Beneath the Pacific Ocean, off the coast of New Zealand, lies a sea’s worth of water, locked within the Earth’s crust. Researchers believe that this sunken reservoir may play an important role in dampening the strength of earthquakes in the Western Pacific.
We tend to think of earthquakes as sudden, often violent events that take place over a matter of seconds. But energy can also be released from the Earth’s crusts in slow motion, over a period of weeks or months. These are called slow slip events and they occur when tectonic plates get temporarily locked together as one attempts to slide past the other.
New Zealand sits at the boundary of two major tectonic plates: the Australian Plate and the Pacific Plate. The boundary between these plates is known as a fault, and this particular Australian-Pacific fault is known for producing these slow-motion earthquakes. But, while experts believe many slow slip earthquakes are associated with buried water under the Earth’s crust, no direct geological evidence for an underground reservoir has been found at this particular site. Until now.
Adrien Arnulf/University of Texas Institute for Geophysics
In a recent study, published in the journal Science Advances, researchers from the University of Texas, GNS Science in New Zealand and Japan’s Agency for Marine-Earth Science and Technology used 3D seismic imaging and ocean drilling to find water 2 miles beneath the ocean floor.
“We can’t yet see deep enough to know exactly the effect on the fault, but we can see that the amount of water that’s going down here is actually much higher than normal,” lead author, Andrew Gase, previously at the University of Texas and now at Western Washington University, said in a statement.
The site where they found the water was formed 125 million years ago, when a vast plume of lava—the size of the United States—erupted from the Earth’s surface. The volcanic plateau that was formed now lies under the ocean, layered in thick sediment. But drilling into the volcanic rock, Gase and his team found that water made up nearly half of its volume.
“Normal ocean crust, once it gets to be about 7 or 10 million years old, should contain much less water,” Gase said. But the rock in this area was more than 10 times that age and still held this volume of water.
The researchers believe that the shallow seas above the eruption eroded away at the volcanoes’ flanks, making them more porous and able to store water. Over time, these rocks turned into clay, locking away even more liquid.
The team hopes that these findings will help improve our understanding of these slow slip events, supporting our ability to predict large-scale earthquakes in the future.
Gase is calling for deeper drilling to find where the water ends up so that the team can determine whether it affects pressure around the fault.