Elastic Strain Accumulation Research Articles

Coupled crystal plasticity-phase field simulation of twin-twin interaction in magnesium

Twin-twin interactions significantly influence the mechanical properties of magnesium and its alloys. A thorough understanding of the underlying mechanisms governing these interactions is essential for designing Mg alloys with enhanced strength and toughness. In this work, a crystal plasticity-twin coupled phase field (CP-TPF) model incorporating multiple extension twin variants and considering the role of dislocation slipping is proposed to investigate the interactions between/among the same twin variants and those between co-zone twin variants in Mg single crystals. The model incorporates an additional energy term to represent the interaction among different twin variants and couples the CP and TPF models through order parameters and stress tensor. The simulated results show that the interaction between the same twin variants can either promote or inhibit the twin propagation, and multiple twins tend to generate concurrently in Mg single crystal to minimize the free energy associated with the accumulation of elastic strain. During co-zone twin-twin interaction, localized thickening of the recipient twin occurs due to the concentrated stresses induced by the intrusion twin, and the mutual extrusion of the two twins leads to blunting of the intrusion twin tip. Both the coalescence of the same twin variants and the formation of twin-twin boundaries between the co-zone twin variants contribute to the effective mechanism of twinning-induced hardening. Moreover, local dislocation accommodation plays a crucial role in twin-twin interactions. It relaxes the stress concentration near the twin tips and twin-twin boundaries and significantly contributes to the uneven migration of the twin boundary.

Selective Epitaxy of Germanium on silicon for the fabrication of CMOS compatible short-wavelength infrared photodetectors

Here we present the selective epitaxial growth of Ge on Si using reduced pressure chemical vapor deposition on SiO2/Si solid masks realized on 200 mm Si wafers, aiming at manufacturing integrated visible/short-wavelength infrared photodetectors. By a suitable choice of the reactants and of the process conditions, we demonstrated highly selective and pattern-independent growth of Ge microstructure featuring high crystalline quality. The Ge “patches” show a distinct faceting, with a flat top (001) facet and low energy facets such as e.g. {113} and {103} at their sidewalls, independently on their size. Interdiffusion of Si in to the Ge microcrystals is limited to an extension of ∼20 nm from the heterointerface. The Ge patches resulted to be plastically relaxed with threading dislocation density values better or on par than those observed in continuous two-dimensional Ge/Si epilayer in the low 107 cm−2 range. A residual tensile strain was observed for patches with size >10 μm, due to elastic thermal strain accumulation, as confirmed by μ-Raman spectroscopy and μ-photoluminescence characterization. Polarization-dependent Raman mapping highlights the strain distribution associated to the tridimensional shape. On this material, Ge photodiodes were fabricated and characterized, showing promising optoelectronic performances.

Fluid environment controls along-strike variation in slip style: Midcrustal geological signatures from the Red River fault, China

Abstract The slip style of continental midcrustal shear zones plays a crucial role in determining the seismogenic potential of faults, but it remains poorly understood because geological observations that can be directly tied to seismic behavior are scarce. We describe frictional-viscous shear zones in the Red River fault, China, which consists of two segments with distinct seismic behaviors and fluid availabilities. The northern segment hosts moderate to large earthquakes, and midcrustal fault slip is localized into mylonitized pseudotachylyte-bearing layers where dynamically recrystallized quartz records flow stresses exceeding 100 MPa and accelerated viscous creep. The southern segment is dominantly aseismic but active microseismically. Fault slip is accommodated in several mylonitized cataclasite layers, comprising interconnected biotite and intervening fractured clasts, with evidence for pervasive dissolution-precipitation creep. Microstructures, paleopiezometry, and microphysical modeling suggest transient aseismic slip in response to increased strain rates during viscous creep at <50 MPa. We interpret that along-strike variations in fluid environment control fault slip styles and seismic behaviors. The dry and strong northern segment is capable of nucleating large earthquakes, while greater fluid availability in the southern segment activates dissolution-precipitation creep at low driving stresses, which limits interseismic elastic strain accumulation at frictional-viscous transition depths. In this model, compaction-driven fluid pressurization and dilatant hardening are invoked to explain the aseismic slip transients in the southern segment.

