Abstract
Estimating the shear wave velocity and thickness of geologic units in a sedimentary structure is important for quantifying the local site effect caused by an earthquake. Inversion of the Rayleigh wave dispersion alone is sensitive to the absolute average shear wave velocity, while the H/V spectral ratio is sensitive to velocity contrasts. The solution of these models in a joint system using conventional inversion techniques suffers from difficulties while evaluating partial derivatives, dependencies to the initial model that is sometimes difficult to estimate, and trapping at a local minimum. Herein, a joint model using the Pareto optimality technique with multiobjective particle swarm optimization was constructed as an effective global optimization method to decrease weakness and increase performance while estimating the depths and velocities. The presented approach is a multiobjective optimization method that does not require weighting, and allows evaluations of the individual objective function separately in a joint system. This study presents 2 synthetic joint system examples to account for a gradient-type and sharp velocity contrast cases, and an application from field data obtained from the Bursa Basin in Turkey. With these examples, an automated parameter search space was demonstrated to account for the abrupt velocity changes and a number of additional key points that are essential for a reasonable optimal solution.
Highlights
The local site effect causes heavy damage to settlements over sedimentary structures, regardless of the distance to the epicenter of the earthquake (Tezcan et al, 2002; Özel et al, 2002; Ergin et al, 2004; Bozdağ and Kocaoğlu, 2005)
Fast and noninvasive methods based on measuring seismic noise have been popular to obtain the Rayleigh wave dispersion (RWD), and horizontal to vertical spectral ratio (HVSR) curves that are strongly related with the ellipticity of Rayleigh waves (Konno and Ohmachi, 1998; Bard, 1999; Parolai et al,. 2001; Ohrnberger et al, 2004; Wathelet et al, 2008; Özalaybey et al, 2011)
This study presents the utility of multiobjective particle swarm optimization with the Pareto optimality technique, which produced satisfying shear wave velocity and thickness of the layers without weighting requirements, and allowed evaluations of the individual objective function separately in a joint system
Summary
The local site effect causes heavy damage to settlements over sedimentary structures, regardless of the distance to the epicenter of the earthquake (Tezcan et al, 2002; Özel et al, 2002; Ergin et al, 2004; Bozdağ and Kocaoğlu, 2005). This study presents the utility of multiobjective particle swarm optimization with the Pareto optimality technique, which produced satisfying shear wave velocity and thickness of the layers without weighting requirements, and allowed evaluations of the individual objective function separately in a joint system. This is the first study to the authors’ knowledge that utilizes multiobjective particle swarm optimization with the Pareto optimality technique for joint modeling of RWD and HVSR curves
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