A large water reservoir discovered beneath the ocean floor near New Zealand may provide insight into the mechanisms of slow-slip earthquakes and tectonic activity.
Researchers have discovered the equivalent of seawater trapped within sediments and rocks in a lost volcanic plateau that is now deep in the Earth’s crust. A 3D seismic image revealed that the water lies two miles below the ocean floor off the coast of New Zealand, where it is likely to cushion a major earthquake fault facing the country’s North Island.
Slow earthquakes and water
Faulting is known to produce slow-moving earthquakes, called slow-slip events. These can release pent-up tectonic pressure harmlessly over days and weeks. Scientists want to know why they occur more often in some defects than others.
Many slow-slip earthquakes are thought to be associated with buried water. However, to date there is no direct geological evidence to suggest the existence of such a large water reservoir in this particular New Zealand rift.
“We can’t yet see deep enough to know exactly what the impact is on the fault, but we can see that the amount of water flowing here is much higher than normal,” said lead author Andrew Ghez, who conducted the study. Working as a postdoctoral fellow at the University of Texas Institute of Geophysics (UTIG).
The research was recently published in the journal Advancement of science It is based on seismic expeditions and scientific ocean drilling led by researchers from UTIG.
Seek deeper understanding
Gase, now a postdoctoral fellow at Western Washington University, is calling for deeper drilling to find where the water ends up so researchers can determine whether it affects the pressure around the fault — an important piece of information that could lead to a more precise understanding. He said of major earthquakes.
Water tank assets
The site where researchers found the water is part of a vast volcanic province formed when a US-sized cloud of lava breached the Earth’s surface in the Pacific Ocean 125 million years ago. This event was one of the largest known volcanic eruptions on Earth and lasted for several million years.
Gaz used seismic scans to build 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.
“Normal ocean crust, when it gets to about 7 or 10 million years old, should contain a lot less water,” he said. The ocean crust in seismic surveys was 10 times older, but it remained much wetter.
Gaz speculates that the shallow seas in which the eruptions occurred have eroded some volcanoes into porous, fractured rocks that store water like an aquifer during burial. Over time, the rocks and their fragments turned into mud, trapping more water.
Implications for understanding earthquakes
This discovery is important because scientists believe that groundwater pressure may be a key element in creating the conditions that release tectonic stress via slow-slip earthquakes. This usually occurs when water-rich sediments become buried with the 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 clayeys — carried large amounts of water down when the rift swallowed them.
UTIG Director Demian Saffer, a co-author of the study and co-chief scientist of the scientific drilling mission, said the results suggest that other earthquake faults around the world could be in similar situations.
“It’s a really clear example of the relationship between fluids and the way a tectonic fault moves — including the behavior of earthquakes,” he said. “This is something we hypothesized from laboratory experiments, and predicted by some computer simulations, but there are very few clear field experiments to test this at the scale of tectonic plates.”
Reference: “Flooding of volcanic-rich upper crust provides fluids for shallow thrust and slow sliding” by Andrew C. Gas, Nathan L. Bangs, Demian M. Safar, Shushu Han, Peter K. Miller, Rebecca E. Bell, Ryota Arai, Stuart A. Henrys, Shuichi Kodaira, Richard Davey, Laura Fram and Daniel H.N. Parker, August 16, 2023, Advancement of science.
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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