Comparison of geodetic slip-deficit and geologic fault slip rates reveals that variability of elastic strain accumulation and release rates on strike-slip faults is controlled by the relative structural complexity of plate-boundary fault systems

Comparison of geodetic slip-deficit rates with geologic fault slip rates on major strike-slip faults reveals marked differences in patterns of elastic strain accumulation on tectonically isolated faults relative to faults that are embedded within more complex plate-boundary fault systems. Specifically, we show that faults that extend through tectonically complex systems characterized by multiple, mechanically complementary faults (that is, different faults that are all accommodating the same deformation field), which we refer to as high-Coefficient of Complexity (or high-CoCo) faults, exhibit ratios between geodetic and geologic rates that vary and that depend on the displacement scales over which the geologic slip rates are averaged. This indicates that elastic strain accumulation rates on these faults change significantly through time, which in turn suggests that the rates of ductile shear beneath the seismogenic portion of faults also vary through time. This is consistent with models in which mechanically complementary faults trade off slip in time and space in response to varying mechanical and stress conditions on the different component faults. In marked contrast, structurally isolated (or low-CoCo) faults exhibit geologic slip rates that are similar to geodetic slip-deficit rates, regardless of the displacement and time scales over which the slip rates are averaged. Such faults experience relatively constant geologic fault slip rates as well as constant strain accumulation rate (aside from brief, rapid post-seismic intervals). This suggests that low-CoCo faultsd "keep up" with the rate imposed by the relative plate-boundary condition, since they are the only structures in their respective plate-boundary zone that can effectively accommodate the imposed steady plate motion. We hypothesize that the discrepancies between the small-displacement average geologic slip rates and geodetic slip-deficit rates may provide a means of assessing a switch of modes for some high-CoCo faults, transitioning from a slow mode to a faster mode, or vice versa. If so, the differences between geologic slip rates and geodetic slip-deficit rates on high-CoCo faults may indicate changes in a fault's behavior that could be used to refine next-generation probabilistic seismic hazard assessments.

Monte Carlo Simulation of Heteroepitaxial Growth of Ge on Pit-patterned Si(100) Substrate and Parallelization of Calculations

Methods and algorithms of Monte Carlo simulation of heteroepitaxial growth of Ge on Si are considered. The computational complexity analysis of simulation program blocks is carried out. Parallelization of time-consuming cycles using directives of the open standard OpenMP is proposed. The Monte Carlo simulation of heteroepitaxial growth of Ge on pitpatterned Si substrate was carried out. The position of Ge nanoislands is determined by the competition between the nucleation process of three-dimensional islands due to the accumulation of elastic strain in the growing layer and the process of diffusion of Ge atoms into the pits serving as a drain.

Assessment of the seismic hazard in North China by combining micro-seismicity records and geodetic observations

North China has suffered numerous devastating historical and recent earthquakes, causing huge loss of life and property. Therefore, it is vital to identify the regions with the greatest potential to generate large earthquakes in the future. Previous studies mainly evaluated the seismic hazard in North China using earthquake records or geodetic methods separately. Here, we evaluated the seismic records and geodetic observations in combination to comprehensively assess the earthquake potential. We first evaluated the earthquake catalog and determined that the completeness range of magnitude is 1.9 to 2.8 based on the b-values estimated by magnitude-frequency distribution using catalogs with different minimum-magnitude cutoffs. We then obtained the spatial distributions of three strain rate parameters, including the maximum shear, the principal, and second invariant of the strain rates, using interseismic Global Navigation Satellite System (GNSS) observations. The robustness of the strain rate model was validated by comparing previous studies. We then analyzed the seismic hazard in North China based on the strain rates and b-values and determined the regions with relatively high seismic hazard potentials. The results suggested that large strain rates are mainly concentrated on the western border of the Ordos Block and the Tangshan fault zone. Different strain rate parameters yielded similar spatial distributions of recurrence intervals with different magnitudes. We further revealed that the western border of the Ordos Block and Tangshan fault regions exhibit relatively short (∼7000–15,000 year) ML 7.5 earthquake recurrence times, compared with those of other regions in North China. Although the results obtained in this study were limited by the completeness of earthquake records, the spatial distribution of the GNSS observation, the assumption of elastic strain accumulation, and the complexity of the mechanisms of intraplate earthquakes, our findings will contribute to the assessment of seismic hazards in North China.

