Static Stress Changes Research Articles

Experimental study on the effect of unloading rate on the damage of coal with boreholes

In coal mining, the gas pre-drainage boreholes in front of working faces are often repeated loading and unloading. Studying the failure characteristics of boreholes under cyclic loading has a guiding significance for clarifying the failure mechanism of gas pre-drainage boreholes. To simulate the influence of the advancing speed of the working face on the deformation instability of the borehole, a cyclic loading path under the influence of different unloading rates was designed. In this paper, the uniaxial cyclic loading test was conducted by the DYD-10 testing machine, and the variation law of mechanical strength characteristics with the unloading rate was obtained. Combined with digital image technology (XTDIC), the sample deformation characteristics were analyzed. The samples' compressive strength rose with the unloading rate. The sample was damaged in the tensile-shear composite form at different unloading rates. Crack opening displacement (COD) with the increase in the number of cycles shows a “stepwise” increase. Near the moment of destruction, COD suddenly increased. The number of surface fractures that could be seen reduced as the unloading rate increased, and reduced fragmentation when the sample failed. The various types of energy of the sample increase nonlinearly with the increase of the number of cycles, and the plastic damage energy drops as the unloading rate increases. When the external stress state enters the next stress state, the internal stress adjustment of the sample takes a particular time, which is manifested as lagging behind the change of the external stress state. The influence mechanism of stress adjustment lag on strength, crack evolution and damage under different unloading rates was proposed. The results of the study contribute to the research of destabilization control technology for gas pre-drainage boreholes.

Shallow Tectonic Stress Magnitudes at the Hikurangi Subduction Margin, New Zealand

AbstractQuantifying tectonic stress magnitudes is crucial in understanding crustal deformation processes, fault geomechanics, and variable plate interface slip behaviors in subduction zones. The Hikurangi Subduction Margin (HSM), New Zealand, is characterized by along‐strike variation in interface slip behavior, which may be linked to tectonic stress variations within the overriding plate. This study constrains in situ stress magnitudes of the shallow (<3 km) overriding plate of the HSM to better understand its tectonics and how they relate to larger scale subduction dynamics. Results reveal σ3: Sv ratios of 0.6–1 at depths above 650–700 m TVD and 0.92–1 below this depth interval along the entire HSM. Additionally, for depths below 650–700 m TVD, SHmax: Sv ratios of 0.95–1.81 in the central HSM and 0.95–2.3 in the southern HSM are estimated. These stress ratios suggest a prevalent thrust to strike‐slip (σ1 = SHmax) faulting regime across the central and southern HSM. In the central HSM, the presence of NNE‐NE striking reverse faults co‐existing with a modern σ1 (SHmax) aligned ENE‐WSW suggests that overtime the stress state here evolved from a contractional to a strike‐slip state, where the compressional direction changes from perpendicular (NW‐SE) to oblique (ENE‐WSW) to the Hikurangi margin. This temporal change in stress state may be explained by forearc rotation, likely combined with the development of upper plate overpressures. In the southern HSM, the modern WNW‐ESE/NW‐SE σ1 (SHmax) and pre‐existing NNE‐NE striking reverse faults indicate that stress state remains contractional and perpendicular (NW‐SE) to the Hikurangi margin overtime.

3D Dynamic Rupture Modeling of the 6 February 2023, Kahramanmaraş, Turkey Mw 7.8 and 7.7 Earthquake Doublet Using Early Observations

Abstract The 2023 Turkey earthquake sequence involved unexpected ruptures across numerous fault segments. We present 3D dynamic rupture simulations to illuminate the complex dynamics of the earthquake doublet. Our models are constrained by observations available within days of the sequence and deliver timely, mechanically consistent explanations of the unforeseen rupture paths, diverse rupture speeds, multiple slip episodes, heterogeneous fault offsets, locally strong shaking, and fault system interactions. Our simulations link both earthquakes, matching geodetic and seismic observations and reconciling regional seismotectonics, rupture dynamics, and ground motions of a fault system represented by 10 curved dipping segments and embedded in a heterogeneous stress field. The Mw 7.8 earthquake features delayed backward branching from a steeply branching splay fault, not requiring supershear speeds. The asymmetrical dynamics of the distinct, bilateral Mw 7.7 earthquake are explained by heterogeneous fault strength, prestress orientation, fracture energy, and static stress changes from the previous earthquake. Our models explain the northward deviation of its eastern rupture and the minimal slip observed on the Sürgü fault. 3D dynamic rupture scenarios can elucidate unexpected observations shortly after major earthquakes, providing timely insights for data-driven analysis and hazard assessment toward a comprehensive, physically consistent understanding of the mechanics of multifault systems.

