Identification methods for anomalous stress region in coal roadways based on microseismic information and numerical simulation

It is believed that the microseismicity induced by mining effect and gas gradient disturbance stress is a precursor to the essential characteristics of roadway unstability. In order to effectively identify and evaluate the stability of coal roadways in the process of mine development and extraction, a microseismic monitoring system was deployed for the study of the stress evolution process, damage degree and distribution characteristics in the tailgate and headgate. The mine under study is the 62113 outburst working face of Xin Zhuangzi coalmine in Huainan mining area. The whole process of microfractures initiation,extension, interaction and coalescence mechanisms during the progressive failure processes of the coal rock within the delineated and typical event clusters were investigated by means of a two dimensional realistic failure process analysis code(RFPA2D-Flow). The results show that the microseismic events gradually create different-sized event clusters. The microseismicity of the tailgate is significantly higher than that of the headgate. The study indicates that the greater anomalous stress region matches the area where microfractures continuously develop and finally connect to each other and form a fissure zone.Due to the mine layout and stress concentration, the ruptured area is mainly located on the left shoulder of the tailgate roof. The potential anomalous stress region of the coal roadway obtained by numerical simulation is relatively in good agreement with the trend of spatial macro evolution of coal rock microfractures captured by the microseismic monitoring system. The research results can provide important basis for understanding instability failure mechanism of deep roadway and microseismic activity law in complex geologic conditions, and it ultimately can be used to guide the selection and optimization of reinforcement and protection scheme.

Characteristics of transfer zones under the influence of preexisting faults and regional stress transformation:Wenchang A subsag,Zhujiang River Mouth Basin,northern South China Sea

A transfer zone in rift basins preserves important information on regional tectonic evolution and plays significant roles in hydrocarbon accumulation.Based on the systematic analysis of 3D seismic data and hydrocarbon accumulation conditions,the geometry,kinematics,and reservoir control of a large synthetic overlapping transfer zone in the south of the Wenchang A subsag in the Zhujiang(Pearl)River Mouth basin were investigated.Results indicate that the development and evolution of the transfer zone was controlled by the interaction between pre-existing faults and regional stress transformation.The intense rifting of the main faults of the transfer zone controlled the development of source rocks and faultcontrolled slope break paleogeomorphology.The strike-slip overprint since the Oligocene is conducive to the formation of a large-scale fault-anticline trap,and the secondary faults in the transfer zone contribute to the hydrocarbon transportation.The conjugate intersection area of the NE-and NW-trending faults offers more opportunity for hydrocarbon migration and accumulation.

Regional stress field in Yunnan revealed by the focal mechanisms of moderate and small earthquakes

We determined focal mechanism solutions of 627 earthquakes of magnitude M ≥ 3.0 in Yunnan from January 2008 to May 2018 by using broadband waveforms recorded by 287 permanent and temporary regional stations. The results clearly revealed predominantly strike-slip faulting characteristics for earthquakes in Yunnan, with focal depths concentrated in the top 10 km of the crust. The earthquake mechanisms obtained were combined with the global centroid moment tensor solutions of 80 additional earthquakes from 1976 to 2016 to invert for the regional variations of stress field orientation by using a damped regional-scale stress inversion scheme.Results of the stress field inversion confirmed that the Yunnan region is under a strike–slip stress regime, with both maximum and minimum stress axes being nearly horizontal. The maximum compressional axes are primarily oriented in a northwest-southeast direction, and they experience a clockwise rotation from north to south, whereas the maximum extensional axes are oriented largely northeast-southwest. The maximum compressional axes are in line with the global positioning system–inferred horizontal velocity field and the southeastward escape of the Sichuan–Yunnan Rhombic Block, whereas the maximum extensional axes are consistent with anisotropy derived from SKS splitting. Against the strike–slip background, normal faulting stress regimes can be seen in the Tengchong volcanic area as well as in other areas with complex crisscrossing fault zones.

