Recent mysterious slow earthquakes in New Zealand may be caused by a hidden "underground ocean" that causes water pressure.
Slow Earthquakes for Weeks, Months
Along several significant fault zones, the Pacific and Australian tectonic plates collide in New Zealand. The largest and most active faultline in the Hikurangi Subduction Zone is created when the Pacific plate subducts beneath the east coast of the North Island. Along this fault, the Australian plate and the Pacific plate that it is atop move toward one another.
The plates have rockier structures in the shallower areas of the water, and when they slide against one another, they momentarily lock together. The lock eventually dissipates, and they resume their original places. Slow slip events (SSE), which are similar to slow earthquakes, are the outcome. In contrast to an earthquake, an SSE leaves behind reverberations that last for weeks or months.
Large volumes of water trapped between the fault lines are linked to numerous SSEs. But up until today, there hasn't been any proof that an 'underground ocean' could be found at this specific New Zealand fault.
Hidden 'Underground Ocean'
Off the coast of New Zealand, scientists found a water reservoir with an ocean's worth of liquid trapped two miles under the ocean floor. This discovery, according to the researchers, is crucial because subsurface water pressure might be a crucial factor in producing the conditions that lead to slow slip earthquakes, which are a method of releasing tectonic stress. According to the researchers, this reservoir may cause fluid overpressures along the megathrust that result in frequent shallow sluggish slip.
The experiment, dubbed NZ3D by the researchers, was created to picture the Hikurangi margin's slow slip event source zone at better image resolutions than had previously been tried. As per the information provided in the news release, the water was found in an area within a vast volcanic region that originated approximately 125 million years ago. This volcanic province was formed when a massive lava plume, roughly equivalent in size to the United States, broke through the Earth's surface in the Pacific Ocean. This event, recognized as one of the most significant volcanic eruptions in Earth's history, persisted for several million years.
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Ancient Hikurangi Volcanic Plateau
The scientists created a 3D model of the extinct Hikurangi volcanic plateau and looked at the stratified sediments that surrounded the volcanoes that were buried.
Laboratory examinations were carried out on samples of volcanic rock obtained from drill cores, revealing that approximately half of the rock's volume consisted of water. These scientific investigations were part of an ocean drilling initiative led by researchers from the University of Texas Institute for Geophysics (UTIG), who were also active participants in the research.
Andrew Gase, the primary author of the study and a postdoctoral scholar affiliated with UTIG, remarked that they observed an unusually high volume of water descending in the area of interest. However, due to the limitations in their ability to probe deeper, the exact impact of this water on the fault remains uncertain.
Can Seismogenic Slow Slip Events (SSEs) potentially trigger significant earthquakes? New Zealand experiences an annual occurrence of up to 15,000 earthquakes, with approximately 150 to 200 of them being of sufficient magnitude to be perceptible, although the majority are too minor to be noticeable. Along plate borders where earthquakes occur, SSEs frequently take place as well. SSEs in New Zealand haven't historically resulted in significant earthquakes, nevertheless.
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