We investigate the accuracy and robustness of moment tensor(MT)and stress inversion solutions derived from acoustic emissions(AEs)during the laboratory fracturing of prismatic Barre granite specimens.Pre-cut flaws in ...We investigate the accuracy and robustness of moment tensor(MT)and stress inversion solutions derived from acoustic emissions(AEs)during the laboratory fracturing of prismatic Barre granite specimens.Pre-cut flaws in the specimens introduce a complex stress field,resulting in a spatial and temporal variation of focal mechanisms.Specifically,we consider two experimental setups:(1)where the rock is loaded in compression to generate primarily shear-type fractures and(2)where the material is loaded in indirect tension to generate predominantly tensile-type fractures.In each test,we first decompose AE moment tensors into double-couple(DC)and non-DC terms and then derive unambiguous normal and slip vectors using k-means clustering and an unstructured damped stress inversion algorithm.We explore temporal and spatial distributions of DC and non-DC events at different loading levels.The majority of the DC and the tensile non-DC events cluster around the pre-cut flaws,where macro-cracks later develop.Results of stress inversion are verified against the stress field from finite element(FE)modeling.A good agreement is found between the experimentally derived and numerically simulated stress orientations.To the best of the authors’knowledge,this work presents the first case where stress inversion methodologies are validated by numerical simulations at laboratory scale and under highly heterogeneous stress distributions.展开更多
The investigation of the in situ stress distribution has always been a key condition for engineering design of deep tunnels and analysis of surrounding rock stability.In this paper,a comprehensive judgment method coup...The investigation of the in situ stress distribution has always been a key condition for engineering design of deep tunnels and analysis of surrounding rock stability.In this paper,a comprehensive judgment method coupled with pressure/tension(P/T)axis mechanism and geological structure is proposed to invert the in situ stress in the Duoxiongla tunnel in Xizang.In the process of TBM tunnel excavation,3887 groups of microseismic events were collected by means of microseismic monitoring technology.By studying the temporal and spatial distribution of 3887 groups of microseismic events,42 groups of microseismic data were selected for in situ stress inversion.Then the focal mechanisms of 42 groups of microseisms were inverted.Combined with the analysis of the previous geological survey,the inversion results of the in situ stress were analyzed.According to the focal mechanism of the tunnel area,the linear in situ stress inversion method was used to invert the in situ stress in the source area.Finally,according to the PTGS(pressure/tension axis mechanism and geological structure)comprehensive judgment method proposed in this paper,the in situ stress of the tunnel microseismic region was determined.The results show that there are mainly three groups of fissures and joint surfaces in the tunnel area,and the in situ stress is dominated by the horizontrun tectonic stress;the main driving force of the rupture surface in the excavation process of Duoxiongla tunnel is the horizontal tectonic stress;the distribution of the maximum and minimum principal stress obtained by the inversion is consistent with the distribution of the P/T axis;combined with the linear in situ stress inversion method and the comprehensive judgment of PTGS,the azimuth and dip angles of the three principal stresses are finally determined as N90.71°E,4.06°,N5.35°W,3.06°,and N8.10W,85.32°,respectively.The study verifies the feasibility of microseismic inversion of in situ stress.展开更多
This article presents an interpretation of the seismic source mechanisms for 905 earthquakes with MS>2.0,occurring in the central and southern sections of the Tan-Lu Fault Zone and its adjacent areas from 1970 to 2...This article presents an interpretation of the seismic source mechanisms for 905 earthquakes with MS>2.0,occurring in the central and southern sections of the Tan-Lu Fault Zone and its adjacent areas from 1970 to 2023.Utilizing the damped stress tensor method,we have inverted the spatial characteristics of the stress field variations in this study area,at a resolution of 1.0°×1.0°.The results indicate that the maximum principal stress direction within the central and southern sections of the Tan-Lu Fault Zone exhibits a spatially continuous change,rotating counterclockwise from East-West(EW)to Northeast-East(NEE),albeit with local variations.When dividing along the Tan-Lu Fault Zone,it is observed that on its western side—the North China block—a near EW stress field predominates.In contrast,on its eastern side—the Ludong-Huanghai Block—stress fields primarily exhibit NEE and Northeast-East(NE)orientations,underscoring the role of the Tan-Lu Fault Zone as a significant boundary between tectonic blocks.In regions located between latitudes 30°-34°N and longitudes 113°-115°E on the western side of these fault zone sections,maximum principal stress follows a radial distribution pattern indicative of a complex stress field.Conversely,on the eastern side of this fault zone,maximum principal stress direction remains relatively consistent,primarily displaying NEE and NE distributions.This reflects the fact that this area is situated under a tectonic background characterized by near NEE-NE direction for the Ludong-Huanghai Block.However,within an area bounded by latitudes 30°-32°N and longitudes 120°-122°E on the eastern flank of the Tan-Lu Fault Zone,maximum principal stress direction appears more intricate,with radial distribution patterns suggesting influences not only from near EW-NEE movements associated with the North China Block,but also from westward subduction processes related to Philippine Sea plate dynamics.Through our analysis of historical earthquakes in this region,we conclude that the moderate to strong seismic activity within this area is significantly related to the tectonic stress environment,with regions of complex tectonic stress often being the most seismically active.展开更多
