Changes in morphological characteristics of drainage basins following coseismic landslides by the 2018 Hokkaido Eastern Iburi Earthquake

The 2018 Hokkaido Eastern Iburi Earthquake (Mj 6.7) caused numerous coseismic landslides (n = 7,837) covering over 700 km2. This study aims to identify the post-earthquake morphological changes in drainage basins affected by the landslides, with particular interests in fluvial and slope processes. The study site is a catchment along the Atsuma River with less artificial modifications after the earthquake. Airborne laser scanning-derived Digital Elevation Models (DEMs) of October 2012 and September 2018, as well as unmanned aerial vehicle-derived multi-temporal DEMs and orthorectified images from April to October 2020 were collected. Based on these data, elevation change detection and analysis on geomorphometric parameters, including watershed geometry, channel networks, drainage patterns ,and stream profiles were conducted using geographical information system to characterize the post-earthquake morphological changes. We infer that, based on the increase in stream length and bifurcation ratio, channels on bare slope surfaces developed progressively to cause potentially higher surface runoff. With the interactions between fluvial and slope processes, as well as the assists by freeze-thaw actions on bare soil surfaces, further soil erosion and slope deformations are expected.

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