The influence of off-fault deformation zones on the near-fault distribution of coseismic landslides

Coseismic 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.

Supplemental Material: The influence of off-fault deformation zones on the near-fault distribution of coseismic landslides

Off-fault deformation (OFD) data, additional methodology, and analysis.<br>

Supplemental Material: The influence of off-fault deformation zones on the near-fault distribution of coseismic landslides

Off-fault deformation (OFD) data, additional methodology, and analysis.<br>

Calculation of the Coseismic Landslide Volume Using DEMs: An Example from the Yingxiu Area, Wenchuan, Sichuan, China

Volume calculation is important for quantifying the erosion driven by coseismic landslides in geomorphology. With the advent of digital elevation models (DEMs), quantifying features of landslide bodies have become possible, permitting to calculate the landslide volume in terms of elevation changes. To further test this approach, this work calculates the volume of landslides near the epicenter of the 2008 Mw 7.9 Wenchuan earthquake in the Yingxiu region, Sichuan, China, by comparing pre- and postearthquake DEMs. Results suggest that effective application of this method needs to consider the DEM resolution and eliminates background errors of individual landslides. The volume of coseismic landslides calculated by the proposed method may represent a minimum value compared to that from the existing empirical V-A formulas. Considering that it is difficult to quantify the coseismic landslide volume throughout in a broad region, this method can be applied to the preliminary stage of characterizing coseismic landslides quantitatively for some key localities of the affected area of major earthquakes.