Segmentation of the surface ruptures associated with the 1891 Nobi earthquake, central Honshu, Japan, based on the paleoseismic investigations

Authors: Yasuo Awata, Yoshihiko Kariya and Koji Okumura(Hiroshima Univ.)

Abstract: The 1891 Nobi earthquake accompanied by 80-kilometers-long surface ruptures is the largest earthquake on land in Japan during the modern history of this country. Therefore segmentation of the 1891 ruptures is the most important subject for the scaling laws of the fault dimensions in Japan. The 1891 ruptures are subdivided into three major segments; the Nukumi, Neodani and Umehara segments from the north, based on the fault geometry and displacement distribution. We excavated a series of trenches on the Neodani and Umehara faults to compare the timings of paleofaulting on each fault. A trench on the Neodani fault revealed that the fault has a recurrence interval of 2700 years during the Holocene Epoch. On the other hand, the penultimate faulting event of the Umehara fault was older than 11 14C ka. Consequently each of the Neodani and Umehara faults is defined as a single behavioral segment.

Surface ruptures associated with the 1891 Nobi earthquake and sites of trenching survey.

BEHAVIORAL SEGMENT Length Dmax Dmode Recurrence interval Slip rate
NUKUMI SEGMENT 16km 3.5m 0.1~1m/ky
NEODANI SEGMENT 31km 7.4m 4-6m 2.7ky ≧2m/ky
UMEHARA SEGMENT 26km 5.3m ≧2m 1114Cky

Major behavioral segments in the 1891 Nobi surface rupture.

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