A team of geoscientists lead by Guido M. Gianni identified a subtle but powerful force driving mountain building and compression of the Earth's crust in Japan and neighboring regions: The so-called "same-dip double subduction" (SDDS) in nearby oceanic trenches has effects reaching hundreds and thousands of kilometres away from the zone of subduction. Guido M. Gianni, from GFZ Helmholtz Centre for Geosciences, and his colleagues from GFZ and the University of Miami, report their findings in the journal Nature Geoscience.
Subduction zones, where tectonic plates dive beneath one another, are already known to be the source of the strongest and most devastating earthquakes as well as for volcanic arcs, and the movement of Earth's crust. The new study reveals that when two nearby subduction zones dip in the same direction, as seen in the Ryukyu and Izu-Bonin-Marianas trenches to the south of Japan, the effect isn't just local. The subduction zones also affect so-called backarc areas.
Backarc areas are part of the larger picture of plate tectonics: Where subduction occurs deep oceanic trenches form. "Behind" the trenches, as seen from the moving direction of the oceanic plate, mountains can form by deforming continental crust during subduction, and on top of the mountains, volcanoes form, often aligned like an arc. And behind that, hence the name, backarc regions emerge.
The researchers used advanced 3-D geodynamic modeling to show the effects of the SDDS system that has been dragging the Pacific trench westward over the past 10 million years. This motion puts stress on the overlying plate in Northeast Japan, initiating a wave of compression that doesn't stem from a direct plate collision. The resulting crustal squeezing has built up mountains in Northeast Japan and possibly even actively triggered a new subduction zone in the backarc Japan Sea area, including the region of the devastating 2024 Noto Peninsula earthquake.
The authors' model of "double subduction-induced orogeny" improves long-held views on how non-collisional mountain building occurs. Their study highlights how distant plate interactions can shape regions up to thousands of kilometers away. "Our models show a significant increase in horizontal stress in the upper plate above the Pacific trench, mirroring the deformation belt of thrust faults along northeast Japan, earthquakes, and crustal deformation extending over 1,000 kilometers into Japan's backarc," says first author Guido M. Gianni. He was working as an Alexander von Humboldt Research Fellow at GFZ's section "Lithosphere Dynamics" at the time of the study. Guido M. Gianni comes from the National Scientific and Technical Research Council (CONICET), in Buenos Aires, Argentina.
Beyond modern Japan, the research suggests that similar SDDS mechanisms may explain ancient mountain-building events in places like the Mediterranean in the Mesozoic and South America in Paleozoic times. Guido M. Gianni says: "These insights not only refine our understanding of tectonic processes but also have implications for seismic hazard assessment in regions experiencing similar subduction interactions."
Thus, the study offers a new way of thinking about how Earth's plates interact, and how those interactions can silently but powerfully reshape the surface of our planet.
Original study: Gianni, G.M., Guo, Z., Holt, A.F. et al. Non-collisional orogeny in northeast Japan driven by nearby same-dip double subduction. Nat. Geosci. 18, 525–533 (2025). https://doi.org/10.1038/s41561-025-01704-5
