Static Stress Changes Research Articles

Insights from Dynamically Triggered and Induced Earthquakes in Oklahoma

AbstractIn the last decade, induced seismicity (earthquakes incited by anthropogenic activity) has drastically increased resulting from subsurface waste-water fluid injection and CO2 sequestration. In addition, seismologists have observed large (M ≥ 7) earthquakes that can trigger other earthquakes via (1) changes in static stress and (2) imposed transient dynamic stressing related to seismic waves generated by a mainshock. Although the exact mechanism for dynamic triggering remains uncertain, observations of earthquake triggering may reveal mechanisms that lead to earthquake failure. Given well-documented instances of induced earthquakes and fluid injection in Oklahoma, we investigate the occurrence of dynamic triggering and mechanisms of failure in the region. We analyze 124 M ≥ 7 remote earthquakes across a seven-year period (2010–2016), utilizing seismic data retrieved from EarthScope’s USArray Transportable Array, the Oklahoma Seismic Network, and a template matched earthquake catalog for Oklahoma to identify dynamically triggered earthquakes. We also identify previously uncataloged events through a short-term to long-term average ratio energy detector and analyst inspection of waveforms. We quantify the results using several statistical approaches to identify significant increases in local seismicity rates following the P-wave arrival of each remote mainshock. We identify 26 mainshocks that dynamically trigger either instantaneous or delayed earthquakes in Oklahoma. We conclude that mainshock transient stresses appear to contribute to natural and induced stress states in Oklahoma and can advance the earthquake cycle in the region. Our results emphasize the identification of instantaneous dynamic triggering; however, we also capture delayed triggering (i.e., past the first few hours following a mainshocks wavetrain passes). We find triggered earthquakes correlate well with regions of sustained fluid injection in Oklahoma, suggesting that increased pore fluid pressure may be lowering the effective normal stress across faults in the region and, thus, increasing susceptibility to transient stressing especially by Rayleigh waves.

Prediction of principal stresses due to external load in sans mass considering its mechanical characteristics

Introduction. A part of the methods for designing earthworks and foundations is based on solutions for predicting the stress state of soils under the action of an external load, which do not take into account the structural features of the material. This is in conflict with current studies, which indicate that changes in the moisture content, density, and shape of material particles entail changes in the mechanism of stress state formation. According to some research, when the type of soil, moisture content and density of the mass change, both its mechanical characteristics and the stress state change, which requires consideration in the design of earthworks and building foundations.The method of research. To study the stress state arising in sandy soil with different mechanical characteristics, experimental studies were carried out to determine the pressures in sand of different density and moisture under the action of an external load from a round stamp with an area of 500 cm2. To do this, at a depth of 5, 15, 25, 40 cm along the axis of a round stamp in an array of sand of medium size, mesdoses were set, after which the pressures were measured when the load was applied. For each value of density and moisture created during the experiment, the mechanical characteristics of the sandy soil were determined.Results. The analysis of the existing dependencies for predicting the maximum principal stresses showed that the Kandaurov and Frohlich’s solutions are the only ones that give a connection between the formation of the stress state and mechanical characteristics and allow predicting the minimum principal stresses. The influence of the mechanical characteristics of sandy soil (the angle of internal friction and the modulus of elasticity at different density and humidity) on the Frohlich’s parameter and the distribution capacity coefficient of the medium of the Kandaurov’s solution was established.Conclusion. The analysis of the results of experimental studies made it possible to derive dependencies for predicting the maximum principal stresses of sandy soil at points located at different depths along the axis of a loaded round stamp. The proposed dependencies are a modification of Kandaurov and Frohlich’s solutions, which take into account the relationship between the mechanical characteristics of sandy soil and the parameters of the distribution capacity of the medium.

Anisotropic 4D seismic response inferred from ultrasonic laboratory measurements: A direct comparison with the isotropic response