Rate of E–W extension in the Volcanic Tableland, California (USA): A comparison of strain rates on two different timescales

Abstract The Eastern California shear zone (USA) is a broad zone of transtensional deformation related to the relative motion between the Pacific and North American plates. Due to its active deformation and seismicity, the zone receives great attention, with specific focus on slip rates of major active faults. To contribute to a better understanding of the long-term strain accumulation in this zone, this study quantifies the long-term E–W-directed extensional strain rate based on the analysis of N–S-trending normal fault scarps in the 765-k.y.-old Bishop tuff (Volcanic Tableland). The average extensional strain rate determined over the past 765 k.y. is 0.29 ± 0.10 mm/yr per 10 km (29 ± 10 nanostrain/yr) and similar to the current rate of elastic strain accumulation rate in the Volcanic Tableland (0.30 ± 0.13 mm/yr per 10 km; 30 ± 13 nanostrain/yr) determined by Global Positioning System (GPS) data. The present-day E–W strain rate across the entire Eastern California shear zone at the latitude of the Volcanic Tableland is 0.36 ± 0.05 mm/yr per 10 km (36 ± 5 nanostrain/yr). This suggests that the local rate of E–W extension has not changed significantly since the mid-Pleistocene. Furthermore, if the Volcanic Tableland is representative of the greater region, as the GPS data suggest, this would also indicate a constant extension rate across the Eastern California shear zone at the latitude of ~37.5°N over the 765 k.y. time period. These results suggest that late Pleistocene and Holocene extension rates of major faults in this zone can be interpreted in light of a presumably unchanged far-field stress system since at least the mid-Pleistocene.

Impact of hyper-elasticity on cyclic sand modelling: A numerical study based on SANISAND-MS

Accurate simulation of foundation response subjected to repeated loading require reliable sand constitutive models to reproduce realistic sand cyclic behaviour. Many elastoplastic constitutive models adopted the hypoelasticity law, which results in physically inaccurate strain accumulation prediction of soil when subjected to elastic cyclic loading. To address this issue, the existing elastoplastic bounding surface model SANISAND-MS has been upgraded with a hyperelastic formulation that is derived from the Helmholtz free energy function. The complete form of the derived nonlinear elasticity functions enhanced by stress induced anisotropy is presented in this work. The calibration of the upgraded SANISAND-MS is briefly discussed. It is demonstrated that the hyperelastic formulation with volumetric-deviatoric coupling: (1) guarantees no accumulation of elastic strain upon elastic cyclic loading, and (2) captures the stress-induced anisotropy of sand under reverse loading. This upgraded SANISAND-MS model with a physical adaptation and thermodynamically consistent elasticity law can predict strain accumulation accurately and is physically appropriate. Moreover, the upgraded SANISAND-MS is suitable for simulating problems with high-cyclic loads and is able to be used in boundary value problem simulations in areas including offshore engineering and railway engineering.

Spatiotemporal distributions of afterslip and locking on the plate interface associated with the 2011 Tohoku-Oki earthquake using a 3-D temperature and strain rate-dependent heterogeneous viscosity model

We introduced a novel approach to produce a 3D heterogeneous viscosity distribution model of the upper mantle below Northeast Japan. The viscoelastic relaxation constitutes a significant portion of the postseismic deformation associated with a megathrust earthquake. Our viscosity distribution was based on a 3D simulation of thermomechanical modeling with realistic 3D oceanic plate geometry and subduction velocity of the Pacific plate in the upper mantle. After obtaining the thermal and strain-rate distributions obtained from the thermomechanical modeling, 3D viscosity distribution was calculated. We used the resulting viscosity distribution in a viscoelastic relaxation model to calculate the viscoelastic response associated with the MW 9.0 2011 Tohoku-Oki earthquake, using a finite element method. We found it necessary to include an elastic cold nose in the mantle wedge and a low-viscosity layer at the subducted lithosphere-asthenosphere boundary to reproduce the observed onshore uplifts and landward horizontal displacements of the seafloor, respectively. We then divided the calculated viscoelastic displacements into 7 one-year intervals and subtracted them from the corresponding observed postseismic displacements to obtain yearly residual displacements. Assuming the residual displacements were the result of afterslip and subduction fault locking on the plate interface, we employed a time-dependent inversion to estimate the spatiotemporal distributions of afterslip and subduction fault locking. Our results showed decrease in the afterslip amount and extent over time, which primarily occurred during the first two years following the 2011 event, which is followed by gradual extension of the subduction fault locking region. We concluded that the plate interface off Northeast Japan is gradually entering an interseismic stage of interplate coupling and elastic strain accumulation within several years after the occurrence of the Tohoku-Oki earthquake.

Inherited Heterogeneities Can Control Viscous Subduction Zone Deformation of Carbonates at Seismogenic Depths.

