The 2023 Turkey earthquake doublet: Earthquake relocation, seismic tomography, and stress field inversion

On February 6,2023,two earthquakes with magnitudes of M_(W) 7.8 and M_(W) 7.5 struck southeastern Turkey,causing significant casualties and economic losses.These seismic events occurred along the East Anatolian Fault Zone,a convergent boundary between the Arabian Plate and the Anatolian Subplate.In this study,we analyze the M_(W) 7.8 and M_(W) 7.5 earthquakes by comparing their aftershock relocations,tomographic images,and stress field inversions.The earthquakes were localized in the upper crust and exhibited steep dip angles.Furthermore,the aftershocks occurred either close to the boundaries of low and high P-wave velocity anomaly zones or within the low P-wave velocity anomaly zones.The East Anatolia Fault,associated with the M_(W) 7.8 earthquake,and the SürgüFault,related to the M_(W) 7.5 earthquake,predominantly experienced shear stress.However,their western sections experienced a combination of strike-slip and tensile stresses in addition to shear stress.The ruptures of the M_(W) 7.8 and M_(W) 7.5 earthquakes appear to have bridged a seismic gap that had seen sparse seismicity over the past 200 years prior to the 2023 Turkey earthquake sequence.

Simulation Analysis of Stress Field of Walnut Shell Composite Powder in Laser Additive Manufacturing Forming

A calculation model of stress field in laser additive manufacturing of walnut shell composite powder(walnut shell/Co-PES powder)was established.The DFLUX subroutine was used to implement the moveable application of a double ellipsoid heat source by considering the mechanical properties varying with temperature.The stress field was simulated by the sequential coupling method,and the experimental results were in good accordance with the simulation results.In addition,the distribution and variation of stress and strain field were obtained in the process of laser additive manufacturing of walnut shell composite powder.The displacement of laser additive manufacturing walnut shell composite parts gradually decreased with increasing preheating temperature,decreasing laser power and increasing scanning speed.During the cooling process,the displacement of laser additive manufacturing of walnut shell composite parts gradually increased with the increasing preheating temperature,decreasing scanning speed and increasing laser power.

Effect of hydraulic fracturing induced stress field on weak surface activation during unconventional reservoir development

Unconventional reservoirs usually contain many weak surfaces such as faults,laminae and natural fractures,and effective activation and utilization of these weak surfaces in reservoirs can significantly improve the extraction effect.In hydraulic fracturing,when the artificial fracture approaches the natural fracture,the natural fracture would be influenced by both the original in-situ stress field and the hydraulic fracturing-induced stress field.In this paper,the hydraulic fracturing-induced stress field is calculated based on the relative position of hydraulic fracture and natural fracture,the original in-situ stress,the net pressure inside the hydraulic fracture and the pore pressure of the formation.Furthermore,the stability model of the natural fracture is established by combining the Mohr-Coulomb rupture criterion,and extensive parametric studies are conducted to explore the impact of each parameter on the stability of the natural fracture.The validity of the proposed model is verified by comparing with the reservoir characteristics and fracturing process of the X-well 150e155 formation in the Songliao Basin.It is found that the stress field induced by the hydraulic fracture inhibits the activation of the natural fracture after the artificial fracture crossed the natural fracture.Therefore,for similar reservoirs as X-well 150e155,it is suggested to connect natural fractures with hydraulic fractures first and then activate natural fractures which can effectively utilize the natural fractures and form a complex fracture network.

Tensile Fractures and in situ Stress Measurement Data Constraints on Cretaceous-Present Tectonic Stress Field Evolution of the Tanlu Fault Zone in Shandong Province,North China Craton

Tectonic stress fields are the key drivers of tectonic events and the evolution of regional structures.The tectonic stress field evolution of the Tanlu fault zone in Shandong Province,located in the east of the North China Craton(NCC),may have preserved records of the NCC’s tectonic history.Borehole television survey and hydraulic fracturing were conducted to analyze the paleo and present tectonic stress fields.Three groups of tensile fractures were identified via borehole television,their azimuths being NNW-SSE,NW-SE and NE-SW,representing multiple stages of tectonic events.Hydraulic fracturing data indicates that the study region is experiencing NEE-SWW-oriented compression and nearly-N-Soriented extension,in accordance with strike-slip and compression.Since the Cretaceous,the orientation of the extensional stress has evolved counterclockwise and sequentially from nearly-NW-SE-oriented to NE-SW-oriented and even nearly N-S-oriented,the stress state having transitioned from strike-slip-extension to strike-slip-compression,in association with the rotating and oblique subduction of the Pacific Plate beneath the NCC,with the participation of the Indian Plate.