Variation of stress field in the source region around a strong shock：an example

An earthquake with magnitude 6.6 occurred on November 16,1983 in the Kaoiki,Hawii.The hierarchical clustering analyses were made by stages for the focal mechanism solutions of 74 earthquakes with M≥3.0 in this area from 1977 to 1985,it was found that each type of focal mechanism is roughly with invariable percentage,and that the strike-slip events including the mainshock,which did not appear in other stages,occurred in the stage around M=6.6 mainshock.The dominant types in the other stages were depressed in the period around the mainshock. This is a believable precursor phenomena.orientation of the principal axes of stress field was inversed by fitting slip vector based on the focal mechanisms in the different periods.The results show that the stress field around the main shock with M=6.6 was more stable,its maximum and minimum principal axes is nearly horizontal in EW and NS direction respectively,the middle one is nearly vertical.The middle principal axis of stress field in the other periods appeared to be horizontal and the corresponding seismic rupture horizontally slip with a small dip.The significant difference between the stress field of source region in the period around the strong shock and that in the other periods shows that the seismogeny and occurrence of the strong shock were controlled by the variation of stress field.The characteristic environment factors of Kaoiki region and its effects were discussed.

In search of potential earthquake source regions in the Chinese mainland in the light of ambient shear stress field

Earth media are incomplete media.There exist many cracks in it. The achievements of fracture mechanics showthat the strength of the incomplete materials will be much lower than that of the complete materials. We consider that earthquake occurrence is the result of unstable propagation of a crack in crust media in proper conditionand the earthquake rupture is the phenomenon of a failure by fast fracture under applied low shear stress. It hasalready been explained by fracture mechanics.The occurrence of failure by fast fracture is necessarily associated with the presence of high level concentration of local stress and strain. The elastic/plastic stress analysis in cracked pieces by Dugdale indicates that thestate of stress at the tip of a crack takes a very important role to crack propagation. A plastic zone has necessarilyformed in the tip of a crack due to stress concentration. Therefore, the dislocations st the tip of a crack are naturally a plastic displacement, rather than elastic one. The plastic displacement, where τ0 is appliedshear stress which is equivalent to initial or tectonic shear stress when the quake occurs, a is the half length of acrack, It is the rigidity,τy is the yield stresses in shear. The main seismic dislocations take place exactly at theends of the crack where the plastic zone had been formed. SO, a critical assumption is adopted, i. e. we assumethe dislocation D(1,,t) as formula (5) in text. The maximum earthquake dislocation, whereL is the fault length. If p is taken the value in the upper crust, μ=33 GPa; and τy is taken the average valuegiven from laboratories,τy= 30 MPa. Thus, according to observation values of Dmax and L, using the formula,one can estimate the initial shear stresses for large earthquakes. Computations show that the initial shear stressesfor large earthquakes all over the world are about 5-20 MPa which have some differences between regions.We further research the characteristics of source spectra and have derived the dependent relation of bodywave magnitude mb on the shear stress τ0 and seismic moment M, as formula (11)in text. Thus, the formulaprovides a POssibility of computation of large amount of tectonic shear stress values from seismic data. We consider that the tectonic shear stress field is a main factor which controls the earthquake occurrence. The regions withhigh tectonic shear stress values are considered to be prone to occur great earthquakes (Ms>6) and called earthquake hazard regions. Based on this criterion, τ0 values for all earthquakes with mb≥3. 8 all over China since1987 have been computed, and the great earthquake hazard regions with magnitude ranges have been zoned inthe Chinese mainland.During April 1992 -January 31, 1994, there were 9 Ms≥6 earthquakes which occurred in the Chinesemainland, 8 earthquakes of the 9 had fallen into the regions delineated by us prior to the earthquake occurrence,with only one failure. This new approach as a method for medium--term prediction of strong earthquakes hasbeen proved by practice to be an efficient one.It has good physical bases and bright prospect and worth furtherresearch. Received February 7,1994 1 Accepted February 10, 1995.Contribution No. 95A0061, Institute of Geophysics,SSB, China.

