Quantifying Seismic Amplification on Topography in New Zealand and Its Relationship to Landslide Occurrence: First Steps Under New Zealand’s Resilience Challenge Programme

Session: Near-Surface Effects: Advances in Site Response Estimation and Its Applications
Type: Oral
Date: 4/28/2020
Time: 03:00 PM
Room: 110 + 140
Description: 

Amplification in areas of significant topography has been observed during several recent New Zealand earthquake sequences. The most notable example is in the Port Hills of Christchurch during the Canterbury earthquake sequence, where narrow steep-sided ridges combined with local lower-velocity material produced amplification up to a factor of 7 in the ridge-perpendicular direction, exacerbating landslides and shaking damage to residential ridge-top housing.

A preliminary analysis of New Zealand’s GeoNet seismic monitoring stations, suggests that ~50% of the sites classed as Soft Rock (NZ1170.5 subsoil class B; based largely on surface geology) experience significant amplification effects. These effects are particularly common amongst sites located on Tertiary age sedimentary rocks or volcanics, and also observed to some degree at sites on older Carboniferous – Cretaceous age greywacke. Our studies as well as recent literature has suggested that unexpected amplification at rock sites may be caused by: i) the topographic shape; ii) the presence of soil layers or weathered rocks; iii) rock fractures related to fault activity or landslide movements; iv) a combination of all of these factors.

We are embarking on a multi-year research project to better quantify the significance of rock-site amplification for different near-surface geological conditions (lithology and structural elements), topographic relief and earthquake source conditions and to understand its influence on landslide susceptibility. One of our key ultimate goals is to improve estimates of probabilistic shaking and landslide occurrence in areas of high relief, also making use of new New Zealand synthetic seismicity models to investigate the influence of the earthquake source.

Presenting Author: Anna E. Kaiser

Authors