Long-Term Recurrence Pattern and Stress Transfer along the Kefalonia Transform Fault Zone (KTFZ), Greece: Implications in Seismic Hazard Evaluation

An effort is exerted to investigate the recurrence pattern of large earthquakes (Mw ≥ 6.0) in the Kefalonia Transform Fault Zone (KTFZ), Greece, by considering the incorporation of the 74-year (1948–2022) evolving stress field. Four earthquake occurrence models—the Poisson, Poisson with the incorporation of the static stress changes (Poisson + ΔCFF), Brownian passage time (BPT) and Brownian passage time with the incorporation of the static stress changes (BPT + ΔCFF)—have been applied to estimate the occurrence probabilities of nearly characteristic earthquakes for the seven fault segments of the study area. The mean recurrence time, Tr, is estimated using the physics-based seismic moment rate conservation method. The results show large variability depending upon fault parameters. Incorporating the state of stress into Tr results in both advanced and delayed recurrence patterns. The occurrence probability estimates for the next 10, 20 and 30 years indicate that the fault segment most likely to be ruptured is the Paliki North fault segment in all models. Overall, the occurrence probabilities, combined with the state of stress along the fault segments, emphasize the high seismic moment rate of the study area. The application of time-dependent models (BPT, BPT + ΔCFF) resulted in significant increases or decreases in the associated seismic hazard.

Improvement and Evaluation of a Device That Determines the Interfacial Shear Strength of Carbon Fiber/Polyphenylene Sulfide Composites.

This study improved homemade apparatus for characterizing the interfacial shear strength (IFSS) of carbon-fiber-reinforced polyphenylene sulfide (PPS/CF) composites. The upgraded generation II experimental device includes a newly developed experimental clamp for samples, as well as testing systems. Compared with the initial generation I apparatus and the commercial Toei instrument, the generation II device is easier and more efficient to operate. The average interfacial adhesion values obtained using these devices were consistently approximately 40 MPa, with relatively low data scatter, showing excellent repeatability and applicability during microbond tests. Notably, the generation II experimental device was equipped with an additional high-frequency data-capturing tool to identify the debonding peak force more precisely, which demonstrated a higher interfacial shear strength of 42.81 MPa during testing. Therefore, the new instrument was able to reflect the change in the interfacial stress state during the interface debonding process more accurately and reliably.

Use of Bender Elements to Evaluate Linkages between Thermal Volume Changes and Shear Modulus Hardening in Drained and Undrained Thermal Triaxial Tests

Abstract This study investigates linkages between volume change, pore fluid drainage, shear wave velocity, and temperature of soft clays using a thermal triaxial cell equipped with bender elements, a measurement approach that has not been explored widely in past thermo-mechanical studies. Two kaolinite specimens were consolidated mechanically to a normally consolidated state and then subjected to drained and undrained heating-cooling cycles, respectively. After cooling, the specimens were subjected to further mechanical consolidation to evaluate changes in apparent preconsolidation stress. Both specimens showed net contractive thermal strains after a heating-cooling cycle and overconsolidated behavior during mechanical compression immediately after cooling. The shear wave velocity increased during drained heating, but negligible changes were observed during drained cooling, indicating permanent hardening because of thermal consolidation during the heating-cooling cycle. The shear wave velocity decreased during undrained heating because of a reduction in effective stress associated with thermal pressurization of the pore fluid but subsequently increased when drainage was permitted at elevated temperature. The shear wave velocity increased slightly during undrained cooling but decreased when drainage was permitted at room temperature. Net increases in small-strain shear modulus of 17 and 11 % after heating-cooling cycles under drained and undrained (with drainage after reaching stable temperatures) conditions, respectively, provide further evidence to the potential of thermal soil improvement of normally consolidated clays. Transient changes in shear modulus also highlight the importance of considering drainage conditions and corresponding changes in effective stress state during heating-cooling cycles.

