The discovery of a buried sea could explain slow-motion earthquakes

Beneath the Pacific Ocean, off the coast of New Zealand, lies a sea full of water trapped in the earth’s crust. Researchers believe this sunken reservoir could 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 occur within a few seconds. But energy can also be released from the earth’s crust in slow motion, over a period of weeks or months. These so-called slow sliding events occur when tectonic plates temporarily become locked together as one attempts to slide past the other.

New Zealand lies on the boundary of two major tectonic plates: the Australian Plate and the Pacific Plate. The boundary between these plates is called 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 linked to buried water beneath the Earth’s crust, no direct geological evidence of an underground reservoir has been found at this particular location. Until now.

In one Recent studypublished in the magazine Scientific advancesResearchers 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 below the ocean floor.

“We can’t yet look deep enough to know exactly the impact on the fault, but we can see that the amount of water flowing down here is actually much higher than normal,” said lead author Andrew Gase, previously at the U of Texas and now at Western Washington University, a statement said.

The place where they found the water was formed 125 million years ago when a huge cloud of lava – the size of the United States – erupted from the Earth’s surface. The resulting volcanic plateau now lies beneath the ocean and is covered by thick sediments. But Gase and his team drilled into the volcanic rock and found that water made up almost half of its volume.

“Normal ocean crust, once it’s about 7 or 10 million years old, should contain much less water,” Gase said. But the rocks in this area were more than ten times as old and still contained that amount of water.

The researchers believe that the shallow seas above the eruption eroded on the flanks of the volcanoes, making them more porous and able to store water. Over time, these stones turned into clay and trapped even more liquid.

The team hopes that these findings will help improve our understanding of these slow slip events and strengthen our ability to predict future large-scale earthquakes.

Gase is calling for deeper drilling to find out where the water ends up so the team can determine if it is affecting the pressure around the fault.