SCEC Award Number 16093 View PDF
Proposal Category Collaborative Proposal (Integration and Theory)
Proposal Title Surface Topography Effects in Three-Dimensional Physics-Based Deterministic Ground Motion Simulations in Southern California
Name Organization
Jacobo Bielak Carnegie Mellon University Ricardo Taborda University of Memphis Doriam Restrepo Universidad EAFIT
Other Participants Andrea Riaño (Ph.D. student, CMU)
SCEC Priorities 6e, 6c, 6a SCEC Groups GMSV, CME, GMP
Report Due Date 03/15/2017 Date Report Submitted 03/15/2017
Project Abstract
The main objective of this work is to estimate the extent to which realistic 3D topography plays a significant role in the seismic site response of the Oxnard plain region. Topographic features are known to be one of the causes that contribute to ground motion amplification. In principle, these amplifications occur due to the constructive interaction between incoming waves with wavelength dimensions comparable to the physical dimensions of raised topographic features. Because of their nature, these effects tend to be more influential at local scales, and particularly significant at higher frequencies. We have developed and implemented a method that allows us to perform large-scale 3D ground motion simulations incorporating explicitly the effects of surface topography in our models. Our method, called virtual topography was applied by conducting a series of simulations in a finite element parallel code part of the SCEC High-F simulation platform (Hercules), for the region of the Oxnard plain and the surrounding geologic structures. Finite element simulations with a maximum frequency of 5 Hz were performed in Hercules, the octree finite element platform developed by the Quake Group at CMU. In the study, a set of point sources scenarios were considered for the following seismic events: (1) 2009 Mw 4.4 Westlake Village earthquake, (2) 2007 Mw 4.7 Chatsworth and (3) 2003 Mw 3.6 Simi Valley earthquake. The findings exhibit significant changes as suggested by previous studies (Ma et al., 2007; Restrepo et al., 2015) and confirm the relevance of topographic effects for the Southern California region.
Intellectual Merit The study contributes to understanding the extent to which local scale and regional scale surface topography features influence the characteristics of ground motion, with particular emphasis on simulations for Southern California. The proposed activities had, directly and indirectly, a positive short-term and long-term impact on projects such as High-F and CyberShake, and the Community Modeling Environment special project. In particular, this proposal falls within Proposal Category B: Theory and Integration. It addresses SCEC’s Fundamental Problem 6: Seismic wave generation and scattering – Pre-diction of strong ground motions, and contributes to Research Priorities 6c and 6e. At the disciplinary and interdisciplinary areas level, the proposed research contributes to one of the Key Problems in Computational Science: Seismic wave propagation – Developing wave propagation incorporating […] topography; and to priorities in Ground Motion Prediction: Developing and refining physics-based simulation methodologies, including problems of scattering in physics-based simulations. In doing so, we contributed to the efforts led by the Earthquake Engineering Implementation Interface and the Technical Activity Group on Ground Motion Simulation Validation. Furthermore, this project allowed to test and advance in the development of Hercules—one of the codes in the SCEC physics-based simulation platforms.
Broader Impacts This project helped to evaluate the accuracy of ground motion simulations, which provides a basis for validating simulations such as those used in physics-based probabilistic seismic hazard analysis. Furthermore, this project is based on concepts deeply regarded by the earthquake engineering community, completion of the project plan translates into closer integration and acceptance of simulations for engineering applications (e.g., building code provisions as intended by the SCEC UGMS committee).

On an educational context, this project has provided direct funds and a research opportunity for Andrea Camila Riano Escandon, a PhD student in the Department of Civil and Environmental Engineering at Carnegie Mellon University. Funding from the project helped support Andrea and allowed her to attend the 2016 SCEC Annual Meeting, where she presented preliminary work leading to the development of the project activities.
Exemplary Figure Figure 1. Metrics comparison for event Mw= 4.42 (rows b to e) and ratio between VT and Flat models for Mw= 4.42 and Mw= 4.66 (rows f to i). (a) Topographic profile and variation of the CVM-S model along the diagonals, (b) square root of the energy, (c) peak ground velocity, (d) Housner intensity, (e) peak ground acceleration, (f) VT/Flat ratio for the square root of the energy, (g) VT/Flat ratio for the peak ground velocity, (h) VT/Flat ratio for the Housner intensity, and (i) VT/Flat ratio for the peak ground acceleration along the diagonals.