The geothermal brines (Surface temp. =100℃) discharged from drillholes (52～250m in depth) at Shimogamo, Shizuoka, Japan, have been analyzed for stable isotopes of hydrogen, oxygen, and sulphur, together with chemical analyses. The chemical and isotopic evidences indicate that the geothermal brines are the mixture of local superficial water and the deep geothermal brine supplied by a single source. The estimated chemical and isotopic composition of the deep geothermal brine are interpreted by a mechanism, in which sea water penetrates into the deep geothermal brine reservoir and changes into Na-Ca-Cl brine through hydrothermal reactions with surrounding rocks. The underground temperature of the deep geothermal brine has been estimated as 221°～335℃ from the oxygen isotopic fractionation between sulphate ion and water in the brine.

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The horizontal deformations of the earth’s crust at two volcanic areas in Kyusyu, Japan have been observed with repeated measurements of the base-line lengths by means of a Geodimeter AGA Model 6 since 1968 and their results for the last three years are reported. In the Sakura-jima area, the network consisted of five base-lines was constructed on the western flank of the volcano Sakura-jima. Each base-line changes its length monotonously for the last three years and principal strain are deduced to be 4∿5×10^-6/year (NNE-SSW) and 0～-1×10^-6/year (ESE-WNW). This results are similar to the manner of horizontal deformations of the earth's crust in the vicinity of Sakura-jima at the great Sakura-jima eruption in 1914 which was found by the triangulations after the eruption (F. Omori, 1920). On the other hand, just after the 1968 Ebino-Yoshimatsu earthquake swarm, a base-line network was established at Yoshimatsu area, western part of Kakuto caldera, where a part of epicentral region is involved. Each base-line changes its length irregularly for the last three years. Taking errors into consideration, we cannot drew any definite conclusions at present for the horizontal deformations in this area, but it seems that there is some correspondence between direction of axes of principal strains and the distributions of initial motion of P wave of Ebino-Yoshimatsu earthquakes (pull～contraction : push～extension).

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Mt. Kurikoma is an active volcano located nearly at the center of the northeastern part of Honshu, Japan. The activity of this volcano has been very low in the last decade, and we have few geophysical data about this volcano. The seismic observation was carried out at Mt. Kurikoma in August and September, 1971 in order to know the seismic activity of this volcano and surrounding area in the quiet period. The hypocenters of sixteen earthquakes observed with a tripartite network were determined under a reasonable assumption of crustal structure. Besides these events, thirty epicenters were estimated from P～S times at Mt. Kurikoma and at several observatories of Tohoku University. Some seismic activity beneath and near Mt. Kurikoma was found separately from the aftershocks of an earthquake, which occurred in the southeastern part of Akita Prefecture on October 16, 1970. The activity has a tendency of successive occurrence. The daily number of events is 0.7 on an average except for the period of group occurrence. The seismic activity, even including the aftershocks, is limited within the region under the central mountain range.

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