Slip Behavior Research Articles

Dependence of Simulated Fault Gouge Frictional Behavior on Mineral Surface Chemistry Quantified by Cation Exchange Capacity

AbstractThe slip behavior of crustal faults is known to be controlled by the composition of the fault gouge, but the exact mechanisms, especially considering the role of water‐rock interactions, are still under investigation. Here, we use a geochemical approach measuring the cation exchange capacity (CEC) of several phyllosilicate minerals and non‐clays, using CEC as a proxy for the ability to bind water to the mineral surfaces and/or develop electrostatic forces between particles. Laboratory shearing experiments show that low CEC materials (<3 mEq/100 g) tend to exhibit high friction, low cohesion, and velocity‐weakening frictional behavior. Phyllosilicate minerals exhibit CEC values up to 78 mEq/100 g and correspondingly lower friction coefficients, higher cohesion, and a tendency for velocity‐strengthening friction. Zeolite behavior is atypical, exhibiting a high CEC value typical of phyllosilicates but the strength and frictional characteristics of a non‐clay with low CEC. This suggests that the structure of the mineral is important for non‐phyllosilicates. For phyllosilicates, our results can be explained by water bound to mineral surfaces, creating bridges of hydrogen or van der Waals bonds between particles. The enhanced particle bonding for high CEC materials is consistent with high cohesion under zero effective stress conditions, and lowered friction by trapping bound water between the mineral surfaces under normal load. Bound water may explain the tendency for velocity‐strengthening friction in high CEC materials by hindering a Dieterich‐type time‐dependent frictional strengthening mechanism.

Using a landscape fingerprint to identify changes in fault-slip behavior

The Gabilan mesa tilts gently southwest away from the San Andreas fault in central California (western United States). Rather than attributing its existence to plate convergence, we argue that this large landform developed in response to a change in slip behavior along the San Andreas fault. Our interpretation is based on results from physical experiments. When we isolate a change in slip behavior (i.e., creeping to locked) as the only variable influencing deformation, a half-dome feature forms alongside the slip transition and mimics the shape and location of the Gabilan mesa adjacent to the San Andreas fault. We show other examples of half-dome features along the North Anatolian (Turkey), Philippine, and Chaman (Afghanistan-Pakistan) faults, suggesting that these domed landforms may provide indications of slip behavior transitions on poorly monitored faults.

Experimental Investigation and Analysis of Bond–Slip Behavior between Geopolymer Concrete and Steel Tube with Varying Structural Measures

In this study, push-out tests were conducted on 20 specimens to explore the bond–slip performance of geopolymer concrete-filled steel tubes. The investigation focused on the effects of various design parameters such as length–diameter ratio, diameter–thickness ratio, concrete strength, and internal structural measures of the steel tube on the bond–slip performance. Analysis of the test phenomena, load–slip curves, and strain distribution curves of each specimen revealed insights into the shear strength calculation methods for welded stud structure and ring rib structure specimens. The results indicated a slight buckling deformation at the loading end of the steel tube in the structural specimen, while no significant deformation was observed in the non-structural specimen. The strain distribution along the height direction of the steel tube exhibited a triangular pattern, with the strain increasing gradually. Improvements in the interfacial bonding performance were noted with reductions in length–diameter ratio and diameter–thickness ratio of the steel tube, as well as increases in concrete strength. When the steel tube wall thickness t increases from 3.5 mm to 4.5 mm, the peak load of GC30-1 increases from 382.13 kN to 419.59 kN, an increase of 9.81%. After improving the concrete strength of GC30-1 and GC30-3 specimens, the peak load increases from 382.13 kN and 274.54 kN to 436.46 kN and 306.12 kN, respectively, an increase of 14.2% and 11.5%. Furthermore, the welding structure of the steel tube significantly enhanced the shear bearing capacity of the interface. The ratio of load calculation value to test value fell within the range of 0.917 to 1.098, indicating good agreement between the calculated and experimental values. These research results can provide reference for engineering applications of geopolymer concrete.

