Trenching study at Kudaritani site across the Magome-toge fault, the Kiso-sanmyaku-seien fault zone, central Japan

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Kiso-sanmyaku-seien fault zone, extending for 60 km along the western front of the Kiso Range, consists of three echelon faults which trend in the N-S to NE-SW direction. We trenched the southernmost Magome-toge fault at Kudaritani site. In the trench walls, we recognized three distinct faulting events: one in the Holocene and two in the Late Pleistocene. Another older events are also inferred from a prismatic gravelly clay bed deposited in front of the fault plain. Our precise sequential <SUP>14</SUP>C dating of the humic soils revealed that the latest faulting event occurred 5,000-3,800 cal yr BP. The penultimate event occurred after the fall of AT tephra (29,000 cal yr BP) and before 11,000 cal yr BP, and the third recent event predated the fall of the AT tephra. Mean faulting interval is therefore estimated to be around 12,000 to 25,000 years. The average vertical displacement per event is roughly estimated to be 1.2-1.6 m.
Japanese Society for Active Fault Studiesの論文