AbstractPore‐pressure depletion causes changes in the triaxial stress state. Pore‐pressure depletion in a flat reservoir, for example, can be reasonably approximated as uniaxial compaction, in which the horizontal effective stress change is smaller than the vertical effective stress. Furthermore, the stress sensitivity of velocities can be angle‐dependent. Therefore, time‐lapse changes in reservoir elastic anisotropy are expected as a consequence of production, which can complicate the interpretation of the 4D seismic response. The anisotropic 4D seismic response caused by pore‐pressure depletion was investigated using existing core velocity measurements. To make a direct comparison between the anisotropic 4D seismic response and the isotropic response based only on vertical velocities, pseudoisotropic elastic properties were utilized, and the two responses were compared in terms of a dynamic rock physics template. A comparison of the dynamic rock physics templates indicates that time‐lapse changes in reservoir elastic anisotropy have a noticeable impact on the interpretation of 4D seismic data. Changes in anisotropy as a result of pore‐pressure depletion cause a time‐lapse amplitude variation with offset response as if there is a reduction in VP/VS (i.e., pseudoisotropic VP/VS decreases), although the vertical VP/VS increases. The impact of time‐lapse changes in anisotropy on the amplitude variation with offset gradient was also investigated, and the time‐lapse anisotropy was found to enhance changes in the amplitude variation with offset gradient for a given case.

Strengthening mechanism of 2219 Al-Cu alloy by room-temperature random vibration

Conventional thermal strengthening treatments face the challenges of high energy consumption, environmental pollution, and low coordination between strength and toughness. This study attempted to suppress these imperfections by proposing a novel approach that employed room-temperature random vibration (RRV). The microstructures were analyzed by scanning electron microscopy and transmission electron microscopy in detail. The 2219 Al-Cu alloy is in a tension–compression bidirectional stress state during random vibration, and its stress state changes with frequency, which induces dislocation movement and multiplication. The dislocation movement eventually develops into a dislocation network, resulting in the dislocation pinning effect. Notably, the dislocation migration promotes the diffusion of solute and forms solute clusters owing to tension–compression deformation. The content of the coarse second phase particles (CSPP) decreased greatly with a small narrow precipitate-free zone (PFZ) width after random vibration treatment. The tensile and yield strength were improved by 13.5% and 17.6%, respectively, after RRV treatment. The ductility increases simultaneously, differing from conventional heat treatment processes, which is attributed to the joint action effect of dislocations, second-phase particles, and solute clusters. The findings confirm a new route for Al-Cu alloys to obtain excellent mechanical properties and provide valuable insight into the strengthening mechanism of room-temperature random vibration.

A new statistical damage model for true triaxial pre-and post-peak behaviors of rock considering intermediate principal stress and initial compaction effects

Deep underground engineering excavation will induce complex change in the true three-dimensional stress state of the surrounding rock, causing rock damage and then leading to a change in mechanical properties. In this research, the true triaxial compression tests are conducted to study the influence of σ2 and σ3 on the mechanical properties of marble, such as the characteristic strength (crack initiation stress σci, damage stress σcd, peak strength σp, and residual strength σr), post-peak deformation, ductility and brittleness. The peak strength σp, crack initiation stress σci and damage stress σcd of rock increase with the increase in σ2, while the variation of residual strength σr with σ2 is different from that of peak strength. As σ2 increases or σ3 decreases, the pre-peak plasticity of the rock decreases, the post-peak curve shape of the rock changes significantly, and the overall shape of the post-peak curve transforms from Class I to Class II. The Mogi-Coulomb strength criterion with intermediate principal stress effect was used to characterize the rock microelement strength, and then the new statistical damage constitutive model considering the initial compaction effect and damage threshold was proposed, and the model validation was carried out based on the experimental results and the effects of the proposed model parameters m and F0 on the rock strength and post-peak curve morphology were further explored.

Spatial and temporal variation of aseismic creep along the dilational jog of the West Valley Fault, Philippines: Hazard implications

Accelerated creep, primarily through vertical displacement, has been occurring along 15 en-echelon faults belonging to a 15 km-long and 1.5 km-wide, N-S-trending dilational jog of the active West Valley Fault (or West Marikina Valley Fault), on the southeastern part of Metro Manila, Philippines. The much-larger-than-known tectonic slip rates had been the only reliable evidence in support of excessive groundwater withdrawal as the trigger of creep in the 1990s. Recently available groundwater extraction data (1977–2019) could more directly and consistently link groundwater withdrawal to accelerated creep in the 1990s. Twenty years (1999–2019) of precise displacement measurements could also reveal significant spatial and temporal links between slip rate changes and patterns of groundwater extraction. Our analysis shows that greater rates of vertical displacement are related to the timing of faster extraction rates. Variations in slip rates between the northern and southern measurement sites are primarily due to regional differences in groundwater extraction, which are influenced by differences in the implementation of water extraction reduction regulations. Proximity to the key source of groundwater recharge (Laguna Lake) is also an influencing factor. Although there are many unknowns inherent to this type of study, continued depressurization could induce static stress changes that could modulate the timescale of earthquake occurrence due to the natural course of stress loading driven by regional tectonics. The current and potential effects of continued depressurization in the areas with high slip rates and surrounding regions are paramount considerations in crafting and implementing tighter and extended groundwater extraction regulations.

