Young oceanic lithosphere flexes as axial topography decays across mid‐ocean ridge shoulders, yet this deformation has been quantified at only a few segments, leaving its global expression poorly constrained. We analyzed 50 across‐axis bathymetric profiles from 21 regions spanning slow to fast spreading rates, identified 1,201 abyssal‐hill‐bounding fault scarps, and measured the change in apparent tectonic strain across the ridge shoulder from cumulative heave. After correcting for apparent‐throw reduction by surface process, three regimes emerge: (a) Axial‐valley ridges record shortening that increases with axial relief, (b) Fast‐spreading axial‐high ridges record extension that increases with relief, (c) Axial‐high ridges at slow‐to‐intermediate spreading rates record negligible flexural strain, because their thicker axial lithosphere acquires little accretional curvature. A simple flexural model with strain proportional to axial relief reproduces these patterns to first order. Flexure, set by axial relief and axial lithospheric thickness, systematically modifies fault‐generated seafloor morphology at divergent plate boundaries.
Ran Li, Zhonglan Liu, Shu-Ming Feng et al.· Geophysical Research Letters· 0 citations
Elastic flexure of tectonic plates shapes large-scale topographic features and can induce notable slip on lithosphere-scale faults. At mid-ocean ridges, recent evidence shows that up to 50% of extensional fault offsets formed within axial valleys can be reversed by compressional slip across valley flanks. While standard models predict the location of this faulting, they consistently underpredict the depth-extent of compression and related surface offsets. Here, using numerical models, we show that elevated pore fluid pressures in compression allow increased slip on flexure-driven reverse faults. Quantitative agreement between modeled and observationally inferred reverse fault–bending strain is achieved only when pore-fluid pressures in reverse faults approach lithostatic levels. These findings highlight the critical role of inherited structural heterogeneities and high pore-fluid pressures in facilitating deep-seated reverse faulting during lithospheric unbending. This mechanism may also amplify flexure-induced seismicity in continental forebulges, such as the 2001 Bhuj earthquake (moment magnitude, 7.6), and underscores pore-pressure modulation as a fundamental control on global tectonic hazards.
Zhonglan Liu, W. R. Buck, J. Olive· Science Advances· 0 citations