‘World First’ Drilling Project to Investigate Quakes

‘World First’ Drilling Project to Investigate Quakes Off Gisborne Coast

An international proposal to use scientific ocean drilling to investigate ‘silent earthquakes’ under the seafloor
east of Gisborne has been scheduled for 2018 by the International Ocean Discovery Program.

The project, which will involve New Zealand scientists, will be undertaken by the research drilling ship Joides Resolution,
which is operated by the United States’ National Science Foundation.

The two-month expedition will be the first undersea drilling project anywhere in the world aimed specifically at
understanding the mechanisms of slow-slip quakes.

Three drill sites up to 1.5km deep are planned: one on the subducting Pacific Plate, another where the plate boundary
surfaces at the seafloor, and a third on the overriding plate directly above the area of slow-slip, about 40km east of Gisborne.

The scheduling is the culmination of a five-year planning and proposal process involving scientists from New Zealand,
the United States, Japan, Canada, and Europe.

‘Silent earthquakes’, also known as slow-slip events, are similar to an earthquake in that they involve more rapid than
normal movement between two pieces of the Earth’s crust along a fault line.

However, in a normal earthquake the slip occurs in a matter of seconds, suddenly releasing seismic energy, whereas
slip in a silent earthquake can take weeks or even months to occur.

The discovery of silent earthquakes has been one of the most important findings in seismology in the past 15 years.
Scientists have proposed numerous theories to explain why silent earthquakes occur, but testing the theories is
challenging as these events typically occur tens of kilometres underground.

Silent earthquakes off the coast of Gisborne have attracted attention from international scientists due to
their close proximity to the Earth’s surface – typically about 5km beneath the seafloor. This means they are accessible
to scientific drilling. This contrasts with many other parts of the world where this phenomenon occurs tens of kilometers below
the Earth's surface.

“An important way to understand the true cause of slow-slip events is to drill into and sample the region surrounding the
plate boundary fault where they are known to occur, and monitor physical and chemical properties near the source of the events,”
said project leader Dr Demian Saffer, of Pennsylvania State University in the United States.

Instruments will be installed in two of the three drill sites to monitor physical and chemical changes in the Earth’s crust
throughout multiple slow-slip event cycles over the coming decade. The offshore monitoring system is being funded by the
United States National Science Foundation. The data will be downloaded every few years using an underwater remotely
operated vehicle.

“The monitoring instruments will give unprecedented, close-up observations of the slow-slip process, and they will
also improve our understanding of the earthquake and tsunami potential of the Hikurangi subduction zone,” said Dr Laura Wallace
of the University of Texas, who is leading the borehole monitoring part of the project.

The project is likely to involve about 50 scientists from eight countries.

Marine geologist Philip Barnes of NIWA and marine geophysicist Stuart Henrys of GNS Science are two of the New Zealand-based
leaders of the project. They believe the drilling programme off the Gisborne coast represents a fantastic opportunity to learn
more about the inner workings of the Hikurangi subduction zone.

“Findings from such a project would have global significance as it has the potential to significantly boost our understanding
of the mechanics of subduction zone faults and the earthquakes that occur on them,” said Dr Henrys.

And Dr Barnes said: “This is an exciting project since scientific drilling will bring a step change in the level of information
about the plate boundary along the East Coast. The project represents a huge international investment in New Zealand science,
in the order of $10 to $20 million.”

Like the Alpine Fault in the South Island, the Hikurangi Subduction zone is the main tectonic plate boundary in the North Island.
In fact, the Hikurangi subduction zone is the most rapidly slipping fault in New Zealand. The Pacific Plate is moving westward at
about 5cm to 6cm-a year off the Poverty Bay coast, where it subducts under the Australian Plate.

The International Ocean Discovery Program is an international marine research collaboration that is funded by 26 nations
dedicated to advancing scientific understanding of the Earth by sampling, instrumenting and monitoring subseafloor
environments using specialised ocean drilling ships staffed by research scientists. New Zealand has been a member of
IODP since 2008, as part of the Australia New Zealand IODP Consortium (ANZIC).

The decision to drill off the Gisborne coast represents the first New Zealand-led IODP project to go through the
complete process from submission to scheduling, during the period that New Zealand has been an ANZIC consortium member.

“This success is likely to be a springboard for additional scientific drilling projects in New Zealand waters,” said Dr Henrys.

ENDS

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