This work links mineral-scale deformation mechanisms with structural evolution during subduction, providing examples showing how grain-scale heterogeneities facilitated viscous creep in calcite at nominally seismogenic temperatures. Carbonates commonly enter subduction zones, either highly concentrated in irregularly distributed sediments or as more distributed precipitates in seafloor volcanics. We present shear zones, localized in calcite veins formed during shallow subduction of calcareous sediment and seafloor volcanics, with viscous shear strains of ≥5. Shear strain localized because secondary phases and chemical variations maintained fine grain sizes in calcite aggregates, activating relatively rapid grain size-sensitive and frictional-viscous creep at temperatures (260±10°C), cooler than predicted from extrapolation of experimental data. Creep at increased strain rates may limit elastic strain accumulation during interseismic periods, reducing the likelihood of large megathrust earthquakes. As shown here for calcite, common inherited natural heterogeneities may induce weakening of viscous mechanisms in other rocks, or at larger scales in the lithosphere.

Accumulation of Elastic Strain toward Crustal Fracture in Magnetized Neutron Stars

This study investigates elastic deformation driven by the Hall drift in a magnetized neutron-star crust. Although the dynamic equilibrium initially holds without elastic displacement, the magnetic-field evolution changes the Lorentz force over a secular timescale, which inevitably causes the elastic deformation to settle in a new force balance. Accordingly, elastic energy is accumulated, and the crust is eventually fractured beyond a particular threshold. We assume that the magnetic field is axially symmetric, and we explicitly calculate the breakup time, maximum elastic energy stored in the crust, and spatial shear–stress distribution. For the barotropic equilibrium of a poloidal dipole field expelled from the interior core without a toroidal field, the breakup time corresponds to a few years for the magnetars with a magnetic-field strength of ∼1015 G; however, it exceeds 1 Myr for normal radio pulsars. The elastic energy stored in the crust before the fracture ranges from 1041 to 1045 erg, depending on the spatial-energy distribution. Generally, a large amount of energy is deposited in a deep crust. The energy released at a fracture is typically ∼1041 erg when the rearrangement of elastic displacements occurs only in the fragile shallow crust. The amount of energy is comparable to the outburst energy on the magnetars.

Megathrust reflectivity reveals the updip limit of the 2014 Iquique earthquake rupture

The updip limit of seismic rupture during a megathrust earthquake exerts a major control on the size of the resulting tsunami. Offshore Northern Chile, the 2014 Mw 8.1 Iquique earthquake ruptured the plate boundary between 19.5° and 21°S. Rupture terminated under the mid-continental slope and did not propagate updip to the trench. Here, we use state-of-the-art seismic reflection data to investigate the tectonic setting associated with the apparent updip arrest of rupture propagation at 15 km depth during the Iquique earthquake. We document a spatial correspondence between the rupture area and the seismic reflectivity of the plate boundary. North and updip of the rupture area, a coherent, highly reflective plate boundary indicates excess fluid pressure, which may prevent the accumulation of elastic strain. In contrast, the rupture area is characterized by the absence of plate boundary reflectivity, which suggests low fluid pressure that results in stress accumulation and thus controls the extent of earthquake rupture. Generalizing these results, seismic reflection data can provide insights into the physical state of the shallow plate boundary and help to assess the potential for future shallow rupture in the absence of direct measurements of interplate deformation from most outermost forearc slopes.

Contemporary state of stress in a stable plate interior (northern Poland): The integration of satellite geodesy, borehole and seismological data

In our study we examined the possibility of using strain rate data, determined from geodetic satellite measurements for estimations of magnitude of contemporary stress in a relatively stable area of northern Poland, comprised of fragments of the East European Craton, the Teisseyre-Tornquist Tectonic Zone and the Palaeozoic Platform. The strain rates and their principal directions were determined from 63 GNSS stations lacking special stabilization. The method for filtrating the unstable stations allowed us to eliminate half of these stations from the final strain rate calculations that included data averaging in a correlation radius of 150 km. A comparison of the horizontal strain directions determined by geodetic methods with the directions of contemporary stress based on borehole data (four of which were determined in this study) showed a high degree of convergence. Also the trends of strain rate variations showed consistency with integrated lithospheric strength of main tectonic units. The strain rates obtained are consistent with those published for the adjacent areas. Stress magnitudes were estimated by calibrating the timing of elastic strain accumulation by earthquakes in the Sambia Peninsula (Kaliningrad Oblast) and assuming a transient state of elastic strain on the craton. Our results indicate that the crystalline upper crust in the analysed part of the craton is in the strike-slip faulting stress regime prevailing over the normal faulting stress regime. The present state of an elastic strain has been accumulated over the last few million years causing stress being far from the critical state in the Mohr-Coulomb frictional criteria, except of the seismically active Sambia Peninsula.

