Research
Research Papers
Tsunami hazard posed by earthquakes on the Hikurangi subduction zone interface
W Power, M Reyners, L Wallace - GNS Science
To the east of the North Island the Pacific tectonic plate is being thrust beneath the Australian plate in a process known as subduction. Large tsunamis, such as the 2004 Indian Ocean Tsunami, are most frequently caused by earthquakes on plate boundaries where subduction takes place. In this project we attempt to determine whether the coast of New Zealand is at risk of tsunamis originating from earthquakes on the Hikurangi (east coast of North Island) plate boundary. To do this we examine the slow deformation of the North Island as measured by GPS, and use this to locate the regions of the plate boundary in which elastic energy is being stored for eventual release in earthquakes. We also examine the distribution of smaller earthquakes on the plate boundary, as these can also be used to identify areas in which energy is being stored.
We find that the Hikurangi plate interface can be best described in terms of three segments” the lower North Island, the Hawke Bay region, and the Raukumara Peninsula. Each of these segments has their own distinctive earthquakes characteristics, and we find that there is a potential tsunami hazard associated with each of them.
The lower North Island segment is found to be storing elastic energy over a wide area, which has the potential to be released in large tsunami-causing earthquakes.
In the Hawke Bay region the region in which the plates are storing energy is considerable narrower; however we find that the Lachlan Fault, which rises from the plate interface under Hawke Bay, is a likely source of hazardous tsunamis.
Seamounts (extinct volcanoes) attached to the Pacific plate are being subducted beneath the Raukumara Peninsula, and this process appears responsible for a characteristic type of earthquake known as a “tsunami earthquake” in which very little shaking is felt, yet dangerous tsunamis are often caused. Two earthquakes near Gisborne in 1947 were probably of this type. Tentative new evidence suggests that the average interval between these events might only be around 70 years. If true, this implies that the probability of such an earthquake occurring in the next couple of decades is higher than previously thought.