Slip Zone Research Articles

Pore water pressures and hydraulic conductivity in the slip zone of a clayey earthflow: Experimentation and modelling

Rainfall is among the most relevant triggering factors of landslides. With the aim of defining a model of the influence of rainfall on deep landslides, this paper presents data of a long-term monitoring of pore water pressures in a clayey earthflow, and the results of many field permeability tests carried out with several procedures. Pore water pressures are being monitored in the Costa della Gaveta slope since 2005. In the last years, new instruments have been installed and permeability tests have been carried out in the stable formation, in the landslide body and in the slip zone. The hydraulic conductivities of the three different zones of the subsoil have been evaluated by two types of field tests: falling head tests (by Casagrande piezometers and test wells), and localized constant head tests (by a permeameter ad hoc designed). The experimental data show that: a) pore water pressures along the slip zone respond to rain more than in the landslide body and in the stable formation, even at about 25 m depth; b) the hydraulic conductivity ksz of the slip zone is much higher than that of the landslide body, kl, in turn higher than the hydraulic conductivity of the stable formation, kf. The numerical 3D modelling of steady-state reference conditions and of transient processes caused by the historical rainfall series shows that the occurrence of ksz higher than kl and kf determines an overall drainage effect which makes the global limit equilibrium safety factor SF greater than that evaluable for other possible conditions. On the other side, even the lowest measured hydraulic conductivity ksz provides seasonal rain effects on water pressures along the slip surface such to determine significant SF variations in phase with the observed seasonal displacement rates.

Seismic fragility analysis of steel intermediate moment frames with column-tree connections

Steel intermediate moment frames (SIMFs) with column-tree connections have an advantage in that they can ensure quality control and decrease construction cost and time by the factory welding of stub beams to columns and field bolting at the beam splice. Furthermore, the amount of steel can be reduced by distributing the seismic lateral load to the entire frame, for which beam-to-column joints are fully restrained. Despite such merits, concerns about slip at the beam splice and concentrated deformation in the weak panel zone also exist. Therefore, the influence of beam splice slip and weak panel zone deformation on the seismic performance of the SIMF with column-tree connections was examined numerically by seismic fragility assessment. For comparison, the seismic fragility of a SIMF with conventional field-welded connections was also examined. The result showed that the beams and panel zones share energy absorption in the SIMF with column-tree connections, even though the panel zones are weaker than the beams, because the beam splice slip can reduce the concentration of deformation on the weak panel zone. The collapse probability of a SIMF with column-tree connections is expected to be reduced to a value as low as a SIMF with conventional connections if the quality of test data and modeling are improved.

Structural Controls Over the 2019 Ridgecrest Earthquake Sequence Investigated by High‐Fidelity Elastic Models of 3D Velocity Structures

AbstractWe develop finite element models of the coseismic displacement field accounting for the 3D elastic structures surrounding the epicentral area of the 2019 Ridgecrest earthquake sequence containing two major events of Mw7.1 and Mw6.4. The coseismic slip distribution is inferred from the surface displacement field recorded by interferometric synthetic aperture radar. The rupture dip geometry is further optimized using a novel nonlinear‐crossover‐linear inversion approach. It is found that accounting for elastic heterogeneity and fault along‐strike curvilinearity improves the fit to the observed displacement field and yields a more accurate estimate of geodetic moment and Coulomb stress changes. We observe spatial correlations among the locations of aftershocks and patches of high slip, and rock anomalous elastic properties, suggesting that the shallow crust's elastic structures possibly controlled the Ridgecrest earthquake sequence. Most of the coseismic slip with a peak slip of 7.4 m at 3.6 km depth occurred above a zone of reduced S‐wave velocity and significant post‐Mw7.1 afterslip. This implies that viscous materials or fluid presence might have contributed to the low rupture velocity of the mainshock. Moreover, the zone of high slip on the northwest‐trending fault segment is laterally bounded by two aftershock clusters, whose location is characterized by intermediate rock rigidity. Notably, some minor orthogonal faults consistently end above a subsurface rigid body. Overall, these observations of structural controls improve our understandings of the seismogenesis within incipient fault systems.