Recent tectonic stress field and major earthquakes of the Bohai Sea basin

渤海位于北华北新生代裂陷盆地的东部，是一个晚第四纪形成的内陆海盆．渤海盆地活动断裂发育，地震活动强烈，交会于渤海中部的NE向营口潍坊断裂带北段、庙西北一黄河口一临邑断裂带及NW向北京一蓬莱断裂带是主要的活动构造带，将海区分成4个次级新构造区，成为现代应力场作用的构造基础．综合研究38个震源机制解和75个井区应力场等资料，以及构造应力场二维数值模拟计算结果表明，渤海及其邻区现代构造应力场的压应力方向为NE60°～90°，张应力为SN—NW30°；以水平和近水平应力作用为主；不同构造区主应力方向存在一定的差异．现今渤海地区地壳发育以NNE-NE和NW-WNW走向的共轭剪切破裂为特征，是控制地震活动的主要构造．

Contemporary tectonic stress field in China

The contemporary tectonic stress field in China is obtained on the basis of Chinese stress field database and Harvard CMT catalogue.Result of the inverted tectonic stresses shows that the maximum principal stress axis strikes nearly north-south direction in the west part of Tibet plateau,ENE direction in North China.In Central China,its strikes show a radiated pattern,i.e.,NNE in north part and NNW in south part.The detailed stress field parameters of nearly whole China are given and can be used in geodynamic stress field simulation and earthquake prediction.

Source mechanism of small-moderate earth- quakes and tectonic stress field in Yunnan Province

In the paper, source mechanisms of 33 small-moderate earthquakes occurred in Yunnan are determined by modeling of regional waveforms from Yunnan digital seismic network. The result shows that most earthquakes occurred within or near the Chuandian rhombic block have strike-slip mechanism. The orientations of maximum compressive stresses obtained from source mechanism are changed from NNW-SSN to NS in the areas from north to south of the block, and tensile stresses are mainly in ENE-WSW or NE-SE. In the eastern Tibetan Plateau, the orientations of maximum compressive stress radiate toward outside from the plateau, and the tensile stress orientations mostly parallel to arc structures. Near 28N the orientations of both maximum compressive stress and tensile stress changed greatly, and the boundary seems to correspond to the southwestern extended line of Longmenshan fault. Outside of the Chuandian rhombic block, the orientations of P and T axes are some different from those within the block. The comparison shows that the source mechanism of small-moderate events presented in the paper is consistence with that of moderate-strong earthquakes determined by Harvard University, which means the source mechanism of small-moderate events can be used to study the tectonic stress field in this region.

Temperature and stress fields of multi-track laser cladding

Based on genetic algorithm and neural network algorithm,the finite element analyses on the temperature fields and stress fields of multi-track laser cladding were carried out by using the ANSYS software.The results show that,in the multi-track cladding process,the temperature field ellipse leans to the cladding formed,and the front cladding has preheating function on the following cladding.During cladding,the longitudinal stress is the largest,the lateral stress is the second,and the thickness direction stress is the smallest.The center of the cladding is in the tensile stress condition.The longitudinal tensile stress is higher than the lateral or thickness direction stress by several times,and the tensile stress achieves the maximum at the area of joint between the cladding and substrate.Therefore,it is inferred that transversal crack is the most main crack form in multi-track laser cladding.Moreover,the joint between cladding and substrate is the crack sensitive area,and this is consistent with the actual experiments.