With waveform data of 613 earthquakes with ML ≥ 2. 5 in the middle section of the Xiaojiang fault and its adjacent area which occurred during January,1998 to September 2007,focal mechanisms were calculated by the dir...With waveform data of 613 earthquakes with ML ≥ 2. 5 in the middle section of the Xiaojiang fault and its adjacent area which occurred during January,1998 to September 2007,focal mechanisms were calculated by the direct wave amplitude ratio of S /P in the vertical component and their characteristics were analyzed. According to regional tectonic features of the middle section of the Xiaojiang fault and its adjacent area,the study region was partitioned into two zones with the Xiaojiang fault as the boundary,e. g. zone A and zone B (including the Xiaojiang fault). In order to research the faults stress in detail,the Xiaojiang fault zone was picked out for independent analysis. The study region was also partitioned into 1°× 1° cells with a 0. 5° step. The stress fields of zone A,B and the fault zone were inverted with the FMSI method (Gephart,1990). The results show that first, the faults are mainly of strike-slip in the middle section and its adjacent area,amounting to 81. 28%,69. 23% and 72. 97% in the A,B and fault zones,respectively. Secondly,the stress inversion also indicates that the directions of maximum principal stress σ1 in the A, B,and fault zones are approximately NNW,NWW and NWW,the stress action is mainly horizontal,and strike-slip faulting is dominant in the study area. On the other hand,the direction of the principal stress field in the central Yunnan block changed from NNW to NWW,however,in the region between the Yuanmou and Pudu River faults,the azimuth of the main compressive stress shows that the north-south slip is obvious. While the direction of the main compressive stress of the Xiaojiang fault zone is nearly NW; in the east of the Xiaojiang fault,the direction of principal compressive stress is NW to NNW in the eastern Yunnan block.展开更多
Using the focal mechanism solutions of 24 moderately strong earthquakes in the northern Tianshan area,we carried out system cluster and stress field inversion analysis.The result indicates that,the focal mechanism sol...Using the focal mechanism solutions of 24 moderately strong earthquakes in the northern Tianshan area,we carried out system cluster and stress field inversion analysis.The result indicates that,the focal mechanism solutions of moderately strong earthquakes are mainly dip-slip reverse faulting in the northern Tianshan area.The principal rupture planes of earthquakes are NW-oriented.It is basically consistent with the strike of earthquake structure in its adjacent area.The direction of the principal compression stress P axis is nearly NS,and its inclination angle is small;while the inclination angle of the principal extensional stress T axis is large.It shows that the regional stress field is mainly controlled by the near-NS horizontal compressive stress.The direction of the maximum principal stress shows a gradation process of NNE-NS-NW from east to west.展开更多
The North Tabriz fault is a segmented dextral fault in Northwest Iran, with a history of major destructive earthquakes that have repeatedly destroyed the city of Tabriz（current population 1.6 million）. The quiescenc...The North Tabriz fault is a segmented dextral fault in Northwest Iran, with a history of major destructive earthquakes that have repeatedly destroyed the city of Tabriz（current population 1.6 million）. The quiescence of the fault（last major temblor in 1854） and a lack of outcrop study have hampered stress analysis. Resolution of the stress states on the fault could be used for seismotectonic study along the North Tabriz fault and for understanding the geodynamics of the Arabia-Eurasia collision zone. Using fault-slip data collected from 88 localities in the fault system, we conducted an inversion analysis of this fault-slip data and analysis of the stratigraphic, geometric, and structural information. As a result, we confirmed that transcurrent deformation is prevalent on the North Tabriz fault and adjacent areas and is generally accomplished by predominant NW-SE-trending dextral and NE-SW-trending sinistral faults. Specifically, three separate tectonic episodes are recognised from the stress inversion data, consistent with the geologic data：（i） a post-Cretaceous and pre-Early Miocene compressional（Laramian） stress regime,（ii） an Early Miocene extensional stress regime, and（iii） modern tectonic episode with different local stress regimes（compressional and extensional） along the different segments of this fault.展开更多
Paleostress plays a significant role in controlling the formation, accumulation, and distribution of reservoirs, and this could be an important factor in controlling the production of hydrocarbons from the unconventio...Paleostress plays a significant role in controlling the formation, accumulation, and distribution of reservoirs, and this could be an important factor in controlling the production of hydrocarbons from the unconventional reservoirs. In this study, we will use 3D seismic reflection data to perform the slip-tendency-based stress inversion to determine the stress field in the basement of the northern slope area in the Bongor Basin. The dataset for this technique is easily available in the oil and gas companies. The stress inversion results from the basement of the northern slope area of Bongor basin show that the maximum principal stress axis (σ1) is oriented vertically, the intermediate principal stress axis (σ2) is oriented N18° and the minimum principal stress axis (σ3) is oriented N105°, and σ2/σ1 = 0.60 and σ3/σ1 = 0.29. The findings of this paper provide significant information to understand the fault reactivation at the critical stage of hydrocarbon accumulation and the regional tectonic evolution.展开更多
A comprehensive study on regional stress field around the Taigu fault zone in Shanxi Province, China, was performed in this study. To get a better understanding of the present-day stress status in this area, 31 focal ...A comprehensive study on regional stress field around the Taigu fault zone in Shanxi Province, China, was performed in this study. To get a better understanding of the present-day stress status in this area, 31 focal mecha- nisms of ML 〉3 earthquakes since 1965 were compiled, and the best stress tensor was then inverted based on the database. Additionally, magnetic fabrics along the Taigu fault zone were investigated to get an indication of the regional stress field in the past. Our results show that the present-day stress field around the Taigu fault zone is characterized by astable NW-SE extension with a strike- slip component, consistent with the geological surveys and recent GPS data. Results from magnetic fabrics indicate that the orientations of principal stress axes from magnetic fabrics of sedimentary rocks in Neogene coincide to the orientations of principal stress axes from focal mecha- nisms. The south segment of the Taigu fault displays more complicated magnetic fabrics and more activity of mod- erate earthquakes. It is connected with the Mianshan west fault and intersects with NW-SE striking Fenyang fault and the north fault of the Lingshi uplift at the south edge of Taiyuan basin. This may be the area needing more atten- tion in terms of seismic risk along the Taigu fault.展开更多
