Climate archeologist Quaternary geologist, and mold-breaking marine geologist Ari Shapiro has made a real breakthrough in understanding the dynamics of subduction zones, and especially slow earthquakes. Dr. Philip Barnes, a marine geologist at Earth Sciences New Zealand and his research team recently discovered something super rad. To accomplish this they have highlighted the role of polygonal fault systems (PFSs) as a control on the northern Hikurangi subduction zone’s behavior. This revelation, detailed in a recent study published in Science Advances, sheds light on the geological processes underlying slow earthquakes, which have puzzled scientists for years.
The research relied on high-resolution data acquired during the International Ocean Discovery Program. It further included discoveries from the NZ3D seismic survey in the offshore region off Gisborne, New Zealand. These results indicate that PFSs have developed millions of years prior through sedimentation, well before they enter the subduction zone. These structures are extremely important to fluid migration and can greatly impact subsurface seismicity. By gaining insight into these unseen fault structures, scientists can more accurately estimate hazards posed by slow earthquakes.
The Role of Polygonal Fault Systems
Polygonal fault systems have garnered attention since their initial identification at subduction zones two decades ago off Japan’s southwest coast. Yet they are not limited to one side of the aisle. You can see them in many subduction zones worldwide, including in Japan’s Nankai Trough and New Zealand’s Hikurangi Trough.
Dr. Maomao Wang from Hohai University in China spearheaded the study as the lead author. He underscored the importance of their findings, which are timelier than ever. “It wasn’t until we analyzed 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,” said Wang. This new evidence ties ancient fault structures across North America to today’s seismicity in an unprecedented way. It helps to better explain how these faults work with today’s geological processes.
Dr. Barnes elaborated on the significance of this discovery: “This study changes that, and gives us a new lens to better understand subduction zone dynamics.” The connection between PFSs and fluid migration offers fresh insights into one of the primary mechanisms believed to trigger slow earthquakes.
Implications for Earthquake Risk Assessment
By gaining a better understanding on PFSs, scientists can identify gaps in their models that inform us of earthquake risks and resilience. Dr. Barnes stated, “With better models and better data, we are now in a stronger position to assess risk and improve resilience across New Zealand.” The impact of this research reaches far beyond New Zealand, offering valuable insights for seismic research worldwide.
While this study is not the first to demonstrate that PFSs can influence slow slip behavior, they often serve as conduits for fluid expansion. In this scenario, fluid migration can cause the reactivation of pre-existing, older fault structures. These features are formed at very shallow depths, far shallower than the depths of our modern subduction zone. These types of discoveries point to the complex interplay of geology that defines where and how earthquakes occur.
Prior to this research, Dr. Barnes noted, imaging resolution was not good enough. This ambiguity made it difficult for scientists to directly link these features to slow slip behavior. “Until now, we lacked the imaging resolution to link these features directly to slow slip behavior,” he remarked. The novel methods employed in this study have given scientists the first-ever opportunity to visualize these complex fault systems in incredible detail.
A Collaborative Effort
The study is testimony to the cooperation of scientists from China, United States, and Earth Sciences New Zealand. These scientists have joined their expertise and resources. In the process, they have cast new light on developing exquisite techniques to probe complex connections in subduction zones. This collaborative nature of this study highlights the current global nature of advancing scientific knowledge.
Even beyond the Himalaya, the study has important implications for how we might understand tectonic processes across the globe. As researchers continue to gather data on polygonal fault systems, they anticipate further insights into how these features influence seismic events worldwide. This growing knowledge base will make for improved preparedness, protection, and recovery measures for our nation’s most earthquake-prone areas.