Spatio-temporal variation of the stress field in the Wenchuan aftershock region

Focal mechanism solutions and centroid depths of 312 M≥4 aftershocks from the 2008 Wenchuan earthquake sequence have been derived by CAP (Cut and Paste) method from broadband waveform data with relatively high signal-to-noise ratio (SNR). Following this, we have analyzed the distribution of focal depths and the stress tensors, as well as the types of focal mechanisms. The major results are: (1) different cross-sections show that the depth ranges of the aftershocks at the southern and northern ends of the aftershock area along the Longmenshan fault zone are wider than those on the central segment, where rare M≥4 aftershocks occurred at depths shallower than 10 km. The main faults trend to the NW on the southern and central segments, and for the northern segment, no dominant trend direction has been determined; (2) stress tensor distribution demonstrates that the majority of the aftershock areas on the cross-section along the major axis are mainly under compressive stress perpendicular to the profile; however, for the areas near Lixian, Beichuan, Qingchuan and the shallow parts of its northern segment, large principal stress components are parallel to the major axis profile direction. On the cross-sections perpendicular to the major axis, the three areas above can be divided into two parts: one with dominantly compressional stress near the major faults of the Longmenshan fault zone on the SE side, and the other with NE-direction push along the fault zone on the NW side; (3) the stress tensor distribution in map view is very similar to those on the vertical cross-sections. In map view, the orientation of the principal compressional stress axis S 1 on the central segment of the aftershock area presents an SE-trending arc shape; (4) the stress tensor slices at different depths show that the orientation of S 1 axis mainly changes on the central segment and at the northern end, indicating that the two segments have different seismogenic structures at different depths; (5) with the exception of the northern end of the aftershock region, the orientation of the S 1 axis changes little during the early and late stages, illustrating the seismogenic structures are relatively stable; (6) preliminary analyses for the seismogenic structures at the northern end indicated that deeper strike-slip quakes occurred on the ENE-striking branch at first, and then the NNE-striking branch faults at the northern end were activated and generated a series of relatively shallow strike-slip earthquakes due to subsequent stress-triggering; (7) the aftershock triggering mechanism that occurred near Lixian is different between the shallow and deep depths, and between the early and late stages, indicating that the main faults and the branch faults responsible for aftershocks are at different depths. Consequently, the relaxation effect of the main shock particularly impacts the branch faults.

Characteristics of evolution of mining-induced stress field in the longwall panel:insights from physical modeling

The evolution of mining-induced stress field in longwall panel is closely related to the fracture field and the breaking characteristics of strata.Few laboratory experiments have been conducted to investigate the stress field.This study investigated its evolution by constructing a large-scale physical model according to the in situ conditions of the longwall panel.Theoretical analysis was used to reveal the mechanism of stress distribution in the overburden.The modelling results showed that:(1)The major principal stress field is arch-shaped,and the strata overlying both the solid zones and gob constitute a series of coordinated load-bearing structures.The stress increasing zone is like a macro stress arch.High stress is especially concentrated on both shoulders of the arch-shaped structure.The stress concentration of the solid zone in front of the gob is higher than the rear solid zone.(2)The characteristics of the vertical stress field in different regions are significantly different.Stress decreases in the zone above the gob and increases in solid zones on both sides of it.The mechanical analysis show that for a given stratum,the trajectories of principal stress are arch-shaped or inverselyarched,referred to as the‘‘principal stress arch’’,irrespective of its initial breaking or periodic breaking,and determines the fracture morphology.That is,the trajectories of tensile principal stress are inversely arched before the first breaking of the strata,and cause the breaking lines to resemble an inverted funnel.In case of periodic breaking,the breaking line forms an obtuse angle with the advancing direction of the panel.Good agreement was obtained between the results of physical modeling and the theoretical analysis.

The Interface Stress Field in the Elastic System Consisting of the Hollow Cylinder and Surrounding Elastic Medium Under 3D Non-Axisymmetric Forced Vibration

The paper develops and employs analytical-numerical solution method for the study of the time-harmonic dynamic stress field in the system consisting of the hollow cylinder and surrounding elastic medium under the non-axisymmetric forced vibration of this system.It is assumed that in the interior of the hollow cylinder the point-located with respect to the cylinder axis,non-axisymmetric with respect to the circumferential direction and uniformly distributed time-harmonic forces act.Corresponding boundary value problem is solved by employing of the exponential Fourier transformation with respect to the axial coordinate and by employing of the Fourier series expansion of these transformations.Numerical results on the frequency response of the interface normal stresses are presented and discussed.