Postseismic Deformation and Afterslip Evolution of the 2015 Gorkha Earthquake Constrained by InSAR and GPS Observations

AbstractIn the past few years, space‐geodesy has measured continued postseismic deformation in the region of the 2015 Gorkha Mw 7.8 earthquake. Previous studies have suggested that the postseismic deformation is dominated by afterslip, but the spatiotemporal evolution of the afterslip, hence its cause and impact on regional seismicity are disputed, and contribution from other postseismic processes has not been well constrained. Here, we constructed an afterslip model using InSAR and GPS observations over three years after the Gorkha earthquake. First, the Sentinel‐1A satellite data were processed using Permanent Scatterer Interferometric Synthetic Aperture Radar method to extract deformational signals at high‐coherence points, and a fitting method was used to extract the postseismic displacement sequences. We then used InSAR and GPS data in a joint inversion for the evolution of afterslip, and compared its contribution to the observed postseismic displacement to that of viscoelastic relaxation and poroelastic rebound. Our results confirm that afterslip has dominated the observed postseismic deformation in the Gorkha region. Within 3 years of the Gorkha earthquake, afterslip released ∼1.20 × 1020 N m, about 14% of that released by the mainshock and the largest aftershock, or equivalent to an Mw 7.32 earthquake. The afterslip has occurred mostly downdip of the coseismic slip zone, in the ductile shear zone, apparently controlled by rheological properties. The updip shallow portion of the Main Frontal Thrust (MFT) zone has not been ruptured by coseismic slip or unlocked by afterslip, thus could potentially produce future earthquakes.

Surge of Mangla reservoir loading promoted failure on active Décollement of western Himalayas

The extreme rainfall weather during the Indian monsoon season has increased in recent decades changing the hydrological mass distribution that may be responsible for triggering regional earthquakes. In the western Himalayas, a shallow Mw 5.7 earthquake took place right after the withdrawal of the 2019 unusual Indian summer monsoon resulting in a rapid increase of ~4.5 km3 of water storage at the nearby Mangla reservoir within three months. Through a joint inversion of space geodetic and teleseismic data, we found that the mainshock occurred on the décollement structure of the Main Himalayan Thrust in the western Himalayas, which was previously underdetermined. The significant water loading, and pore pressure diffusion led to Coulomb stress increases of ~10 kPa on the maximum coseismic slip zone promoting fault failure. Our findings demonstrate that climate change could influence certain reservoir-associated earthquakes in the Himalayas. We provide recommendations to improve the regulations for the reservoir operations in Mangla and probably other contexts with similar tectonic settings in the Himalayas during the monsoon season.

Meso- to nano-scale evidence of fluid-assisted co-seismic slip along the normal Mt. Morrone Fault, Italy: Implications for earthquake hydrogeochemical precursors

Fluids play an important role in seismic faulting both at hypocentral depths during earthquake nucleation and at shallower crustal levels during rupture propagation. Pre- to co-seismic anomalies of crustal fluid circulation have been identified by hydrogeochemical and seismological monitoring and interpreted as potential precursors of strong earthquakes. To shed light on the role of fluids in seismic and precursory mechanisms, the active carbonate-hosted principal slip zone (7-8 cm thick) of the exhumed (exhumation < 3 km) normal Mt. Morrone Fault (central Apennines) has been investigated with a multi-disciplinary approach from the macro- to the nano-scale. The distal slip zone consists of white cementitious calcite-rich bands and red cataclastic bands composed of dolomite and calcite clasts embedded in a clay-rich matrix. The proximal slip zone consists of subparallel ultracataclastic layers separated by sharp slip surfaces. The ultracataclastic layers mutually inject/overprint, bearing evidence of granular fluidization, dolomite thermal decomposition, and clay amorphization. Fluid inclusions and the distribution of both trace and major elements reveal the inflow of both shallow and deep external fluids into the slip zone. Presumably, the deep fluids originated from a magmatic-like source and ascended along the fault during pre-seismic dilation and seismic ruptures, interacting with shallow phyllosilicate-rich flysch deposits and the fluids hosted within them. In this context, vanadium-rich fluidized microlayers along the exhumed Mt. Morrone Fault are reminiscent of vanadium-rich potential hydrogeochemical precursors arose in the shallow aquifers of the study area since a few months before the 2016 Mw 6.0 Amatrice earthquake.

