Studies on the mechanism and countermeasure of natural disaster caused by mud volcano and mud diapir

泥火山活动被认为是由地下深处产生的异常水压引起的，并对铁路隧道等地下建筑造成严重问题，研究泥火山的地下结构和异常水形成机理，对泥火山地下设施的选址和安全评价具有重要意义，如隧道塌方等严重事故，泥火山地下结构的破坏，泥火山地下结构的破坏，由于泥火山下180米深处发生了岩石膨胀。这段150米长的路段，历时10余年才开挖完成。在日本中部新泻第三纪沉积盆地中发现4座泥火山，它们均沿着地形盆地边缘分布，位于东北-西南走向的山地顶部，沿着背斜翼分布。盆地内部地质构造受严重扰动，新建设边坡出露死泥火山， 关于我们 可观察到泥火山内部的通气构造和引道。泥火山口直径约30 m，由泥角砾岩和鳞片状网状粘土组成，推测泥火山口形成于水力压裂及随后的泥岩与地下水的水-岩作用，喷发出的地下水为高盐型，电导率为15 mS/cm，高^<18>O/^<16>O同位素比值为1.2‰。此外，镜质组反射率为1.5%至1.9%，这在地表附近暴露的沉积岩中是不期望的。因此，推测这些喷发物是从地下4000 m深处引入的，利用CSA-MT物探方法对地下构造进行了探测，获得了从地表到800 m深处的电阻率剖面。在泥火山下600 m深、200 m厚、直径800 m的地下，发现了一个因高矿化度而形成的小于1Ωm的盘状低阻带。此外，低电阻率带沿着盆地构造边缘一直延伸到地表，类似于泥火山活动的火山破火山口。少

Activity of mud volcano is thought to be caused by an abnormal water pressure generated in deep underground and make a serious problem for underground constructions such as railway tunnel, underground facility for radwaste and so on. It is important to investigate the underground structure of a mud volcano and the mechanism of abnormal water formation for site selection and safety assessment of such facilities.Serious trouble such as tunnel wall collapse due to the rock swelling has happened 180m deep under mud volcanoes. It took more than 10 years to excavate the section of 150m long. 4 terrestrial mud volcanoes were found in the Tertiary sedimentary basin in Niigata, central JapanAll the mud volcanoes are distributed along the rim of the topographic basin that is located at the NE-SW trending crest of mountainous area and distributed along the wing of anticline. Geological structure inside basin is heavily disturbed.The extinct mud volcano is exposed in the side-slope of newly constr … More ucted road and the internal vent structure of mud volcano can be observed. The vent is 30m in diameter and is consisted of mud breccia and scaly network clay that is thought to be generated by hydro-fracturing and the following water-rock interaction between mudstone and groundwater.Groundwater erupted from mud volcano is highly saline with electric conductivity of 15mS/cm and high ^<18>O/^<16>O isotope ratio of 1.2‰. Also, the vitrinite reflectance is 1.5 to 1.9% that is not expected in the sedimentary rocks exposed near ground surface. As a result, it is assumed that these erupted materials were introduced from the deep underground about 4000m deep.CSA-MT geophysical exploration was carried out to survey the underground structure and obtained the profile of electrical resistivity from the surface to 800m in depth. It is found that the disk-shaped low resistivity zone less than 1Ωm due to the high salinity content is identified in underground 600m deep, 200m thick and 800m in diameter under the mud volcanoes. Moreover, low resistivity zone is continuing to the ground surface along the rim of the basin structure similar to volcanic caldera where mud volcanoes are active. Less