Explosive stress wave propagation and fracture characteristics of rock-like materials with weak filling defects

Filling-type defects have a non-negligible effect on the propagation of explosive stress waves in rock. Combined with the new dynamic caustics experimental system and ANSYS/LS-DYNA numerical simulation platform, the research on the propagation characteristics of explosive stress wave and fracture characteristics of rock-like materials containing weak filling defects with different ductility has been carried out. Firstly, we analyzed the influence of weak filling on the propagation of blast-induced cracks, explored the “guiding” and “stopping” effects of weak filling on cracks, and analyzed the mechanical characteristics of crack propagation. Secondly, the effect of planar weak filling ductility on the damage degree of blasted medium was quantitatively evaluated. Thirdly, the influence of weak filling on the fluctuation characteristics of explosive stress wave was investigated. Then, the mechanical response behavior of the specimens was analyzed, and the results showed that the compaction and slip behaviour characteristics of the weak filling have some variability in degree, some continuity in time, some correlation in space and are affected by the ductility of the planar weak filling. In addition, the stress wave and weak filling interaction mechanism was elucidated. The conclusions of the analysis have positive reference value for understanding the explosion mechanics mechanism of defective rock masses.

Inertial flow-induced fluid pressurization enhances the reactivation of rate-and-state faults

We reveal that inertial flow can introduce additional pressure perturbations which accelerate the instability of critically stressed faults. We integrate a poroelastic spring-slider model with rate-and-state friction (RSF), a nonlinear flow model characterized by the improved Izbash equation, and a universal visco-inertial permeability model. The effect of inertial flow depends on the fracture network properties, proximity to faults, and injection parameters. Significant inertial flow results in higher pressure magnitudes and pressurization rates, causing notable differences in predictions between linear and nonlinear flow models, as well as aging and slip laws. The impact of inertial flow is particularly pronounced within a specific permeability range and is enhanced by high-rate injections. The fault reactivation is delayed due to fault strengthening with RSF in response to increased pressurization rates. Conversely, the presence of inertial flow enhances fault reactivation and promotes unstable slip behaviors. Furthermore, the results demonstrate that cyclic injection increases the critical stiffness of faults without an adequate release of pore pressure in each cycle. The time interval of the cyclic injection is prolonged as inertial flow generates higher pressure levels. This study highlights the importance of inertial flow in the stability analysis of critically stressed faults.

Fibre-reinforced geopolymer (FRG) cemented aeolian sand flexural properties and microproduct evolutionary processes

To reveal the flexural behaviour and microproduct evolution mechanism of FRG cemented aeolian sand, four factors, namely, sodium hydroxide dosage, water-solid ratio, fibre dosage, and fibre length, were classified into mutually independent levels and combined to form a set of test matrices for the design of orthogonal tests. Using DIC digital scattering technology to analyze the evolutionary process of specimen ring-breaking and employing scanning electron microscopy to explore the polymerization product micro-morphology, evolutionary process, pore defects, and analyze the fiber endowment morphology and the destruction mode; the use of EDS spectroscopy, X-ray diffraction, Fourier IR spectroscopy, and other technical means to analyze the polymerization product chemical composition, elemental distribution, and evolutionary characteristics. The results of the study show that the 28-day flexural performance of FRG cemented wind-blown sand as a filling material is significantly affected by various factors in the following order of magnitude: sodium hydroxide dosage > water-solid ratio > fibre dosage > fibre length. The optimal combination from the local test is: sodium hydroxide dosage of 1.4 %, the water-solid ratio of 0.32, the fibre dosage of 0.5 %, and the fibre length of 12 mm. With the increase in load, the value of the displacement field increases continuously, indicating a greater degree of specimen damage. As the reaction proceeds, the polymerization product's morphology evolves from rod-like to flaky, ultimately stabilizing into a network structure. The main elements in the product include C, O, Si, Al, and Ca, indicating that the polymerization product is a C-(A)-S-H gel. A reasonable distribution of discrete ductile fibers can play a positive role inside the specimen, acting as a bridge. The damage behavior under bridging can be divided into fiber debonding, producing slippage behavior, and fiber damage, leading to fracture behavior. The results of the study provide a scientific basis for the design, preparation, and application of solid waste filling materials, thereby promoting the development of materials science and engineering.