Coseismic Kinematics of the 2023 Kahramanmaras, Turkey Earthquake Sequence From InSAR and Optical Data

AbstractWe derive the ALOS‐2 coseismic interferograms, pixel‐offsets and Sentinel‐2 sub‐pixel offsets of the 2023 Mw7.8 and Mw7.7 Kahramanmaras, Turkey earthquake sequence. Offset maps show that the sequence ruptured ∼300 km along the East Anatolian Fault (EAF) and ∼180 km along the secondary Cardak and Dogansehir faults. We infer the coseismic slip distribution and interseismic fault motion by inverting the co‐ and inter‐seismic observations. Inversion results show that the coseismic slip (∼8.0 m) and interseismic strike‐slip rate (∼4.6 mm/yr) on the main rupture of the Mw7.8 event are basically consistent with the ∼8.4 m and ∼3.9 mm/yr of the Mw7.7 event. Most coseismic slips of the Mw7.8 and Mw7.7 events occur within 10 and 12 km at depth, respectively, in keeping with the interseismic locking depth of 10.4 ± 3.3 km and 11.1 ± 3.1 km. This implies that the coseismic rupture kinematics correlate with the interseismic strain accumulation. Moreover, static stress changes show that the Mw7.7 event is likely promoted by ∼2 bar stress increase from the Mw7.8 event on the central section of its main rupture.

The 2023 Mw 7.8 and 7.6 Earthquake Doublet in Southeast Türkiye: Coseismic and Early Postseismic Deformation, Faulting Model, and Potential Seismic Hazard

Abstract On 6 February 2023, Mw 7.8 and 7.6 earthquakes struck southeast Türkiye and northwest Syria. They are the largest earthquakes in Türkiye in over 80 yr, causing significant damage and fatalities. We used Advanced Land Observation Satellite-2 and Sentinel-1 Synthetic Aperture Radar images to obtain near-field coseismic displacements by Differential Interferometric Synthetic Aperture Radar (DInSAR) and pixel offset tracking (POT). Discontinuities of the surface deformation suggest that the Mw 7.8 event ruptured ∼320 km along the East Anatolian fault, and the Mw 7.6 event ruptured ∼150 km near Elbistan, southern Türkiye. We inverted these earthquakes' fault geometry and slip distribution based on Global Navigation Satellite Systems, DInSAR, and POT displacements. The estimated fault slip model shows that the first Mw 7.8 event ruptured a steeply southeast-dipping fault, and the seismogenic fault of the second Mw 7.6 event is north-dipping with complex geometry. The dip angle of subfaults of the Mw 7.6 earthquake decreases from east to west. Faults responsible for the two earthquakes are dominated by left-lateral strike-slip motion, with the maximum slip of ∼9.1 m. Early postseismic deformation within two months exhibits displacement discontinuities in the Amanos and Pazarcık segments and the Çardak fault, suggesting that the afterslip partially compensated the coseismic slip deficit at the shallow depths. Furthermore, static Coulomb failure stress changes induced by the two earthquakes indicate that the southwestern Pütürge segment of the East Anatolian fault has a high risk of future rupture.

Creep Instability Mechanism and Control Technology of Soft Coal Roadways Based on Fracture Evolution Law

To address the challenging issues of large deformation, control difficulties, and susceptibility to failure in the support structure of soft coal roadways, this study utilizes the CVISC block creep model in UDEC software. The model incorporates Coulomb slip without cohesive contact to simulate the characteristics of soft coal, such as its loose, fragile, and small-block nature. Additionally, a soft coal nonlinear discrete element creep model is developed to investigate the creep characteristics of soft coal under triaxial compression, with the aim of revealing the underlying creep destabilization mechanism in soft coal tunnels. Based on the research findings, a primary, strong active support technology is proposed. This approach involves the use of high-preload, high-strength anchor rods and anchor cables, as well as the implementation of steel mesh and plastic woven mesh to enhance surface protection. The study highlights that: (1) The shear cracks inside the coal body of the soft coal specimen transform into tensile cracks under external force, leading to an increase in the number of tensile cracks. This is an important symbol of accelerated creep in soft coal. Improvement in peripheral pressure helps inhibit the generation of tensile cracks inside the specimen. (2) The rapid development of creep and inter-particle tensile fissures within the coal body particles themselves, along with the change in stress state after the excavation of the roadway, are the main reasons for the overall creep damage of the roadway. (3) The support force in the early stage of shed cable support is small, which cannot inhibit the accelerated development of tensile fissures. This leads to continuous deformation of the roadway, resulting in the failure of the support structure in the later stage and aggravated roadway damage. (4) The new support technology helps control surface deformation by enhancing the strength of the roadway protection surface. This suppresses the development speed and number of tensile fissures during roadway deformation, improves the starting strength of the roadway for accelerated creep, and enables effective control of the overall deformation of the soft coal roadway. Thus, the effectiveness of roadway support is remarkable.