Discrete element modelling of multi-stage hydroshearing stimulation in Enhanced Geothermal System

In contrast to the conventional single stage hydraulic stimulation carried out simultaneously on the whole open hole section, the multi-stage stimulation, applying fluid injection on a selected interval of open hole for each stage, may provide an alternative for better reservoir permeability improvement while reducing the maximum seismic event magnitude and preventing short circulation during the production. We presented coupled hydro-mechanical modellings of the hydroshearing process on natural fractures for both the single stage and multi-stage stimulation strategies. The modellings have demonstrated that the single stage stimulation commonly caused the concentration of slip on the fracture with a higher initial aperture, potentially leading to large magnitude events. Adopting the strategy of multi-stage stimulation, it was able to develop the slip zone on multiple fractures and avoid. to induce large slip zone on specific fractures with a high initial aperture. It has been demonstrated there is general effectiveness of the multi-stage stimulation on homogenizing and enlarging the stimulated reservoir area with the lowering of possible maximum seismic event magnitude.

Slip localization in Inconel 718: A three-dimensional and statistical perspective

The slip localization behavior of the polycrystalline nickel base superalloy Inconel 718 during monotonic tensile loading at room temperature, is investigated for the first time in relation to the 3D microstructure. Multi-modal data merging tools are used to recombine high resolution digital image correlation (HR-DIC) data with 3D electron back-scatter diffraction tomography (3D EBSD), over a wide region of interest. This procedure enables reconstruction of the slip band planes in the 3D microstructure. Statistical analyses conducted over 500 individual slip bands reveal strong correlations between their location and specific microstructure configurations. In particular, over half of the slip bands emanate from triple junction lines (3D lines defined by the junction of three crystals). Moreover, the most intense and longest slip bands, which would become critical fatigue crack nucleation sites during cyclic loading, are located close and parallel to particular annealing twin boundaries and are simultaneously connected to triple junction lines. Crystal plasticity finite elements calculations are performed on the experimental microstructure to identify the slip activity that results in the formation of high intensity slip bands (localized plasticity) or zones of high lattice rotation (non-localized plasticity) in these particular microstructure regions.

Indentation of an elastic half-space by the cylindrical flat punch with a rounded edge under non-monotonic loading

The paper presents a novel approach to solving the contact problem for interaction with friction between a rigid cylindrical flat punch with rounded corners and a linearly elastic half-space. Increasing and decreasing normal loads act on the punch sequentially. Coulomb’s law is used to account for friction. The contact problem is reduced to nonlinear operator equations that must be solved at each step of the discrete loading process. The numerical method is applied. This method includes regularization of the equation, discretization of the regularized equations and the usage of an iterative process to obtain the approximate solution. The calculations were performed for different values of the relative radius of the flat area of the punch base. Distributions of contact traction and configuration of the stick and slip zones are studied at each monotonic stage of the loading process.

Напряженное состояние в контакте колеса и рельса при наличии скольжения и сцепления

Objective: Predicting the stress-strain state of a wheel or rail during their interaction depending on the normal pressure. Methods: The study of the stress-strain state in the car wheel and in its contact with the rail using the finite element method with all possible combinations of loading factors and taking into account the influence of temperature, dynamic influences, contact parameters, fatigue phenomena and the forces of interaction between the wheel and the rail are calculated, determining the stress state of the wheel, wear and deterioration of the contact surfaces and, as a consequence, the reliability of the carriage and traffic safety. Results: The effect of tangential loads on the stress-strain state when there is sliding in the wheel-rail contact zone was evaluated. The parameters of dangerous stresses are given depending on the axial load. Experimental and theoretical approaches to determining the stress-strain state of contacting elements in the presence of both slip and adhesion in the wheel-rail contact are shown. The components of the stress tensor are obtained depending on the contact pressure according to the calculation formulas. Diagrams of the distribution of shear stresses in the contact of the wheel with the rail in the presence of a zone of adhesion and sliding are made. The intensity of the stress state change in the wheel-rail contact is calculated. Practical importance: The results obtained show how the slip and adhesion zones affect the stress state in the contact zone in comparison with full slip. They are useful from the point of view of predicting the stress-strain state of a wheel or rail during their interaction depending on the normal pressure.

