Discovery of hidden faults sheds gentle on thriller of ‘sluggish earthquakes’   | Earth Sciences New Zealand

A brand new worldwide research, revealed in Science Advances, identifies hidden fault constructions known as polygonal fault techniques (PFSs) as a significant affect on the behaviour of the northern Hikurangi subduction zone.

These shallow geological options, present in sediments getting into the subduction zone, seem to play a essential function in the place and the way sluggish slip earthquakes happen.  

“This discovery helps explain why slow earthquakes occur where they do,” says Dr Philip Barnes, marine geologist at Earth Sciences New Zealand (previously NIWA) and co-author of the research. “It also shows that these events may be influenced by the reactivation of old fault structures that formed much closer to the surface than the present depths of the subduction zone.”  

In the Hikurangi subduction zone, the Pacific Plate is diving beneath the Australian Plate. While the southern part of this zone stays locked and able to producing large earthquakes over magnitude 8, the northern half behaves in another way. It commonly produces sluggish slip occasions, actions that unfold over days to months, releasing tectonic stress with out sudden shaking.  

“Slow slip events do not cause violent shaking themselves, but they can increase stress on nearby faults and may trigger more damaging earthquakes. Understanding what controls them is vital to improving earthquake and tsunami warnings.”  

The worldwide research was a collaboration between researchers from China, the US, and Earth Sciences New Zealand, utilizing information from the International Ocean Discovery Program and the high-resolution three-dimensional NZ3D seismic survey carried out off Gisborne. Using high-resolution 3D seismic imaging, deep-sea drilling information from the International Ocean Discovery Program, and superior pc modelling, the analysis group was capable of map out PFSs in unprecedented element and to judge their function within the subduction zone.  

“These faults form over millions of years during sedimentation, long before and initially away from the subduction zone. But as the seafloor is dragged into the subduction zone during the convergence of the tectonic plates, they can be reactivated and evolve into major thrust faults. Our analysis also shows they provide important pathways for fluids, which play a major role in fault slip.”  

This connection between fault construction and fluid migration provides new perception into one of many key processes thought to set off sluggish earthquakes. The research additionally confirms that these fault techniques create a posh and variable construction alongside the megathrust, which may affect stress patterns and pressure distribution.  

“Until now, we lacked the imaging resolution to link these features directly to slow slip behaviour,” says Dr Barnes. “This study changes that, and gives us a new lens to better understand subduction zone dynamics.”  

While scientists first recognized the PFS sort of fault at subduction zones 20 years in the past off the southwest coast of Japan, they couldn’t decide how these complicated constructions influenced subduction and seismic slip, says lead creator Maomao Wang, a marine geologist at Hohai University in China. “It wasn’t until we analysed these beautiful 3D seismic images that we confirmed their widespread presence along New Zealand’s north Hikurangi margin, revealing their potential role in shaping slow earthquakes.”  

The findings may have implications past New Zealand. “Similar fault systems have been observed in subduction zones around the world, including Japan’s Nankai Trough. By highlighting the mechanical and hydrological effects of PFSs, the study adds a missing piece to the global understanding of how slow earthquakes work.”  

“This is a major step forward in understanding the geological processes happening beneath our coastlines,” says Dr Barnes. “With better models and better data, we are now in a stronger position to understand how subduction zones work.”