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于地下深部产生的异常水压造成的，给铁路隧道、放射性废物地下设施等地下工程带来了严重的问题。研究泥火山的地下结构和异常水的形成机制，对于泥火山的选址和安全评估具有重要意义。泥火山地下180米处曾发生过因岩石膨胀而导致隧道坍塌等严重事故。挖掘这段150米长的路段花了10多年的时间。在日本中部新泻的第三系沉积盆地中发现了4座陆相泥火山。所有泥火山均沿地形盆地边缘分布，该盆地位于山区的NE-西南向峰顶，沿背斜翼分布。盆地内部地质构造受到严重干扰，新建成的…斜坡上暴露出已死的泥火山可以观察到更多的沟渠和泥火山的内部喷口结构。喷口直径30m，由泥质角砾岩和鳞片状网络粘土组成，被认为是水力压裂和泥岩与地下水之间的水岩相互作用产生的。泥火山喷发的地下水为高盐度，电导率为15mS/cm，高^&lt；O/^&lt；16&g；O同位素比值为1.2mS/‰。此外，镜质组反射率为1.5%~1.9%，这在近地表裸露的沉积岩中是不可能的。因此，假设这些喷发物质是从大约4000米深的地下深处引入的。进行了CSA-MT地球物理勘探，调查了地下结构，获得了从地表到800米深的电阻率剖面。研究发现，在地下600m深、200m厚、800m直径的泥火山中，由于含盐量高，形成了小于1Ωm的盘状低阻带。此外，低电阻率带沿着盆地边缘延续到地表，类似于泥火山活动的火山喷口。较少

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