Slip behavior of high-density polyethylene at small shear stresses in the presence of esterified polyethylene glycol

Viscoelastic instabilities in polymer melts can be mitigated using polymer processing aids (PPAs) that impose slip between melts and substrates. In this study, the effect of a newly synthesized esterified polyethylene glycol (PEG) on the slip behavior of a high-molecular-weight high-density polyethylene at small shear stresses was investigated. Rheological measurements were employed to capture the dependence of slip velocities on shear stress and calculate extrapolation lengths and friction coefficients. Our findings showed that the incorporation of PEG-based PPA increased slip velocities while an increase at temperature suppressed slip. At 190 °C, there was a strong slip zone at shear stresses smaller than 9 kPa for all samples with and without PEG. In this zone, the extrapolation length showed ascending and descending behavior while its values were almost constant beyond this zone. The incorporation of PEG-based PPA at 190 °C doubled the extrapolation length from 300 to 600 μm and amplified its variation in the first zone. The study of the slip behavior at 210 °C revealed that the samples did not experience the first zone. They showed a second zone with extrapolation lengths well below 100 μm, signifying the presence of a weak slip regime. This study highlights the importance of PPAs in altering the slip mechanisms for high-molecular-weight polymer melts.

Coseismic fault lubrication by viscous deformation

Despite the hazard posed by earthquakes, we still lack fundamental understanding of the processes that control fault lubrication behind a propagating rupture front and enhance ground acceleration. Laboratory experiments show that fault materials dramatically weaken when sheared at seismic velocities (>0.1 m s−1). Several mechanisms, triggered by shear heating, have been proposed to explain the coseismic weakening of faults, but none of these mechanisms can account for experimental and seismological evidence of weakening. Here we show that, in laboratory experiments, weakening correlates with local temperatures attained during seismic slip in simulated faults for diverse rock-forming minerals. The fault strength evolves according to a simple, material-dependent Arrhenius-type law. Microstructures support this observation by showing the development of a principal slip zone with textures typical of sub-solidus viscous flow. We show evidence that viscous deformation (at either sub- or super-solidus temperatures) is an important, widespread and quantifiable coseismic lubrication process. The operation of these highly effective fault lubrication processes means that more energy is then available for rupture propagation and the radiation of hazardous seismic waves. Viscous deformation is a potentially prevalent mechanism of fault lubrication during earthquakes, according to laboratory experiments that simulate seismic faulting of various rock-forming minerals.

Experimental study of unsaturated-saturated permeability characteristics of slip zone soil in deposits

Experimental study of unsaturated-saturated permeability characteristics of slip zone soil in deposits

Formation of Nanocrystalline and Amorphous Materials Causes Parallel Brittle‐Viscous Flow of Crustal Rocks: Experiments on Quartz‐Feldspar Aggregates

AbstractThe brittle‐viscous transition in the lithosphere occurs in a region where many large earthquakes nucleate. To study this transition, we sheared bimineralic aggregates with varying ratio of quartz and potassium feldspar. We deformed the samples in a solid‐medium deformation apparatus at temperature, T = 750°C and pressure, Pc = 800 MPa under either constant displacement rate or constant load boundary conditions. Under constant displacement rate, samples reach high shear stress (τ = 0.4–1 GPa depending on mineral ratio) and then weaken. Under constant load, the strain rate shows low sensitivity to stress below τ ≈ 400 MPa, followed by a higher stress sensitivity (stress exponent, n = 9–13) at higher stresses irrespective of mineral ratio. Strain is localized along “slip zones” in a C and C′ orientation. The material in the slip zones shows extreme grain size reduction and flow features. At peak strength, 1–2 vol% of the sample is composed of slip zones that are straight and short. With increasing strain, the slip zones become anastomosing and branching and occupy up to 9 vol%; this development is concomitant with strain‐weakening of the sample. Slip zones delimit larger cataclastic lenses, which develop a weak foliation. Our results suggest that strain localization leads to microstructural transformation of the rocks from a crystalline solid to a fluid‐like material in the slip zones. The measured rheological response is a combination of viscous flow in the slip zones and cataclastic flow in coarser‐grained lenses and can be modeled as a frictional slider coupled in parallel with a viscous dashpot.