Research on the Dynamic Change of Regional Stress Fields before the M_S8.0 Wenchuan Earthquake

Using the digital telemetric seismic waveform data of Chengdu and Kunming, this article studies the focal mechanism solutions and the apparent stress values of a large number of small earthquakes, and then analyzes the dynamic variation of regional stress fields and the spatio- temporal distribution of apparent stress values. The annual variation values of the azimuth of average principal stress field before the May 12, 2008 Ms8.0 Wenchuan earthquake in the Sichuan-Yunnan region were 58° from 2003 to 2004, 85° from 2003 to 2005,61° from 2006 to 2007 and 90° from 2006 to April 2008 respectively. In recent years, deflection or disturbances occurred in the azimuth of the average principal stress field in the Sichuan-Yunnan region. Analysis shows that this may be related to the change of stress field states of crustal blocks before and after the December 26, 2004 Ms9.0 Sumatra earthquake and the 2008 Ms8.0 Wenchuan earthquake. The ratio of thrust-type earthquakes in the Sichnan-Qinghai block was on the higher side in the period from 2006 to 2007, and the source faulting type of the regional moderate and small earthquakes had changed before the Ms8.0 Wenchnan earthquake. The change of state of the stress field is consistent with the changes in block displacement fields revealed by GPS data and the crustal shortening velocity vertical to the Longmenshan fault zone. Based on the radiation energy calculated from all bands of the seismic waveform, the value of apparent stress σapp is obtained. The fluctuation shape of the fitting trend of the apparent stress is related to the intensity of regional seismicity. It reveals that the micro- dynamic fluctuation process of the regional stress value is similar to the azimuth transition of the regional principal compressive stress field, which can be used to probe for pregnant physical processes. Areas with a higher value of apparent stress σapp are possible areas of potential seismic risk. It can be seen from the spatial distribution of the medium and shortterm apparent stress σapp before the Ms8.0 Wenchuan earthquake, the Longmenshan fault zone is in a low stress distribution area, and the relatively high apparent stress is in the peripheral area. These images may show medium and short-term locking phenomena near the seismogenic tectonics of the Ms8.0 Wenchuan earthquake. For example, changes with time of the focal parameter consistency of the sub-blocks in Sichuan and Yunnan Provinces, continual increase of thrust-type earthquakes in the Sichuan-Qinghai block and the appearance of spatial distribution areas of high apparent σapp stress. The work on this aspect was continued after the Ms8.0 Wenchuan earthquake, and the results seem to be shown a clearer relationship between these phenomena and future great earthquakes.

Influence of regional background stress fields on the spontaneous rupture of the major faults around Xiluodu dam,China

Simulations of the spontaneous rupture of potential earthquakes in the vicinity of reservoir dams can provide accurate parameters for seismic resilience assessment,which is essential for improving the seismic performance of reservoir dams.In simulations of potential spontaneous ruptures,fault geometry,regional stress fields,constitutive parameters of the fault friction law,and many other factors control the slip rate,morphology,and dislocation of the rupture,thereby affecting the simulated ground motion parameters.The focus of this study was to elucidate the effects of the background stress field on the nucleation and propagation of spontaneous ruptures based on the factors influencing potential M>7 earthquake events on the Leibo Middle Fault(LBMF)and the Mabian-Yanjing Fault(MB-YJF)in the Xiluodu dam(XLD)region.Our simulation results show that the magnitude of the regional background stress field plays a decisive role in whether a destructive earthquake exceeding the critical magnitude will occur.We found that the direction and magnitude of the regional stress significantly affect the range of rupture propagation on the fault plane,and fault geometry affects the spatial distribution of the rupture range.Under the same regional stress field magnitude and orientation,a more destructive,high-magnitude earthquake is more likely to occur on the LBMF than on the MB-YJF.

Region Division and Stress Analysis for Plate Roller Leveling Process

The flatness of leveled plate is settled by residual stress. According to stress distribution simulated by FEM software ANSYS/LS-DYNA, the plate can be divided into non-steady region and steady region. The nonsteady region is composed of four zones, two of which are about half of leveling roller pitch at leading and end edges and other two are about 10% of the width at lateral edges. The steady region is the rest part enclosed by the non-steady regions. It is helpful to improve the leveling process by analyzing forming mechanism of each region and selecting suitable processes settings.

