New Geotechnical Maps and 3D Basin Velocity Model for Central Wellington, New Zealand, Following the Mw 7.8 Kaikoura Earthquake: Explaining Site Effects in a Shallow, Steep-Sided Sedimentary Basin

Date: 4/26/2019

Time: 11:15 AM

Room: Pine

Wellington’s shallow steep-sided 3D basin structure has a critical influence on the spatial patterns of ground motion observed in major earthquakes (e.g. Mw 7.8 Kaikoura). Detailed modelling of the subsurface and geotechnical mapping can guide efforts to mitigate future damage and risk.

We compile a new 3D basin model and updated geotechnical maps for central Wellington, including parameters of site period, basin depth and New Zealand site classification. Our contribution extends the previous work of Semmens et al. (2010) by using modern modelling techniques to integrate complementary new geophysical and geological data throughout the central city. Specifically we have incorporated 1400+ borelogs and 400+ new geophysical site period measurements and associated uncertainty, as well as new LiDAR elevation information. These measurements have allowed us to better define both the shallow subsurface layers (based largely on borehole and CPT/SPT logs) and the deeper basin response (based largely on the geophysical measurements).

This compilation provides an overview of spatial variations and key features within the Wellington basin on a block-by-block scale. We also investigate the role of site and 2D/3D basin effects through correlation of key geotechnical parameters with observed ground motion amplification in Wellington during major events such as the 2016 Mw 7.8 Kaikoura earthquake.

Presenting Author: Anna E. Kaiser

Authors