Climatological and geological controls on seismic earthflows in coastal areas

Abstract

Seismic earthflows, as special seismic landslides, have occurred in several recent coastal earthquakes, causing catastrophic consequences, but few studies have focused on these landslides. Thus, this study adopts cases induced by recent earthquakes, e.g., the 2018 Palu, 2018 Eastern Iburi, 2018 Lombok and 2022 Pasaman earthquakes, to analyze the characteristics of occurrence and movement. The results show that the Palu, Eastern Iburi, Lombok and Pasaman events induced 8, 7006, 1155 and 33 typical earthflows, respectively, which are in two material layers: volcanic deposits (Eastern Iburi, Lombok and Pasaman events) and alluvial deposits (Palu event). Earthflows in volcanic deposits are very sensitive to rainfall; all earthflows occur in high-rainfall areas, and they are shallow landslides. The corresponding average mobility values (H/L) range from approximately 0.20 ∼ 0.35. The earthflows induced by the Palu event exhibit extremely high mobility levels (average H/L = 0.021). Different liquefied layers could explain the liquefaction mechanism of earthflows in the two material layers. Additionally, compared to other seismic landslides, earthflows occur on gentler hills and have higher mobility.