Cretaceous-Cenozoic regional stress field evolution from borehole imaging in the southern Jinzhou area, western Liaoning, North China Craton

The Mesozoic Yanshanian Movement affected the tectonic evolution of the North China Craton(NCC).It is proposed that Mesozoic cratonic destruction peaked~125 Ma,possibly influenced by subduction of the western Pacific Plate beneath the Euro-Asian Plate in the Early Cretaceous.The southern Jinzhou area in the eastern block of the NCC preserves clues about the tectonic events and related geological resources.Studies of the regional stress field evolution from the Cretaceous to the Cenozoic can enhance our understanding of the tectonics and dynamics of the NCC.Borehole image logging technology was used to identify and collect attitudes of tensile fractures from 11 boreholes;these were subdivided into four groups according to dip direction,i.e.,NNW-SSE,NWW-SEE,W-E and NE-SW.The development of these fractures was controlled primarily by the regional tectonic stress field;temperature,lithology,and depth contributed to some extent.In 136-125 Ma in the Early Cretaceous,the area was characterized by extension that was oriented NNW-SSE and NWW-SEE;from 125-101 Ma the extension was oriented W-E;after 101 Ma it was NE-SW.This counterclockwise trend has persisted to the present,probably related to oblique subduction of the Pacific Plate,and is characterized by ongoing extension that is nearly N-S-oriented and NEE-SWW-oriented compression.

Mesozoic–Cenozoic stress field magnitude in Sichuan Basin, China and its adjacent areas and the implication on shale gas reservoir: Determination by acoustic emission in rocks

The Sichuan Basin is one of the vital basins in China,boasting abundant hydrocarbon reservoirs.To clarify the intensity of the tectonic stress field of different tectonic episodes since the Mesozoic and to identify the regional dynamic background of different tectonic movements in the Sichuan Basin and its adjacent areas,the characteristics of the acoustic emission in rocks in different strata of these areas were researched in this paper.Meanwhile,the tectonic stress magnitude in these areas since the Mesozoic was restored.The laws state that the tectonic stress varied with depth was revealed,followed by the discussion of the influence of structural stress intensity on structural patterns in different tectonic episodes.These were conducted based on the paleostress measurement by acoustic emission method and the inversion principle of the stress fields in ancient periods and the present,as well as previous research achievements.The results of this paper demonstrate that the third episode of Yanshanian Movement(Yanshanian III)had the maximum activity intensity and tremendously influenced the structural pattern in the study area.The maximum horizontal principal stress of Yanshanian III varied with depth as follows:0.0168 x+37.001(MPa),R^2=0.8891.The regional structural fractures were mainly formed in Yanshanian III in Xujiahe Formation,west Sichuan Basin,of which the maximum paleoprincipal stress ranging from 85.1 MPa to 120.1 MPa.In addition,the law stating the present maximum horizontal principal stress varies with depth was determined to be 0.0159 x+10.221(MPa),R^2=0.7868 in Wuling Mountain area.Meanwhile,it was determined to be 0.0221 x+9.4733(MPa),R^2=0.9121 in the western part of Xuefeng Mountain area and 0.0174 x+10.247(MPa),R^2=0.8064 in the whole study area.These research results will not only provide data for the simulation of stress field,the evaluation of deformation degree,and the prediction of structural fractures,but also offer absolute geological scientific bases for the elevation of favorable shale gas preservation.

Effects of fault movement and material properties on deformation and stress fields of Tibetan Plateau

We compare the factors which affect the movement of Tibetan Plateau by building three types of finite element models: an elastic materials (M-EC), a continuous model composed by non-linear materials (M-PC), and an elastic model with discontinuous fault movements (M-ET). Both in M-ET and M-EC, the materials in Qiangtang and Lhasa block are elastic, and in M-ET, discontinuous movement of faults is considered for evaluating the effects of strike-slip faults. In model M-PC Druker-Prager plastic materials are used in Qiangtang and Lhasa block. Comparisons of the numerical simulation and the GPS observations show following characteristics: (1) Under present tectonic environment, short-term deformation of Tibetan Plateau can be simulated well by elastic models; (2) Discontinuous fault activities increase the lateral extrusion of the eastern part of Tibetan Plateau, reduce the stress field level in Qiangtang, Tarim and Qaidam blocks and strengthen the E-W extensional force in the east and the west parts of Qiangtang block; (3) Properties of plastic materials reduce the total stress field and the E-W extensional force, thus, the normal fault earthquakes in southern Tibet is mainly owed to the effect of active fault movement. Based on the numerical simulations we speculate that faults movement may play a more important role on the kinematic pattern of Tibetan Plateau than bulk properties.

