In the final stages of the Matsushiro earthquake swarm (August 1965-October 1967, a large volume of groundwater was generated that continues to flow as of this writing. We studied the spring water origin by measuring oxygen/hydrogen isotope ratios and concentrations of Na and Cl , the main dissolved ions. We took water samples from June 1999 to October 2000. Data plots for 6 180 vs. 6 D are distributed along a well determined linear regression line having an endpoint, i. e., river water, at the ordinary value of rainwater. The regression line can be extrapolated toward estimated 6 '80 and 6 D of "andesitic magmatic water" originating from magma in subduction zones. This implies that the Matsushiro groundwater can be regarded simply as a mixture of 2 fluids, i.e., surface water and andesitic magmatic water. We obtained the carbon isotope ratio of CO2, the main component of free gas in spring water. 6 13C ranges from -7.1%0 to -3.1%o, suggesting that the source of CO2 is alsc magmatic. The ratio 'He/ 'He shows that He in the free gas is from the mantle or magma. These 3 pieces of evidence -(1) 6 'BO and 6 D values, (2) 6 '3C of CO2, and (3) 3He/ 4He-suggest that the origin of Matsushiro water is magmatic. Considering the presence of an electric conductive layer and seismic reflective layers 15 km beneath the Matsushiro area, we presume that this andesitic magmatic water accumulates as a thin layer at this depth. An impermeable sheet presumably lying just above the water layer was formed by precipitates from magmatic water.We present the following model of the relation between groundwater and earthquakes: When the impermeable sheet broke and high-pressure water with CO2 rose into the upper crust, the crust wa: weakened, causing the Matsushiro earthquake.

Gamma-ray surveys at the giant clam colonies on the deep-sea floor in Sagami Bay in Japan were carried out using an NaI(T1) detector fixed at the side of "SHINKAI 2000." The gamma-ray spectrum was obtained with a multichannel pulse height analyzer. The giant clams get the biological energy from the upwelling fluid coming from the bottom of the sea. Therefore, relatively strong venting of fluid is expected through the colony. The upwelling rate is affected by the crustal activity (e.g., crustal movement, earthquake, and volcanism). The colony is a suitable place for monitoring the crustal activity. A gamma-ray method was useful on the colony area to detect the upwelling rate of fluid.Relatively strong intensity of the gamma-rays of 214Bi, an offshoot of inert gas 222Rn,was observed at living clam colony sites as expected. A large difference in the intensity among the colonies was also observed. This was due to the difference in the composition of rocks at the deep part of the site.14C concentration on 34 shells collected from the colonies was measured . It was discovered that the data of 14C concentration in the shell were scattered. It could be understood from the phenomena that 14C concentration did not correspond to the age of the shell because upwelling carbon compounds, which are the source of the shell, should have no 14C. Therefore, the 14C concentration also indicated the activity of fluid upwelling. The data of gamma-ray survey and 14C concentration in shells strongly indicated the existence of fluid transportation from the deep part of the seafloor in the colonies. It was proven that the gamma-ray method and the measurement on 14C concentration in the shell at the colony were useful for estimating the crustal activity.

No abstract

No abstract

No abstract