A first international (36)Cl interlaboratory comparison has been initiated. Evaluation of the final results of the eight participating accelerator mass spectrometry (AMS) laboratories on three synthetic AgCl samples with (36)Cl/Cl ratios at the 10(-11), 10(-12), and 10(-13) level shows no difference in the sense of simple statistical significance. However, more detailed statistical analyses demonstrate certain interlaboratory bias and underestimation of uncertainties by some laboratories. Following subsequent remeasurement and reanalysis of the data from some AMS facilities, the round-robin data indicate that (36)Cl/Cl data from two individual AMS laboratories can differ by up to 17%. Thus, the demand for further work on harmonising the (36)Cl-system on a worldwide scale and enlarging the improvement of measurements is obvious.

Recent seismic monitoring mainly by the Hi-net High sensitivity seismograph network in Japan for the last decade has been revealing the 3D structure of velocity anomaly in the crust and mantle due to heterogeneous presence of deep-seated fluids and fluid-related deep low frequency earthquakes in subduction zones of Japan arc. Petrological water circulation models combined with geophysical subduction models quantitatively show the water budget in the solid earth. The recent findings infer the importance of deep hydrothermal fluid on the occurrence of inland earthquakes. As the models are built with the result obtained by monitoring, experimental techniques or simulations, implications from evidence-based geochemical and geological studies are expected for the proof of water circulation models. Hence, we examined chemical features of deep groundwaters in SW Japan arc, and showed spatial distribution of deep-seated fluid mixed into groundwater. We found that the deep-seated fluid, whose isotopic composition is similar to magmatic, has the high Li/Cl ratio 0.001 in wt. ratio and concluded that Li/Cl is a good indicator for detecting the slab-related deep-seated fluid in groundwaters. Spatial distribution of Li/Cl reveals that slab-related deep-seated fluid upwells along the faults and tectonic lines, and at close to Quaternary volcanoes in SW Japan arc. In most cases, upwelling places are found close to the areas where deep low frequency DLF earthquakes are occurring, implying that deep-seated fluid causes DLF events.

1The 36 Cl/Cl ratios of groundwater samples were measured by AMS in order to investigate 2 the potential use of 36 Cl as a dating tool for modern groundwater. Groundwater samples were 3 obtained from several piezometers in the Oderbruch in northeastern Germany. The shallow 4 confined aquifer of the area is mainly recharged by the infiltration from the River Oder. From 5 the results of measurements, the pre-bomb and the recent background 36 Cl/Cl ratios in the basin 6 of the Oder were estimated to be 7-9 × 10 −14 . The 36 Cl fallout values estimated from the 36 Cl/Cl 7 ratios of the Oderbruch samples, which were dated by the 3 H/ 3 He method, show good agreement 8 with Dye-3 ice core data. These results suggest that the distribution of 36 Cl in groundwaters 9 reflects the influence of the 36 Cl bomb pulse. This, in turn, suggests that the distribution of 10 36 Cl/Cl in modern groundwaters could reveal groundwater ages and flow systems in a region. 11 12 PACS: 92.40.Kf; 91.67.Qr; 93.30.Ge; 06.60.Ei 13

Abstract:Major ion chemistry, oxygen isotope and multivariate statistical method were used to investigate aquifers interaction in the southwestern foot of Mt. Fuji, the largest Quaternary stratovolcano in Japan. Groundwater samples were taken from different aquifers which are in descending order: the superficial aquifer, aquifers residing in the New Fuji Lava and the Old Fuji Aquifer. The geochemical signatures of groundwaters, notably the molar Na/Cl and Na/Ca ratios, oxygen stable isotope and the nitrate contents evolution, in conjunction with the hierarchical cluster analysis allowed to highlight three groundwater systems differing by their hydrochemical facies and residence time: 1) The shallow and highly polluted groundwaters of the superficial aquifer, 2) Groundwaters of the New Fuji Lava moderately mineralized and polluted, 3) The non-polluted groundwaters of the Old Fuji Aquifer. Waters of these systems are interacting. In fact, nitrate contamination, in provenance from the superficial aquifer, was detected in the New Fuji Lava layers and the deep groundwaters of the Old Fuji. Furthermore, many samples taken from the Old Fuji Aquifer were characterized by a relatively enriched δ 18 O. These results prove that groundwaters of the New Fuji layers could be mixed with groundwaters of the overlaying superficial aquifer and that these groundwaters, supposed to flow only horizontally, can flow vertically through the cracks, causing the mixing of deep and old groundwater of the Old Fuji with groundwaters recently recharged and polluted.