Geodetic and Geological Deformation of the Island Arc in Northeast Japan Revealed by the 2011 Tohoku Earthquake

Northeast Japan is a typical island arc related to the Pacific plate subduction. The 2011 Mw9.0 Tohoku-oki earthquake provided a unique opportunity to analyze crustal deformation with different boundary conditions, similar to a gigantic rock deformation experiment. We review findings obtained through various observations and data analyses in Northeast Japan, focusing on the crustal deformation in different timescales. The occurrence of the M9 earthquake solved the ongoing paradox that the geodetic strain rate is an order of magnitude larger than the geologic estimate, showing that the centennial geodetic observation had mainly captured the elastic strain accumulation. Along the localized contraction zone along the Japan Sea coast, a comparison of postseismic and interseismic deformation patterns revealed a significant contribution of inelastic deformation, which plays an essential role in long-term deformation. Along the Pacific coast, rapid interseismic subsidence and unexpected coseismic subsidence were followed by a rapid postseismic uplift, indicating that viscous relaxation in the mantle is of essential importance. These findings advance our understanding of plate interactions and the tectonic evolution of the island arc. ▪ The 2011 Tohoku-oki earthquake provided the most complete crustal deformation data set ever for interseismic, coseismic, and postseismic periods. ▪ The discrepancy between the geologic and geodetic deformation rates in Northeast Japan is attributed to an elastic strain due to interplate locking. ▪ A significant contribution of inelastic deformation in the island arc crust is identified through a comparison of interseismic and postseismic deformations.

Crustal deformation analysis of Thessaly (central Greece) before the March 2021 earthquake sequence near Elassona-Tyrnavos (northern Thessaly)

Thessaly lies on the Aegean (micro-)plate, undergoing internal crustal deformation due to the plate relative motion against the adjacent Anatolian and Nubian plates. As a result, the whole Thessalian Basin was supposed to be under an extensional tectonic regime of N-S direction. However, the recent earthquake sequence of March 2021 which occurred close to the northwestern margin of the basin revealed NE-SW direction of extension. Based on 7-year GPS measurements recorded by stations installed within and around the basin we assessed four deformational parameters for Thessaly aiming at the understanding of the deformation processes that control the region. These parameters are i) the Maximum Horizontal Extension (MAHE), ii) the Total Velocity (TV), iii) the Maximum Shear Strain (MSS), and iv) the Area Strain (AS). The results show that during the monitoring period, Thessaly moved toward the S-SW with a simultaneous clockwise rotation and underwent dispersed deformation mostly associated with dilatation. Focusing on the epicentral area of the 2021 sequence, strain during the 7-year period was rather low in all three strain parameters, implying a mature stage of elastic strain accumulation before the fault rupture.

GPS Imaging of Vertical Bedrock Displacements: Quantification of Two‐Dimensional Vertical Crustal Deformation in China

AbstractThe Global Positioning System (GPS) derived bedrock displacements respond to multiple geophysical effects, ranging from surface elastic loads to tectonic sources or viscoelastic uplifts stemming from Earth’s viscous mantle. In this study, the GPS‐inferred vertical crustal velocities are rigorously estimated in mainland China. We integrate the GPS vertical velocity field with Gravity Recovery and Climate Experiment (GRACE) and GRACE Follow‐On (GFO) data, adopting an empirical Spatial Structure Function (SSF), to image tectonic deformation in mainland China with respect to the International Terrestrial Reference Frame (ITRF) 2014. We present four profiles across China, which indicate that our new robust results are superior to kriging. Furthermore, we use the GRACE/GFO products to account for elastic deformation due to surface mass changes to isolate tectonic deformation signals at GPS sites within mainland China from 2002 to 2019. By integrating GPS and GRACE/GFO measurements, our results reveal the long‐term spatial patterns of vertical tectonic motion in different blocks in mainland China. We conclude that significant steep velocity gradients occur at tectonic block boundaries that are attributable to locking and elastic strain accumulation on active block boundary faults.

