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[SSS31-15] Vertical slip rate estimated from young lacustrine sediment core samples across the Kamishiro fault, Itoigawa-Shizuoka Tectonic Line, central Japan
Keywords:Itoigawa-Shizuoka Tectonic Line, Kamishiro fault, vertical slip rate, sediment core, radiocarbon dating
We interpret that the sudden lithofacies change from overlying inclined strata to underlying horizontally-laminated strata, commonly shown in the both cores, is penetrating the Kamishiro fault. This interpretation is supported by 14C ages of the two cores. Thus, 14C age is younger (ca. 16,000 yr BP in the KMS-1 core, ca. 24,000 yr BP in the KMS-2 core) just below the horizon shown by the sharp boundary than that above the boundary (ca. 30,000 yr BP in the KMS-1 core, older than 50,000 yr BP in the KMS-2 core). On the basis of altitude of facies boundaries and over fifty radiocarbon ages, cumulative vertical displacements are 12—14 m at 9,000 yr BP, 16—17 m at 11,000 yr BP, ≥41 m at 21,000—24,000 yr BP, respectively. These vertical separations and ages indicate that average rates of vertical displacement in the study area are 1.2—1.4 mm/yr during the past 10 ka, and higher than 1.6 mm/yr during the past 25 to 30 ka, respectively. It implies that a coseismic vertical slip of 0.3—0.5 m at the 2014 earthquake released a strain accumulated during the past 210 to 420 years.