New Insight on the Active Fault System in the Halmahera Volcanic Arc, Indonesia, Derived from the 2022 Tobelo Earthquakes

Abstract On 9 January 2022, two shallow earthquakes occurred in the east arm of Halmahera, Indonesia, with magnitudes of Mw 5.2 and 5.4 felt at III–V modified Mercalli intensity. The existence of the causative fault for the earthquakes was unknown. One possible explanation is that the earthquakes were caused by the activity of an inactive fault striking in the southeast–northwest direction, and possibly linked to the volcanic activities in Halmahera. Thus, further analysis of their characteristics is crucial to identify the previously an inactive fault. In this study, we relocated the associated earthquake hypocenters using the double-difference method with an updated velocity model, and determined the focal mechanisms by employing full waveform inversion using moment tensor analysis. The focal parameters were used to analyze the static stress changes. The relocated hypocenters show specific hypocenter clusters, aligning in the north–south direction, associated with left-lateral faulting mechanisms. This north–south alignment differs from the northeast–southwest trend of some other active faults in Halmahera. We propose that the newly found Tobelo fault dips at an angle of around 80° to the west. The seismic stress change from the mainshock and the foreshock of the Tobelo earthquakes corresponds with the distribution of the aftershocks. A detailed analysis of unidentified faults in the high seismicity area is essential to comprehend the tectonic study of Halmahera Island and its seismic hazard assessments.

Theoretical study on dynamic stress redistribution around circular tunnel with different unloading paths

This study presents a solution for stress redistribution induced by dynamic excavation of a rock tunnel in hydrostatic and non-hydrostatic stress states. Considering rock as an elastic medium, the analytical solution of dynamic excavation unloading was derived in the Laplace transform space utilizing the wave function expansion method and mode decomposition, and transformed into the time domain using the approximate numerical inversion method. The effects of the unloading path (linear, cosine, and exponential), unloading rate, and initial stress state on stress redistribution were analyzed. The analytical results indicated that a high unloading rate led to a high stress concentration and oscillations around the tunnel, and instantaneous dynamic unloading caused 20–30% stress concentration. When dynamic unloading is complete, the stress state around the tunnel converges to the Kirsch solution. The 3D numerical results indicated that deformation of the tunnel boring face increased as the initial stress increased. Moreover, the accumulation and release of strain energy and stress state change paths were analyzed and discussed. The results of this study provide a theoretical basis for understanding the stress adjustment and failure of surrounding rock induced by excavation of deep-buried openings in hydrostatic and non-hydrostatic stress states.

Time-lapse imaging of seismic scattering property and velocity in the northeastern Japan

Investigating spatio-temporal changes in crustal structure is a key to understanding the dynamic processes in the earth's crust associated with large earthquakes and volcanic activities. The dense seismic network in the northeast part of Japan (Tohoku region) allows us to apply seismic interferometry to continuous records of ambient noise data for studying crustal changes related to the 2008 Mw 6.9 Iwate-Miyagi Nairiku earthquake and the 2011 Mw 9.0 Tohoku-oki earthquake. We track changes in both seismic scattering properties and velocities over five years and spatially localize them based on the coda wave decorrelation and travel time sensitivity kernels calculated from the solution of the radiative transfer equation. The 2008 Iwate-Miyagi Nairiku earthquake caused significant changes in both seismic scattering properties and seismic velocities in the vicinity of the epicenter subjected to dynamic or/and static stress perturbations. Changes in scattering properties associated with the 2011 Tohoku-Oki earthquake around some active volcanoes in the Tohoku region are likely related to geofluid migrations triggered by strong vibrations during the large earthquake. The decrease in seismic velocity exists mainly along the eastern coastal region and extends to the central Quaternary volcanic chains under the combined dynamic and static stress changes by the earthquake. The waveform correlation is possibly sensitive to the fluid content and might be a useful indicator of fluid migration in the crust. This is the first comprehensive demonstration and comparison of the spatio-temporal changes of seismic scattering properties and velocities at long-term and regional scales under the influence of two large earthquakes.