Estimation of the stress levels in the focal region before and after the 2001 M=8.1 Western Kunlun Mountain Pass earth-quake

A method estimating the stress level in the focal region of an earthquake is proposed here. Taking the 2001 M=8.1 Western Kunlun Mountain Pass earthquake as an example, we estimate its stress level in the focal region before and after it by this method. The results show that the stress level in the focal region just prior to the initiation of this event is approximately 6.3-8 MPa, and about 5-6.7 MPa remained in the focal region after its occurrence. The stress in the focal region decreased by roughly twenty percent after this event.

Regional Stress Field and Seismic Dynamics Along the Border Zone Between Fujian, Guangdong and Jiangxi Provinces

The regional stress field and seismic dynamics along the border zone between Fujian, Guangdong and Jiangxi Provinces are studied based on the seismo-geological data,GPS measurement, and seismicity. The results show that: (1) the principal compressional stress of the stress field is oriented in NW-SE direction and the principal extensional stress is in NE-SW direction; (2) the WNW-ward compression and collision of the Philippine Sea Plate to the eastern coast of Taiwan Island are the most direct and most important dynamic source for preparation and occurrence of strong earthquakes in the Taiwan Region and along the border zone between Fujian, Guangdong and Jiangxi Provinces.

Determinations of directions of the mean stress field in Sichuan-Yunnan region from a number of focal mechanism solutions

Based on the spatial orientation and slip direction of the fault plane solutions, we present the expression of corresponding mechanical axis tensor in geographic coordinate system, and then put forward a method for calculating average mechanical axis tensor and its eigenvalues, which involves solving the corresponding eigenequation. The method for deducing mean stress field from T, B, and P axes parameters of a number of focal mechanism solutions has been verified by inverting data of mean stress fields in Fuyun region and in Tangshan region with fitting method of slip direction, and both results are consistent. To study regional average stress field, we need to choose a population of focal mechanism solutions of earthquakes in the massifs where there are significant tectonic structures. According to the focal mechanism solutions of 256 moderate-strong earthquakes occurred in 13 seismic zones of Sichuan-Yunnan region, the quantitative analysis results of stress tensor in each seismic zone have been given. The algorithm of such method is simple and convenient, which makes the method for analyzing tectonic stress field with large amount of focal mechanism solution data become quantified.

Characteristics of the Mesozoic and Cenozoic Tectonic Stress Fields of the Urumqi-Usu Region, Xinjiang

Based on the study of folds and related conjugate shear joints, the tectonic stress fields of the Urumqi-Usu region to the north of the North Tianshan Mountains have been reconstructed. Furthermore the author discussed the tectonic movements and their dynamic features. The early tectonic movement in the investigated region occurred from the end of the Late Jurassic to the initial stage of the Early Cretaceous, with the maximum (tensile) and minimum (compressional) principal stress trajectories in the tectonic stress field being in E-W and S-N directions respectively; the late tectogenesis took place from the end of the Early Pleistocene to the initial Middle Pleistocene, with the maximum and minimum principal stress trajectories in the late stress field striking in WNW and NE-NNE directions respectively. Through computer-aided simulated calculation by the finite element method and analysis of geological structure, it has been ascertained that the early tectogenesis is a nearly N-S compressive movement and the late one a NE to nearly N-S compressive movement with reverse shear. The dynamic force which caused the tectogeneses came from the movement of the southern major fault, i.e. the North Tianshan Mountains.

Ambient tectonic shear stress field in Southern California and seismic hazard regions

ccording to the fracture mechanics rupture model of earthquakes put forward by us, several equations to compute tectonic ambient shear stress value τ0 have been derived [equations (1), (2), (3), (5)].τ0 values for intermediate and small earthquakes occurred in Chinese mainland and Southern California have been calculated by use of these equations. The results demonstrate that the level and distribution of τ0 are closely related to the location where large earthquakes will occur, i.e. the region with higher level of τ0 will be prone to occur large earthquakes and the region with lower level will usually occur small earthquakes. According to the spatial distribution of τ0 , the seismic hazard regions or the potential earthquake source regions can in some degree be determined. According to the variation of τ0 with time, the large earthquake occurrence time can be roughly estimated. According to the distribution of τ0 in Southern California and variation with time, three high stress level regions are determined, one (Goldfield area) of them is the present seismic hazard region.

