Bignardi, Samuel (2011) Complete Waveform Inversion Approach To Seismic Surface Waves And Adjoint Active Surfaces. Tesi di Dottorato , Università degli Studi di Ferrara.

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Abstract
The idea to exploit the dispersive mechanism of surface waves as a probing tool for investigating subsurface structure was introduced about 30 years ago, and afterwards a very intense research field has developed. Currently many methods known generally as Surface Wave Methods exist, and are well established, most of them assuming layered or depth dependent ground models. In most cases the parallel layer assumption is correct because the soil structure is expected to negligibly depart from a layered structure at a typical surface testing scale for engineering and geotechnical purposes however to exploit the amount of information achievable, it is necessary to extend the research, relaxing at least one of the underlying model assumptions. Indeed in classical SWM’s, surface waves are assumed to be Rayleigh waves, this means that a parallel layered model has been implicitly assumed. As a consequence search for a soil model geometry other than the assumed one can only result in slight perturbations. The only possible deduction is that overcoming limitations of layered models requires to exploit P and S waves which are indeed general solutions of the elastodynamic problem. Geometry can then be retrived by a complete waveform inversion based on a forward model capable of successfully reproducing all of the features of the displacement field in presence of complex scattering phenomena. In this research effort an inversion approach has been introduced which exploits the Boundary Element Method as forward model. Such approach is appealing from a theoretical point of view and is computationally efficient. Although in the present work a monochromatic signal traveling in a system constituted by a layer over an half space was investigated, this method is suitable for any number of layers, and multifrequency environments. The boundary element approach can be easily generalized to threedimensional modeling; moreover viscoelasticity can be introduced by the elasticviscoelastic principle of correspondence. Finally BEM can be easily implemented for parallel computing architecture. Synthetic cases of high and low impedance Jump were investigated for typical SWM setups and a first example of application on real data was performed. Finally an elegant analytic form of the minimization flow named Adjoint Active Surfaces was obtained combining Computer Vision technique of Active surfaces and the Adjoint Field method.
Tipologia del documento:  Tesi di Dottorato (Tesi di Dottorato) 

Data:  11 Marzo 2011 
Relatore:  Santarato, Giovanni  Fedele, Francesco 
Coordinatore ciclo:  Beccaluva, Luigi 
Istituzione:  Università degli Studi di Ferrara 
Dottorato:  XXIII Anno 2008 > SCIENZE DELLA TERRA 
Struttura:  Dipartimento > Scienze della terra 
Soggetti:  Area 04  Scienze della terra > GEO/11 Geofisica applicata 
Parole chiave:  surface waves inversion, lateral heterogeneous, inversione onde superficiali, variazioni laterali 
Depositato il:  13 Apr 2012 15:01 
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