Focal Mechanism and Regional Fault Activity Analysis of 2022 Luding Strong Earthquake Constraint by InSAR and Its Inversion

On 5 September 2022, an Ms6.8 magnitude earthquake occurred in Luding County, Sichuan Province, China. Based on Sentinel-1 SAR images, this paper uses the D-InSAR approach to obtain the displacement field of the earthquake, invert the coseismic sliding distribution, and then calculate the static coulomb stress changes of the coseismic deformation on the aftershock distribution and surrounding faults. Further, the seismic structure is analyzed and discussed. The InSAR coseismic deformation field demonstrates that the maximum LoS displacement of the surface deformation caused by the Luding earthquake is about 15 cm. The Luding Ms 6.8 earthquake is dominated by the Moxi fault, which is a left-lateral strike-slip fault that ruptures along the NNW-SSE trend at about 160.3°, and the dip is 81°. The fault depth is mainly 5~15 km, the maximum sliding amount is about 174.8 cm, and the corresponding depth is 8.5 km. The seismic moment tensor obtained by inversion is 1.06 × 1019 Nm, Mw = 6.65. The Coulomb stress generated by the Luding earthquake on the northern end of the Anninghe fault zone exceeded the trigger threshold. The risk of the Anninghe fault’s future earthquake was greater, and continuous monitoring and risk assessment were required.

Measurement of strain and determination of stress state using a multi-chamber vertical cylindrical tank model

Designing a new construction of large-volume multi-chamber tanks or converting existing single-chamber tanks into multi-chamber for storage of various types of petroleum products is a very demanding and responsible job, from the aspect of strain-stress analysis and the need to ensure structural integrity. From a wide range of conducted theoretical and experimental-numerical research, this paper singles out the applied method of similarity mechanics. The research was performed on a model of a four-chamber tank with dimensions reduced by 20 times (1:20) in relation to the real tank, made of steel sheets of quality S.0361. During the cold-water pressure test on the tank model (hydro test), the change of strain and stress state was monitored in the zones that were defined as critical by the preliminary numerical analysis by the finite element method (FEM). The results of these measurements, along with other reliable methods, can be very useful in the design of multi-chamber tanks with 5.000 m3 volume.

Absolute stress levels in models of low-heat faults: Links to geophysical observables and differences for crack-like ruptures and self-healing pulses

Absolute levels of stress on faults have profound implications for earthquake physics and fault mechanics. A number of observations suggest that well-developed, mature faults such as the San Andreas Fault are generally “weak,” i.e. operate at much lower levels of shear stress compared to the higher expected shear resistance ∼100 MPa at seismogenic depths. In particular, low heat flow measurements suggest shear stress levels of ∼10 MPa or less on highly localized faults. Geodynamic constraints based on topography and similar considerations also support “weak” fault operation, and are comparable with heat-based constraints for some mature faults, but potentially higher for regions with substantial topography. Here, we investigate measures of average fault shear stress and their relationship to geophysically inferable quantities using numerical simulations of earthquake sequences on rate-and-state faults with low heat production, due to chronic fluid overpressure and/or enhanced dynamic weakening from the thermal pressurization of pore fluids. We review the earthquake energy balance, focusing on energy-based definitions of average shear stress and how the average fault prestress (a measure of fault strength plausibly relevant to geodynamic constraints) can be expressed as the sum of the dissipation-based average rupture stress (which can, in principle, be inferred from shear-heating constraints), and seismologically inferable source properties, such as the static stress drop and apparent stress. Our modeling demonstrates that rapid dynamic weakening and healing of shear resistance during ruptures, as exhibited in self-healing pulses, allows faults to maintain higher average interseismic stress levels despite low dynamic resistance and realistic static stress drops, providing a physical explanation for potential differences between topography-based and heat-based constraints on fault shear stress. In our models, the difference is related to stress undershoot and apparent stress, which can be as large as 1-3 times the static stress drop based on our simulations. Yet suitably large values of apparent stress (and hence radiated energy) are rarely inferred for natural earthquakes, either because radiated energy is underestimated, or suggesting that most large earthquakes do not propagate as sharp enough self-healing pulses with sufficiently large undershoot. Our results emphasize the distinction between dynamic versus static stress changes when relating earthquake source observations to absolute levels of fault stress and suggest that reviewing estimates of radiated energy and static stress drop from large earthquakes, with input from finite-fault numerical modeling, may improve constraints on absolute fault stress levels.

