Effects of topography on 3D seismic ground motion simulation with an application to the Valley of Aburrá in Antioquia, Colombia
Fecha
2013
Autores
Restrepo Sánchez, Doriam Leidin
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Editor
Universidad EAFIT
Resumen
This dissertation presents a numerical scheme based upon the finite element framework for the numerical modeling of earthquake-induced ground motion in the presence of realistic topographic variations of the Earth’s crust -- We show that by adopting a non-conforming meshing scheme for the numerical representation of the surficial topography we can obtain very accurate representations of earthquake induced ground motion in mountainous regions -- From the computational point of view, our methodology proves to be accurate, efficient, and more importantly, it allows us to preserve the salient features of multi-resolution cubic finite elements -- We implemented the non-conforming scheme for the treatment of realistic topographies into Hercules, the octree-based finite-element earthquake simulator developed by the Quake Group at Carnegie Mellon University -- We tested the benefits of the strategy by benchmarking its results against reference examples, and by means of convergence analyses -- Our qualitative and quantitative comparisons showed an excellent agreement between results -- Moreover, this agreement was obtained using the same mesh refinement as in traditional flat-free simulations -- Our approach was tested under realistic conditions by conducting a comprehensive set of deterministic 3D ground motion numerical simulations in an earthquake-prone region exhibiting moderate-to-strong surficial irregularities known as the Aburr´a Valley in Antioquia-Colombia -- We proposed a 50 50 25 km3 volume to perform our simulations, and four Mw = 5 rupture scenarios along a segment of the Romeral fault; a significant source of seismic activity of Colombia -- We created and used the Initial Velocity Model of the Aburr´a Valley region (IVM-AbV) which takes geology as a proxy for shear-wave velocity -- Each earthquake model was simulated using three different models: (i) realistic 3D structure with realistic topography; (ii) realistic 3D structure without topography; and (iii) homogeneous half space with realistic topography. Our results show how topographic irregularities greatly modify the ground response -- In particular, they highlight the importance of the combined interaction between source-effects, focusing, soft-soil conditions, and 3D topography -- We provide quantitative evidence of this interaction and show that topographic amplification factors at some locations can be as high as 500 percent, while some other areas experience reductions -- These are smaller than the amplifications, on the order of up to 100 percent