真昼山地・和賀岳付近に認められる小崖地形の発達過程

概要

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Uphill-facing scarps occur perpendicular or slightly oblique to slopes on eastern flank of Mt. Waga of Mts. Mahiru, Ohu Backbone Range, Northeast Japan (Plate 1, 2; Fig. 2). The scarps of which relative height are ca. 5.5 meters run straight (Fig. 3), being concordant with the dominant strike of the joint system around them (Fig. 4). Toppling of base rock around the scarps was discovered (Plate 3; Fig. 5). Sediments burring the linear depression just below Mt. Waga were dislocated to dip to west, the ridge side, and slightly faulted (Fig. 6). Induced from those deformed features of topography, young sediments and base rocks, the uphill-facing scarps have been caused by relative subsidence of the ridge top subsequent to the toppling of the lower mountain slope. Rock mechanics implies the deformation around the ridge top of Mt. Waga has been triggered by earthquakes with recurrence interval of 3, 000yrs. more or less. The last event formed the scarps was presumably the Riku-u Earthquake of 1896 AD. because the dislocated sediments intercalate a thin layer of air fall volcanic ash named To-a of ca 1, 000yrs. B. P.
東北地理学会の論文