The discovery of a huge underwater water reservoir may explain the mysterious earthquakes that struck New Zealand

The discovery of a huge underwater water reservoir may explain the mysterious earthquakes that struck New Zealand

A seismic imager trails behind a research vessel during a survey of the Hikurangi subduction zone in New Zealand. The investigation, conducted by the Institute of Geophysics at the University of Texas, discovered the existence of a huge ancient water reservoir buried miles under the seabed. Credit: University of Texas Geophysics Institute/Adrian Arnulf

A large water reservoir discovered beneath the ocean floor near New Zealand could provide insight into the mechanisms of slow-slip earthquakes and tectonic activity.

Researchers have discovered a sea of ​​water trapped in the sediments and rocks of a lost volcanic plateau that now lies deep within the Earth’s crust. A 3D seismic image revealed that the water lies three kilometers below the ocean floor off the coast of New Zealand, where it could protect the large seismic fault facing the North Island of the country.

Earthquakes and slow sliding water

Faulting is known to produce slow earthquakes, called slow-slip events. These can release pent-up tectonic pressure harmlessly for days and weeks. Scientists want to know why these phenomena occur more often in some faults than others.

Many slow-slip earthquakes are thought to be related to groundwater. However, to date there is no direct geological evidence indicating the existence of such a large water reservoir at this particular New Zealand rift.

The Hikurangi Plateau is the remains of a series of epic volcanic eruptions that began 125 million years ago in the Pacific Ocean. A recent seismic survey (red rectangle) conducted by the University of Texas Institute of Geophysics imaged the plateau as it sank into the Hikurangi subduction zone in New Zealand (red line). Credit: Andrew Gas

“We can’t yet see deep enough to know exactly the impact on the fault, but we can see that the amount of water flowing here is much higher than normal,” said the study’s lead author, Andrew Ghez, who works as an engineer. Postdoctoral fellow at the University of Texas Institute of Geophysics (UTIG).

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The research was recently published in the journal Scientists advanced It is based on seismic campaigns and scientific ocean drilling carried out by UTIG researchers.

Seek deeper understanding

Gaz, now a postdoctoral researcher at Western Washington University, is calling for deeper drilling to determine where the water ends up, so researchers can determine whether it affects pressure around the fault, important information that could lead to a more precise understanding. He said big earthquakes.

Origin of water tank

The site where researchers found the water is part of a large volcanic province that formed when a US-sized lava cloud breached the Earth’s surface in the Pacific Ocean 125 million years ago. It is one of the largest volcanic eruptions known on Earth and has lasted for several million years.

Gaz used seismic scans to create a 3D image of the ancient volcanic plateau, where he saw thick, layered sediments surrounding buried volcanoes. His collaborators at UTIG conducted laboratory experiments on samples of volcanic rock and found that water made up nearly half of its volume.

A seismic image of the Hikurangi Plateau reveals details about the Earth’s interior and what it is made of. The blue-green layer below the yellow line shows water buried in the rocks. Researchers at the University of Texas Geophysics Institute believe water could mitigate earthquakes in the nearby Hikurangi subduction zone. Credit: Andrew Gas

“Normal oceanic crust, when it is about 7 or 10 million years old, should contain much less water,” he said. The oceanic crust observed in seismic analyzes was ten times older, but remained wetter.

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Gaz speculates that the shallow seas in which the eruptions occurred led to the erosion of some volcanoes, turning them into porous, fractured rocks that store water as an aquifer when buried. Over time, the rocks and rock fragments turned into mud, trapping more water.

Implications for understanding earthquakes

This discovery is important because scientists believe that groundwater pressure could be a key element in creating the conditions that release tectonic stresses via slow-slip earthquakes. This usually occurs when water-rich sediments are buried within a fault, trapping water underground. However, the New Zealand Rift contains few of these typical oceanic deposits. Instead, researchers believe ancient volcanoes and metamorphic rocks – now clayey – carried large amounts of water as they were swallowed by the fault.

UTIG Director Demian Saffer, co-author of the study and co-chief scientist of the scientific drilling mission, said the findings suggest other seismic faults around the world can be found in similar situations.

“This is a very clear example of the relationship between fluids and the way tectonic faults move, including seismic behavior,” he said. “This is something we hypothesized from laboratory experiments and predicted by some computer simulations, but there are very few bright-field experiments to test this at the scale of tectonic plates.”

The research was funded by the US National Science Foundation and the science and research agencies of New Zealand, Japan and the United Kingdom.

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