Two earthquakes of Ms=6.0 and Ms=6. 1 consecutively occurred on December 31, 1994 and January 10, 1995 in Beibuwan region, China. By using the generalized reflection-transmission coefficient matrix and the discrete sl...Two earthquakes of Ms=6.0 and Ms=6. 1 consecutively occurred on December 31, 1994 and January 10, 1995 in Beibuwan region, China. By using the generalized reflection-transmission coefficient matrix and the discrete slowness integration method in the calculation of Green's functions, we obtained the focal mechanisms of these earthquakes using long-period waveforms of regional body waves recorded by the China Digital Seismograph Network (CDSN) by means of moment tensor inversion method in frequency domain. The results inverted indicate that the focal mechanisms of these two earthquakes were similar to each other. Their principal compressional stresses are in NW-SE direction and principal tensional stresses are in NE-SW direction. It turns out that the occurrence of the two earthquakes was controlled by the same tectonic environment related to the collision of the Philippine Plate and the Eurasian Plates. On the other hand, the results imply that the stress field in the seismogenic region has a significant change after the Ms=6.0 earthquake. It may be proposed that the occurrence of the Ms=6. 1 earthquake could be related to the stress field adjustment caused by the Ms=6.0 earthquake.展开更多
It has been proved through experiments that the electromagnetic radiation energy of a substance will vary when stress acts on the substance. This moment, the electromagnetic radiation energy (observation value) receiv...It has been proved through experiments that the electromagnetic radiation energy of a substance will vary when stress acts on the substance. This moment, the electromagnetic radiation energy (observation value) received by the remote sensor is triggered not only by the substance temperature and also by the stress. Separating quantitatively these two kinds of electromagnetic radiation energy and then inversing the actual temperature state and stress state of a medium is a matter with practical significance in earthquake prediction and stability monitoring for the large-scale geotechnical engineering. In this paper the principle and the mathematical method for inversing stress by using multiband remote sensing data are discussed in detail. A calculation example is listed.展开更多
Rock masses in alpine canyon areas exhibit strong heterogeneity,discontinuity,and are subject to strong tectonic effects and stress unloading,leading to extremely complex distribution of in-situ stress.In addition,the...Rock masses in alpine canyon areas exhibit strong heterogeneity,discontinuity,and are subject to strong tectonic effects and stress unloading,leading to extremely complex distribution of in-situ stress.In addition,the occurrence of layered rock masses makes it more complex,with obvious anisotropic mechanical properties.This study proposes a comprehensive method for evaluating the stability of layered rock spillway tunnels in a hydropower station in an alpine canyon.First,the failure criterion and mechanical model of layered rock masses considering the anisotropy induced by the bedding plane and the true triaxial stress regime were established;an inversion theory and calculation procedure for in-situ stress in alpine canyon areas were then introduced.Finally,by using a self-developed numerical tool,i.e.CASRock,the stability of the layered rock spillway tunnel in a hydropower station was numerically analyzed.The results show that,affected by geological structure and stratigraphic lithology,there is significant differentiation in the in-situ stress in alpine canyons,with horizontal tectonic stress as the main factor.The occurrence of layered rock masses in the region has a significant impact on the stability of surrounding rock,and the angle between the bedding strike and the tunnel axis as well as the bedding dip both exert a significant influence on the failure characteristics of the surrounding rock.展开更多
On October 7,2021,a magnitude 5.9 earthquake struck the Harnai(Baluchistan)region of Pakistan,causing several fatalities and injuries within the epicentral area.First-order tectonic deformation in this region is cause...On October 7,2021,a magnitude 5.9 earthquake struck the Harnai(Baluchistan)region of Pakistan,causing several fatalities and injuries within the epicentral area.First-order tectonic deformation in this region is caused by the convergence of the Indian Plate with respect to the Eurasian Plate.The Katwaz Block hinders the motion of the Indian Plate,resulting in the formation of strike-slip faults.In this study,the P-wave first-motion polarity technique was used to determine the mainshock faulting style.Cyclic scanning of the polarity solutions was applied to determine the most suitable focal mechanism solution among the available solutions generated by the FOCMEC(focal mechanism)software.The nodal planes correspond to different faulting styles(i.e.,thrust and strike-slip faulting).A nodal plane oriented in the NW-SE direction corresponded to a strike-slip mechanism,which was considered to be the fault plane.Tectonically,this earthquake was associated with the Harnai-Karahi strike-slip fault zone owing to the fault strike and direction of slip.The apparent stress drop,fault length,and moment magnitude of the Harnai earthquake were 35.4 bar,6.1 km,and 5.9,respectively.A lower b-value for the Gutenberg-Richter law was observed prior to the earthquake.Higherα-than b-values(α>b)indicate that this earthquake was governed by large events as opposed to small-magnitude events.The Harnai sequence had a decay exponent close to unity,lasted for 145 days,and produced few aftershocks.The study will help the future hazard mitigation in the region.展开更多
The 2022 M_(W)6.7 Menyuan earthquake ruptured the western end of the Tianzhu seismic gap,providing an opportunity to study the regional seismogenic characteristics and seismic hazards.Here we use interferometric synth...The 2022 M_(W)6.7 Menyuan earthquake ruptured the western end of the Tianzhu seismic gap,providing an opportunity to study the regional seismogenic characteristics and seismic hazards.Here we use interferometric synthetic aperture radar(InSAR)and seismic data to study the mainshock rupture,early afterslip and the second largest aftershock of the 2022 Menyuan earthquake sequences.Our modeling results show that the mainshock ruptured the Lenglongling fault and the Tuolaishan fault with a maximum slip of~3 m.Rapid postseismic transient deformation occurred at the center of the Lenglongling fault.Our afterslip modeling reveals that the majority of afterslip occurred in the deeper part of the Lenglongling fault.A high-angle conjugated faulting event is found at the middle section of the Lenglongling fault.We use the stress inversion to investigate the possible triggering mechanism of the conjugated rupture event.The results indicate the maximum principal stress direction is in~222°,forming a~22°angle between the conjugated fault of second largest aftershock and the mainshock.The calculated normal stress changes indicate the region is within a pull-apart stress field,which favors such a conjugated rupturing event.Our study will help understand the rupture behavior of such kind of conjugated fault in other regions.展开更多