STRESS METAMORPHISM AND ISOTOPIC AGE OF SHEAR ZONE GRANITOID TECTONITES OF IRTYSH SHEAR ZONE (ALTAI REGION)

The Irtysh shear zone (ISZ) of Altai region is the lineament structure of the collision suture type, where granites of Kalba complex and granodiorites of Zmeinogorsk complex are exposed to regional gneiss formation and stress metamorphic alterations. This study is based on detailed structural observations at special grounds using optical and electron microscopy, and on the behavior analysis of isotopic systems from altered granitoids.Within the ISZ area we have established the continuous rows of granitoid stress metamorphism from initial recrystallization of protolite, its cataclasis and mechanical flaring up to complete recrystallization with alteration of mineral composition and formation of the streaky complexes of granite tectonites of blastomylonite and blastocataclasite types. The directed alteration of rocks has several impulse and is expressed by a change in morphology of mineral grains and their relations, magnification of deformation component in the rock structure, and formation of new mineral phases on the basis of initial ones without surface fluidization. At transformation of isotopic systems from granitoid, their feldspars, biotite and hornblende, we can observe “rejuvenation” of the rock substrate from 270-290 Ma for Kalba granitoids to 220-235 Ma for their tectonites, and for Rudny Altai granodiorites, their ages changes from 285-317 Ma to 232-257 Ma for their tectonites.

Changes in stress within grassland ecosystems in the three counties of the source regions of the Yangtze and Yellow Rivers

Based on a database of more than 40 years of second production process and energy flow records for Maduo,Qumalai and Yushu counties,a dynamic model of the stress within grassland ecosys-tems was established using a nonlinear regression method for this source regions of the Yangtze and Yel-low Rivers.The results show that dynamic curves of stress within grassland ecosystems in the three coun-ties were in the shape of an inverted 'U' during the period 1965-2007.It also revealed that the variation in actual amount of livestock inventories reflected the general trends of the stress within the grassland eco-systems in the source regions,although there were many other factors for the increase or reduction in grassland ecosystem stress.

Quantifying the impacts of soil water stress on the winter wheat growth in an arid region,Xinjiang

Wheat growth in response to soil water deficit play an important role in yield stability. A field experiment was conducted for winter wheat (Triticum aestivum L.) during the period of 2002-2005 to evaluate the effects of limited irrigation on winter wheat growth. 80%, 70%, 60%, 50% and 40% of field capacity was applied at different stages of crop growth. Photosynthetic characteristics of winter wheat, such as photosynthesis rate, transpiration rate, stomatal conductance, photosynthetically active radiation, and soil water content, root and shoot dry mass accumulation were measured, and the root water uptake and water balance in different layer were calculated. Based on the theory of unsaturated dynamic, a one-dimensional numerical model was developed to simulate the effect of soil water movement on winter wheat growth using Hydrus-1 D. The soil water content of stratified soil in the experimental plot was calculated under deficit irrigation. The results showed that, in different growing periods, evapotranspiration, grain yield, biomass, root water uptake, water use efficiency, and photosynthetic characteristics depended on the controlled ranges of soil water content. Grain yield response to irrigation varied considerably due to differences in soil moisture contents and irrigation scheduling between seasons. Evapotranspiration was largest in the high soil moisture treatment, and so was the biomass, but this treatment did not produce the highest grain yield and root water uptake was relatively low. Maximum depth of root water uptake is from the upper 80 cm in soil profile in jointing stage and dropped rapidly upper 40 cm after heading stage, and the velocity of root water uptake in latter stage was less than that in middle stage. The effect of limited irrigation treatment on photosynthesis was complex owing to microclimate. But root water uptake increased linearly with harvest yield and improvement in the latter gave better root water uptake under limited irrigation conditions. Appropriately controlled soil water contents can improve the root water uptake and grain yield. Consistently high values of root water uptake and grain yield were produced under conditions of mild water deficit at the seedling and start of regrowth to stem-elongation stages, in addition to a further soil water depletion at the physiological maturity to harvest stage. We suggest that periods of mild soil water depletion in the early vegetative growth period together with severe soil water depletion in the maturity stage of winter wheat is an optimum for limited irrigation regime in this oasis. Considerable potential for further improvement in agricultural water use efficiency in the arid zone depends on effective conservation of moisture and efficient use of the limited water.

