A time-averaged 30-m-depth shear wave velocity ( V S30) map is developed for New Zealand as a weighted combination of a geology-based and a terrain-based model. A Bayesian updating process allows local V S30 measurements to control model estimates where data exist and uses model estimates developed for other parts of the world where local data are sparse or nonexistent. Geostatistical interpolation is performed on the geology-based and terrain-based models using local V S30 measurements to constrain the model in the vicinity of data. Conventional regression kriging is compared with a flexible multivariate normal (MVN) approach that allows for arbitrary assumptions regarding measurement uncertainty at each data location. A modification to the covariance structure in the MVN application allows for more realistic estimates by reducing undesirable extrapolation across geologic boundaries. The results of kriging and MVN approaches are compared. The geology-based and terrain-based MVN models are combined to produce a final model suitable for engineering applications. The 100-m resolution map outputs are publicly available.
This study describes an approach for modeling wave scattering and the spatial variability of ground motion in geotechnical site-response analysis by modeling soil heterogeneity through 2D correlated random fields. Importantly, the required site-specific inputs to apply the proposed approach in a practical setting are the same as those associated with conventional 1D site-response analysis. The results, which are affected by wave scattering attenuation, are compared to those from conventional laterally homogeneous 1D site-response analyses and 1D analyses with randomized velocity profiles extracted from heterogeneous 2D velocity model realizations. A sensitivity study, involving 5400 2D model realizations, investigates the influence of random field input parameters on wave scattering and site response. The computed ground surface acceleration waveforms and transfer functions show that this method is capable of scattering seismic waves. Multiple ground-motion intensity measures are analyzed to quantify this influence and distinguish between the effects of 1D vertical heterogeneities and averaging across many nodes and realizations, from the effects of wave scattering and 2D ground-motion phenomena. The redistribution of ground-motion energy across wider frequency bands and scattering attenuation of high-frequency waves in the 2D analyses resemble features observed in empirical transfer functions computed in other studies. While analyses with 1D randomized velocity profiles are able to replicate median results from 2D analyses for some low-frequency intensity measures (e.g. transfer functions at [Formula: see text] Hz, and spectral acceleration at the fundamental period), medians and standard deviations of high-frequency intensity measures (e.g. transfer function at [Formula: see text] Hz, [Formula: see text], and Arias intensity), which are influenced by wave scattering, are not appropriately captured. Given the equivalent input information requirements as conventional 1D analysis, and the availability of large computational resources, we advocate that the proposed 2D (and eventually 3D) approach is a fruitful path forward to improve the modeling of site-response physics and realize improved predictive capabilities.
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