Discovery Of Hidden Faults Sheds Light On Mystery Of 'Slow Earthquakes'
Press Release: Earth Sciences New Zealand
Seismic reflection profiles illustrating the frontal accretionary wedge and PFSs in Nankai Trough, Japan, and Hikurangi Trough, New Zealand. (A) Nankai Trough, offshore Japan. (B) Hikurangi Trough, New Zealand (IL 135 in NZ3D volume). (C) Locations of study areas. (D) Partial enlargement of the PFSs in (B). (E) Seismic coherence depth slice at 4396 m showing the PFSs in the incoming pelagic sequence. Seismic images in (D) and (E) are derived from the NZ3D seismic volume collected in the northern Hikurangi Margin Credit: ScienceAdvances Bathymetric map showing the location of the NZ3D seismic volume at the northern Hikurangi Margin. Credit: Science Advances
Scientists have uncovered a key piece of the puzzle behind the unusual 'slow earthquakes' occurring off the east coast of New Zealand's North Island.
A new international study, published in Science Advances, identifies hidden fault structures called polygonal fault systems (PFSs) as a major influence on the behaviour of the northern Hikurangi subduction zone. These shallow geological features, found in sediments entering the subduction zone, appear to play a critical role in where and how slow slip earthquakes occur.
"This discovery helps explain why slow earthquakes occur where they do," says Dr Philip Barnes, marine geologist at Earth Sciences New Zealand (formerly NIWA) and co-author of the study. "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 section of this zone remains locked and capable of producing massive earthquakes over magnitude 8, the northern part behaves differently. It regularly produces slow slip events, movements that unfold over days to months, releasing tectonic stress without 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 international study was a collaboration between researchers from China, the US, and Earth Sciences New Zealand, using data from the International Ocean Discovery Program and the high-resolution three-dimensional NZ3D seismic survey conducted off Gisborne. Using high-resolution 3D seismic imaging, deep-sea drilling data from the International Ocean Discovery Program, and advanced computer modelling, the research team was able to map out PFSs in unprecedented detail and to evaluate their role in 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 structure and fluid migration offers new insight into one of the key processes thought to trigger slow earthquakes, says Dr Barnes. The study also confirms that these fault systems create a complex and variable structure along the megathrust, which can influence stress patterns and strain 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 identified the PFS type of fault at subduction zones 20 years ago off the southwest coast of Japan, they couldn't determine how these complex structures influenced subduction and seismic slip, says lead author 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 also have implications beyond 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"
© Scoop Media
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Beneath the waves off New Zealand's east coast, scientists have uncovered a hidden network of ancient faults that may hold the key to understanding mysterious slow-motion earthquakes. A new international study, published in Science Advances, identified hidden fault structures called polygonal fault systems (PFS) as a major influence on the behaviour of the north Hikurangi subduction zone. Earth Sciences NZ marine geologist Philip Barnes said the discovery would help explain why slow earthquakes occurred where they did. "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 off the east coast of the North Island, the Pacific plate went below the Australian plate. ADVERTISEMENT While the southern section of this zone remained locked and could produce massive earthquakes over magnitude 8, the northern part behaved differently. It regularly produced slow slip events, movements that unfold over days to months, releasing tectonic stress without sudden shaking. These slow slip events did not cause violent shaking themselves but could increase stress on nearby faults and trigger more damaging earthquakes, Barnes said. "Understanding what controls them is vital to improving earthquake and tsunami warnings." Earth Sciences New Zealand marine geologist Dr Philip Barnes has undertaken research into the zone that's considered New Zealand's largest earthquake and tsunami hazard. (Source: Earth Sciences NZ) The study, a collaboration between Chinese and American researchers as well as Earth Sciences NZ (formerly NIWA), used data from the International Ocean Discovery Program and the high-resolution three-dimensional NZ3D seismic survey conducted off Gisborne. Fault systems were mapped in "unprecedented detail" with high-resolution 3D seismic imaging, deep-sea drilling data from the International Ocean Discovery Program, and advanced computer modelling. ADVERTISEMENT The faults formed over millions of years during sedimentation long before and initially far from the subduction zone, Barnes said. "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." Connecting fault structure and fluid migration offered new insight into one of the key processes thought to trigger slow earthquakes, he added. "Until now, we lacked the imaging resolution to link these features directly to slow slip behaviour. This study changes that and gives us a new lens to better understand subduction zone dynamics." Barnes said it was a "major step forward" in understanding the geological processes happening beneath our coastlines. "With better models and better data, we are now in a stronger position to understand how subduction zones work."
