Poster #046, Ground Motions

Topographic control of ground motions and landslides from the 2015 Gorkha earthquake

Audrey Dunham, Eric Kiser, Jeffrey Kargel, Umesh Haritashya, Scott Watson, Dan Shugar, Amanda N. Hughes, & Peter DeCelles
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Poster Presentation

2021 SCEC Annual Meeting, Poster #046, SCEC Contribution #11556 VIEW PDF
Landslides caused by seismic shaking are a common secondary hazard of earthquakes, particularly in high mountainous regions where rugged topography predisposes the landscape to failure. Topography can also amplify the wavefield by focusing seismic energy within ridge systems, a phenomenon known as topographic amplification, which can lead to coseismic mass movements. The relationship between topographic amplification and coseismic landslides from large earthquakes is extremely important for post-earthquake landslide hazard mitigation, but is generally poorly understood due to a lack of seismic data in regions of rugged topography. This study uses numerical methods to investigate the link bet...ween the ground motions, topographic amplification, and the 25,000 coseismic landslides from April 25, 2015, Mw7.8 Gorkha earthquake. We use the spectral element method implemented in SPECFEM3D to model the kinematic rupture of the Gorkha earthquake in both high resolution and smoothed topography, obtaining a topographic amplification factor by comparing these two simulations. Large-scale trends show that most landslides are concentrated north of the earthquake’s highest peak ground accelerations (PGA). The highest PGAs are located in relatively gentle topography, not predisposed to landsliding, whereas to the north, there are steeper slopes that require significantly less shaking to trigger mass movements, exemplifying the complex nature of understanding coseismic landslide hazard. We also see that the largest landslides initiated where the highest topographic amplification, highest elevations, and steepest slopes converged, typically in glacially sculpted terrain. As glaciers continue to thin and retreat at increasing rates in the Himalaya due to climate change, the topography left behind is primed for increased topographic amplification that could produce larger and more devastating coseismic landslides from future earthquakes. Finally, we find that the source ridge of the largest coseismic landslide in the Langtang Valley experienced three previously unknown episodes of topographic amplification throughout the rupture due to the orientation of the ridge relative to the propagating wavefield. These results show that characterizing topographic amplification is essential for understanding where large and potentially devastating coseismic landslides are likely to occur during future major earthquakes in mountainous regions around the world.