Time-varying elastic wave mode conversion in vibrating elastic beams with subwavelength nonlinearity

Introduction of time-varying properties in a background medium can enable unconventional wave behavior. Furthermore, it is well-known that subjecting nonlinear materials to time-varying stress can be used for material characterization [Appl. Phys. Lett. 94, 011905 (2009)]. We propose a technique called Dynamic Asymmetric Transmission Measurement (DATM) that combines structural dynamic (SD) and ultrasonic (US) testing modalities in an elastic waveguide to detect and characterize changes in the global stress state of a structure that result in local time-varying stress conditions due to local nonlinearity. Asymmetric geometric features in beams and plates, paired with time-varying stress conditions, result in asymmetric mode conversion of guided US waves that depend on large-scale structural dynamics. The DATM technique is explored through finite element modeling, semi-analytical methods, and experiments and discussed in a structural health monitoring context. We also discuss the use of dynamic structures with engineered defects to introduce time-varying stress conditions for the purpose of manipulating elastic waves. [Sandia National Laboratories is a multimission laboratory managed and operated by the National Technology & Engineering Solutions of Sandia, LLC, a wholly owned subsidiary of Honeywell International Inc., for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-NA0003525.]

ПОРІВНЯННЯ РОБОТИ БАГАТОПОВЕРХОВИХ СТАЛЕВИХ КАРКАСІВ ПРИ ПОЖЕЖІ ЗА РІЗНИХ ПОЧАТКОВИХ УМОВ ТА ЇХ ВПЛИВ НА ЖИВУЧІСТЬ

The researches devoted multi-storey buildings steel frames fire vitality was analyzed. It was found that the existing measures to increase the viability significantly increase the frames metal content. No detailed analysis of potential destruction mechanisms depending on different initial conditions has been identified. The need to research the frame elements stress state during a fire before the first destruction and subsequent potential mechanisms of destruction for a better vitality understanding. This publication analyzes the stress state of 2d multi-storey steel frames during a fire. Various frame elements load capacity factor dependence graphs on time are done. The frames operation in case of fire with different beam-to-column connections and different fire source locations are compared. It was found that during a fire in the beam frame elements, the stress state changes from bending to compressed-bent. It has been established that the frame elements should be designed in such a way that plastic deformations appear before local buckling occurs. It is necessary to design sections according to the Eurocode classification, where there is a classification depending on the geometry. The frames operation in case of fire with different initial load capacity factor is compared. It was found that in no the frame element temperature before the first onset of the limit state does not reach 400oC, at which the steel yield strength begins to decrease. It is established that the frames fire resistance of is more influenced not by the steel characteristics reduction, but by the forces distribution. The frames with rigid and hinged beam-to-column connections are compared in terms of vitality and fire resistance. It is established that frames with hinged connections are more fire-resistant, and with rigid connections ‒ more vitally to fire. The method of increasing the time to steel frame vitality loss is determined.

Comparison of the effect of water jet cavitation peening on stress corrosion cracking behavior of nickel-based alloy 600 and alloy 182 in high temperature water

PurposeThis paper aims to understand the effect of water jet cavitation peening (WJP) on stress corrosion cracking (SCC) behavior of alloy 600 and alloy 182 in high temperature water.Design/methodology/approachSurface and cross-section morphology, grain boundary microstructure, residual stress and strain distribution, hardness and surface roughness in water jet cavitation peened alloy 600 and alloy 182 were characterized.FindingsA superior stress corrosion cracking resistance was obtained in 600MA, which can be attributed to the formation of the ultrafine grain layer and the higher magnitude residual compressive stress.Originality/valueRelationship between WJP-induced microstructure and stress state change and SCC susceptibility was conducted. It could provide a theoretical basis for developing application of WJP in nuclear power plants.

