MW6.6 Earthquake Offshore Gisborne
The epicentre of the 20 Dec 2007 MW6.6 earthquake that shook the East Coast of the North Island last night was offshore only 50 km SSE of Gisborne, beneath the New Zealand continental slope.
The earthquake was approximately 40 km deep, which means that it occurred within the Pacific Plate. This plate is sliding beneath the North Island at a rate of ~4.5 cm per year. The top of the subducting Pacific Plate is only approximately 20 km deep beneath Gisborne. NIWA collects and interprets multibeam bathymetry and seismic data from its Research Vessel Tangaroa in the region to identify active faults and landslides. We can see much evidence of landslides affecting the continental slope offshore from Gisborne. Yesterday's earthquake would almost surely have triggered submarine landslides in the continental slope. However, these landslides were either (luckily) too deep or too small to generate a tsunami. In 2008, NIWA will start a research programme to find evidence of great inter-plate earthquakes (MW >8) that may have occurred in geological time. The big scientific question at present it whether a great earthquake has occurred on the plate interface and the likely recurrence of such event. If such events have happened they would undoubtedly have generated huge landslides [Science Leader Geoffroy Lamarche].