Stress Field of Non-equilibrium Grain Boundaries in Nano-crystalline Metals

Introducing the stress distribution near grain boundaries to improve the dislocation pileup model for the Hall-Petch (H-P) relation, the continuous distribution of dislocations in the pileup could be solved by means of Tschebysheff polynomials for the Hubert transformation. An analytical formula of the stress intensity factor for the dislocation pileup is obtained. The reverse H-P relation may be explained by the modified dislocation-pileup-model.

On Mars, Location and Orientation of Dykes Exposed along the Valles Marineris Walls Reveal Expected and Unexpected Stress Fields

Structural and geomorphological analysis of the Martian surface in the visible spectral range using the NASA/Viking images in the 90’s,complemented by experimental modelling(Mège and Masson,1996a;Mège et al.,2003)suggested that the Valles Marineris trough(chasma)system is aligned with a mafic dyke swarm,named the Syria Planum Dyke Swarm.Cross-cutting relationships

Geometrical shape of in-plane inclusion characterized by polynomial internal stress field under uniform eigenstrains

The internal stress field of an inhomogeneous or homogeneous inclusion in an infinite elastic plane under uniform stress-free eigenstrains is studied. The study is restricted to the inclusion shapes defined by the polynomial mapping functions mapping the exterior of the inclusion onto the exterior of a unit circle. The inclusion shapes, giving a polynomial internal stress field, are determined for three types of inclusions, i.e., an inhomogeneous inclusion with an elastic modulus different from the surrounding matrix,an inhomogeneous inclusion with the same shear modulus but a different Poisson's ratio from the surrounding matrix, and a homogeneous inclusion with the same elastic modulus as the surrounding matrix. Examples are presented, and several specific conclusions are achieved for the relation between the degree of the polynomial internal stress field and the degree of the mapping function defining the inclusion shape.

Evolution of 3D tectonic stress field and fault movement in North China

Based on data of fault movement surveying, we simulate the evolution process of three dimensional stress field in North China by three dimensional finite element method. Evolutional patterns in one-year time scale from 1986 to 1997 have been illustrated and the evolution characteristics of stress field have been analyzed. In comparison with the seismic activity among that time interval in North China, we have primarily discussed the relationship between the evolution of stress field and seismic activity.

Three-Dimensional Stress Fields in Finite Thickness Plate with Hole Under Shear Load

The theoretical solutions are obtained for the three-dimensional(3-D)stress field in an infinite isotropic elastic plate with a through-the-thickness circular hole subjected to shear load at far field by using Kane and Mindlin′s assumption based on the stress function method.Based on the present solutions,the characteristics of 3-D stress field are analyzed and the emphasis is placed on the effects of the plate thickness and Poisson′s ratio on the deviation of the present 3-D in-plane stress from the related plane stress solutions,the stress concentration and the out-of-plane constraint.The present solutions show that the stress concentration factor reaches its peak value of about 8.9% which is higher than that of the plane stress solutions.As expected,the out-of-plane stress constraint factor can reach 1on the surface of the hole when the plate is a very thick one.

Double-sided subduction with contrasting polarities beneath the Pamir-Hindu Kush:Evidence from focal mechanism solutions and stress field inversion

The Pamir-Hindu Kush region at the western end of the Himalayan-Tibet orogen is one of the most active regions on the globe with strong seismicity and deformation and provides a window to evaluate continental collision linked to two intra-continental subduction zones with different polarities.The seismicity and seismic tomography data show a steep northward subducting slab beneath the Hindu Kush and southward subducting slab under the Pamir.Here,we collect seismic catalogue with 3988 earthquake events to compute seismicity images and waveform data from 926 earthquake events to invert focal mechanism solutions and stress field with a view to characterize the subducting slabs under the Pamir-Hindu Kush region.Our results define two distinct seismic zones:a steep one beneath the Hindu Kush and a broad one beneath the Pamir.Deep and intermediate-depth earthquakes are mainly distributed in the Hindu Kush region which is controlled by thrust faulting,whereas the Pamir is dominated by strike-slip stress regime with shallow and intermediate-depth earthquakes.The area where the maximum principal stress axis is vertical in the southern Pamir corresponds to the location of a highconductivity low-velocity region that contributes to the seismogenic processes in this region.We interpret the two distinct seismic zones to represent a double-sided subduction system where the Hindu Kush zone represents the northward subduction of the Indian plate,and the Pamir zone shows southward subduction of the Eurasian plate.A transition fault is inferred in the region between the Hindu Kush and the Pamir which regulates the opposing directions of motion of the Indian and Eurasian plates.