Cyclic inelastic performance evaluation of locking bolt demountable shear connectors in steel-concrete composite structures

This study extends the research on the Locking Bolt Demountable Shear Connector (LBDSC), previously introduced and extensively analysed under monotonic loading through both experimental and numerical methods. The focus here shifts towards the inelastic cyclic performance of the LBDSC, a critical aspect for applications in seismic regions. The LBDSC, designed for use in composite floors or decks, such as in-situ solid slabs, profiled deck slabs, or precast slabs in buildings and bridges, features a grout-filled steel tube bolted to the top flange of steel sections. The design incorporates a unique 'locking bolt' technique to counteract the influence of construction tolerances on undesirable initial slip behaviour, significantly facilitating the deconstruction and reuse of steel sections without the need for recycling. Following the Eurocode 4 guidelines, a series of standard push out tests were conducted to explore the LBDSC's inelastic cyclic characteristics. The experimental results confirm the LBDSC's capability for high strength, high initial stiffness, and adequate slip capacity under cyclic loading, with ductile shear failure modes observed at the bolt shank and local concrete crushing above the steel flange. The cyclic loading tests reveal a larger zone of damaged concrete compared to monotonic loading conditions, yet the monotonic and cyclic force-slip curves closely align. Based on these findings, and supported by validated finite element analyses, this paper proposes theoretical monotonic and cyclic models for LBDSC under push out loading, aimed at accurately predicting the load-slip response. These models are intended to facilitate the efficient analyses, design and numerical modelling of composite structures incorporating LBDSCs, and to support the broader adoption of LBDSCs in earthquake-prone areas, promoting sustainable steel-concrete composite construction practices.

Interlaminar fracture behaviour of emerging laminated-pultruded CFRP plates for wind turbine blades

Laminated pultruded composite plates are gaining interest for use in wind turbine blades due to their excellent structural performance with affordable cost. However, there is limited understanding of their fracture properties. The present work explores the interlaminar fracture behaviour of pultruded composite plates, bonded through resin infusion, to form thick CFRP structures. Mode-I, −II, and mixed-mode (I/II) tests were performed to obtain fracture properties at different mixed-mode ratios. Mode I crack propagation exhibits stick–slip behaviour, resulting in brittle failure in a few steps, while mode II provides more stable crack propagation along with cohesive failure. The mixed-mode fracture patterns follow the trend of the mode-mix ratios, in which higher mode-mix ratios (more mode II) induce more stable crack propagation. Benzeggagh-Kenane and power law criteria were compared regarding their prediction of crack initiation toughness given a mode mix ratio, and a linear relation between the mixed-mode I/II fracture toughness components could exist at interfaces of laminated pultruded plates. Meanwhile, applicability of testing standards and the effect of manufacturing-induced defects on fracture properties are thoroughly discussed. The results show that existing standards provide sufficient support for characterising fracture properties of bonded pultruded plates; and that manufacturing-induced defects can be detrimental to crack propagation and cause more brittle behaviour in mode I dominant cases, while beneficial effect of defects by toughening the interface was exhibited in mode II dominant cases.

The Role of Deformation and Microstructure Evolution on Texture Formation of a TA15 Alloy Subjected to Plane Strain Compression.

In this study, the texture formation mechanism of a TA15 titanium alloy under different plane strain compression conditions was investigated by analyzing the slipping, dynamic recrystallization (DRX) and phase transformation behaviors. The results indicated that the basal texture component basically appears under all conditions, since the dominant basal slip makes the C-axis of the α grain rotate to the normal direction (ND, i.e., compression direction), but it has a different degree of deflection. With an increase in deformation amount, temperature or strain rate, {0001} poles first approach the ND and then deviate from it. Such deviation is mainly caused by a change in slip behaviors and phase transformation. At a smaller deformation amount and higher strain rate, inhomogeneous deformation easily causes a basal slip preferentially arising from the grain with a soft orientation, resulting in a weak basal texture component. A greater deformation amount can increase the principal strain ratio, thereby promoting other slip systems to be activated, and a lower temperature can increase the critical shear stress of the basal slip, further causing a dispersive orientation under these conditions. At a higher temperature and a lower strain rate, apparent phase transformation will induce the occurrence of lamellar α whose orientation obeys the Burgers orientation of the β phase, thereby disturbing and weakening the deformation texture. As for DRX, continuous-type (CDRX) is most common under most conditions, whereas CDRX grains have a similar orientation to deformed grains, so DRX has little effect on overall texture. Moreover, the microhardness of samples is basically inversely proportional to the grain size, and it can be significantly improved as lamellar α occurs. In addition, deformed samples with a weaker texture present a higher microhardness due to the smaller Schmidt factors of the activated prism slip at ambient loading.

