Application and evaluation of a rapid response earthquake-triggered landslide model to the 25 April 2015 Mw 7.8 Gorkha earthquake, Nepal

• Published in: Tectonophysics Vol. 714-715; pp. 173 - 187
• Main Authors: Gallen, Sean F., Clark, Marin K., Godt, Jonathan W., Roback, Kevin, Niemi, Nathan A.
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 13.09.2017
• Subjects: Coseismic landslide; Newmark analysis; Peak ground acceleration; Rock strength; Coseismic landslide; Rock strength; Newmark analysis; Peak ground acceleration
• ISSN: 0040-1951; 1879-3266
• DOI: 10.1016/j.tecto.2016.10.031

The 25 April 2015 Mw 7.8 Gorkha earthquake produced strong ground motions across an approximately 250km by 100km swath in central Nepal. To assist disaster response activities, we modified an existing earthquake-triggered landslide model based on a Newmark sliding block analysis to estimate the extent and intensity of landsliding and landslide dam hazard. Landslide hazard maps were produced using Shuttle Radar Topography Mission (SRTM) digital topography, peak ground acceleration (PGA) information from the U.S. Geological Survey (USGS) ShakeMap program, and assumptions about the regional rock strength based on end-member values from previous studies. The instrumental record of seismicity in Nepal is poor, so PGA estimates were based on empirical Ground Motion Prediction Equations (GMPEs) constrained by teleseismic data and felt reports. We demonstrate a non-linear dependence of modeled landsliding on aggregate rock strength, where the number of landslides decreases exponentially with increasing rock strength. Model estimates are less sensitive to PGA at steep slopes (>60°) compared to moderate slopes (30–60°). We compare forward model results to an inventory of landslides triggered by the Gorkha earthquake. We show that moderate rock strength inputs over estimate landsliding in regions beyond the main slip patch, which may in part be related to poorly constrained PGA estimates for this event at far distances from the source area. Directly above the main slip patch, however, the moderate strength model accurately estimates the total number of landslides within the resolution of the model (landslides≥0.0162km2; observed n=2214, modeled n=2987), but the pattern of landsliding differs from observations. This discrepancy is likely due to the unaccounted for effects of variable material strength and local topographic amplification of strong ground motion, as well as other simplifying assumptions about source characteristics and their relationship to landsliding. •Coseismic landslide model applied for rapid response effort following an event.•Assumed rock strength strongly effects estimated magnitude of landsliding.•Model results are compared to coseismic landslide inventory.•General landslide patterns mimicked with moderate-high rock strength model.•Detailed distribution of landsliding not well described by model results.