3D Modeling of the Kathmandu Basin Effects on Ground Motions for the 2015 Gorkha earthquake

Amrit Bal, Alice-Agnes Gabriel, & Thomas Ulrich

Published August 12, 2021, SCEC Contribution #11304, 2021 SCEC Annual Meeting Poster #034

The 2015 Mw7.8 Gorkha earthquake unzipped a locked portion of the Main Himalayan Thrust, which caused nearly 9000 fatalities across Nepal. However, the damage was less severe in Kathmandu when compared to empirical hazard estimates, particularly when compared to the damages from the 1934 Mw8.2 earthquake, which suggests that ground motions were weaker than expected for a Mw7.8 earthquake at that distance (Galetzka et al., 2015). Previous 3D strong motion simulations suggest that the Kathmandu sedimentary basin structures amplify ground shaking at a dominant frequency of 0.2-0.25 Hz (Wei et al., 2018). A detailed 3D model, one that includes complex topography and accounts for the complex geometries and structure of the sedimentary basin, is needed to effectively simulate seismic wave propagation and ground motions. Yet, incorporating topography and sedimentary basin effects in physics-based ground motion modeling is a challenge in computational seismology. In this study, we use the simulation software SeisSol, which uses unstructured, tetrahedral meshes and high-performance computing to approximate complex 3D model geometries. We generate a detailed model of the Kathmandu Valley and simulate seismic wave propagation and ground motions of the 2015 Gorkha earthquake mainshock and a large aftershock in a complex 3D sedimentary basin geometry shielded by strong local topography contrasts. We investigate the correlation between basin geometry and the dominant resonance of surface waves as well as frequency-dependent tradeoffs between topographic shielding and sedimentary amplifications with implications for physics-based seismic hazard assessment.

Key Words
Ground Motions, Simulations, Gorkha earthquake

Citation
Bal, A., Gabriel, A., & Ulrich, T. (2021, 08). 3D Modeling of the Kathmandu Basin Effects on Ground Motions for the 2015 Gorkha earthquake. Poster Presentation at 2021 SCEC Annual Meeting.

Related Projects & Working Groups
Ground Motions