Objective:The programmed death process of cells according to gene coding belongs to apoptotic natural extinction(PCD).The purpose of this study is to explore the phenomenon of“returning to old age and rejuvenating ch...Objective:The programmed death process of cells according to gene coding belongs to apoptotic natural extinction(PCD).The purpose of this study is to explore the phenomenon of“returning to old age and rejuvenating children”in the extreme anoxia,no nutrients and survival in the extreme environment of fish and earthworm.Methods:the adult earthworms were put into the sealed quartz sand or fine yellow sand plastic bottle with humidity of 35-40%70 ml and poured out 100-150 d,then put back into the natural environment(simulated natural plastic basin)and raised 100-150 d,to collect the experimental information.The same object can be observed repeatedly.Results:The earthworms which were closed in the little oxygen-free and nutrition-deficient vials were reduced by autophagy,and the rings and reproductive pores disappeared completely.When they were put back into the natural environment for two or three months,they were all restored to their original morphological structure.Conclusion:Most of the same subjects underwent 1-3 years of cyclic observation.The biological structure was adapted to the changing environment.It was helped by the resonance of many biota and complex stress factors.展开更多
The southwestern region of the Delhi-National Capital Region (NCR) experiences sporadic micro (M ≤ 3.0) and occasional small (M > 3.0) earthquakes with a seasonal influence. This study integrates remote sensing an...The southwestern region of the Delhi-National Capital Region (NCR) experiences sporadic micro (M ≤ 3.0) and occasional small (M > 3.0) earthquakes with a seasonal influence. This study integrates remote sensing and seismological data to elucidate the seismotectonic scenario and identify potential unmapped faults. Analysis of DEM data (Cartoset) reveals numerous multidirectional minor faults, some coincident or conjugate to known major faults. Earthquake epicentres spatially correlate with several of these delineated faults. Fault plane solutions suggest a transition from central normal faulting to peripheral thrust faulting. Moment tensor decomposition indicates dominant double-couple mechanisms with significant non-double-couple components for earthquakes ranging from Mw 2.5 to 4.4. A major variation in principal stress orientation is apparent between the eastern and western regions of the study area. Stress inversion reveals a NW-SE shortening direction and unusual principal axis plunges, suggesting a rare “odd” or “unknown” faulting regime. These findings suggest ongoing rifting in the eastern Alwar basin may be inducing thrusting in the surrounding region along pre-existing Aravalli-Delhi fold belt thrusts. Seismogenesis likely results from a complex interplay of faulting, regional tectonics, and fluid interaction. This study highlights the value of a multidisciplinary approach for unravelling the intricacies of seismotectonic in low-to-moderate seismicity regions, with varying strengths due to diverse structural heterogeneity associated with mapped or unmapped (hidden) faults, which have been delineated in this study, as an additional information for assessing seismic hazard potential for Delhi-NCR.展开更多
Middle-lower crust and mantle rocks are generally widely exposed in metamorphic core complex or gneiss dome,which is an ideal place to study the exhumation process related to regional extension and rheology.The Laojun...Middle-lower crust and mantle rocks are generally widely exposed in metamorphic core complex or gneiss dome,which is an ideal place to study the exhumation process related to regional extension and rheology.The Laojunshan metamorphic complex in southeastern Yunnan is located in a special tectonic position surrounded by the Cathaysia,Yangtze and Indochina blocks.It is composed of different metamorphic-deformation rocks and granitic intrusions.There also are many economic deposits(e.g.,tin and tungsten)that are spatially and genetically associated with the formation and exhumation of the Laojunshan gneiss dome.Based on detailed analysis of macro-and microscopic structure,stress field distribution and deformation condition,the tectonic units of the Laojunshan metamorphic complex show obvious characteristics of doming,as well as of typical structural units of metamorphic core complex.It has strongly deformed metamorphic gneiss core(footwall),detachment fault system and sedimentary cover(hanging wall)with lightly metamorphism and deformation.The footwall of gneiss dome presents a strongly ductile deformation domain,accompanied by different ages of granitic intrusions.The distribution of developed foliation and lineation within granitic gneisses are arc-shaped and radial,respectively,with a nearly N-S trending from the footwall to the hanging wall.Mylonitization of deformed rocks gradually weakens and transits to orthogneiss as it moves away from the detachment fault toward the footwall.The low angle detachment fault between the footwall and the hanging wall shows an arc-like shape feature.Mylonite fabrics are preserved in the deformed rocks of the detachment fault,which are mainly composed of chloritized schist,fault breccia,cataclasite and fault gouge.A large number of normal faults are developed in detachment faults and hanging wall,and their stress fields radiate in an arc around the footwall.Zircon U-Pb ages of amphibolite and granitic gneiss from the footwall range from 445 to 420 Ma,indicating the timing of Caledonian magmatic emplacement and the main formation period of the Laojunshan gneiss dome.U-Pb ages of the zircon metamorphic rims are 241-230 Ma,representing the timing of high temperature metamorphism and shortened deformation of the Indosinian collision.In this period,the Laojunshan gneiss dome experienced the tectonic compression in association with high temperature metamorphism-deformation,which was superimposed by detachment and extensional exhumation in association with intense hydrothermal interaction and mineralization in the late stage.展开更多
文摘We investigate the accuracy and robustness of moment tensor(MT)and stress inversion solutions derived from acoustic emissions(AEs)during the laboratory fracturing of prismatic Barre granite specimens.Pre-cut flaws in the specimens introduce a complex stress field,resulting in a spatial and temporal variation of focal mechanisms.Specifically,we consider two experimental setups:(1)where the rock is loaded in compression to generate primarily shear-type fractures and(2)where the material is loaded in indirect tension to generate predominantly tensile-type fractures.In each test,we first decompose AE moment tensors into double-couple(DC)and non-DC terms and then derive unambiguous normal and slip vectors using k-means clustering and an unstructured damped stress inversion algorithm.We explore temporal and spatial distributions of DC and non-DC events at different loading levels.The majority of the DC and the tensile non-DC events cluster around the pre-cut flaws,where macro-cracks later develop.Results of stress inversion are verified against the stress field from finite element(FE)modeling.A good agreement is found between the experimentally derived and numerically simulated stress orientations.To the best of the authors’knowledge,this work presents the first case where stress inversion methodologies are validated by numerical simulations at laboratory scale and under highly heterogeneous stress distributions.