Multi-scale investigation of silane coupling agent for enhanced corrosion resistance in reinforced concrete

Reinforcement corrosion is a significant factor leading to the deterioration of building performance. In order to enhance the serviceability of reinforced concrete under corrosive environments, this study employs a silane coupling agent (γ-aminopropyltriethoxysilane) for steel reinforcement treatment. The anti-corrosion mechanism, crack propagation patterns, and modified corrosion resistance of the steel are investigated at multiple scales. Experimental techniques such as scanning electron microscopy (SEM), X-ray energy-dispersive spectroscopy (EDS), and Fourier-transform infrared spectroscopy (FT-IR) are utilized to explore the influence of the self-assembled coating of the silane coupling agent on the microscopic morphology, elements, and functional groups of the steel. Concrete specimens with treated reinforcement are fabricated, and electrochemical accelerated corrosion tests are conducted to compare corrosion differences among different specimens. Using untreated specimens as a control group, digital image correlation (DIC) technology is employed to capture the full-field strain and displacement distribution during the loading process. The crack propagation and slip behavior at the steel-concrete interface in the composite specimens are analyzed. The research findings indicate that, at the optimal concentration of 1.2 %, the self-assembled coating of the silane coupling agent successfully adheres to the steel surface, significantly enhancing the interfacial abrasion resistance and mechanical strength of the steel-concrete interface, thereby validating the improved corrosion resistance of the steel. This study proposes the self-assembly mechanism and interfacial enhancement mechanism of the silane coupling agent on steel at multiple scales, contributing to a comprehensive understanding of its effectiveness.

Relocation of the 2018–2022 seismic sequences at the Central Gulf of Corinth: New evidence for north-dipping, low angle faulting

The Gulf of Corinth, Central Greece, is a highly active half-graben, characterized by seismicity which is more intense in its western part, while destructive earthquakes have also occurred towards its eastern end. We herein present an analysis of the seismicity in the Central Gulf of Corinth, for the period from June 2018 to December 2022. We applied the EQTransformer machine-learning model to enhance the initially available data, adding missing P- and S-wave arrival-times or improving existing ones. The events were initially located using a new local velocity model and then relocated using the double-difference method, including waveform cross-correlation data from local stations. The hypocenters, generally distributed at depths between 5 and 15 km, along with the focal mechanisms of significant earthquakes (1965 through 2022) and the geometry of mapped faults on the surface were co-examined to better understand their possible connection. It is shown that major outcropping north-dipping structures, such as the East Helike fault and its eastward offshore extension, match only with the southern bounds of seismicity. The Mw = 5.9, 1970 Antikira and Mw = 5.7, 1992 Galaxidi earthquakes cannot be associated with known mapped faults on the surface and likely occurred on low-angle, north-dipping planes. The variability in slip behavior of the low-angle detachment in the Gulf of Corinth, ranging from seismic slip to aseismic creep, probably accounts for the most part of the N-S extensional deformation. The spatial pattern of the 2018–2022 microseismicity delineates the edges of the rupture planes of major events that occurred during the instrumental era, including the Mw = 6.3, 1995 Aigion earthquake. The lack of aftershocks for significant earthquakes, including the Mw = 5.0, 8 October 2022 event, south of Desfina, is interpreted in terms of different pore pressure conditions, variations in fault-rock strength, and the preferred accumulation of high stress inside the upper crust.

