A GNS Science-led investigation of a handful of active faults in the wider Dunedin area has a mix of good and bad news for the city.
While the overall seismic hazard of the city is unchanged, one of the faults extends closer to the city than previously thought and a couple of new fault sources were uncovered.
However, the ‘new’ fault sources described in the study have been assigned a low level of activity and therefore don’t alter the overall hazard profile of the city, according to study leader Pilar Villamor of GNS Science.
“Importantly, the pilot study has shown the worth of a portfolio of scientific techniques for elucidating the threat from previously unknown and poorly known faults near our cities,” Dr Villamor said.
The study in Dunedin follows a recommendation from the Canterbury Earthquakes Royal Commission for more research to paint a better picture of the quake risk faced by population centres.
GNS chose Dunedin for this initial study because active faults that were already known could potentially extend under the city, and it is a compact city where local scientists are already working on earthquake research. In addition, Dunedin has similar heritage buildings to Christchurch.
The study probed the sub-surface both on land and off the Dunedin coast.
Scientists used a brace of techniques including conventional geological studies, geophysical techniques, GPS, satellite imagery, and deployment of seismometers.
“A better understanding of the presence of active faults beneath, and close to, our cities is important for land use planning, risk management, and emergency response activities.
“The study has provided a baseline for Dunedin city that should be reviewed as new data becomes available, including GPS data from new sites set up as part of this study,” Dr Villamor said.
The study makes a range of recommendations for future work in the Dunedin region including acquiring more GPS data, satellite imagery, offshore and onshore geophysical studies, and further physical probing of known faults to better understand fault behaviour.
The findings will be incorporated into planning and policy development in a number of organisations to make Dunedin city safer.
The study team comprised 18 researchers from GNS Science, the University of Otago, and the Geological Survey of Spain.
It was funded jointly by the National Hazards Research Platform, GNS Science, the University of Otago, and the Earthquake Commission.