Multicomponent reduced scale seismic modelling: upgrade of the MUSC laboratory with application to polarization observations
Résumé
Reduced scale physical modelling is a useful intermediate step to fill the gap between field measurements and numerical simulations. In many different areas of seismology, multicomponent measurements are now commonly recorded and processed. However, up to now, laboratory facilities providing flexible and accurate reproduction of large multicomponent seismic experiments have not reached maturity. Within this context, we present an improvement of a measurement facility (MUSC) developed previously to enable the flexible and versatile reproduction of seismic experiments at reduced scale. This new measurement system provides simultaneous measurements of the vertical and the horizontal components of seismic wavefields by taking advantage of recent developments in laser ultrasonic sensing technologies. Reference measurements on an aluminum block are carried out in order to quantitatively evaluate multicomponent measurements. Noise characterization, surface wave ellipticity analysis and waveform comparisons with a semi-analytical model are presented. To enable the simultaneous comparison of phase and polarization attributes, we also introduce a regularized version of the polarization attributes and apply it to synthetic and experimental data. These comparisons demonstrate that high fidelity multicomponent reduced scale physical modelling is possible with this new facility. An illustrative example with a model containing a shallow cavity is presented. In this case, multicomponent measurements help to identify the cavity signature but multiples have a detrimental effect on regularized instantaneous polarization attributes. By assessing the reliability of the MUSC measurement facility in the performance of massive high-quality multicomponent data acquisition at the laboratory scale, this study highlights the interesting potentials of reduced scale modelling of seismic wave propagation for a large variety of applications