Influence of the Source, Seismic Velocity, and Attenuation Models on the Validation of Deterministic Ground Motion Simulations

Abstract eng:
This study investigates the accuracy of deterministic, regional-scale ground motion simulations of moderate magnitude earthquakes, and the influence that the source, seismic velocity, and attenuation models have on synthetic results when compared to data. Thanks to recent advances in earthquake ground motion simulation algorithms and models, and to the continuous growth of high performance computing systems and applications, regional-scale simulations of earthquake ground motion using numerical approaches are now becoming commonplace in research environments. However, before these simulations can be transferred to earthquake engineering practice, much work needs to be done to confirm the robustness of models and simulation methods. This requires a continuous effort on simulation validation, which entails, among other things, the comparison of synthetics against recorded ground motions of past earthquakes. These comparisons provide confidence and help improve simulation procedures and models over time. To this end, we evaluate the accuracy of simulations using quantitative metrics that compare synthetics and data. We use metrics that have physical meaning to both seismologists and engineers. In previous efforts we have shown (separately) that validation results are significantly controlled by the choice of the velocity model. Here, we reinforce the influence of velocity models and further investigate the effects of attenuation parameters and models, as well as the influence of the source. We first focus our attention on the selection of the appropriate velocity model by performing a large set of simulations for multiple historical events in southern California, using the different community velocity models available for this region. After identifying the model that consistently yields best possible approximations, we concentrate in one recent event of moderate magnitude in the greater Los Angeles basin area for which there are significant number of high-quality data. Through validation of simulations for this event, we investigate the influence of relationships of the attenuation quality factor with respect to the shear wave velocity (Qs-Vs relationships), and the behavior of attenuation as a frequency dependent parameter. Here, intrinsic attenuation is represented using a viscoelastic model to mimic the effects of internal friction in the transmitting media. We also explore the relative influence of the source model. We analyze the results from point source and extended source models. Our results shed light on the relative weight of these factors with respect to each other, and how they influence validation results, and thus simulations as a whole.

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