Scientists have found that deep under the earth's crust, there is an ocean of water. Three dimensional (3D) seismic imaging revealed the water, which sits about two miles underneath the floor of the ocean near New Zealand. This vast amount of water could also be preventing slippage in a major fault off the coast of New Zealand's North Island. This fault can generate slow-motion earthquakes that are known as slow-slip events. Instead of a huge cataclysm in a sudden release, the tectonic pressure at slow-slip events is released gradually over a period of days and weeks, without causing harm.
Researchers have been trying to determine why slow-slips happen more often at some faults compared to others. It's been suggested that buried water is linked to slow-slip earthquakes. But this is the first work to connect a huge reservoir of water to this fault near New Zealand. The findings have been reported in Science Advances.
The water is part of a vast site where a gargantuan plume of lava about the size of the United States penetrated the surface of the Earth, around 125 million years ago in the Pacific Ocean. This particular eruption is thought to have gone on for several million years, and was one of the largest to ever impact Earth.
“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,” said lead study author, Andrew Gase, PhD, now of Western Washington University.
Seismic scans were used to generate a 3D image of the ancient volcanic plateau, which contained thick layers of sediment around buried volcanoes. The volcanic rock that was obtained during drilling at the location was found to be almost 50 percent water by volume.
Normally, ocean crust that is 7 to 10 million years old contains far less water, noted Gase. The crust that was scanned was ten times older and still carried a lot of water. The eruptions that took place here may have broken up volcanic rock so it was more porous, and acted like an aquifer as it was buried. Over time, even more water may have seeped in as the rock transformed into clay, suggested Gase.
Gase added that deeper drilling should be done at the site to determine how it might be affecting pressure neat the fault. This information could help us learn more about large earthquakes.
Other faults around the world may be in a similar situation, the study authors suggested. Water pressure might be a crucial part of how tectonic stress is released in slow-slip earthquakes.