Aug 2026· Science Advances· Vol 12· 0 citations· 39 references
Medicine
Abstract
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.
Identifying diagnostic signatures of coseismic slip in the geological record is essential for constraining fault rheology and earthquake dynamics, yet unambiguous geological markers of past seismic ruptures are still scarce. Among seismic slip indicators, solidified frictional melt is widely regarded as the most reliable; however, its restrictive formation conditions and poor preservation limit the geological record of seismic rupture. Here, we investigated fluidized fault gouge injections into host cataclasites preserved in the clay-rich fault zones of the Altyn Tagh fault (northern Tibetan Plateau) and Carboneras fault (southeast Spain), two structurally distinct strike-slip systems showing similar injection geometries and microstructures. The injections display elongate tips with pinch-out terminations and internal undulated foliation surfaces with irregular, lobate geometries, indicating flow within relatively more viscous, quartz-rich host cataclasites. The injected material embeds clasts derived from the host rock, and fractal dimensions of the clast size distribution exceeding 3 are consistent with extreme comminution comparable to that documented in faults accommodating coseismic slip. We interpret gouge fluidization and injection as resulting from transient fluid overpressure, a process that may play a key role in dynamic fault weakening. Therefore, such injections may represent reliable geological indicators of past earthquakes and provide constraints on rupture dynamics in structurally and rheologically complex fault zones.
Leonardo Del Sole, L. Aldega, Liu-Zeng Jing et al.· Seismological Research Lette...· 0 citations
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
In order to clarify the main controlling factors influencing fluid pressure changes in fault zones during the seismic cycle, we conducted laboratory rock friction experiments where fluid pressure was monitored in situ during sequences of quasi-static loading followed by dynamic slip events. The simulated fault was a 30$^\circ$ saw-cut in a Westerly granite cylinder, saturated with water, tested under triaxial conditions. Pore pressure was held constant at the boundaries of the block, but the low hydraulic diffusivity of Westerly granite made the fault hydraulically disconnected from the boundaries. During quasi-static loading while the fault was locked, we observed pore pressure increases which we interpret as poroelastic closure of the fault. During dynamic slip events, pore pressure systematically dropped by amplitudes commensurate to the normal stress drop. A large contribution to the pore pressure drop is interpreted as poroelastic opening of the fault. Deviations from the poroelastic effects are observed: in small events, pore pressure dropped further than anticipated, indicating inelastic dilation. In a few large events, pore pressure dropped less than anticipated, which could be the sign of compaction or thermal pressurisation. Prior to macroscopic slip events, we detect systematic pore pressure decreases by up to around 1 MPa, correlated to the occurrence of inhomogeneous preslip along the fault. Slip nucleation, inferred by kinematic inversion of local strain gauge data, is linked to local slip magnitudes of the order of 1 to 10 $\mu$m, and appears to lead to inelastic dilation. A stability analysis of fault slip including dilatant and poroelastic effects shows that poroelastic coupling tends to compensate normal stress variations, leading to faults operating under mostly constant effective normal stress if conditions are undrained.
N. Brantut, F. Passelegue, P. Dublanchet· Earth and Planetary Science...· 0 citations
Secular cooling of Mercury’s interior drove planetary contraction, forming widespread lobate scarps that are the surface expressions of thrust faults and fold-and-thrust belts. Despite their importance to Mercury’s global tectonics, the mechanics and rheology of these features remain poorly understood. Using Critical Taper analysis calibrated by friction experiments, we estimate the maximum basal friction (µb) from observed wedge geometry and show that the topography of large fold-and-thrust belts is consistent with weak graphite-bearing, low-angle fault zones. This finding indirectly supports models proposing a graphite flotation crust during Mercury’s early differentiation. We infer that remnants of this carbon-rich layer, heterogeneously distributed within Mercury’s crust because of early impacts, caused the weakening of large portions of the crust during later contraction, allowing the nucleation of weak, low-angle thrust faults. Since the gently dipping, frictionally weak thrusts require greater horizontal shortening to build the observed relief than steeper, stronger faults, Mercury’s cumulative radial contraction may exceed previous, more conservative estimates. Laboratory experiments and mechanical modeling show that Mercury’s widespread low-angle thrust faults likely formed due to graphite-rich layers in its crust, which acted as a solid lubricant and weakened fault zones during planetary contraction. These findings suggest that remnants of an early graphite flotation crust facilitated the development of weak, shallow-dipping faults, indicating Mercury’s total radial contraction may be greater than previously estimated.
N. A. Vergara Sassarini, M. Massironi, T. Tesei et al.· Nature Communications· 0 citations
Horizontal slab tearing, the lateral detachment of a subducting oceanic slab from continental lithosphere, is widely inferred from seismic tomography, yet its surface expressions in mountain belts and foreland basins remain ambiguous and, in many cases, contradictory. Existing geodynamic models commonly predict rapid horizontal tear propagation, implying that associated surface and stratigraphic signals should be too transient to be preserved in the geological record. In contrast, field observations, including lateral migration of foreland-basin depocenters and systematic basin thickening in the direction of inferred tear propagation, suggest more persistent and coherent surface responses. This discrepancy highlights a long-standing disconnect between geodynamic model based predictions and geological evidence. Here, we resolve this paradox by demonstrating that lateral variations in passive-margin strength exert a first-order control on the initiation, propagation, and surface expression of horizontal slab tearing. Using fully coupled three-dimensional thermo-mechanical and surface-process simulations, we show that passive-margin strength heterogeneity can substantially slow tear propagation and generate long-lived tectonostratigraphic signatures consistent with natural examples from the Alps, Carpathians, Zagros, and other orogenic belts. Our results bridge deep mantle dynamics and foreland-basin records, providing a unified framework for identifying, interpreting, and reconstructing slab tearing in orogenic systems worldwide.
Giridas Maiti, N. Andrić‐Tomašević, A. Balázs et al.· 17th EGU Émile Argand Confer...· 0 citations
The High Atlas Mountains constitute a major intracontinental orogen shaped by the long-term convergence between the Nubian and Eurasian plates. However, the present-day seismotectonic deformation and stress regime of the Western High Atlas remains insufficiently constrained. Here, we analyze relocated earthquakes recorded between 2014 and 2023, with local magnitudes ranging from 3.3 to 6.8, along with focal mechanism solutions and stress tensor inversion, to develop an updated seismotectonic interpretation of the Western High Atlas and to better constrain the mechanisms governing crustal deformation. The focal mechanism solutions indicate a predominance of oblique-reverse faulting, with secondary strike-slip and local normal components. Stress tensor inversion yields a nearly horizontal, approximately N-S to NNW-SSE oriented maximum compressive stress axis (σ1), consistent with the inferred regional SHmax direction. These results support active compressional to transpressive deformation within the Western High Atlas and suggest that crustal shortening is partly accommodated by the reactivation of inherited structures. The results indicate that strain partitioning is controlled by the interaction between far-field Nubia-Eurasia convergence and local crustal heterogeneities. This study provides new constraints on the active tectonic framework of the Western High Atlas and contributes to seismic hazard assessment in this intraplate mountain belt.
B. Oujane, Lahcen El Moudnib, Saïd Badrane et al.· Journal of Earthquake and Ts...· 0 citations