基金National Postdoctoral Program for Innovative Talent of China,Grant/Award Number:BX20200191National Natural Science Foundation of China,Grant/Award Number:52079068The State Key Laboratory of Hydroscience and Hydraulic Engineering,Grant/Award Number:2021-KY-04。
文摘The investigation of the in situ stress distribution has always been a key condition for engineering design of deep tunnels and analysis of surrounding rock stability.In this paper,a comprehensive judgment method coupled with pressure/tension(P/T)axis mechanism and geological structure is proposed to invert the in situ stress in the Duoxiongla tunnel in Xizang.In the process of TBM tunnel excavation,3887 groups of microseismic events were collected by means of microseismic monitoring technology.By studying the temporal and spatial distribution of 3887 groups of microseismic events,42 groups of microseismic data were selected for in situ stress inversion.Then the focal mechanisms of 42 groups of microseisms were inverted.Combined with the analysis of the previous geological survey,the inversion results of the in situ stress were analyzed.According to the focal mechanism of the tunnel area,the linear in situ stress inversion method was used to invert the in situ stress in the source area.Finally,according to the PTGS(pressure/tension axis mechanism and geological structure)comprehensive judgment method proposed in this paper,the in situ stress of the tunnel microseismic region was determined.The results show that there are mainly three groups of fissures and joint surfaces in the tunnel area,and the in situ stress is dominated by the horizontrun tectonic stress;the main driving force of the rupture surface in the excavation process of Duoxiongla tunnel is the horizontal tectonic stress;the distribution of the maximum and minimum principal stress obtained by the inversion is consistent with the distribution of the P/T axis;combined with the linear in situ stress inversion method and the comprehensive judgment of PTGS,the azimuth and dip angles of the three principal stresses are finally determined as N90.71°E,4.06°,N5.35°W,3.06°,and N8.10W,85.32°,respectively.The study verifies the feasibility of microseismic inversion of in situ stress.
基金supported by the National Natural Science Foundation of China(Grant Nos.41802224)Science for Earthquake Resilience of China Earthquake Administration(Grant Nos.XH23019YC and Nos.XH24021C)+2 种基金Joint Open Fund of Mengcheng National Geophysical Observatory(Grant Nos.MENGO-202306)Key R&D and Achievement Transformation Projects of the Science and Technology Program in Wuhu City,Anhui Province(2023yf007)Open Fund of Wuhan,Gravitation and Solid Earth Tides,National Observation and Research Station(Grant Nos.WHYWZ202209).
文摘This article presents an interpretation of the seismic source mechanisms for 905 earthquakes with MS>2.0,occurring in the central and southern sections of the Tan-Lu Fault Zone and its adjacent areas from 1970 to 2023.Utilizing the damped stress tensor method,we have inverted the spatial characteristics of the stress field variations in this study area,at a resolution of 1.0°×1.0°.The results indicate that the maximum principal stress direction within the central and southern sections of the Tan-Lu Fault Zone exhibits a spatially continuous change,rotating counterclockwise from East-West(EW)to Northeast-East(NEE),albeit with local variations.When dividing along the Tan-Lu Fault Zone,it is observed that on its western side—the North China block—a near EW stress field predominates.In contrast,on its eastern side—the Ludong-Huanghai Block—stress fields primarily exhibit NEE and Northeast-East(NE)orientations,underscoring the role of the Tan-Lu Fault Zone as a significant boundary between tectonic blocks.In regions located between latitudes 30°-34°N and longitudes 113°-115°E on the western side of these fault zone sections,maximum principal stress follows a radial distribution pattern indicative of a complex stress field.Conversely,on the eastern side of this fault zone,maximum principal stress direction remains relatively consistent,primarily displaying NEE and NE distributions.This reflects the fact that this area is situated under a tectonic background characterized by near NEE-NE direction for the Ludong-Huanghai Block.However,within an area bounded by latitudes 30°-32°N and longitudes 120°-122°E on the eastern flank of the Tan-Lu Fault Zone,maximum principal stress direction appears more intricate,with radial distribution patterns suggesting influences not only from near EW-NEE movements associated with the North China Block,but also from westward subduction processes related to Philippine Sea plate dynamics.Through our analysis of historical earthquakes in this region,we conclude that the moderate to strong seismic activity within this area is significantly related to the tectonic stress environment,with regions of complex tectonic stress often being the most seismically active.
