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Mid-ocean ridge unfaulting revealed by magmatic intrusions
Mid-ocean ridges (MORs) are quintessential sites of tectonic extension1,2,3,4, at which divergence between lithospheric plates shapes abyssal hills that cover about two-thirds of the Earth’s surface5,6. Here we show that tectonic extension at the ridge axis can be partially undone by tectonic shortening across the ridge flanks. This process is evidenced by recent sequences of reverse-faulting earthquakes about 15 km off-axis at the Mid-Atlantic Ridge and Carlsberg Ridge. Using mechanical models, we show that shallow compression of the ridge flanks up to the brittle failure point is a natural consequence of lithosphere unbending away from the axial relief. Intrusion of magma-filled fractures, which manifests as migrating swarms of extensional seismicity along the ridge axis, can provide the small increment of compressive stress that triggers reverse-faulting earthquakes. Through bathymetric analyses, we further find that reverse reactivation of MOR normal faults is a widely occurring process that can reduce the amplitude of abyssal hills by as much as 50%, shortly after they form at the ridge axis. This ‘unfaulting’ mechanism exerts a first-order influence on the fabric of the global ocean floor and provides a physical explanation for reverse-faulting earthquakes in an extensional environment.
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File | Pages | Size | Access | |
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Publisher's official version | 19 | 14 Mo | ||
Supplementary Methods describing the fault scarp dataset from the Chile Ridge and detailing a simple analytical model for the depth of the compressive zone taking into account the effect of ... | 8 | 567 Ko | ||
Relocated earthquakes at the Mid-Atlantic Ridge and the Carlsberg Ridge. Event code follows the convention of Global CMT catalogue. Table also includes depth estimates for four events from the 2022... | - | 20 Ko | ||
Unfaulting earthquakes. List of reverse earthquakes from the Global CMT catalogue that occurred in areas mapped with high-resolution shipboard echosounders. | - | 10 Ko | ||
ompilation of unfaulting signatures in high-resolution seafloor bathymetry. Best-fitting slope T of cumulative fault offset versus distance to the ridge axis near the axis (T best, with maximum and .. | - | 24 Ko | ||
Normal faults along the Chile Ridge. Original dataset from ref. 24. Each fault is identified along a ridge-normal transect by the position of the bottom and top of its seafloor scarp (locations 1 ... | - | 203 Ko | ||
Author's final draft | 43 | 19 Mo |