Slip Rate of the Danghe Nan Shan Thrust Fault from 10Be Exposure Dating of Folded River Terraces: Implications for the Strain Distribution in Northern Tibet

AbstractThe northeastward motion of the Tibetan Plateau along the Altyn Tagh strike‐slip fault causes thrust faulting in three parallel mountain ranges (Qilian Shan, Daxue Shan, and Danghe Nan Shan) in the plateau interior, and leads to NNE‐directed crustal shortening and plateau growth. While slip rates at the plateau margin (i.e., along the Qilian Shan and the Altyn Tagh fault) are well constrained, rates of thrust faulting and the strain distribution in the plateau interior remain poorly resolved. Here, we use field investigations, a high‐resolution DEM, and 10Be exposure dating to quantify the shortening rate across the Danghe Nan Shan thrust fault from fluvial terraces, which are deformed by a growing NNE‐vergent anticline. 10Be exposure ages from two terrace levels range from 70 ± 5 to 92 ± 7 ka. When combined with uplift values of 37–68 m along the fold hinge, the 10Be ages yield a mean uplift rate of 0.6 ± 0.2 mm/year. Using the cross‐sectional area of the fold and the subsurface geometry of the listric thrust fault, we obtain a shortening rate of 0.8 ± 0.2 mm/year, which is consistent with the rate of elastic strain accumulation recorded by GPS data. Together with published fault slip rates and GPS data, our results indicate that northern Tibet experiences NNE‐directed shortening at a rate of ∼5 mm/year between the Qaidam Basin and the Hexi Corridor. In the plateau interior, this shortening is accommodated by several range‐bounding thrust faults and closely coupled with the eastward decrease in the slip rate of the Altyn Tagh fault.

Why is local stress statistics normal, and strain lognormal?

In the present study we elucidate the nature of local strain statistics evolution during tensile deformation in polycrystalline materials. A rate-independent formulation was implemented within a crystal plasticity framework by the means of representative volume element (RVE) analysis. Local elastic strain, as well as stress, were found to obey a normal distribution, whereas the statistics of local plastic strain conforms to a lognormal distribution. In line with experimental observations, the plastic strain becomes progressively localised and the local regions of large strains make significant contribution to the overall average strain increase. The results reveal the nature of strain inhomogeneity at the microscale and emphasize the fact that in metallic materials the elastic strain accumulation represents an additive process, whereas plastic deformation is a multiplicative process.

Seismicity and Active Faulting around the Metropolitan Area of Athens, Greece

ABSTRACTThe existence of active faults near large cities poses significant risk to the life and property of its inhabitants as well as to its public infrastructure. Here, we investigate the interplay between seismicity, active faulting, and interseismic strain accumulation within a radius of ∼50 km from the metropolitan area of Athens, the capital of Greece. We find that during the period 2011–2018, a total of 4722 earthquakes were recorded, the majority of which had local magnitudes <3.0 with only four events being of moderate magnitude (ML 4.1–4.3). Precise relative locations with horizontal and vertical errors of ≤1 and 2 km, respectively, were obtained for 2666 of these events using the double-difference algorithm. Earthquake relocation was compared to the surface traces of 31 active and 49 “less-active” normal faults drawn from high-resolution (∼5 m pixel size) digital elevation models and complemented by analysis of geodetic data from 30 permanent Global Positioning System (GPS) stations. Joint analysis of these datasets suggests that microseismicity mostly clusters along the “less-active” faults, whereas the faults associated with impressive postglacial scarps (indicating recent activity) and historic seismicity are mostly quiet. Interestingly, GPS data indicate that both fault types currently accumulate elastic strain that ranges from 0.5 to 2.3 mm/yr. Based on their estimated rupture area, more than half of the recorded faults (N=54) are capable of generating earthquakes with moment magnitudes between 6.0 and 6.6. Although some of these sources are characterized by impressive postglacial scarps, many others have long earthquake recurrence intervals (i.e., have not ruptured during the past ∼16 ka) and are associated with intense microseismicity and elastic strain accumulation, calling for future investigations on their seismogenic potential.

Influence of Loading Sequence on Low Cycle Fatigue Behavior of Normal Weight Concrete under Direct Tension

Abstract Under seismic action, concrete can be considered to be subjected to multistage constant cyclic loads. Moreover, the failure of concrete is predominantly manifested in cracking caused by tension. This article studies the dynamic mechanical properties of concrete specimens under direct cyclic tension. According to the experimental results, this article discusses selections of damage parameters and the establishment of the evolution model on the basis of elastic modulus degradation and plastic strain accumulation. According to reasonable damage parameters, the damage evolution mechanism is investigated to propose a modified model, by which the failure process and the fatigue life of concrete under cyclic loading can be predicted. Additionally, the proposed damage evolution model is used to analyze the experimental data of the related literature and this study, which both turn out a good match in the prediction.