基金sponsored by the National Key Technology R&D Program (2006BAC1B03-03-01),Chinathe Joint Earthquake Science Foundation(A07058),China
文摘With waveform data of 613 earthquakes with ML ≥ 2. 5 in the middle section of the Xiaojiang fault and its adjacent area which occurred during January,1998 to September 2007,focal mechanisms were calculated by the direct wave amplitude ratio of S /P in the vertical component and their characteristics were analyzed. According to regional tectonic features of the middle section of the Xiaojiang fault and its adjacent area,the study region was partitioned into two zones with the Xiaojiang fault as the boundary,e. g. zone A and zone B (including the Xiaojiang fault). In order to research the faults stress in detail,the Xiaojiang fault zone was picked out for independent analysis. The study region was also partitioned into 1°× 1° cells with a 0. 5° step. The stress fields of zone A,B and the fault zone were inverted with the FMSI method (Gephart,1990). The results show that first, the faults are mainly of strike-slip in the middle section and its adjacent area,amounting to 81. 28%,69. 23% and 72. 97% in the A,B and fault zones,respectively. Secondly,the stress inversion also indicates that the directions of maximum principal stress σ1 in the A, B,and fault zones are approximately NNW,NWW and NWW,the stress action is mainly horizontal,and strike-slip faulting is dominant in the study area. On the other hand,the direction of the principal stress field in the central Yunnan block changed from NNW to NWW,however,in the region between the Yuanmou and Pudu River faults,the azimuth of the main compressive stress shows that the north-south slip is obvious. While the direction of the main compressive stress of the Xiaojiang fault zone is nearly NW; in the east of the Xiaojiang fault,the direction of principal compressive stress is NW to NNW in the eastern Yunnan block.
基金sponsored by the Subject of City ActiveFault Exploration Program of Urumqi and Joint Foundation of Earthquake Administration of Xinjiang Uygur Autonomous Region (200704),China
文摘Using the focal mechanism solutions of 24 moderately strong earthquakes in the northern Tianshan area,we carried out system cluster and stress field inversion analysis.The result indicates that,the focal mechanism solutions of moderately strong earthquakes are mainly dip-slip reverse faulting in the northern Tianshan area.The principal rupture planes of earthquakes are NW-oriented.It is basically consistent with the strike of earthquake structure in its adjacent area.The direction of the principal compression stress P axis is nearly NS,and its inclination angle is small;while the inclination angle of the principal extensional stress T axis is large.It shows that the regional stress field is mainly controlled by the near-NS horizontal compressive stress.The direction of the maximum principal stress shows a gradation process of NNE-NS-NW from east to west.
文摘The North Tabriz fault is a segmented dextral fault in Northwest Iran, with a history of major destructive earthquakes that have repeatedly destroyed the city of Tabriz（current population 1.6 million）. The quiescence of the fault（last major temblor in 1854） and a lack of outcrop study have hampered stress analysis. Resolution of the stress states on the fault could be used for seismotectonic study along the North Tabriz fault and for understanding the geodynamics of the Arabia-Eurasia collision zone. Using fault-slip data collected from 88 localities in the fault system, we conducted an inversion analysis of this fault-slip data and analysis of the stratigraphic, geometric, and structural information. As a result, we confirmed that transcurrent deformation is prevalent on the North Tabriz fault and adjacent areas and is generally accomplished by predominant NW-SE-trending dextral and NE-SW-trending sinistral faults. Specifically, three separate tectonic episodes are recognised from the stress inversion data, consistent with the geologic data：（i） a post-Cretaceous and pre-Early Miocene compressional（Laramian） stress regime,（ii） an Early Miocene extensional stress regime, and（iii） modern tectonic episode with different local stress regimes（compressional and extensional） along the different segments of this fault.
文摘Paleostress plays a significant role in controlling the formation, accumulation, and distribution of reservoirs, and this could be an important factor in controlling the production of hydrocarbons from the unconventional reservoirs. In this study, we will use 3D seismic reflection data to perform the slip-tendency-based stress inversion to determine the stress field in the basement of the northern slope area in the Bongor Basin. The dataset for this technique is easily available in the oil and gas companies. The stress inversion results from the basement of the northern slope area of Bongor basin show that the maximum principal stress axis (σ1) is oriented vertically, the intermediate principal stress axis (σ2) is oriented N18° and the minimum principal stress axis (σ3) is oriented N105°, and σ2/σ1 = 0.60 and σ3/σ1 = 0.29. The findings of this paper provide significant information to understand the fault reactivation at the critical stage of hydrocarbon accumulation and the regional tectonic evolution.
基金partly funded by Open Fund of State Key Laboratory of Earthquake Dynamics,CEA(LED2011B05)the Foundation for the Returned Overseas of Shanxi Province(121)the National Science Fund of Shanxi Province(Youth,2010021005)
文摘A comprehensive study on regional stress field around the Taigu fault zone in Shanxi Province, China, was performed in this study. To get a better understanding of the present-day stress status in this area, 31 focal mecha- nisms of ML 〉3 earthquakes since 1965 were compiled, and the best stress tensor was then inverted based on the database. Additionally, magnetic fabrics along the Taigu fault zone were investigated to get an indication of the regional stress field in the past. Our results show that the present-day stress field around the Taigu fault zone is characterized by astable NW-SE extension with a strike- slip component, consistent with the geological surveys and recent GPS data. Results from magnetic fabrics indicate that the orientations of principal stress axes from magnetic fabrics of sedimentary rocks in Neogene coincide to the orientations of principal stress axes from focal mecha- nisms. The south segment of the Taigu fault displays more complicated magnetic fabrics and more activity of mod- erate earthquakes. It is connected with the Mianshan west fault and intersects with NW-SE striking Fenyang fault and the north fault of the Lingshi uplift at the south edge of Taiyuan basin. This may be the area needing more atten- tion in terms of seismic risk along the Taigu fault.