Numerical simulation and experimental investigation of bending deformation mechanism during post-rolling air cooling of AH36 L-beam

L-beam is a widely used structural steel. The study of the three-stage bending deformation mechanism of L-beam under non-uniform cooling conditions is of great significance to ensure the quality, improve the yield of steel, and reduce the stress level in the finished L-beam. However, it is difficult to investigate experimentally due to the high temperature and simultaneous changes of various influencing factors during the air-cooling process of the L-beam. Numerical simulation provides a convenient and feasible method to study the bending deformation mechanism of the L-beam. To investigate the effects of phase transformation and cooling shrinkage on the bending deformation of AH36 L-beam, a three-dimensional thermal-metallurgical-mechanical coupling model was established in this study; the microstructure distribution, hardness, strain, deformation status, and stress during the air cooling of L-beam were calculated. The results show that the microstructure distribution and deformation condition calculated by the model considering the phase transformation effect better agree with the actual situation. Considering the phase change effect is the key to improving the accuracy of the model calculation. The change of heat transfer coefficient caused by phase transformation affects the deformation tendency of the L-beam, while the transformation strain affects the amount of deformation of the L-beam. The alternating changes in the sum of the transformation strain and the cooling shrinkage strain result in a change of stress state which ultimately also results in a three-stage bending deformation of the L-beam.

The continuous Airy-based for stress-singularities (CASS) method: an energy-based numerical formulation for unilateral materials

Unreinforced masonry buildings represent a large part of the world's architectural heritage. Despite their significant diffusion, their mechanical behaviour is still subjected to increasing scientific investigations as modelling difficulties arise from the negligible tensile strength in tension. Because of this unilateral response, masonry constructions can flexibly accommodate different loading and displacement-like boundary conditions in a new deformed configuration through the formation of crack patterns. The internal stress state changes accordingly and can be represented through stress singularities. Defining the internal stress states compatible with general boundary conditions is primarily essential from an engineering perspective.This paper presents the Continuous Airy-based for Stress-Singularities (CASS) method, a new numerical strategy to model the internal stress state in unilateral materials, whose main peculiarity is the ability in describing singular stress fields independently of the discretisation. The internal equilibrium is guaranteed using the Airy stress potential discretising the domain with plate-type finite elements. The compatibility with boundary displacements is satisfied through a variational formulation based on the minimum of the Total Complementary Energy. The boundary value problem is then reduced to a second-order cone programming where the linear objective function represents the work of the emerging stress for the boundary displacements, and the constraints enforce the boundary equilibrium and the material compatibility. The CASS method is benchmarked against analytical solutions and other numerical strategies on several 2D problems, also used to illustrate and discuss its main features. Lastly, a real masonry façade is considered to show the method's effectiveness clearly.

Fractal Seismicity and Coulomb Stress Pattern Analysis for 7 January 2020 Mw 6.4 Puerto Rico Earthquake

Abstract This study aims to understand the variation of the correlation fractal dimension and static stress changes associated with the 2019 Puerto Rico sequence with special reference to the January 2020 Mw 6.4 mainshock. On examining the seismicity data from 1988 to 2020, we find a shift in the seismicity pattern after the 2019 Puerto Rico sequence. A detailed examination of changes in the correlation fractal dimension (Dc) indicates diffused seismicity throughout the study region until the year 2003 that is demonstrated by relatively high Dc values. Toward the end of 2019, a drastic drop in Dc is observed; it is associated with a tight clustering of events to the south-southwest of Puerto Rico Island (PRI), suggesting the onset of the 2019 sequence. We observed a persistent clustering and significant drop in Dc before the Mw 6.4 earthquake, hinting at the presence of a numerical precursor for this event. Over 30 yr of historical earthquakes have contributed positive Coulomb stress distributions mainly in the northern region of PRI. A deflection in this pattern was reflected after the 2019 Puerto Rico sequence. Based on the static stress analysis, we demonstrated that the Mw 6.4 mainshock was triggered by the 2019 Puerto Rico sequence. The new cluster of events, which contains the Mw 6.4 mainshock, exhibits higher stress levels in the south-southwest region of PRI. The eastern end of Septentrional fault (SF), the zone between SF and North Puerto Rico Slope fault, the middle segment of South Puerto Rico Slope fault, South Lajas fault, Punta Montalva fault, and Central fault are the highly stressed regions at present. Stress perturbation induced by the destructive Mw 6.4 event on the adjacent fault system is a potential threat for PRI, where population density is very high. The combined analysis of Dc and static stress changes indicates the presence of a numerical precursor and highly stressed regions southwest of PRI.

