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Urban Geological Mapping

Understanding the geology of New Zealand cities is a critical part of understanding and planning to mitigate geological hazards such as landslides and earthquake-vulnerable ground conditions, and to locate and manage geological resources such as aggregate and groundwater. New geological maps of urban areas are being compiled using a mix of conventional 2D surface mapping and its integration with subsurface information obtained from drill holes, geotechnical probes and interpretation of geophysical data to create 3D geological models.

In addition Consultancy services are offered, commonly with specialist geotechnical or other components.

Urban geological maps are typically at detailed scales e.g. 1:10 000 which are more appropriate for informing building, infrastructure and urban planning. The geological mapping of cities generally has less outcrop to work with and typically includes more Quaternary sediments (in flat-lying areas). Subsurface geological variation is difficult but important to characterise for building foundations and this requires interpretation of drill hole data and geotechnical probe tests in combination with interpretation of geophysical data and surface geology.

Geological model of subsurface central Christchurch derived from ground probe testing

Geological model of subsurface central Christchurch derived from ground probe testing.

The research component of this work has prioritised cities according to total population, population growth, quality of existing information, and staff availability and logistics.

In the wake of the large Canterbury earthquakes of 2010 and 2011, Christchurch City has been the focus of much geotechnical analysis of ground conditions as a precursor to re-building. The geotechnical work has resulted in improved geological understanding of the area through detailed analysis and 3D geological modelling of thousands of drill holes and geotechnical probes. The geological model will feed back into improved geotechnical understanding.