Research on stability analysis of structural loess slopes based on combined tensile-compression-shear strength theory

The long-term stable existence of western high and steep loess slopes is closely related to the special structural properties of loess, and there are often tensile stress areas at the top of the slope. It is important to evaluate the stability of upright slopes by reasonably considering the tensile strength of loess. Based on the combined tensile-compressive-shear strength theory of structural loess, the structural parameter field, displacement increment contour distribution field and small principal stress distribution field law characteristics of an upright slope are analyzed and studied by using the finite method of strength discounting. The results show that when there is no load or constant load on the top of the slope, the structural parameter distribution field and displacement increment contour field of the slope show an obvious “slip zone”, and the “slip zone” becomes more and more shallow with the increase of water content; when there is a uniform load on the top of the slope, the slip zone becomes more and more shallow with the increase of water content. When there is a uniform load at the top of the slope, the “shear zone” becomes more and more shallow with the increase of load intensity, and the surface uniform load intensity is bigger with the same water content, and there is a risk of local sliding; when there is no load at the top of the slope or the load remains unchanged, the small main stress field of the slope has different degrees of tension zone penetration, and the smaller the water content is, the bigger the tension zone is, and the amplitude is also bigger; when the slope has no load at the top of the slope or the load remains unchanged, the small main stress field of the slope has different degrees of tension zone penetration. The smaller the water content is, the larger the tensile zone is, and the amplitude is also large; when there is a uniform load on the top of the slope, the location of the tensile zone on the slope changes, shifting from the original back edge of the slope surface to a certain range on the top of the slope, and with the increase of the load strength, the tensile zone becomes smaller and smaller, and with the increase of the water content, the tensile zone also becomes smaller and smaller.

To the development of the theory of contact interaction in two-roll modules

The results of the study of the stress-strain state in a two-roll module are presented. The angles that determine the characteristic points of the physical model of the roll contact curves are defined for the case when the strain properties of the material layer and elastic roll coatings are given by power dependences. Formulas are derived for calculating the angles of entering and exit, the angles separating the no-slip zones from the lag and advance slip zones, neutral angles and angles of maximum normal stresses of the two-roll module. It was stated that an increase in the friction coefficient of the roll with the material being processed leads to a decrease in the percentage of slip zones in the contact curve in the driven roll. It was revealed that with an increase in the dynamic coefficient, the slip lag zone decreases, and the advance slip zone increases. It was determined that the faster the feeding rate of the material layer, the greater the percentage of the no-slip zone in the roll contact curve. It was revealed that in the driven roll the neutral angle is inclined towards the entrance of the material layer into the contact zone of the rolls.

Variations in the Characteristic Amplitude of Tectonic Tremor Induced by Long‐Term Slow Slip Events

AbstractLong‐term slow slip events (L‐SSEs) often excite short‐term slow slips events (S‐SSEs) and tectonic tremor in the zone of episodic tremor and slip (ETS). However, the factors controlling the occurrence of primary versus excited tremor events remain unclear. To elucidate these factors, we analyzed tectonic tremor events in and around the Bungo Channel (Nankai subduction zone), where L‐SSEs are known to excite tremor and S‐SSEs in the ETS zone. We focused on the spatial distribution of the characteristic amplitude (CA) of tremor, determined from the duration‐amplitude distributions of tremor events, as an indicator of the properties of the tremor source. CAs are large in L‐SSE slip areas and small in adjacent areas. The difference between CA values during tremor‐excitation periods (L‐SSEs) and the intervening periods (ΔCA) is positive in the slip area, negative in adjacent areas, and tends toward zero in the far field. We suggest that the heterogeneous distributions of CA and ΔCA reflect the heterogeneous effective strengths of tremor patches, which might be related to petrological properties, and stress and pore‐fluid pressure variations induced by L‐SSEs, respectively. The upward migration of fluid from the ETS zone along the plate interface might modulate the effective stress and strength states of tremor patches during L‐SSEs.

