High-density shallow shear wave velocity characterisation of the urban Christchurch, New Zealand region (2015)
This report summarizes the development of a region-wide surficial soil shear wave velocity (Vs ) model based on the unique combination of a large high-spatial-density database of cone penetration test (CPT) logs in the greater Christchurch urban area (> 15, 000 logs as of 1 February 2014) and the Christchurch-specific empirical correlation between soil Vs and CPT data developed by McGann et al. [1, 2]. This model has applications for site characterization efforts via maps of time-averaged Vs over specific depths (e.g. Vs30, Vs10), and for numerical modeling efforts via the identification of typical Vs profiles for different regions and soil behaviour types within Christchurch. In addition, the Vs model can be used to constrain the near-surface velocities for the 3D seismic velocity model of the Canterbury basin  currently being developed for the purpose of broadband ground motion simulation. The general development of these region-wide near-surface Vs models includes the following general phases, with each discussed in separate chapters of this report. • An evaluation of the available CPT dataset for suitability, and the definition of other datasets and assumptions necessary to characterize the surficial sediments of the region to 30 m depth. • The development of time-averaged shear wave velocity (Vsz) surfaces for the Christchurch area from the adopted CPT dataset (and supplementary data/assumptions) using spatial interpolation. The Vsz surfaces are used to explore the characteristics of the near-surface soils in the regions and are shown to correspond well with known features of the local geology, the historical ecosystems of the area, and observations made following the 2010- 2011 Canterbury earthquakes. • A detailed analysis of the Vs profiles in eight subregions of Christchurch is performed to assess the variablity in the soil profiles for regions with similar Vsz values and to assess Vsz as a predictive metric for local site response. It is shown that the distrubution of soil shear wave velocity in the Christchurch regions is highly variable both spatially (horizontally) and with depth (vertically) due to the varied geological histories for different parts of the area, and the highly stratified nature of the nearsurface deposits. This variability is not considered to be greatly significant in terms of current simplified site classification systems; based on computed Vs30 values, all considered regions can be categorized as NEHRP sites class D (180 < Vs < 360 m/s) or E (Vs < 180 m/s), however, detailed analysis of the shear wave velocity profiles in different subregions of Christchurch show that the expected surficial site response can vary quite a bit across the region despite the relative similarity in Vs30
CitationMcGann CR, Bradley BA, Cubrinovski M (2015). High-density shallow shear wave velocity characterisation of the urban Christchurch, New Zealand region. University of Canterbury, Christchurch, New Zealand. Department of Civil & Natural Resources Engineering. University of Canterbury, Christchurch, New Zealand. 67pp-.
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ANZSRC Fields of Research40 - Engineering::4005 - Civil engineering::400506 - Earthquake engineering
37 - Earth sciences::3706 - Geophysics::370609 - Seismology and seismic exploration
40 - Engineering::4005 - Civil engineering::400502 - Civil geotechnical engineering
04 - Earth Sciences::0403 - Geology::040312 - Structural Geology
05 - Environmental Sciences::0503 - Soil Sciences::050305 - Soil Physics
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McGann, C.R.; Bradley, Brendon; Cubrinovski, M. (University of Canterbury. Civil and Natural Resources Engineering, 2015)This paper summarizes the development of a high-resolution surficial shear wave velocity model based on the combination of the large high-spatial-density database of cone penetration test (CPT) logs in and around ...
McGann CR; Bradley, Brendon; Cubrinovski M (2015)This paper provides a summary of the development of a shear wave velocity (Vs) model for the greater urban area of Christchurch, New Zealand. The model is based on the application of the recently developed Christchurch-specific ...
Ongoing development of a near-surface shear wave velocity (Vs) model for Christchurch using a region-specific CPT-Vs correlation McGann, C.R.; Bradley, Brendon; Cubrinovski, M. (University of Canterbury. Civil and Natural Resources Engineering, 2015)This paper summarizes the development of a region-wide surficial shear wave velocity model based on the combination of the large high-spatial-density database of cone penetration test (CPT) logs in and around Christchurch, ...