Geological constraints on dynamic changes of fluid pressure in seismic cycles

Fluid pressure along faults plays a significant role in fault behaviors in seismic cycles in subduction zones. When a thermal pressurization event occurs, the fluid pressure rises; conversely, when a fault-valve behavior event occurs, the fluid pressure falls. The stress state changes with seismic cycles from a reverse fault regime to a normal fault regime, as observed in both geophysical observations and geological records. Fluid pressure has been estimated for both modern accretionary prisms and exhumed accretionary complexes. However, changes in fluid pressure on seismogenic faults have not been connected to seismic cycles. Here, we quantitatively show the dynamic change in fluid pressure in a seismogenic fault with geological evidence from an exhumed accretionary complex. We found extensional veins related to seismogenic fault records that exchanged stress states the during seismic cycles. We also constrained the fluid pressure quantitatively, both at an increasing stage during an event and at a decreasing stage after an event. In this procedure, we propose new methods to constrain the magnitude of vertical stress and rock tensile strength.

Stress State Change and Fault-Slip Tendency Assessment Associated with Gas Injection and Extraction in the Hutubi (China) Underground Gas Storage

Summary The Hutubi (HTB) gas reservoir in northwest China was active in production from 1998 to 2012; beginning in 2013, it was used for gas storage. Several earthquakes occurred during the early operation of the Hutubi underground gas storage (HTB-UGS) project, so it is important to explore their relationship with gas injection and extraction from the viewpoint of stress state change and faulting susceptibility. We study the evolution of the stress state and slip tendency associated with the operation of the HTB-UGS to understand the relationship between pore pressure variation and induced seismicity. We constrain the stress state in the reservoir at the time of cessation of production in 2012 using image-logged wellbore breakouts. We then estimate stress state variation over time as a result of pore pressure changes, based on the assumption of poroelastic coupling between horizontal elastic stresses and pore pressure. The maximum principal stress in the reservoir region before the HTB-UGS operation is oriented N23°±6°E, which is consistent with that of the prevailing tectonic stress derived from earthquake focal mechanisms. Our results show that the vertical stress (Sv) and the minimum horizontal principal stress (Shmin) were initially similar in magnitude before petroleum production; the magnitude of Shmin gradually decreased during petroleum production. Gas injection, initiated in 2013, raised the Shmin magnitude, returning it to approximately that of Sv. We use the estimated variations in the reservoir stress state over time to calculate temporal changes in slip tendency of the main faults in the reservoir. The fault-slip tendency decreased continuously with petroleum production and then increased with gas injection. The first earthquake swarm associated with gas injection occurred approximately 2 months after the start of injection, possibly due to the slow pore pressure diffusion. Thereafter, earthquakes were induced whenever gas was injected. Our assessment of slip tendency suggests that earthquake swarms were induced during increasing pore pressure phases when slip tendency reached a value of 0.43 ± 0.04. The maximum allowable pore pressure for avoiding earthquakes (ML > 1.5) is 29.0 ± 4.5 MPa, which might increase through stress adjustments and a newly attained balance. This study provides a possible method for induced earthquake analysis associated with gas injection and extraction from the perspective of stress state change and faulting susceptibility.

The Effect of Mining Remnants on Elastic Strain Energy Arising in the Tremor-Inducing Layer

A vast majority of hard coal deposits in Poland have a multi-seam structure, hence the presence of mining remnants left from previous operations. The impact of those remnants (exploitation edges or residual pillars) can further intensify geomechanical phenomena occurring in the rock mass, leading to changes in the original state of stress. This applies to all layers within the rock strata, including thick and coherent ones (referred to as tremor-inducing layers) where the impacts of mining remnants are likely to trigger tremors, thus enhancing the rock bursts hazard. In the light of the geomechanical model of rock strata recalled in the study, it is assumed that homogeneous and isotropic elastic layers are found between the considered mining remnant (which is revealed as the stress distribution), and the rock medium modelled as a homogeneous and isotropic half-plane. Development of the state of stress in the bedded medium was brought down to the analysis of interacting elastic layers, where the biharmonic equation is satisfied for each layer and for each respective half-plane. This equation can be solved by the integral Fourrier transform method. The impacts of the exploitation edge and the residual pillar on the elastic strain energy in the tremor-inducing layer is illustrated by recalling the Burzyński’s stress criterion. Strain energy in the tremor-inducing layer was analysed for various deformation properties of the surrounding strata and for various methods of coal extraction from the seam underneath the tremor-inducing layer. The results of the study evidence that a change in deformation properties of strata in the vicinity of the tremor-inducing layer may affect the state of stress and strain energy, which impacts on the tremor hazard levels in the vicinity of mining remnants areas.

