Na-Cl type thermal water dissolving anhydrite in the green tuff formation at different temperatures. If the difference in Ca/Na ratio is due to the difference in the temperature at which the thermal water is saturated with anhydrite, the saturation temperatures are estimated to be 120°C and 70°C in the upstream and downstream areas, respectively. The Sr/Ca ratio in the thermal water also supports the dissolution of anhydrite in the green tuff formation.
The seismic noise survey was carried out from 1980 to 1983 by continuous measurements at six observa-tion sites in Takinoue (Kakkonda) geothermal area, Iwate prefecture. Stability and secular change of seismic noise were discussed. The instruments used in-situ measurement consist of a horizontal component seismometer, amplifier and tape recorder. The system has flat response to ground velocity in frequency range of 1 to 40 Hz. The data were analyzed in laboratory with microcomputer. The original analog data were degitized at 100/sec. Fourier spectra of 2048 selected samples were computed using the fast Fourier transform. The results are summarized as follows. 1) The seismic waves generated by the swift stream of river and by the activities of the steam supply system have spectral characteristics of high frequency. 2) The seismic noise measured at observation sites distant from the river and the steam supply system is predominantly in the spectral band of 4-12 Hz, vary hardly with the passage of time. It is regarded that the amplitude and spectral characteristics of seismic noise are generally stable. 3) When production wells were closed, the amplitude of seismic noise decreases besides the spectral characteristics vary at the observation sites near geothermal reservoir.
The Goshogake geothermal area shows intensive surface geothermal manifestations, such as hot pools, fumaroles, hot springs, boiling springs and mud volcanoes. Hot grounds and thermally altered zones exist extensively around the above manifestations. The detailed distribution of ground temperatures at 1 m depth was clarified. By using the ground temperature data, conductive heat discharge was estimated to be 4.3×106 cal/sec, which is much larger than those from ordinary geothermal areas. Pattern of the temperature distribution obtained in this study is similar to that obtained before about 30 years. The most characteristic feature of the geothermal area is an existence of a hot pool called Oyunuma. Water and heat budgets of the hot pool were investigated based on various measurements such as water depth, surface and deep water temperature, evaporation and radiation etc. The area of the pool is about 3000m2. The western half of the hot pool is generally deeper than 10 m, but the eastern half of it is rather shallower than 5 m. Mean surface temperature is 83.4°C in 1982 and 81.0°C in 1983. Surface temperature in the eastern half of the hot pool are higher than those in the western half. Vertical temperature profiles show that the temperature increases gradually from the surface to 1 or 2 m depth, then to about 10 m depth is constant and below the depth increases rapidly to about 120°C at the right above the bottom. Evapora-tion rates were estimated to be 2.2×105 cc/min and 7.4×104 cc/min by the direct and indirect (micro-meteorological) methods, respectively. Heat discharges are also estimated to be 1.2×108 cal/min and 4.1×107 cal/min, depending on the direct and indirect methods, respectively. The values obtained by the direct method are a little larger than those by the indirect one. In this paper by using the data obtained by the direct method, the following water and heat budgets model was proposed: The hot water of about 90 to 95°C is supplied to the hot pool at a rate of 4 t/h, from the shallow bottom in the eastern half of it and the saturated vapor of about 120°C is supplied to the hot pool at a rate of 9 t/h, from the deep bottom in the western half of it. The supplied water is lost only by evaporation at the water surface. Chemical analyses were made for hot springs in the geothermal area and surface and deep hot water in the hot pool. The hot springs are sulphate springs and the pH of them is about 2.5 on the average. Ac-companying with the suppled hot water and vapor, SO4-S of 0.6 kg/h and H2S-S of 5.1 kg/h are brought into the hot pool. These sulphur compounds were deposited at the bottom of the hot pool. The shifts of the geothermal activity in the hot pool may be caused by such a deposition process.
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