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Maestría en Ingeniería / Estudiantes Skip Navigation Linkseffects-topography-3d Effects of Topography on 3D Seismic Ground Motion Simulation with an Application to the Valley of Aburra in Antioquia, Colombia

EAFITProgramas académicosPosgradosMaestría en IngenieríaMaestría en Ingeniería / EstudiantesEffects of Topography on 3D Seismic Ground Motion Simulation with an Application to the Valley of Aburra in Antioquia, Colombia

Effects of Topography on 3D Seismic Ground Motion Simulation with an Application to the Valley of Aburra in Antioquia, Colombia

Doriam L Restrepo

​2013

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 ex-hibiting moderate-to-strong surficial irregularities known as the Aburra Valley in Antioquia- Colombia. We proposed a 50×50×25km3 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 Aburra, 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.