地震　第2輯

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The Yanagase-Yoro fault system extends from Japan Sea to Ise Bay, central Japan, in a NNW-SSE direction with a left-lateral strike-slip component of displacement. We carried out geomorphological and geological surveys on the Kajiya fault in the fault system to reveal its paleoseismic activities. Two trenches at sites A on the upper terrace and one trench at site B on the lower terrace were excavated. A high-angle fault cutting terrace deposits and black soil layers was exposed on the trench walls at site A. At site B, a fault was observed to cut bedrock and terrace deposits. These trench surveys and radiocarbon dates reveal that the latest faulting event on the Kajiya fault occurred after 1034 AD. This faulting event may be correlated to the 1325 AD Shochu earthquake or the 1586 AD Tensho earthquake. The penultimate and antepenultimate events seem to have occurred in about 3,000-3,500 years ago and about 7,000 years ago. The vertical slip-rate at site B is estimated to be 0.3 to 0.4 m/ky from the correlation of terrace gravels between the bore-hole core and the trench wall.

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