Holocene Activity and the Latest Faulting Event of the Kakuda-Yahiko Fault Based on Active-fault Survey at Offshore of Echigo Plain, Central Japan: ——完新世における活動性と最新活動——

Offshore extension of the Kakuda-Yahiko fault and its fault-propagating fold are investigated based on combination of high-resolution seismic surveys and sedimentary analysis to evaluate their Holocene activity. High-resolution multi-channel seismic surveys with the boomer sonar (13 lines) and high-frequency seismic survey with the chirp sonar (3 lines) ran across the fault line and its extension, and provided us sharp imageries of stratigraphic succession formed after the last lowstand. We can clearly recognize progressive deformation at the eastern-wing of the fault-propagating fold in the observed succession. To determine actual ages of the seismic strata, we measured radiocarbon dates from sedimentary cores obtained by 2 offshore borings and 2 vibro-coring surveys. Based on deformation of strata between 10.8 ka and 4.7 ka, averaged 地 震 第 2 輯 第 71 巻(2018)63-85 頁 DOI: 10.4294/zisin.2017-9