Assessing the fracture and fatigue resistance of nanostructured thin films

Fatigue failure through sustained loading of ductile materials manifests in irreversible motion of dislocations, followed by crack initiation and growth. This contrasts with the mechanisms associated with brittle ceramics, such as nanostructured physical vapor deposited thin films, where inhibited dislocation mobility typically leads to interface-controlled damage. Hence, understanding the fatigue response of thin films from a fundamental viewpoint – including altered atomic bonds, crystal structures, and deformation mechanisms – holds the key to improved durability of coated engineering components. Here, a novel method utilizing quasi-static and cyclic-bending of pre-notched, unstrained microcantilever beams coupled with in situ synchrotron X-ray diffraction is presented to study the fracture toughness and fatigue properties of thin films under various loading conditions. Investigating a model system of sputter-deposited Cr and Cr-based ceramic compounds (CrN, CrB2, and Cr2O3) demonstrates that the fatigue resistance of such thin films is limited by the inherent fracture toughness. In fact, cantilever cycling close to the critical stress intensity is sustained up to 107 load cycles on all materials, without inducing noticeable material damage, structural or stress-state changes. The observed variation in fracture toughness is put into context with linear-elastic fracture theory and complementary micro-pillar compression, thereby elucidating the wide range of values from as low as 1.6±0.2 MPa√m for Cr1.79O3 up to 4.3±0.3 MPa√m for Cr1.03B2, respectively. Moreover, possible mechanisms governing the elastic-plastic deformation response of all coatings, both in quasi-static and cyclic-loading conditions, are discussed. Our findings contribute key-insights into the underlying mechanisms dictating the damage tolerance of PVD coated components by relating fatigue strength limits to fundamental material properties.

Mechanical behavior and interfacial damage of carbon steel-stainless steel corrosion resisted-alloy (CRA) cladded plate: Hybrid analysis based on experiment and finite element modeling

The deformation behavior of a hot roll-bonded stainless steel/carbon steel (STS/CS) clad plate is investigated by focusing on the mechanical properties-microstructure relationship along the plate thickness and clad interface. In detail, the mechanical responses of the STS/CS clad plate and its constituents are evaluated using uniaxial tension, interfacial debonding tests (in normal and shear modes), and various microstructure characterization techniques, which clarify the interfacial heterogeneity of the STS/CS clad plate. The results of experimental analysis present the validity for applying a hybrid numerical–experimental identification procedure for the cohesive zone model (CZM) in the simulation of heterogeneous STS/CS interface using finite element (FE) method. Especially, the mixed-mode bilinear CZM coupled with the inhomogeneously distributed elastic-plastic properties over thickness can be optimized to accurately predict the measured load-displacement curves and springback in the two debonding tests and the V-bending test. Finally, the interfacial failure characteristics of the STS/CS clad are further presented through the comparison between the FE method and fractography analysis at the clad interface. The combined experimental and numerical study reveal interesting aspects beyond commonly reported interfacial behavior. These include: (1) The failure along the STS/CS clad interface is controlled by both “material factors” such as the carbon migration from the interface and its resultant differential strengthening through the thickness, and “process factors” that includes the gradient of strength and temperature across the clad and rolling tools. (2) The major deformation mode is variable according to locations and the mixed normal-shear mode is dominant at tool contacts for initiating the failure during the V-bending test. (3) The interfacial failure mechanism of cladding featured not only in a confined deformation zone where contact directly with tools, but also the exterior area where springback after unloading caused a drastic change of stress state. These abrupt interfacial failures could be clarified via stress state and local damage analysis of the well-reproduced FE model of cladding material.