Experimental and analytical investigation of the shear behavior of steel-bamboo composite I-beams with composite connections

In steel-bamboo composite beams, the debonding failure and slip behavior of steel-bamboo pure bonding interfaces at the flanges often lead to premature failure of beams and underutilization of material strengths. Therefore, a novel steel-bamboo composite I-beam with composite connections was presented in this study, in which the pure bonding interfaces at the beam's flanges were reinforced by self-tapping screws (STSs). 13 beams were designed and fabricated with interface type, shear span-to-depth ratio, height-to-thickness ratios of bamboo and steel at the web, and width-to-thickness ratio of steel at the flange as main parameters. Then, shear tests and theoretical analysis were performed to evaluate the beam's shear behavior. The results indicated that the debonding failure and slip behavior of the beams were effectively limited, and the shear resistance, deformation capacity, and ductility were significantly improved. The shear resistance of beams was improved by reducing the shear span-to-depth ratio, height-to-thickness ratios of the bamboo and steel at the web, and steel flange width-to-thickness ratio. Finally, the developed analytical models can be concluded to be used to accurately predict the interfacial shear stress at the beam flanges in the serviceability limit state (SLS) and ultimate shear capacity of the beams.

Micropillar compression of single-crystal single-phase (Co, Cu, Mg, Ni, Zn)O

Bulk, polycrystalline (Co, Cu, Mg, Ni, Zn)O was synthesized using solid-state sintering. Micropillars were prepared and mechanically deformed along three crystallographic orientations: (001), (101), and (111). Pillars (001) and (111) cracked, while Pillar (101) remained intact. Pillars (001) and (101) exhibited activated slip systems, confirmed by a large stress drop, and the presence of slip bands, respectively. Schmid factor (SF) analysis was performed to examine the effect of grain orientations on dislocation activity and slip behavior. SF values range from 0 to 0.5, with non-zero values indicating potential for slip. Six slip systems exist in the (Co, Cu, Mg, Ni, Zn)O rock salt crystal structure: 1/2⟨110⟩11¯0. For the (001) orientation, four slip systems are potentially active (SF = 0.5). For the (101) orientation, there are four potentially active slip systems (SF = 0.25). For the (111) orientation, no potentially active slips systems exist (SF = 0). Dislocation structures, which were observed post-compression via transmission electron microscopy, demonstrated variations in size, number, and distribution across the pillar, depending on micropillar orientation. Entangled dislocations created misorientation in Pillar (001), which led to the possible formation of subgrains, while singular dislocations were observed in Pillar (101), and a lack of dislocations was observed in Pillar (111). Zener–Stroh type dislocation entanglement-mediated cracking is the proposed cause of the transgranular-type cracks in Pillar (001). The possible subgrain formation, or lack of formation, respectively, caused intergranular-type cracks to additionally form in Pillar (001), while Pillar (111) only exhibited transgranular-type brittle fracture. In combination, these findings highlight the importance of dislocation activity, without the need for elevated temperature, and grain orientation in controlling the mechanical deformation response in single-phase (Co, Cu, Mg, Ni, Zn)O.

Experimental study on the shear and slip behaviors of perfobond strip connectors with low elastic modulus material wrapped perforated rebars

Adopting Ultra-high performance concrete (UHPC) endows steel-UHPC composite beams with numerous benefits, including high cracking capacity, high durability, light self-weight, etc. However, the cracking load of the steel-UHPC composite beams under negative moments reaches only 13–40 % of their ultimate load, with cracking properties being the primary constraint to the development of steel-UHPC composite beams. This study proposed a novel uplift-restricted and slip-permitted (URSP)-PBL connector to improve the crack resistance in the negative moment regions of continuous steel-UHPC composite beams. A total of ten push-out tests were conducted to investigate the behaviors of the URSP-PBL connector. The effects of perforated rebar diameter, rubber thickness, and row numbers on the URSP-PBL connector were investigated by evaluating the failure mode and the load-slip relationship of the push-out specimens. Additionally, numerical analyses were carried out to investigate the effect of various parameters on the mechanical properties of the connector. Based on the analysis results, a load-slip curve model of the URSP-PBL connector was established as a reference for the promotion of the URSP-PBL connector in steel-UHPC composite structures.

