Abstract
AbstractCoseismic landslides are observed in higher concentrations around surface-rupturing faults. This observation has been attributed to a combination of stronger ground motions and increased rock mass damage closer to faults. Past work has shown it is difficult to separate the influences of rock mass damage from strong ground motions on landslide occurrence. We measured coseismic off-fault deformation (OFD) zone widths (treating them as a proxy for areas of more intense rock mass damage) using high-resolution, three-dimensional surface displacements from the 2016 Mw 7.8 Kaikōura earthquake in New Zealand. OFD zones vary in width from ~50 m to 1500 m over the ~180 km length of ruptures analyzed. Using landslide densities from a database of 29,557 Kaikōura landslides, we demonstrate that our OFD zone captures a higher density of coseismic landslide incidence than generic “distance to fault rupture” within ~650 m of surface fault ruptures. This result suggests that the effects of rock mass damage within OFD zones (including ground motions from trapped and amplified seismic waves) may contribute to near-fault coseismic landslide occurrence in addition to the influence of regional ground motions, which attenuate with distance from the fault. The OFD zone represents a new path toward understanding, and planning for, the distribution of coseismic landslides around surface fault ruptures. Inclusion of estimates of fault zone width may improve landslide susceptibility models and decrease landslide risk.
Highlights
Coseismic landslides are among the most widespread and impactful hazards resulting from earthquakes (e.g., Marano et al, 2010)
Coseismic landslide susceptibility models (e.g., Xu et al, 2012; Reichenbach et al, 2018) that rely on a combination of geologic, hydrologic, morphologic, and seismologic parameters are used to inform policy makers and emergency management plans
This higher incidence of landslides near faults has been attributed to two broad categories of physical processes: (1) stronger ground motions that attenuate with increasing distance from seismic sources (Meunier et al, 2007; Tatard and Grasso, 2013), and (2) geologic conditions and seismic site characteristics resulting from lithological contrasts, topography, and rock mass damage near faults (Ben-Zion and Sammis, 2003; Kim et al, 2004; Meunier et al, 2008; Gallen et al, 2015; Peacock et al, 2017; Wang et al, 2019)
Summary
Coseismic landslides are among the most widespread and impactful hazards resulting from earthquakes (e.g., Marano et al, 2010). We compared the decrease in landslide density with increasing distance from surface fault rupture, using the latest 2016 Kaikōura earthquake landslide inventory (Massey et al, 2020), to the extent of the OFD zone and ground motion attenuation models published for the Kaikōura earthquake. Logistic regression models suggested that, in order of importance, the independently tested parameters of geology, mean slope, distance to surface fault rupture (“distance to fault”), local slope relief, peak ground velocity, and mean elevation contributed significantly to the locations of landslides during the Kaikōura event (Massey et al, 2020). The OFD zone was locally variable across the components of displacement and along fault traces This variability likely resulted from factors including lithology and thickness of any overlying sediment, near-surface fault geometry and kinematic variability along strike, slip partitioning over several fault strands, and interaction between faults at depth (Zinke et al, 2014)
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