Assessment of the level of activity of advective transport through faults and fractures is essential for guiding the geological disposal of radioactive waste. In this study, the advective flow (active, inactive) of meteoric water through fractures is assessed by comparing stable isotopes (δD and δ¹⁸O) between fracture and pore waters obtained from four boreholes in marine deposits in the Horonobe area, Japan. At 27–83-m depth in one borehole and 28–250 m in another, the isotopic compositions of pore and fracture water reflect mixing with meteoric water, with stronger meteoric-water signatures being observed in the fracture water than in pore water of the rock matrix. At greater depths in these boreholes and at all sampling depths in the other two studied boreholes, the isotopic compositions of fracture and pore waters are comparable. These results suggest that the advective flow of meteoric water is active at shallow depths where fossil seawater is highly diluted in the two boreholes. This interpretation is compatible with the occurrence of present or paleo meteoric waters and tritium, whereby present meteoric water and tritium are limited to those depths in the two boreholes. This difference in the level of activity of advective flow is probably because of the glacial–interglacial difference in hydraulic gradients resulting from sea-level change. Although fractures are hydraulically connected to the surface through the sedimentary rock, advective flow through them is inferred to remain inactive so long as sea level does not fall substantially.

评估通过断层和裂缝的平流输送活动水平对于指导放射性废物的地质处置至关重要。在本研究中，通过比较稳定同位素（δD 和^δ18O）在日本Horonobe地区海洋沉积物中的四个钻孔中获得的裂缝和孔隙水之间。在一个钻孔 27-83 米和另一个钻孔 28-250 米处，孔隙水和裂缝水的同位素组成反映了与大气水的混合，在裂缝水中观察到的大气水特征比在孔隙水中更强岩石基质。在这些钻孔的更深处和其他两个研究钻孔的所有采样深度，裂缝和孔隙水的同位素组成是可比的。这些结果表明，在两个钻孔中化石海水被高度稀释的浅层深处，大气水的平流流动是活跃的。这种解释与现在或古大气水和氚的出现相一致，因此，目前的大气水和氚仅限于两个钻孔中的那些深度。这种平流活动水平的差异可能是由于海平面变化导致的冰期 - 间冰期水力梯度的差异。尽管裂缝通过沉积岩与地表水力相连，但只要海平面没有大幅下降，通过裂缝的平流就被推断为保持不活跃。