GIS-based microzonation for liquefaction-induced ground damage in Auckland Region

Abstract

Although Auckland is one of the country's least seismically active regions, the earthquake hazard in the region cannot be disregarded given the potential social and economic impacts. As part of this, a good understanding of the co-seismic hazards across the region is of key importance. This paper presents on the methodology adopted for the GIS-based microzonation for liquefaction hazard across the Auckland region and the updated liquefaction-induced ground damage maps based on the recently developed MBIE guidance. Geology-based screening is initially applied across the region to identify areas where liquefaction is unlikely, with a separate categorisation for alluvial deposits with volcanic content in this region. The remaining areas are classified as “liquefaction damage is possible”, a broad classification that can only be refined where additional data is available. Borehole-based investigation data and elevation details are used to further screen out areas where non-liquefiable deposits are present. Where CPT soundings and groundwater data are available, detailed liquefaction assessments are carried out that enable refinement of classification beyond the high-level geology-based screening. LSN values for 100- and 500-year return period ground motions are used to classify areas where similar geotechnical conditions are present with liquefaction vulnerabilities ranging from very low to high. With these multiple approaches, regional liquefaction-induced ground damage maps are developed for Auckland region for different levels of investigation detail.