Liquefaction and flowage at archaeological sites in the inner belt of central Japan: Tectonic and hazard implications

Abstract

All archaeological data gathered at 55 archaeological sites excavated in the alluvial plains and basins of the inner belt of central Japan revealed the occurrence and age of events of liquefaction and flowage. The alluvial plains and basins are bounded on one or both sides by active faults, representing tectonic or block boundary lines. The excavated sites with liquefaction and flowage events identified, are found distributed within a 15-km-wide zone along the tectonic or block boundary lines of the alluvial plains and basins. This suggests that seismic hazards caused by liquefaction and flowage mainly occur within this 15-km-wide zones along the tectonic lines. Sand-filled dikes of various shapes were found and are thought to represent evidence of liquefaction and flowage. The sand-filled dikes can be classified into two main types; a lenticular type arrangeden echelon; and a cylindrical type opening upward in a fan shape. Archaeological age estimates indicate that the liquefaction and flowage were induced by earthquakes which occurred during three periods; around 1000 B.C., between 0 and 500 A.D., and after 1500 A.D., suggesting that active seismic periods occurred at an interval of approximately 1000 years.