Source mechanisms and triggering process for the April 12th and 13th, 2014 earthquake doublet in the Solomon Islands

Mw 7.6 and Mw 7.4 earthquakes occurred 16 h apart on April 12 and April 13, 2014, at depths of 15 km and 35 km, respectively, southwest of Makira Island (San Cristobal) in the Solomon Islands. We study the source mechanisms to investigate the interrelation between the two events, and to investigate why the Solomon Islands have a historically high rate of doublet earthquakes. Teleseismic P waveform data for both events were used to obtain the slip distributions for the two earthquakes by a finite fault slip inversion method. The Mw 7.6 event is an east–west left-lateral strike slip, where the maximum slip is observed 8–24 km east of the hypocenter. The Mw 7.4 earthquake is a thrust event with north and south-dipping nodal planes. The fault plane is not clear from the aftershock distribution, but the north-dipping plane considered to be the likely fault plane because of the simpler slip distribution compared to the south-dipping plane. The static Coulomb failure stress changes caused by the first earthquake were calculated in the region of the second earthquake. The results show that there was a + 48.59 kPa change at the hypocenter for the assumed north-dipping plane and + 18.24 kPa for the assumed south-dipping plane of the Mw 7.4 event. The temporal pattern of aftershocks shows a possible rate increase of stress prior to the occurrence of the Mw 7.4 events, which may also contribute to the triggering of the second event by static Coulomb Stress changes. We propose a model that supports the geological complexity of the region that may encourage such doublet events.Graphical

Steady-state and transient mechanical response analysis of superelastic nitinol lattice structures prior to additive manufacturing: An in-silico study

The additive manufacturing (AM) of nitinol (NiTi) has gained considerable attention due to the capability of this material and processing combination to produce complex structures with desired shape memory or superelastic properties. Finite element analysis models were developed in this work to simulate the load-bearing capability of Laser Powder Bed Fusion (PBF-LB) produced NiTi lattice structures. The Auricchio numerical method, with exponential hardening law, was implemented within the FEA model to take account of the martensite-austenite reorientation upon change of stress state. The strut diameter and the unit cell side length were varied which in turn varied the lattice relative density. The lattice structures were subjected to 7 % compressive strain under isothermal conditions. The highest energy absorption efficiency of 40 % was achieved from the lattice structure with a strut diameter of 2 mm, a 6 mm unit cell side length, and a relative density of 42 %; however, the highest specific peak stress was recorded within the lattice structure having a strut diameter of 2.5 mm, a 4 mm unit cell side length, and a relative density of 62 %. Transient analysis was performed by varying the compression rate from 0.25 mm/s to 1 mm/s. For all loading conditions, the energy absorption increased linearly until a stable stress plateau was reached. Moreover, for these examined compression rates, the maximum stress absorption efficiencies varied within the range of 25 %–33 %.

Effects of elevated temperature exposure on the residual stress state and microstructure of PVD Cr coatings on SiC investigated via in situ X-ray diffraction and transmission electron microscopy

Pure Cr coatings are being considered as corrosion-resistant layers for SiC-SiCf composite fuel cladding in light water reactors. The residual stress state and interdiffusion behavior of Cr coatings deposited on SiC substrates using bipolar high-power impulse magnetron sputtering (B-HiPIMS) and direct current impulse magnetron sputtering (DCMS) were studied using in situ X-ray diffraction experiments at 300 °C, 700 °C, and 1200 °C. After elevated temperature exposure, evolution of the coating microstructure and coating/substrate interdiffusion was characterized by transmission electron microscopy. The compressive residual stress of the dense B-HiPIMS coating at room temperature was gradually relieved at 300 °C, while the stress transitioned to a tensile state at 700 °C. Grain growth of the Cr coating and a Cr–SiC interdiffusion layer consisting of newly formed Cr–C and Cr–Si phases were observed in the B-HiPIMS coating after exposure at 700 °C. The phases in the interdiffusion layer were identified to be Cr7C3, Cr3Si, and Cr5Si3Cx experimentally and by thermodynamic predictions. For the DCMS coating, however, changes in residual stress and microstructure at the elevated temperatures were limited by the inherent porosity and inhomogeneous structure of the as-deposited coating. At 1200 °C, both coating types interacted rapidly with the underlying SiC substrate in the early stages of the experiment. The results from this study suggest that the characteristics of the Cr coatings do not significantly change at the reactor operating temperature of 300 °C, while changes in microstructure and stress state are expected in off-normal conditions of 700 °C and 1200 °C. The results from this study suggest the B-HiPIMS coating is best-suited as a protective coating for SiC fuel cladding.

