Regional-scale liquefaction susceptibility assessment for the Otago region, New Zealand

ABSTRACT
Regional-scale liquefaction susceptibility assessments have been completed for the Otago region.
The assessment used an office-based evaluation of existing information, equating to a ‘Level A’
basic desktop assessment as per MBIE guidelines for liquefaction-prone land. Information sources
included geological maps, landform and soil maps, topographic information from maps, lidar
surveys, aerial and ground photography, geological information from borehole records, and
measurements of depths to groundwater. A GIS map-dataset of liquefaction-susceptibility was
compiled. The project methodology utilised geotechnical specialists with expert knowledge from
site investigations at numerous locations in Otago to review and provide advice on drafts of the
liquefaction-susceptibility map.
The map applies a three-fold liquefaction-susceptibility classification. Domain A is underlain by
rock or firm sediments and liquefaction damage is unlikely. Domain B represents poorly
consolidated river or stream sediments with a shallow groundwater table; there may be localised
areas of liquefaction-susceptible materials and liquefaction damage is possible. Domain C is
underlain by poorly consolidated marine or estuarine sediments with a shallow groundwater table; it
is moderately to highly likely that at least some areas of liquefaction-susceptible materials are
present and liquefaction damage is possible.
By area, more than 95% of the Otago region is classified as Domain A – terrain that has little or no
liquefaction susceptibility. Domains B and C are ‘liquefaction awareness areas’. They are not
hazard zones but rather highlight areas where liquefaction is a potential hazard to consider. Land
classified as domains B or C respectively occupy 3% and 1% by area of the region