文摘Two earthquakes of Ms=6.0 and Ms=6. 1 consecutively occurred on December 31, 1994 and January 10, 1995 in Beibuwan region, China. By using the generalized reflection-transmission coefficient matrix and the discrete slowness integration method in the calculation of Green's functions, we obtained the focal mechanisms of these earthquakes using long-period waveforms of regional body waves recorded by the China Digital Seismograph Network (CDSN) by means of moment tensor inversion method in frequency domain. The results inverted indicate that the focal mechanisms of these two earthquakes were similar to each other. Their principal compressional stresses are in NW-SE direction and principal tensional stresses are in NE-SW direction. It turns out that the occurrence of the two earthquakes was controlled by the same tectonic environment related to the collision of the Philippine Plate and the Eurasian Plates. On the other hand, the results imply that the stress field in the seismogenic region has a significant change after the Ms=6.0 earthquake. It may be proposed that the occurrence of the Ms=6. 1 earthquake could be related to the stress field adjustment caused by the Ms=6.0 earthquake.
基金State Natural Science Foundation of China (40041001) Joint Seismological Science Foundation of China (201012).
文摘It has been proved through experiments that the electromagnetic radiation energy of a substance will vary when stress acts on the substance. This moment, the electromagnetic radiation energy (observation value) received by the remote sensor is triggered not only by the substance temperature and also by the stress. Separating quantitatively these two kinds of electromagnetic radiation energy and then inversing the actual temperature state and stress state of a medium is a matter with practical significance in earthquake prediction and stability monitoring for the large-scale geotechnical engineering. In this paper the principle and the mathematical method for inversing stress by using multiband remote sensing data are discussed in detail. A calculation example is listed.
基金supported by the National Natural Science Foundation of China(Grant No.52125903).
文摘Rock masses in alpine canyon areas exhibit strong heterogeneity,discontinuity,and are subject to strong tectonic effects and stress unloading,leading to extremely complex distribution of in-situ stress.In addition,the occurrence of layered rock masses makes it more complex,with obvious anisotropic mechanical properties.This study proposes a comprehensive method for evaluating the stability of layered rock spillway tunnels in a hydropower station in an alpine canyon.First,the failure criterion and mechanical model of layered rock masses considering the anisotropy induced by the bedding plane and the true triaxial stress regime were established;an inversion theory and calculation procedure for in-situ stress in alpine canyon areas were then introduced.Finally,by using a self-developed numerical tool,i.e.CASRock,the stability of the layered rock spillway tunnel in a hydropower station was numerically analyzed.The results show that,affected by geological structure and stratigraphic lithology,there is significant differentiation in the in-situ stress in alpine canyons,with horizontal tectonic stress as the main factor.The occurrence of layered rock masses in the region has a significant impact on the stability of surrounding rock,and the angle between the bedding strike and the tunnel axis as well as the bedding dip both exert a significant influence on the failure characteristics of the surrounding rock.
文摘On October 7,2021,a magnitude 5.9 earthquake struck the Harnai(Baluchistan)region of Pakistan,causing several fatalities and injuries within the epicentral area.First-order tectonic deformation in this region is caused by the convergence of the Indian Plate with respect to the Eurasian Plate.The Katwaz Block hinders the motion of the Indian Plate,resulting in the formation of strike-slip faults.In this study,the P-wave first-motion polarity technique was used to determine the mainshock faulting style.Cyclic scanning of the polarity solutions was applied to determine the most suitable focal mechanism solution among the available solutions generated by the FOCMEC(focal mechanism)software.The nodal planes correspond to different faulting styles(i.e.,thrust and strike-slip faulting).A nodal plane oriented in the NW-SE direction corresponded to a strike-slip mechanism,which was considered to be the fault plane.Tectonically,this earthquake was associated with the Harnai-Karahi strike-slip fault zone owing to the fault strike and direction of slip.The apparent stress drop,fault length,and moment magnitude of the Harnai earthquake were 35.4 bar,6.1 km,and 5.9,respectively.A lower b-value for the Gutenberg-Richter law was observed prior to the earthquake.Higherα-than b-values(α>b)indicate that this earthquake was governed by large events as opposed to small-magnitude events.The Harnai sequence had a decay exponent close to unity,lasted for 145 days,and produced few aftershocks.The study will help the future hazard mitigation in the region.
基金the National Science Fund for Distinguished Young Scholars(No.41925016)National Key Research and Development Program(No.2022YFB3903602)+1 种基金National Natural Science Foundation of China(No.42174023)the Frontier Cross Research Project of Central South University(No.2023QYJC006).
