Earthquakes along a complex series of faults in the upper plate of New Zealand’s northern Hikurangi Subduction Margin were responsible for coastal uplift in the region, according to a new evaluation of local marine terraces.
The findings, reported in the Bulletin of the Seismological Society of America, could shape new evaluations of seismic hazard in New Zealand. They suggest that earthquakes rupturing multiple faults may contribute more than subduction earthquakes to damaging uplift in the area.
Using radiocarbon and other methods to date the marine terraces at two North Island sites, Puatai Beach and Pakarae River mouth, Nicola Litchfield of GNS Science and her colleagues conclude that the uplift events that created the terraces occurred at different times between the two sites. This suggests that the uplift was not the result of subduction earthquakes or single-fault upper plate earthquakes.
The pattern of uplift seen in the marine terraces led the researchers to map new offshore faults in the region, which they think may be one source of these upper-plate earthquakes, said Litchfield.
The Hikurangi Subduction Margin lies along the eastern edge of North Island, where the Pacific and Australian tectonic plates collide and the Pacific plate slips under the island. Recent New Zealand earthquakes involving multiple fault ruptures and coastal deformation, such as the magnitude 7.8 Kaikoura earthquake in 2016, have prompted seismologists to evaluate the mechanisms behind these complicated sequences–especially along the remote areas of the northern Margin where there have been fewer studies overall.
Continue reading at Seismological Society of America
Image via Seismological Society of America
