Abstract
The relationship between the distribution of liquefied sites caused by the 1944 Tonankai Earthquake and landforms in the Otagawa Lowlands, Shizuoka prefecture, was studied. Because liquefaction is likely to occur on the loose sandy layer under the groundwater level, liquefied sites have been considered to correspond to the microtopographies on alluvial plains such as natural levees, point bars, former river channels, and edges of sand bars or sand dunes. However, in some cases liquefied sites are located in muddy back marshes.
Coarse-grained sediments under fine-grained sediments comprising the present flood basin were observed by hand-boring. The location of sand volcanoes in the flood basin closely corresponds to the location of part of these coarse-grained sediments. These sediments occur along shallow buried valleys and are similar to sediments occurring in present natural levees. Thus, these sediments are likely derived from buried natural levees. There are also traces of sand volcanoes formed by liquefication in these buried natural levee deposits at archeological sites. After liquefication due to paleo-earthquakes, the buried natural levee deposits appeared to have beeen liquefied again in the 1944 Tonankai Earthquake.
