The Neogene marine sedimentary rock area in the eastern marginal region of the Japan Sea is an area with some of the highest landslide densities in Japan. Some of the landslides in this area have been known to involve saline groundwater, which can be the cause of these landslides. In order to demonstrate the relationships between landslides and saline water, topographic, geological, groundwater, and electromagnetic surveys were performed in the eastern marginal region of the Japan Sea. Many landslides and gravitational slope deformations with linear depressions and small scarps were recognized in the study area. The resistivity profile obtained by an electromagnetic survey suggests that there is a wide zonal distribution of saline water with salt concentrations equivalent to seawater at depths of 50–100 m or more and that the groundwater shallower than 50 m has an electrical conductivity of less than 100 mS/m. The shallow resistive groundwater is inferred to be meteoric water that replaced the saline groundwater, which likely weakened the bedrock, resulting in landslides. A ridge of competent tuff overlying mudstone has many linear depressions from gravitational slope deformation and low‐resistivity water to a depth of 600 m, which suggests that the mudstone was weakened by water replacement and deformed under the tuff caprock. The saline groundwater is inferred to be fossil seawater trapped in pores during sediment deposition, which is brought near the ground surface along with rocks by tectonic movement in the hills. Thus, the saline water and its fresh water replacement are among the important basic causes of the landslides. The oil well data obtained in the eastern marginal region of the Japan Sea suggest that such saline water replacement has occurred widely and that replacement is likely one of the predispositions for the frequent landslides there.

中文翻译：

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日本海东部边缘地区新泻的化石海水分布及其在新近系沉积岩滑坡中的作用

日本海东部边缘地区的新近纪海相沉积岩地区是日本滑坡密度最高的地区。已知该地区的一些滑坡涉及地下水，这可能是造成这些滑坡的原因。为了证明滑坡与盐水之间的关系，在日本海东部边缘地区进行了地形，地质，地下水和电磁测量。在研究区域中，人们认识到许多滑坡和重力坡度变形，具有线性凹陷和小陡坡。通过电磁勘测获得的电阻率曲线表明，在50–100 m或更大的深度处，盐水浓度与海水相当，分布在宽广的带状区域中；浅于50 m的地下水的电导率小于100 mS / m。浅层电阻性地下水被认为是代替了盐水的地下水，这很可能削弱了基岩，导致了滑坡。从重力斜坡变形和低电阻率水到600 m的深度，上覆凝灰岩上覆的粘性凝灰岩脊具有许多线性凹陷，这表明该泥岩因补水而变弱，并在凝灰岩盖层下变形。盐碱地下水被推断为沉积物沉积过程中捕获在孔隙中的化石海水，通过山丘中的构造运动将其与岩石一起带到地面附近。因此，盐水和淡水的补充是滑坡的重要基本原因。在日本海东部边缘地区获得的油井数据表明，这种盐水置换已广泛发生，而置换很可能是那里频繁发生滑坡的诱因之一。