Morphological differences across the Shumagin-Semidi fault segments control slip behaviors and tsunami genesis in the Aleutian-Alaska subduction zone

Rupture behaviors of a subduction megathrust define the slip type, the extent and the associated tsunami hazard. They are, however, difficult to be defined precisely due to limited fault-zone observations. Here, we integrate GNSS, tsunami-waveforms, seismic-profiles, and earthquake-cycle modeling to delineate the slip-extent of the 2020 Mw 7.8 Simeonof and the 2021 Mw 8.2 Chignik earthquakes in the Semidi segment; and to understand the possible structural and mechanical control on the distinct rupture behaviors of this segment and its neighboring Shumagin segment at the Aleutian-Alaska subduction zone. We show that both the Simeonof and Chignik earthquakes slipped a compact area at depth between ∼20 and 40 km that is well constrained by the combination of GNSS and tsunami-waveform data. We explain the distinct slip behaviors associated with the Semidi and Shumagin segments by highlighting the morphological changes in the fault along the strike direction. Beneath the Shumagin Island, we identify a structural-mechanical boundary that separates the megathrust into Semidi (east) and Shumagin (west) two segments. Semidi is gentle and curved; while Shumagin is steep and planar. The Semidi segment produces spatially-heterogenous stress field, and generates partial, full, complex ruptures as indicated in modeled cycles and in historical seismic observations. Meanwhile the Shumagin segment, coincides with the ocean-continent transition boundary – the Beringian margin, tend to generate slow-slip-events, tremors, otherwise, generates small or moderate seismicity as indicated in the modeled cycles and in seismic records since 1750. Our findings indicate that Semidi is likely to rupture in a chaotic fashion with major or large earthquakes, resulting a greater tsunami hazard like the 1938 Mw 8.2 event. The tsunami potential in the Unimak segment may also remain high.

Bond-Slippage Characteristics between Carbon Fiber Reinforced Polymer Sheet and Heat-Damaged Geopolymer Concrete

The present study investigates the behavior of bond slip between carbon fiber reinforced polymer (CFRP) sheets and heat-damaged geopolymer concrete specimens that have been exposed to various elevated temperatures (20°C, 200°C, 400°C, and 600°C). The research aims to address the challenges posed by elevated temperatures on the bond strength and to highlight our original achievements in understanding and mitigating these effects. To assess the effect of different CFRP bonding widths and lengths, geopolymer concrete specimens were cast and bonded to sheets of CFRP. A total of 32 samples were tested under double-shear tension, examining the mechanical properties of geopolymer concrete, failure modes, bond force-slip curves, ultimate bond force and slip, stiffness, energy absorption, and scanning electron microscopy (SEM) analysis. The study found that temperatures up to 200°C caused a slight decline in mechanical properties and bond-slip behavior, with a 5% decrease in bond force and slippage. At 400°C, bond force and slippage reduced by 16%. Exposure to 600°C led to a significant 42% reduction in bond-slip behavior. The developed bond slippage model showed good agreement with experimental results, providing a valuable tool for predicting bond behavior under high-temperature conditions. Doi: 10.28991/CEJ-2024-010-07-03 Full Text: PDF

3D shear wave velocity and azimuthal anisotropy structure in the shallow crust of Binchuan Basin in Yunnan, Southwest China, from ambient noise tomography

The Binchuan Basin in northwest Yunnan, southwest China, is a rift basin developed at the intersection of the Red River Fault and Chenghai Fault, where historical earthquakes have occurred. Understanding the fine velocity structure of the shallow crust in this region can help improve earthquake location accuracy and our understanding of the relationship between fault zone structures and fault slip behaviors. Using the continuous waveform data recorded by 381 dense array stations in 2017, we obtained 7 915 Rayleigh-wave phase velocity dispersion curves in the period band of 0.2–6 ​s from ambient noise cross-correlation functions after rigorous data processing and quality control. We determined 3D isotropic and azimuthally anisotropic shear wave velocity models at depths above 6 ​km in the shallow crust based on the direct surface wave azimuthal anisotropic tomography method. The isotropic model reveals a strong correspondence between the S-wave velocity structure at depths of 0–1 ​km and the regional topography and lithology. The Binchuan depocenter, Zhoucheng depocenter, Xiangyun Basin, and Xihai Rift Basin are primarily composed of Quaternary deposits, which show low-velocity anomalies, while the regions with the Paleozoic shale, limestone, and basalt exhibit high-velocity anomalies. The nearly N–S orientation of fast directions from azimuthal anisotropy models are mainly controlled by the active Binchuan Fault with N–S strike as well as the NNW-oriented primary compressive stress.