Correlation of porosity variations and rheological transitions on the southern Cascadia megathrust

The unknown onshore extent of megathrust earthquake rupture in the Cascadia subduction zone represents a key uncertainty in earthquake hazard for the Pacific Northwest that is governed by the physical state and mechanical properties of the plate interface. The Cascadia plate interface is segmented into an interseismically locked zone located primarily offshore that is expected to rupture in large earthquakes, a region of aseismic slow slip at greater depth, and an intervening transition zone of uncertain rupture potential. Here we image the evolution of the ratio of seismic compressional to shear wave velocities from the locked zone to the transition zone, which is related to changes in fluid content of the plate boundary zone, using a dense onshore–offshore seismic dataset from southernmost Cascadia. The locked zone shows evidence of high fluid content implying a high porosity, yet the downdip transition zone shows an order of magnitude lower porosity. This strong variation is consistent with models that contain a ductile region between the earthquake rupture and slow slip zones that would inhibit onshore propagation of future large earthquake ruptures and hence reduce seismic hazard. The transition between the locked and slowly slipping regions of the southern Cascadia megathrust has a lower porosity than these regions, according to seismic imaging. This suggests that the transition area is ductile, which may limit rupture propogation.

Thermal Weakening Friction During Seismic Slip: Experiments and Models With Heat Sources and Sinks

AbstractExperiments that systematically explore rock friction under crustal earthquake conditions reveal that faults undergo abrupt dynamic weakening. Processes related to heating and weakening of fault surfaces have been invoked to explain pronounced velocity weakening. Both contact asperity temperature Ta and background temperature T of the slip zone evolve significantly during high‐velocity slip due to heat sources (frictional work), heat sinks (e.g., latent heat of decomposition processes), and diffusion. Using carefully calibrated High‐Velocity Rotary Friction experiments, we test the compatibility of thermal weakening models: (1) a model of friction based only on T in an extremely simplified, Arrhenius‐like thermal dependence; (2) a flash heating model which accounts for the evolution of both V and T; (3) same but including heat sinks in the thermal balance; and (4) same but including the thermal dependence of diffusivity and heat capacity. All models reflect the experimental results but model (1) results in unrealistically low temperatures and model (2) reproduces the restrengthening phase only by modifying the parameters for each experimental condition. The presence of dissipative heat sinks in stage (3) significantly affects T and reflects on the friction, allowing a better joint fit of the initial weakening and final strength recovery across a range of experiments. Temperature is significantly altered by thermal dependence of (4). However, similar results can be obtained by (3) and (4) by adjusting the energy sinks. To compute temperature in this type of problem, we compare the efficiency of three different numerical approximations (finite difference, wavenumber summation, and discrete integral).

The Constitutive Model of a Unidirectional SiC Fiber-Reinforced Titanium Matrix Composite During Spectrum Loading

An approach to simulate the constitutive model of a unidirectionally SiC fiber-reinforced titanium matrix composite during spectrum loading was developed in this paper. Based on the assumption that there is a microcrack in the matrix and the maximum shear stress criterion, the debonding length and the distribution of interfacial slip zone under spectrum loading were derived. The stress at a loading point was divided into four stages including crack opening section, positive slip zone, reverse slip zone, and bond zone. Based on the partial crack shear-lag model, the stress of fiber and matrix in the four stages was derived, and the constitutive model of the composite under spectrum loading was established. At last, the effects of different damages on the constitutive model and interfacial debonding zone of a unidirectionally SiC fiber-reinforced titanium matrix composite were investigated.