Surface topography effects in three-dimensional physics-based deterministic ground motion simulations in southern California

Andrea C. Riaño, Doriam Restrepo, Ricardo Taborda, & Jacobo Bielak

Published August 24, 2016, SCEC Contribution #6557, 2016 SCEC Annual Meeting Poster #294

Topographic features are known to contribute to ground motion amplification, especially at mountain ridges and edges. These amplifications occur due to the constructive interference between incoming motion with wavelengths comparable to the physical dimensions of the surficial irregularities. Because of their nature, these effects tend to be more influential at local scales, and particularly significant at higher frequencies (above 1 Hz). In the past, these effects have been typically ignored in most 3D low-frequency regional-scale earthquake ground motion simulations. However, simulations above 1 Hz are now commonplace, and a variety of effects associated with higher frequencies need to be considered, including topography. In this study we perform a series of 5-Hz 3D simulations for the region of the Oxnard plain including the surrounding geologic structures, and focus on the effects of the topography on the ground response. We do so by comparing the results from models with and without the surface topography. Simulations are done using Hercules, a finite element parallel code part of the SCEC High-F simulation platform. Hercules implements a virtual topography method which allows one to perform ground motion simulations explicitly incorporating the effects of the surface topography in the models. This method has been tested in various idealized and realistic conditions, but it has not been used previously in simulations for southern California. We study the Oxnard plain region because of the presence of the Ventura Hills, San Cayetano Ridge, Oak Ridge, Simi Hills and the Santa Monica Mountains, where topographic amplification has been observed; and because this is an area under significant seismic hazard, which poses considerable risk for the growing communities of Ventura County. Our simulations highlight the relevance of topographic effects for the southern California region and contribute to advancing the development of physics-based ground motion prediction. The simulations were done on Blue Waters at the National Center for Supercomputing Applications.

Key Words
Earthquake ground motions, Computational seismology, Topography Effects

Citation
Riaño, A. C., Restrepo, D., Taborda, R., & Bielak, J. (2016, 08). Surface topography effects in three-dimensional physics-based deterministic ground motion simulations in southern California. Poster Presentation at 2016 SCEC Annual Meeting.

Related Projects & Working Groups
Ground Motion Simulation Validation (GMSV)