Liquefactions of Historical Earthquake in the Niigata Prefecture, Japan : Part 1

Many liquefaction phenomena caused by historical earthquakes are identified in the trenches of remains in Niigata Prefecture. These liquefaction phenomena are described in detail according to the following features; locality of the remains, age of the remains, mode of occurrence of liquefaction, age of liquefaction, grain size of liquefied material, etc. In ancient liquefactions, as observed in the trenches of the remains, sand-boiling, sand-dyke, “draw-in” phenomena and deformation of liquefied soil beds were found. The draw-in phenomena can be distinguished from the “intrusion-spout”. This draw-in process is followed by the intrusion-spout process during the final stage of liquefaction. In previous studies, the “intrusion-spout of sand” is recognized as an exclusive phenomena of the liquefaction. The recognition of this type of liquefaction in addition to the draw-in phenomena and deformation of liquefied soil beds are important in understanding the whole deformation process of alluvial soil beds, caused by earthquake motions