Examinando por Autor "Jaramillo, J."

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    Analysis of the role of diffraction in topographic site effects using boundary element techniques
    (Seismological Society of China, 2013-01-01) Gomez, J.; Restrepo, D.; Jaramillo, J.; Valencia, C.; Mecánica Aplicada
    The role played by the diffraction field on the problem of seismic site effects is studied. For that purpose we solve and analyze simple scattering problems under PandSVin-plane wave assumptions, using two well known direct boundary-element-based numerical methods. After establishing the difference between scattered and diffracted motions, and introducing the concept of artificious and physically based incoming fields, we obtain the amplitude of the Fourier spectra for the diffracted part of the response: this is achieved after establishing the connection between the spatial distribution of the transfer function over the studied simple topographies and the diffracted field. From the numerical simulations it is observed that this diffracted part of the response is responsible for the amplification of the surface ground motions due to the geometric effect. Furthermore, it is also found that the diffraction field sets in a fingerprint of the topographic effect in the total ground motions. These conclusions are further supported by observations in the time-domain in terms of snapshots of the propagation patterns over the complete computational model. In this sense the geometric singularities are clearly identified as sources of diffraction and for the considered range of dimensionless frequencies it is evident that larger amplifications are obtained for the geometries containing a larger number of diffraction sources thus resulting in a stronger topographic effect. The need for closed-form solutions of canonical problems to construct a robust analysis method based on the diffraction field is identified. © The Seismological Society of China, Institute of Geophysics, China Earthquake Administration and Springer-Verlag Berlin Heidelberg 2013.
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    Effects of realistic topography on the ground motion of the Colombian Andes - A case study at the Aburra Valley, Antioquia
    (OXFORD UNIV PRESS, 2016-03-01) Restrepo, D.; Bielak, J.; Serrano, R.; Gómez, J.; Jaramillo, J.; Mecánica Aplicada
    This paper presents a set of deterministic 3-D ground motion simulations for the greater metropolitan area of Medellin in the Aburra Valley, an earthquake-prone region of the Colombian Andes that exhibits moderate-to-strong topographic irregularities. We created the velocity model of the Aburra Valley region (version 1) using the geological structures as a basis for determining the shear wave velocity. The irregular surficial topography is considered by means of a fictitious domain strategy. The simulations cover a 50 x 50 x 25 km(3) volume, and four M-w = 5 rupture scenarios along a segment of the Romeral fault, a significant source of seismic activity in Colombia. In order to examine the sensitivity of ground motion to the irregular topography and the 3-D effects of the valley, each earthquake scenario was simulated with three different models: (i) realistic 3-D velocity structure plus realistic topography, (ii) realistic 3-D velocity structure without topography, and (iii) homogeneous half-space with realistic topography. Our results show how surface topography affects the ground response. In particular, our findings highlight the importance of the combined interaction between source-effects, source-directivity, focusing, soft-soil conditions, and 3-D topography. We provide quantitative evidence of this interaction and show that topographic amplification factors can be as high as 500 per cent at some locations. In other areas within the valley, the topographic effects result in relative reductions, but these lie in the 0-150 per cent range.
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    The scattering of SH waves by a finite crack with a superposition-based diffraction technique
    (Akademie Ved Ceske Republiky, 2017-01-01) Valencia, C.; Gomez, J.; Jaramillo, J.; Saenz, M.; Vergara, J.; Mecánica Aplicada
    The problem of diffraction of cylindrical and plane horizontally polarized shear waves (SH waves) by a finite crack embedded in a plane bidimensional elastic full-space is revisited. Particularly, we construct an approximate solution by the addition of independent diffracted terms. In our method the derivation of the fundamental case of a semi-infinite crack obtained as a degenerate case of a generalized wedge is first considered. This result is then used as a building block to compute the diffraction of the main incident waves. The interaction between the opposite edges of the crack is later considered in terms of a series, one term at a time until a desired tolerance is reached. Moreover, we propose a procedure to determine the number of required interactions as a function of frequency. The solution derived with the superposition technique is shown to be effective at low and high frequencies and as shown by comparisons with a direct boundary element method software, highly accurate solutions are obtained after retaining just a few terms of the infinite series. © 2017, Institute of Geophysics of the ASCR, v.v.i.