Effects of slope instability on coseismic landslide susceptibility during earthquakes

• Published in: Bulletin of engineering geology and the environment 2022-12, Vol.81 (12), Article 515
• Main Authors: Doi, Issei, Matsuura, Sumio, Osawa, Hikaru, Shibasaki, Tatsuya, Tosa, Shinichi
• Format: Article
• Language: English
• Subjects: Earth and Environmental Science; Earth Sciences; Foundations; Geoecology/Natural Processes; Geoengineering; Geotechnical Engineering & Applied Earth Sciences; Hydraulics; Nature Conservation; Original Paper
• ISSN: 1435-9529; 1435-9537
• DOI: 10.1007/s10064-022-03015-0

Hazard mapping of earthquake induced landslides depends on precise understanding of how slope instability influences coseismic landslide susceptibility during earthquakes. It was theoretically mentioned that destabilized landslides could move with weaker seismic motion; however, it has not been demonstrated through field monitoring data. This study interprets continuous observations of seismic motion and displacement within a coastal landslide whose factor of safety was gradually decreasing due to toe erosion. In addition to steady-state movement, coseismic landslide displacements of 0.2–1.2 mm occurred during three earthquakes within the observation period. Peak ground acceleration from these events ranged from 9.6 to 28.5 cm/s 2 and fell short of values reported to date. Coseismic landslide displacement did not occur while the landslide was stationary even during much greater peak ground acceleration. Critical acceleration, the magnitude of the acceleration at which the landslide initiates, was found to decrease with increases in landslide instability. Coseismic landslide displacements were found to occur in cases of weaker seismic motion with re-occurrence of a large slide event. For smaller volumes of the moving body, seismic wave coherency within the landslide increased. As a result, the smaller seismic motion was able to initiate landslide movement. Landslides which experience toe erosion due to wave action or cyclic inundation by an adjacent water body or those with pore water pressure enhanced by precipitation likely express reduced safety factors. Risk assessment for landslides such as these requires closer consideration of the degree of landslide instability.