ボーリング調査で明らかとなった濃尾活断層系梅原断層の新期断層運動

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The Nobi Earthquake in October 28,1981 is one of the largest onland earthquakes (M=8.0) which have occurred in the history of Japan. At this time, the Nobi earthquake fault system, extending ca 80km from NW to SE, was appeared with the surface rupture. This system consists mainly of Nukumi, Kurotsu, Neodani, and Umehara Faults and has been accompanied predominantly with left-lateral displacement. Unlike most Nobi Earthquake Faults, the Umehara Fault trending in the direction of WNW to ESE was associated with large component of vertical displacement. As northeast side of the Fault was relatively subsided, some ponds had taken place after the earthquake. One of the largest pond, which extent was about 25ha, was situated at Umehara, Takatomi Town, Gifu Prefecture. We carried out a boring of 25m deep at the central part of this subsided area. And samples obtained from this core were investigated from stratigraphical and chronological points of view. As a result, three cycles, which show the phenomena from abrupt change of facies to gradual shallowing of pond, were recognized within this core. Those cycles changing from humic layer to silty or sandy layer are considered to indicate the event of abrupt subsidence caused by the faulting. ^<14>C-dating reveals that events deduced from the aprupt subsidence have taken place at the times ; before 31,000yr.B.P., 46,000yr.B.P. and pre-59,000yr.B.P. Thus, the movement along the Umehara Fault have taken place at the interval of 15,000-30,000 years. The activity of the Umehara Fault is obviously lower than the Neodani Fault ; the major segment of the Nobi Fault System.
名古屋大学の論文

ボーリング調査で明らかとなった濃尾活断層系梅原断層の新期断層運動

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