Spatiotemporal Distribution of Shallow Tremors Along the Nankai Trough, Southwest Japan, as Determined From Waveform Amplitudes and Cross‐Correlations

AbstractShallow slow earthquakes in subduction zones are related to spatiotemporal variations of stress on the plate boundary adjacent to a megathrust earthquake. A dense network (DONET) of cabled ocean‐bottom seismometers (OBSs) deployed in the Nankai Trough seismogenic zone, southwest Japan, has enabled real‐time monitoring of tremors. Because the amplitudes of tremor signals are very low, even when recorded by OBSs, we developed a hybrid method that simultaneously uses traveltimes based on cross‐correlations and amplitudes of waveforms to determine tremor hypocenters. We applied our method to waveforms observed during five years of continuous DONET recording from April 2016 to September 2021 to detect more than 6,500 tremors, including three major episodes in 2016, 2018, and 2020–2021. The tremors of each episode were distributed over distances of >100 km along the trench axis in two regions, southeast of the Kii Peninsula and off Cape Muroto. We also estimated seismic energy rates and found that for the three major tremor episodes, energy rates increased gradually with time. The 2018 and 2020–2021 episodes began near a subducted seamount and a subducted ridge, respectively, and were likely related to fluid movements controlled by the topography of the downgoing plate. We showed that the tremors were spatiotemporally synchronized with slow slip events, and their spatial variations of energy rate corresponded to stress heterogeneity on the shallow plate boundary. Future real‐time monitoring of shallow tremors will contribute to our understanding of changes of stress state due to slow earthquakes at the shallow plate boundary.

On the Patterns and Scaling Properties of the 2021–2022 Arkalochori Earthquake Sequence (Central Crete, Greece) Based on Seismological, Geophysical and Satellite Observations

The 27 September 2021 damaging mainshock (Mw6.0) close to Arkalochori village is the strongest earthquake that was recorded during the instrumental period of seismicity in Central Crete (Greece). The mainshock was preceded by a significant number of foreshocks that lasted nearly four months. Maximum ground subsidence of about 18 cm was estimated from InSAR processing. The aftershock sequence is located in an almost NE-SW direction and divided into two main clusters, the southern and the northern ones. The foreshock activity, the deformation area, and the strongest aftershocks are located within the southern cluster. Based on body-wave travel times, a 3-D velocity model was developed, while using combined space and ground-based geodetic techniques, the co-seismic ground deformation is presented. Moreover, we examined the co-seismic static stress changes with respect to the aftershocks’ spatial distribution during the major events of the foreshocks, the Mw = 6.0 main event as well as the largest aftershock. Both the foreshock and the aftershock sequences obey the scaling law for the frequency-magnitude distribution as derived from the framework of non-extensive statistical physics (NESP). The aftershock production rate decays according to the modified Omori scaling law, exhibiting various Omori regimes due to the generation of secondary aftershock sequences. The analysis of the inter-event time distribution, based on NESP, further indicates asymptotic power-law scaling and long-range correlations among the events. The spatiotemporal evolution of the aftershock sequence indicates triggering by co-seismic stress transfer, while its slow migration towards the outer edges of the area of the aftershocks, related to the logarithm of time, further indicates a possible afterslip.

Analysis of Multistorey RCC Frame subjected to Mainshock and Aftershock Earthquake

Abstract: Structure analysis and design are significantly influenced by earthquake. It is believed that seismic evaluation is required for the viability and serviceability of both present and future building structures. When a structure's base is subjected to a certain type of ground motion, a time history analysis is performed to examine the dynamic reaction of the structure at each time interval. The near-field earthquake ground motion verification may have specific impacts for both forward and backward directivity. The initial's velocity and displacement motions, respectively, exhibit pulse and fling-step characteristics. Therefore, it is crucial to assess how well structures built solely to withstand the primary shock would work through future aftershocks. Using modern seismic protection systems, such as base isolations or / and supplemental dampening devices, that significantly reduce building damages during main shocks and their related aftershocks is one of the appropriate solutions to this issue. Due to changes in both static and dynamic stress that take place during the earthquake process, aftershock events are set off by the primary shock. In order to better understand the ground motion features of a sizable collection of mainshock and subsequent aftershock ground motion data recorded in accelerograph stations around the region, this study reviews pertinent literature in the field. The G+9 RCC building will be used in this study to conduct a time history analysis of the mainshock and aftershock data of the Chamoli earthquake provided by the Centre for Engineering Strong Motion Research Ground Motion Database. For designing purposes, the IS 456-2000 code is taken into consideration. Live loads are measured in accordance with IS 875-part 1, and seismic zone IV is selected for analysis in accordance with IS 1893-2016. Storey drift, base shear, joint reactions, and storey displacement are just a few of the variables that can have an impact on how well a building performs. Since each of these variables has a significant impact on how a structure responds to seismic loads, they are also taken into account when evaluating the results.