Deformation mechanisms and slip behaviors of tectonically deformed conglomerates from the Central Apennines fold-and-thrust belt: Implications for shallow aseismic and seismic slip

Fold-and-thrust belts and accretionary prisms exhibit considerable variability in slip behaviors along active faults. While numerous studies have investigated fault mechanics and slip behaviors in carbonate-, shale-, and sandstone-hosted faults as well as clay-rich portions of shallow accretionary prisms, the deformation mechanisms and slip behaviors of deformed, thrust-top molasse-type conglomerates remain poorly understood. To fill this knowledge gap, we conducted structural and microstructural analyses on exhumed and deformed conglomerates in the footwall of an out-of-sequence thrust from the Central Apennines fold-and-thrust belt (Italy). Our findings aim to constrain conglomerate deformation mechanisms and infer possible slip behaviors. We observed flattened pebbles and an intense foliation comprising densely spaced, thrust-parallel, clay-rich stylolites that indicate slow deformation attributed to carbonate dissolution during aseismic creep. In contrast, quartz clasts with calcite micro veins and micrometer-thick slip increments in slickenfibers suggest fast brittle failure and fluid overpressure in competent pebbles, while the matrix continues to deform aseismically through pressure solution. The general structure is similar to block-in-matrix textures observed in tectonic mélanges from exhumed subduction zones and accretionary prisms. Our results provide new insights into the slip behaviors of shallow (<∼1 km) portions of fold-and-thrust belts, complementing existing understandings of deformation mechanisms and slip behaviors across different depth ranges in fold-and-thrust belts and accretionary prisms.

Fault rock structure-related stiffness contrast explains earthquakes in creeping faults

Abstract Fault rocks exhibit structures resulting from different styles of shear deformation (either distributed or localized) during fault displacement. However, how the fault rock structures affect fault slip behavior remains poorly understood. We conducted shear experiments on thick and thin gouge layers of various mineral compositions, which simulate the predominant development of velocity-strengthening distributed deformation zones and velocity-weakening shear localized zones, respectively. Here, we show that deformation zones with contrasting structures and frictional properties can be developed together in a single fault. If the rheological stiffness of shear localization zones in the fault exceeds the elastic stiffness of neighboring wall rocks, stick-slip can intermittently occur along the localization zones while stable slip persists in the distributed deformation zones. These findings suggest that contrasting rheological stiffnesses resulting from fault rock structures may induce the simultaneous operation of multiple slip modes in a fault and explain the occurrence of earthquakes in creeping faults.

Effect of mineral dissolution on fault slip behavior during geological carbon storage

Geological carbon dioxide storage is one of the most effective technologies to reduce greenhouse gas emissions to the atmosphere. The mineral dissolution is inevitable during the long-term storage process, while the chemical effect on fault slip behavior remains poorly understood. In this paper, we present a hydro-chemical–mechanical coupled fault reactivation study using the unified pipe-interface element method (UP-IEM). The impact of chemical dissolution on stress redistribution is considered. The accuracy of the numerical method to simulate reactive solute transport and fault frictional slip are confirmed by analytical solution and numerical verification. Two different fault tectonic scenarios, of which fault locating in the caprock and fault crosscutting the reservoir and caprock, are designed to investigate the fault slip behavior induced by mineral dissolution. The effect of dissolved CO2 solute concentration, fault aperture, reservoir permeability and chemical reaction rate are discussed. Results show that fault locating in the caprock is easier to be activated. The chemical reaction has a more significant effect on fault slip behavior than fluid pressure during the long-term low-velocity CO2 leakage. The increase of CO2 solute concentration and reservoir reaction rate cause an obvious growth on fault slip displacement. The decrease of fault initial aperture results in the fault slip velocity slower and the slipping area smaller. The high-permeability reservoir keeps the fault more stable than low-permeability reservoir under the influence of mineral dissolution.