A channelised long run-out debris slide triggered by the Noto Hanto Earthquake in 2007, Japan |
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| Authors: | Yasuhiko Okada Hirotaka Ochiai Ushio Kurokawa Yasuhiro Ogawa Shiho Asano |
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| Institution: | (1) Forestry and Forest Products Research Institute, Incorporated Administrative Agency, 305-8687 Matsunosato 1 Tsukuba, Ibaraki, Japan |
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| Abstract: | A strong earthquake (M
J 6.9, M
W 6.6–6.7) at about 11 km depth hit the western shore of the Noto Peninsula on Honshu, Japan, at about 00:42 coordinated universal
time (9:42 a.m. local time) on 25 March 2007 (the Noto Hanto Earthquake in 2007). The earthquake triggered only 61 landslides, with most
traveling short distances. It caused one long run-out landslide in the Nakanoya district of Monzen town, Wajima city, Ishikawa
Prefecture, when a portion of a deep-seated landslide transformed into a moderate debris slide down a channel. The rock slide
occurred on a south-facing convex-shaped slope on a small spur where earthquake ground shaking likely was strongly amplified
by topography. A portion of the rock slide reached a small channel floored by materials containing abundant groundwater. Constant-volume
box-shear tests on normally consolidated saturated specimens revealed that the apparent angle of internal friction of the
channel-floor material was 33–36° at 10-mm shear displacement and did not show much decrease in effective normal stress during
shearing. In situ rock-sliding testing on the exposed channel materials showed a low kinetic-friction angle of about 21°.
We suggest that an unsaturated portion of the rock slide slid down the channel, with sliding between the rock-slide mass and
the channel floor. Because the slope angle of the travel path nearly equaled the kinetic-friction angle, the unsaturated rock
slide mass may have traveled at a moderately slow speed, or it might have decelerated and accelerated. Slow speed is supported
by accounts from local residents that suggest movement of debris continued for 3 days after the main shock. |
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| Keywords: | Debris slide Run-out distance Topographic amplification Earthquake |
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