Characteristics of landslides in forests and grasslands triggered by the 2016 Kumamoto earthquake

Kenta Koyanagi; Takashi Gomi; Roy C Sidle

doi:10.1002/esp.4781

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Characteristics of landslides in forests and grasslands triggered by the 2016 Kumamoto earthquake

Journal article

Peer reviewed

Characteristics of landslides in forests and grasslands triggered by the 2016 Kumamoto earthquake

Kenta Koyanagi, Takashi Gomi and Roy C Sidle

Earth Surface Processes and Landforms, Vol.45(4), pp.893-904

2020

DOI: https://doi.org/10.1002/esp.4781

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Abstract

landslide

earthquake

land cover

residual sediment

wood pieces

We examined the characteristics of landslides triggered by the 2016 Kumamoto earthquake (Mw = 7.0: focal depth=10.0 km) in forests and grasslands within two affected watersheds (Tokosegawa: 6.9 km2 and Nigorigawa: 6.1 km2) in southwestern Japan. We identified 190 landslides using aerial photographs and analyzed their sizes by geographic information system (GIS). Field investigations were conducted to obtain landslide depth, volume and residual sediment for 38 selected landslides (21 in forests and 17 in grasslands). The minimum area of detected landslides in grasslands (400 m2) was smaller than in forests (1000 m2), probably because of reduced detectability of landslides under tree cover. The ratio of total area occupied by landslides for a given range of slope gradient in the watersheds increased from 3.2% on gentle grassland slopes (10-15°) to 15.5% on steep (>45°) slopes, whereas the maximum landslide-area ratio in forest sites (7.4%) occurred on relatively gentle slopes (25-30°). Estimated landslide volume ranged from 27 to 9622 m3, based on mean depth of each landslide measured around individual landslide scars. Moreover, the volumetric ratio of landslide deposit volume to total landslide volume exceeded 100% for 48% of the landslides within forests and 35% of the landslides within grasslands. Our findings show that land cover had extensive and recognizable effects on the characteristics of landslides and resulting in-channel sediment accumulations. Resetting sediment dynamics after earthquakes associated with different land cover distributions needs to be considered within watersheds.

Details

Title: Characteristics of landslides in forests and grasslands triggered by the 2016 Kumamoto earthquake
Authors: Kenta Koyanagi (Corresponding Author) - University of Eastern Finland
Takashi Gomi (Author) - Tokyo University of Agriculture and Technology
Roy C Sidle (Author) - University of the Sunshine Coast
Publication details: Earth Surface Processes and Landforms, Vol.45(4), pp.893-904
Publisher: John Wiley & Sons Ltd.
Date published: 2020
DOI: 10.1002/esp.4781
ISSN: 0197-9337
Organisation Unit: University of the Sunshine Coast, Queensland; Sustainability Research Cluster
Language: English
Record Identifier: 99450842502621
Output Type: Journal article

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Collaboration types: Domestic collaboration; International collaboration
Web Of Science research areas: Geography, Physical; Geosciences, Multidisciplinary

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