文摘The 2022 M_(W)6.7 Menyuan earthquake ruptured the western end of the Tianzhu seismic gap,providing an opportunity to study the regional seismogenic characteristics and seismic hazards.Here we use interferometric synthetic aperture radar(InSAR)and seismic data to study the mainshock rupture,early afterslip and the second largest aftershock of the 2022 Menyuan earthquake sequences.Our modeling results show that the mainshock ruptured the Lenglongling fault and the Tuolaishan fault with a maximum slip of~3 m.Rapid postseismic transient deformation occurred at the center of the Lenglongling fault.Our afterslip modeling reveals that the majority of afterslip occurred in the deeper part of the Lenglongling fault.A high-angle conjugated faulting event is found at the middle section of the Lenglongling fault.We use the stress inversion to investigate the possible triggering mechanism of the conjugated rupture event.The results indicate the maximum principal stress direction is in~222°,forming a~22°angle between the conjugated fault of second largest aftershock and the mainshock.The calculated normal stress changes indicate the region is within a pull-apart stress field,which favors such a conjugated rupturing event.Our study will help understand the rupture behavior of such kind of conjugated fault in other regions.
文摘Objective:The programmed death process of cells according to gene coding belongs to apoptotic natural extinction(PCD).The purpose of this study is to explore the phenomenon of“returning to old age and rejuvenating children”in the extreme anoxia,no nutrients and survival in the extreme environment of fish and earthworm.Methods:the adult earthworms were put into the sealed quartz sand or fine yellow sand plastic bottle with humidity of 35-40%70 ml and poured out 100-150 d,then put back into the natural environment(simulated natural plastic basin)and raised 100-150 d,to collect the experimental information.The same object can be observed repeatedly.Results:The earthworms which were closed in the little oxygen-free and nutrition-deficient vials were reduced by autophagy,and the rings and reproductive pores disappeared completely.When they were put back into the natural environment for two or three months,they were all restored to their original morphological structure.Conclusion:Most of the same subjects underwent 1-3 years of cyclic observation.The biological structure was adapted to the changing environment.It was helped by the resonance of many biota and complex stress factors.
基金the National Center for Seismology for providing waveform data and other necessary infrastructural support and computational facilitiessupervision of the entire research for completion of this researchwork.
文摘The southwestern region of the Delhi-National Capital Region (NCR) experiences sporadic micro (M ≤ 3.0) and occasional small (M > 3.0) earthquakes with a seasonal influence. This study integrates remote sensing and seismological data to elucidate the seismotectonic scenario and identify potential unmapped faults. Analysis of DEM data (Cartoset) reveals numerous multidirectional minor faults, some coincident or conjugate to known major faults. Earthquake epicentres spatially correlate with several of these delineated faults. Fault plane solutions suggest a transition from central normal faulting to peripheral thrust faulting. Moment tensor decomposition indicates dominant double-couple mechanisms with significant non-double-couple components for earthquakes ranging from Mw 2.5 to 4.4. A major variation in principal stress orientation is apparent between the eastern and western regions of the study area. Stress inversion reveals a NW-SE shortening direction and unusual principal axis plunges, suggesting a rare “odd” or “unknown” faulting regime. These findings suggest ongoing rifting in the eastern Alwar basin may be inducing thrusting in the surrounding region along pre-existing Aravalli-Delhi fold belt thrusts. Seismogenesis likely results from a complex interplay of faulting, regional tectonics, and fluid interaction. This study highlights the value of a multidisciplinary approach for unravelling the intricacies of seismotectonic in low-to-moderate seismicity regions, with varying strengths due to diverse structural heterogeneity associated with mapped or unmapped (hidden) faults, which have been delineated in this study, as an additional information for assessing seismic hazard potential for Delhi-NCR.
基金This work was financially supported by the National Key Research and Development Program(Grant No.SQ2017YFSF040030)the National Natural Science Foundations of China(Grant Nos.41972220&41722207).
文摘Middle-lower crust and mantle rocks are generally widely exposed in metamorphic core complex or gneiss dome,which is an ideal place to study the exhumation process related to regional extension and rheology.The Laojunshan metamorphic complex in southeastern Yunnan is located in a special tectonic position surrounded by the Cathaysia,Yangtze and Indochina blocks.It is composed of different metamorphic-deformation rocks and granitic intrusions.There also are many economic deposits(e.g.,tin and tungsten)that are spatially and genetically associated with the formation and exhumation of the Laojunshan gneiss dome.Based on detailed analysis of macro-and microscopic structure,stress field distribution and deformation condition,the tectonic units of the Laojunshan metamorphic complex show obvious characteristics of doming,as well as of typical structural units of metamorphic core complex.It has strongly deformed metamorphic gneiss core(footwall),detachment fault system and sedimentary cover(hanging wall)with lightly metamorphism and deformation.The footwall of gneiss dome presents a strongly ductile deformation domain,accompanied by different ages of granitic intrusions.The distribution of developed foliation and lineation within granitic gneisses are arc-shaped and radial,respectively,with a nearly N-S trending from the footwall to the hanging wall.Mylonitization of deformed rocks gradually weakens and transits to orthogneiss as it moves away from the detachment fault toward the footwall.The low angle detachment fault between the footwall and the hanging wall shows an arc-like shape feature.Mylonite fabrics are preserved in the deformed rocks of the detachment fault,which are mainly composed of chloritized schist,fault breccia,cataclasite and fault gouge.A large number of normal faults are developed in detachment faults and hanging wall,and their stress fields radiate in an arc around the footwall.Zircon U-Pb ages of amphibolite and granitic gneiss from the footwall range from 445 to 420 Ma,indicating the timing of Caledonian magmatic emplacement and the main formation period of the Laojunshan gneiss dome.U-Pb ages of the zircon metamorphic rims are 241-230 Ma,representing the timing of high temperature metamorphism and shortened deformation of the Indosinian collision.In this period,the Laojunshan gneiss dome experienced the tectonic compression in association with high temperature metamorphism-deformation,which was superimposed by detachment and extensional exhumation in association with intense hydrothermal interaction and mineralization in the late stage.
