Topographic Control on Ground Motions and Landslides From the 2015 Gorkha Earthquake

Abstract

Landslides triggered by earthquake shaking pose a significant hazard in active mountain regions. Steep topography promotes gravitational instabilities and can amplify the seismic wavefield; however, the relationship between topographic amplification and landsliding is poorly understood. Here, we use numerical methods to investigate the link between low‐frequency ground shaking, topographic amplification, and the landslide distribution from the 2015 Gorkha, Nepal earthquake. Results show that the largest landslides initiated where the highest topographic amplification, highest elevations, and steepest slopes converged, typically in glacially‐sculpted terrain, with additional controls of rock strength and absolute ground motions. Additionally, the initiation of the largest and most fatal landslide was likely influenced by amplification throughout the rupture due the orientation of the ridge with respect to the propagating wavefield. These results indicate that topographic amplification is one of the key factors for understanding where large and potentially devastating landslides are likely to occur during future major earthquakes.

From ground motion simulations to landslide occurrence prediction

“…The use of ground motion simulations to examine coseismic landslides are quite limited in the literature (Harp et al, 2014;Chen and Wang, 2022;Dunham et al, 2022;Feng et al, 2022;Sun and Huang, 2023). Their focus mainly gravitates around better assessment of landslide displacements by coupling their simulation results with physically-based methods or the effect of topographic amplification on landslide sizes.…”

“…Using numerical simulations, several works (e.g., Bouchon, 1985;Geli et al, 1988;Tripe et al, 2013) found the high relevance of the site effects of a slope on the amplification of the ground motion. Following this, many works also saw how the 3d effects from geology and topography are relevant in landslide occurrence by studying the incoming waves (e.g., Khalil and Lopez-Caballero, 2021;He et al, 2020;Dunham et al, 2022). Because those analyses are at local scales, they implement complex constitutive models for the soil materials' resistance and rupture.…”

“…Given these constraints, there are only a few studies aiming to exploit 3D earthquake simulations to better assess the occurrence of co-seismic landslides. Those studies either couple the spectral element method with the Newmark sliding block analysis (Huang et al, 2020;Chen and Wang, 2022;Sun and Huang, 2023) or the material point method (Feng et al, 2022) to accurately identify landslide displacements, or examine the spatial distribution of co-seismic landslides with respect to peak modeled ground motions (Harp et al, 2014;Dunham et al, 2022). Among these studies, the research carried out for the 2015 Gorkha earthquake (Dunham et al, 2022) is particularly important because this was the first time that topographically amplified seismic velocity and acceleration and their relation to landslide sizes were investigated for such a large area (1°×2°) and a large earthquake-induced landslide event ( 25,000 co-seismic landslides) using a 3D earthquake simulation.…”

Shaking up Assumptions: Earthquakes Have Rarely Triggered Andean Glacier Lake Outburst Floods

“…It is known that fault geometry and slip are responsible for producing the broad wavefield of earthquakes, and the details of the wave fields affect the propagation and the local scattering, attenuation, and amplification of seismic wavefields. Wave attenuation tends to occur in valleys, and amplification occurs near peaks and high up on ridges (Dunham et al., 2022), but the details of this here are unknown. Another possible influence could have been deep bedrock weathering and fracture structure, such as has been implicated in the Chamoli, Uttarakhand, India ridge failure on 7 February 2021 (Reynolds et al., 2021; Richardson & Reynolds, 2000; Shugar et al., 2021).…”

“…Seismic body waves (p-waves and swaves) arriving obliquely toward the surface tend to attenuate near valley floors, where glacier lakes occur, helping to protect moraine dams against damage from seismic shaking. Seismic waveform modeling of the 2015 Nepal Gorkha earthquake (Dunham et al, 2022) and previous related work , Lee, Chan, et al, 2009 has highlighted the role of seismic body-wave attenuation deep in valleys, and amplification on ridges and some valley walls. Surface waves, such as Love waves and Rayleigh waves 3) for the 59 earthquakes (shown in Figure 1) and timing for the 67 GLOFs in the comprehensive Peruvian and Bolivian inventory (Emmer, Wood, et al, 2022).…”