New Zealand reef, raised by massive quake, provides new insights

Scientists are beginning to piece together a more detailed picture of the magnitude 7.8 earthquake that rocked New Zealand last week.

The massive quake extended existing fault ruptures by several miles and even raised one underwater reef several meters above sea level. The drastic changes provided both the need and the opportunity for new geological mapping.

Researchers say new data could be essential – not just for understanding the earthquake’s behavior, but for assessing future seismic hazard in the region as well.

Researchers from GNS Science surveyed the exposed reef in Kaikoura, a town on the east coast of New Zealand's South Island. They discovered segments of seabed raised by 6 meters, or almost 20 feet.

“These fault scarps form very, very quickly," Kelvin Berryman, a geologist with GNS Science, told The Australian. "Probably this fault scarp ruptured across here at a speed of about three kilometers a second." 

“The locals here described not the earthquake noise but the noise of water running off the top of the uplifted platform,” Dr. Berryman added. “They said that the noise was just horrendous.”

In the Marlborough region of New Zealand’s South Island, scientists from Canterbury University observed new faulting along the coast. One piece of land had been pushed more than 7 feet laterally and almost 5 feet upward, the Otago Daily Times reports. The total fault zone was almost two miles across, and most fault traces there had not previously been mapped.

Meanwhile, researchers from the National Institute of Water and Atmospheric Research (NIWA) have surveyed the nearby sea floor to observe post-earthquake conditions.

From the NIWA vessel Tangaroa, researchers collected 61 sediment cores in hopes of identifying sediment flows from underwater landslides, ODT reports. Scientists also surveyed for possible fault ruptures, using multibeam echosounders to map the seabed along the Marlborough coast.

Researchers say the Needles Fault, a submarine extension of the terrestrial Kekerengu Fault, ruptured as a result of seismic activity. That break formed new scarps along the sea floor and may extend the Kekerengu-Needles rupture by more than 20 miles.

Core samples revealed that the quake had agitated sediments in the Hikurangi Trough. A layer of recently-deposited turbidite, as much as 7 inches thick in some areas, covered a region extending almost 200 miles from the coast.

New Zealand sits on the “Ring of Fire,” an earthquake- and volcano-prone region that encircles the Pacific Ocean. The country, home to some 4.7 million people, was largely shaped by tectonic activity. 

The Christian Science Monitor’s Christina Beck reported:

The South Island’s coastline is not the only thing affected by the earthquake. The nearby Kekerengu fault is a vertical fault, which means that many local roads now feature steep drop offs, or suffered landslides as a result of the earthquake.

It took less than three minutes for the earthquake to reshape the landscape, including creating the beach feature. It would have been an astounding sight if it had been light enough to witness the change.

Researchers say marine life will also be affected by changes along the coastline.

“There will be a major shift in the community of marine species. Many seaweeds and animals that would normally be permanently covered by water will now be struggling to exist in a zone of transition between air and sea,” GNS Science researchers wrote in their initial report. “As the animals not suited to this environment die from the reef, they will be replaced by seaweed and animals appropriate for the new tidal level.”

This report includes material from the Associated Press.