Dig for sea shells could shed light on past earthquakes

Sea shells recovered from 90-metre-long trench at Aramoana could shed light on past earthquakes and tsunami. Photo / Supplied

Scientists searching for sea shells have dug a 90-metre long trench at a Hawke's Bay beach in the hope of uncovering evidence of past earthquakes.

GNS scientists dug the trench at Aramoana, southern Hawke's Bay, as the site has been uplifted in a series of large earthquakes.

Over the last 8000 years, earthquakes have created three marine terraces. The terraces usually provide good evidence to date past earthquakes.

The research project will aim to uncover information to help understand the earthquake and tsunami risk along the East Coast of the North Island of New Zealand.

Project Leader Nicola Litchfield said: "We are specifically looking for shells that we can later radiocarbon date in the lab to try and pinpoint the timing of past earthquakes and tsunami.

"If we identify evidence for an earthquake at only one location, then it is likely this event occurred on nearshore faults, which will have uplifted and shaken a relatively small area.

"But if we identify evidence at multiple site, that points to a Hikurangi subduction zone earthquake."

The research forms part of the five-year Ministry of Business, Innovation and Employment (MBIE) research programme Hikurangi Subduction Earthquakes and Slip Behaviour.

Scientists have known for a long time that the East Coast has experienced a number of large earthquakes in the past but are still trying to figure out how big the events were and how often they occurred.

GNS Science experts are trenching in many coastal locations, while Niwa, Victoria University of Wellington and the University of Auckland are also looking at sites off the coast at Aramoana for evidence of earthquakes.

These two studies will combine to build a picture of past earthquakes.