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Discovery Of Hidden Faults Sheds Light On Mystery Of ‘Slow Earthquakes'
Press Release – Earth Sciences New Zealand 'This is a major step forward in understanding the geological processes happening beneath our coastlines' Seismic reflection profiles illustrating the frontal accretionary wedge and PFSs in Nankai Trough, Japan, and Hikurangi Trough, New Zealand. (A) Nankai Trough, offshore Japan. (B) Hikurangi Trough, New Zealand (IL 135 in NZ3D volume). (C) Locations of study areas. (D) Partial enlargement of the PFSs in (B). (E) Seismic coherence depth slice at 4396 m showing the PFSs in the incoming pelagic sequence. Seismic images in (D) and (E) are derived from the NZ3D seismic volume collected in the northern Hikurangi Margin Credit: ScienceAdvances Bathymetric map showing the location of the NZ3D seismic volume at the northern Hikurangi Margin. Credit: Science Advances Scientists have uncovered a key piece of the puzzle behind the unusual 'slow earthquakes' occurring off the east coast of New Zealand's North Island. A new international study, published in Science Advances, identifies hidden fault structures called polygonal fault systems (PFSs) as a major influence on the behaviour of the northern Hikurangi subduction zone. These shallow geological features, found in sediments entering the subduction zone, appear to play a critical role in where and how slow slip earthquakes occur. 'This discovery helps explain why slow earthquakes occur where they do,' says Dr Philip Barnes, marine geologist at Earth Sciences New Zealand (formerly NIWA) and co-author of the study. '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 section of this zone remains locked and capable of producing massive earthquakes over magnitude 8, the northern part behaves differently. It regularly produces slow slip events, movements that unfold over days to months, releasing tectonic stress without 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 international study was a collaboration between researchers from China, the US, and Earth Sciences New Zealand, using data from the International Ocean Discovery Program and the high-resolution three-dimensional NZ3D seismic survey conducted off Gisborne. Using high-resolution 3D seismic imaging, deep-sea drilling data from the International Ocean Discovery Program, and advanced computer modelling, the research team was able to map out PFSs in unprecedented detail and to evaluate their role in 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 structure and fluid migration offers new insight into one of the key processes thought to trigger slow earthquakes, says Dr Barnes. The study also confirms that these fault systems create a complex and variable structure along the megathrust, which can influence stress patterns and strain 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 identified the PFS type of fault at subduction zones 20 years ago off the southwest coast of Japan, they couldn't determine how these complex structures influenced subduction and seismic slip, says lead author 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 also have implications beyond 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' Content Sourced from Original url
Scoop
a day ago
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Discovery Of Hidden Faults Sheds Light On Mystery Of 'Slow Earthquakes'
Wednesday, 20 August 2025, 12:09 pm Press Release: Earth Sciences New Zealand Seismic reflection profiles illustrating the frontal accretionary wedge and PFSs in Nankai Trough, Japan, and Hikurangi Trough, New Zealand. (A) Nankai Trough, offshore Japan. (B) Hikurangi Trough, New Zealand (IL 135 in NZ3D volume). (C) Locations of study areas. (D) Partial enlargement of the PFSs in (B). (E) Seismic coherence depth slice at 4396 m showing the PFSs in the incoming pelagic sequence. Seismic images in (D) and (E) are derived from the NZ3D seismic volume collected in the northern Hikurangi Margin Credit: ScienceAdvances Bathymetric map showing the location of the NZ3D seismic volume at the northern Hikurangi Margin. Credit: Science Advances Scientists have uncovered a key piece of the puzzle behind the unusual 'slow earthquakes' occurring off the east coast of New Zealand's North Island. A new international study, published in Science Advances, identifies hidden fault structures called polygonal fault systems (PFSs) as a major influence on the behaviour of the northern Hikurangi subduction zone. These shallow geological features, found in sediments entering the subduction zone, appear to play a critical role in where and how slow slip earthquakes occur. "This discovery helps explain why slow earthquakes occur where they do," says Dr Philip Barnes, marine geologist at Earth Sciences New Zealand (formerly NIWA) and co-author of the study. "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 section of this zone remains locked and capable of producing massive earthquakes over magnitude 8, the northern part behaves differently. It regularly produces slow slip events, movements that unfold over days to months, releasing tectonic stress without 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 international study was a collaboration between researchers from China, the US, and Earth Sciences New Zealand, using data from the International Ocean Discovery Program and the high-resolution three-dimensional NZ3D seismic survey conducted off Gisborne. Using high-resolution 3D seismic imaging, deep-sea drilling data from the International Ocean Discovery Program, and advanced computer modelling, the research team was able to map out PFSs in unprecedented detail and to evaluate their role in 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 structure and fluid migration offers new insight into one of the key processes thought to trigger slow earthquakes, says Dr Barnes. The study also confirms that these fault systems create a complex and variable structure along the megathrust, which can influence stress patterns and strain 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 identified the PFS type of fault at subduction zones 20 years ago off the southwest coast of Japan, they couldn't determine how these complex structures influenced subduction and seismic slip, says lead author 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 also have implications beyond 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" © Scoop Media
