Detección fina de cambios laterales en la geología superficial y en los suelos y caracterización de su influencia en la respuesta sísmica local: aplicación a Barcelona

• Autores: Victor Salinas Naval
• Directores de la Tesis: Josep Oriol Caselles Magallón (dir. tes.), Luis Gonzaga Pujades Beneit (dir. tes.)
• Lectura: En la Universitat Politècnica de Catalunya (UPC) ( España ) en 2015
• Idioma: español
• Tribunal Calificador de la Tesis: Francisco Luzón Martínez (presid.), María Vega Pérez Gracia (secret.), Sara Figueras Vila (voc.)
• Programa de doctorado: Programa de Doctorado en Ingeniería Sísmica y Dinámica Estructural por la Universidad Politécnica de Catalunya
• Materias:
  • Ciencias de la tierra y del espacio
    • Geofísica
      • Sismología y prospección sísmica
• Enlaces
  • Tesis en acceso abierto en: TDX
• Resumen

  • A complete and reliable Seismic Soil Response prediction requires a thorough knowledge of the Geotechnical and Geological structure, as well as algorithms to find the transfer function. This fact entails a significant complexity and, consequently, strengthens empiric methods, as for instance the well-known Horizontal to Vertical Spectral Ratios (HVSR). Moreover, the long return periods of earthquakes, especially in low- to-moderate-seismicity regions as Barcelona, hinder the comparison between predictive studies and observations in case of earthquake. In these sites, methods based on ambient vibration (seismic noise) become important. In this PhD thesis the Seismic Soil Response phenomenon is approached trough new theoretical contributions and applications. The main purpose has been to provide new insights and to generate new tools to improve the comprehension and the resolution of Seismic Soil Response related problems. In this way, innovative theories as Surface Sources (DSS) and Diffuse Fields (DFA) have been applied to solve the HVSR direct problem in horizontal layered media, among others. Also, specific field studies have been performed on test sites of the Barcelona plain with three main purposes: i) to improve the knowledge of the soil by means of array techniques based on ambient vibration, ii) to provide new techniques to allow an easy and fast analysis of the lateral heterogeneities and to accurately locate soil anomalies; iii) to suggest and apply smart techniques to densify HVSR measurement sites. Thus, an innovative outcome of this work has been using Ground Penetrating Radar (GPR) for preliminary detection and characterization of anomalous subsoil sections, with special emphasis in those due to paleochannels and to seasonal streams draining rainwater in mountain-sea direction. The observed HVSR curves (one station measurements) are compared with the theoretical ones obtained from DSS and DFA. Moreover, empiric dispersion curves of the Surface Waves (array measurements) are compared with the theoretical ones corresponding to the soil layered structure. Both procedures allow to check for the suitability of the new proposed tools and, to establish the reliability of the found parameters. Thus, we have been able to increase the knowledge, resolution and reliability of the soil parameters in test sites of the Barcelona plain leading to a better knowledge of the Transfer Functions. From different configurations of the DFA formulation it has been shown that, for a specific site, the HVSR response for ambient vibration is linked to HVSR response when the source is a wave-field where every spectral component is obtained by averaging the spectral components of the records of a great number of earthquakes. When lateral homogeneity assumption fails, the horizontal layered formulations are not suitable and discrepancies between empirical and theoretical responses appear. These differences have been attributed to lateral effects. In this sense, analytical results have been obtained for a constant-section valley illuminated by a two-dimensional diffuse field. This approximation enables finding specific properties of HVSR due to lateral contacts. Finally, this work has shown the need for taking into account the detailed subsoil structure in seismic micro-zonation and risk studies, as these heterogeneities may have significant importance on seismic response. So several advanced tools based on GPR have been provided, allowing, in an easy and quick way, detecting and sizing the heterogeneous areas and suggesting sections where ambient vibration measurement should be intensified.