Generalised Parametic Function and Spatial Correlations for Seismic Velocities in the Canterbury Region based on Dynamic Site Characterisation
Background and objectives This poster presents the development of generalised parametric functions to compute seismic velocities within the sedimentary deposits of the Canterbury region, with spatial correlations to represent the unexplained velocity variability in space. Previous studies characterised the 3D structure of geologic deposits throughout Canterbury for use in ground motion simulations and site response analysis but the velocity structure within these geologic formations are yet to be considered in detail. This study makes use of the results of geophysical testing (passive and active source testing) at 23 sites throughout Christchurch city and the wider Canterbury region, as shown in Figure 1a. In the shallow near-surface (<200m), 18 sites shown are underlain by interbedded fine-grained sediments and gravels while the 5 remaining sites are predominantly gravel. Beneath these shallow interbedded layers lies the deep Tertiary layers. Due to the dispersive nature of surface waves, dispersion curves for each site were generated and theoretical shear wave velocity (Vs) profiles were obtained through inversion. The inversion process was constrained using a priori geotechnical and geologic data to constrain the allowable velocity range and depths to geologic horizons – shown in Figure 1b. The median velocity profile of the 1000 lowest misfit profiles at each site was adopted for use in this analysis.
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