2003 Volume 57 Issue 1-2 Pages 73-82
Derorinatio ndsuc to liguefactie nin peat bcds are describc di'ru itnhrec localit ; Takasaki City and Itakura Town, Gumma Prefecture and Echigo-Kawaguti Town, Niigata Prefecture. The liquefaction in Takasaki occurs in a late Pleistocene pumice bed, part of the Maebashi Peat Formation, originated from Asama Volcano. The thickncss of the pumice bed is laterally hig}hly variable showing flame-like structure in places. The age of the liquefaction is estimated to be 16 thousand years BP from radiometric ages of the peat bed and overlying pumice fall. The liquefaction trace at Itakura Town is observed in the Holocene peat and sand beds. Due to lateral flow of sand bed at the time of liquefaction, wedge and ball structures are formed. At Echigo-Kawaguchi, structures due to lateral movement of sand bcds within peat beds of thc river terrace deposits are observed. In all the cases clear upward-intrusions and sand dikes are not seen, but the deformation of peat beds accompanying lateral movement of liquefied materials are observed resulting in chaotic structures. It is impossible to make a conclusion that these structures have been formed by paleo-earthquakes. but there is a large poessibililty left. The recognition of these characteristic features may be effective to clarify a local seismic history.