Improved stress release model: Application to the study of earthquake prediction in Taiwan Region

Stress release model used to be applied to seismicity study of large historical earthquakes in a space of large scale. In this paper, we improve the stress release model, and discuss whether the stress release model is still applicable or not in the case of smaller spatio-temporal scale and weaker earthquakes. As an example of testing the model, we have analyzed the M greater than or equal 6 earthquakes in recent about 100 years. The result shows that the stress release model is still applicable. The earthquake conditional probability intensity in Taiwan Region is calculated with the improved stress release model. We see that accuracy of earthquake occurrence time predicted by the improved stress release model is higher than that by Poisson model in the test of retrospect earthquake prediction.

COMPUTATION OF STRESS INTENSITY FACTORS BY THE SUB-REGION MIXED FINITE ELEMENT METHOD OF LINES

Based on the sub-region generalized variationM principle, a sub-region mixed version of the newly-developed semi-analytical ＇finite element method of lines＇ （FEMOL） is proposed in this paper for accurate and efficient computation of stress intensity factors （SIFs） of two-dimensional notches/cracks. The circular regions surrounding notch/crack tips are taken as the complementary energy region in which a number of leading terms of singular solutions for stresses are used, with the sought SIFs being among the unknown coefficients. The rest of the arbitrary domain is taken as the potential energy region in which FEMOL is applied to obtain approximate displacements. A mixed system of ordinary differential equations （ODEs） and algebraic equations is derived via the sub-region generalized variational principle. A singularity removal technique that eliminates the stress parameters from the mixed equation system eventually yields a standard FEMOL ODE system, the solution of which is no longer singular and is simply and efficiently obtained using a standard general-purpose ODE solver. A number of numerical examples, including bi-material notches/cracks in anti-plane and plane elasticity, are given to show the generally excellent performance of the proposed method.

基于Region多层结构P2P计算网络应用层多播协议分析

在基于Region多层结构P2P计算网络模型下,对表征该模型下实施应用层多播协议的数据通道传输质量指标压力和伸展率进行了较为详尽研究,分析了Region规模k和网络规模N对数据通道传输质量指标的影响,并量化了指标,给出了计算公式,并提出了在实际应用中应综合考虑伸展率和压力的思想。通过理论和模拟仿真分析得:伸展率与网络或Region的规模几乎无关,压力与网络或Region的规模成正比;降低伸展率会导致压力增加,反之亦然;数据通道上的伸展率为O(logN),节点的压力为O(1)。

基于Region多层结构P2P计算网络模型

分布式P2P网络Gnutella模型中共享信息查询的路由协议为“洪泛”算法,其协议机制仅在应用层实现,缺乏对Internet底层通信子网路由资源的利用,存在可扩展性、性能与效率不高的问题.以“小世界和幂规律”模型为理论基础,以层和域为基本逻辑管理单位,按用户需求和共享目的组织域,提出了基于Region多层结构P2P网络模型RLP2P(region-layerP2P),实现了其系统原型;实现了一个优化的MultilayerLight-Gossip分级路由策略;量化分析了表征模型数据通道质量指标的压力和伸展率,提出了综合考虑压力和伸展率的思想.模拟分析表明,RLP2P模型可以有效地解决可扩展性、性能与效率不高问题,且网络规模越大,其综合性能的优越性越明显,因此,模型是合理、有效的.