Abstract
The Kakuda-Yahiko fault is a west-dipping blind thrust along the western margin of the Niigata plain, central Japan. The slip rate has not clearly estimated because the fault is buried under thick sediments. We obtained and analyzed three core samples (GS-KNM-1, GS-SGT-1, and AK-1) crossing the fault, and we recognized the Holocene vertical movement on the basis of correlation of detailed description, radiocarbon ages, and diatom assemblages. Based on these analyses, we interpreted nine sedimentary facies: the late Pleistocene marine sediments, meandering river sediments, salt to freshwater marsh sediments, offshore sediments, lower and upper shoreface sediments, foreshore sediments, modern river sediments, dune sediments, and surface soils, in ascending order. The average vertical-slip rate is estimated 3.6-4.6 mm/yr based on the vertical-offsets of the ravinement surface dated 9.4-8.2 cal kyr BP and the pumice layer dated 6-5 cal kyr BP. However, this slip rate might contain at best 1.3 mm/yr compaction effects of unconsolidated muddy sediments. Therefore, the average vertical-slip rate of Kakuda-Yahiko fault would be estimated about 3 mm/yr.
