Applicability of silty material brought by black tsunami to estimation of inundation area

Abstract

Tsunami is said to be recurrent according to historical sources. Estimation of inundation area of paleotsunamis have been done by finding tsunami deposit in stratum by using sandy material in it as a clue. However, Black stream of 2011 Tohoku Earthquake left silty black tsunami deposit beyond the area where sandy material is found. It was expected that silty material as additional clue will bring better accuracy to estimation of inundation area. Formation of tsunami deposit during 2011 Tohoku Tsunami was numerically simulated. Soil core samples were obtained at Sendai Plain to find silty black tsunami deposit of AD 869 Jogan Tsunami. Silty material reached 90% of distance between the front edge of inundation area and the shorelines in the simulation result of 2011 Tohoku Tsunami. Silty black tsunami deposit of AD 869 Jogan Tsunami was found from all 18 soil core samples within inundation area of 2011 Tohoku Earthquake. Silty material was found in the simulation result at 15 out of 18 sampling points. Black tsunami deposit which contains rich amount of silty material can be another clue to estimate inundation area of paleotsunamis.