Genesis of Low CBM Production in Mid-Deep Reservoirs and Methods to Increase Regional Production: A Case Study in the Zhengzhuang Minefield, Qinshui Basin, China.

With the increase of the burial depth of the no. 3 coal seam in the Zhengzhuang minefield of Qinshui Basin, the production of surface coal bed methane (CBM) vertical wells was low. By means of theoretical analysis and numerical calculation, the causes of low production of CBM vertical wells were studied from the aspects of reservoir physical properties, development technology, stress conditions, and desorption characteristics. It was found that the high in situ stress conditions and stress state changes were the main controlling factors of the low production in the field. On this basis, the mechanism of increasing production and reservoir stimulation was explored. An L-type horizontal well was constructed alternately among the existing vertical wells on the surface to initiate a method to increase the regional production of fish-bone-shaped well groups. This method has the advantages of a large fracture extension range and a wide pressure relief area. It could also effectively connect the pre-existing fracture extension area of surface vertical wells, realizing the overall stimulation of the low-yield area and increasing the regional production. Through the optimization of the favorable stimulation area in the minefield, 8 L-type horizontal wells that adopted this method were constructed in the area with high gas content (greater than 18 m3/t), a thick coal seam (thicker than 5 m), and relatively rich groundwater in the north of the minefield. The average production of a single L-type horizontal well reached 6000 m3/d, which was about 30 times that of the surrounding vertical wells. The length of the horizontal section and the original gas content of the coal seam had a significant influence on the production of the L-type horizontal wells. This method for increasing the regional production of fish-bone-shaped well groups was an effective and feasible low-yield well stimulation technology, which provided a reference for increasing the production and efficiently developing CBM under the high-stress conditions in mid-deep high-rank coal seams.

Source Model of the 2023 Turkey Earthquake Sequence Imaged by Sentinel-1 and GPS Measurements: Implications for Heterogeneous Fault Behavior along the East Anatolian Fault Zone

On 6 February 2023, a devastating doublet of earthquakes with magnitudes of Mw 7.8 and Mw 7.6 successively struck southeastern Turkey near the border of Syria. The earthquake sequence represents the strongest earthquakes in Turkey during the past 80 years and caused an extensive loss of life and property. In this study, we processed Sentinel-1 and GPS data to derive the complete surface displacement caused by the earthquake sequence. The surface displacements were adopted to invert for the fault geometry and coseismic slip distribution on the seismogenic faults of the earthquake sequence. The results indicate that the coseismic rupture of the Turkey earthquake sequence was dominated by left-lateral strike slips with a maximum slip of ~10 m on the East Anatolian Fault Zone (EAFZ) and the Sürgü fault (SF). Significant surface ruptures are recognized based on the geodetic inversion, which is consistent with the analysis of post-earthquake satellite images. The cumulative released moment of the two earthquakes reached 9.62 × 1020 Nm, which corresponds to an event of Mw 7.95. Additionally, the interseismic fault slip rates and locking depths along the central and western segments of the EAFZ were estimated using the high-resolution long-term velocity field. The results reveal significant lateral variations of fault slip rates and locking depths along the central and western segments of the EAFZ. Generally, the estimated fault locking zone showed good spatial consistency with the coseismic fault rupture of the Mw 7.8 shock on the EAFZ. The static coulomb failure stress (CFS) change due to the Mw 7.8 earthquakes suggests that the subsequent Mw 7.6 event was certainly promoted by the Mw 7.8 shock. The stress transfers from the fault EAFZ to the fault SF were realized by unclamping the interface of the fault SF, which significantly reduces the effective normal stress on the fault plane. Large CFS increases in the western Puturge segment of the EAFZ, which was not ruptured in the 2020 Mw 6.8 and the 2023 Mw 7.8 earthquakes, highlight the future earthquake risk in this fault segment.