Numerical Simulation of Coal Floor Fault Activation Influenced by Mining

By means of the numerical simulation software ANSYS, the activation regularity of coal floor faults caused by mining is simulated. The results indicate that the variation in horizontal, vertical and shear stresses, as well as the horizontal and vertical displacements in the upper and the lower fault blocks at the workface are almost identical. Influ- enced by mining of the floor rock, there are stress releasing and stress rising areas at the upper part and at the footwall of the fault. The distribution of stress is influenced by the fault so that the stress isolines are staggered by the fault face and the stress is focused on the rock seam around the two ends of the fault. But the influence in fault activation on the upper or the lower fault blocks of the workface is markedly different. When the workface is on the footwall of the fault, there is a horizontal tension stress area on the upper part of the fault; when the workface is on the upper part of the fault, it has a horizontal compressive stress area on the lower fault block. When the workface is at the lower fault block, the maximum vertical displacement is 5 times larger then when the workface is on the upper fault block, which greatly in- creases the chance of a fatal inrush of water from the coal floor.

Sliding modes of fault activation under constant normal stiffness conditions

Fault activation has been the focus of research community for years.However,the studies of fault activation remain immature,such as the fault activation mode and its major factors under constant normal stiffness(CNS)conditions associated with large thickness of fault surrounding rock mass.In this study,the rock friction experiments were conducted to understand the fault activation modes under the CNS conditions.Two major parameters,i.e.the initial normal stress and loading rate,were considered and calibrated in the tests.To reveal the response mechanism of fault activation,the local strains near the fault plane were recorded,and the macroscopic stresses and displacements were analyzed.The testing results show that the effect of displacement-controlled loading rate is more pronounced under the CNS conditions than that under constant normal load(CNL)conditions.Both the normal and shear stresses drop suddenly when the stick-slip occurs.The decrease and increase of the normal stress are synchronous with the shear stress in the regular stick-slip scenario,but mismatch with the shear stress during the chaotic stick-slip process.The results are helpful for understanding the fault sliding mode and the prediction and prevention of fault slip.

Analysis of insidious fault activation and water inrush from the mining floor

Based on the stress field distribution rule of the mining floor under abutment pressure, we have established a simplified mechanical model, which contains multiple factors relating to activation and evolution of insidious water-conductive faults. The influence of normal and shear stresses on fault activation and effective shear stress distribution in the fault plane was acquired under mining conditions.Using fracture mechanics theory to calculate the stress intensity factor of an insidious fault front, we have derived the criterion for main fault activation. Results indicate that during the whole working face advance, transpressions are exerted on fault planes twice successively in opposite directions. In most cases, the second transpression is more likely to lead to fault activation. Activation is influenced by many factors, predominant among which are: burial depth of the insidious fault, friction angle of the fault plane, face advance direction and pore water pressure. Steep fault planes are more easily activated to induce a sustained water inrush in the face.

Analysis on activation laws caused by coal mining in fault footwall and its criterion

The system research aimed at activation laws caused by coal mining in fault footwall based on the rock strata me- chanics theory in this paper. According to the three-belt characteristics of overlying strata above mined-out area, the fault acti- vation effect was divided into the following three periods： the initial activation, the excessive activation and the ultimate activation. Corresponding activation criterion was also deduced by the mechanics theory. Results of engineering example and numerical analysis show that the activation criterion can reflect the activation laws of fault caused by coal mining.

Dynamic response of mountain tunnel,bridge,and embankment along the Sichuan-Tibet transportation corridor to active fault based on model tests

The Sichuan-Tibet transportation corridor is prone to numerous active faults and frequent strong earthquakes.While extensive studies have individually explored the effect of active faults and strong earthquakes on different engineering structures,their combined effect remains unclear.This research employed multiple physical model tests to investigate the dynamic response of various engineering structures,including tunnels,bridges,and embankments,under the simultaneous influence of cumulative earthquakes and stick-slip misalignment of an active fault.The prototype selected for this study was the Kanding No.2 tunnel,which crosses the Yunongxi fault zone within the Sichuan-Tibet transportation corridor.The results demonstrated that the tunnel,bridge,and embankment exhibited amplification in response to the input seismic wave,with the amplification effect gradually decreasing as the input peak ground acceleration(PGA)increased.The PGAs of different engineering structures were weakened by the fault rupture zone.Nevertheless,the misalignment of the active fault may decrease the overall stiffness of the engineering structure,leading to more severe damage,with a small contribution from seismic vibration.Additionally,the seismic vibration effect might be enlarged with the height of the engineering structure,and the tunnel is supposed to have a smaller PGA and lower dynamic earth pressure compared to bridges and embankments in strong earthquake zones crossing active faults.The findings contribute valuable insights for evaluating the dynamic response of various engineering structures crossing an active fault and provide an experimental reference for secure engineering design in the challenging conditions of the Sichuan-Tibet transportation corridor.

Formation mechanism of fault accommodation zones under combined stress in graben basin:Implications from geomechanical modeling

A fault accommodation zone is a type of structure that is defined as regulating displacement and strain between faults structure.Increasing numbers of fault accommodation zones are being identified in graben basins,indicating the potential exploration target and petroleum accumulation areas.This study aims to analyze the formation mechanism and development of fault accommodation zones under combined stress by a numerical simulation method considering geomechanical modeling.Using three-dimensional(3-D)seismic interpretation and fractal dimension method,exampled with the Dongxin fault zone,the fault activity and fault combination pattern were conducted to quantitatively characterize the activity difference in fault accommodation zones.Combined with mechanical experiment test,a geomehcanical model was established for fault accommodation zones in a graben basin.Integrating the paleostress numerical simulations and structural physical simulation experiment,the developmental characteristics and genetic mechanism of fault accommodation zones were summarized.Influenced by multi movements and combined stresses,three significant tectonic evolution stages of the Dongxing Fault Zone(DXFZ)were distinguished:During the E_(s)^(3)sedimentary period,the large difference in the stress,strain,and rupture distribution in various faults were significant,and this stage was the key generation period for the prototype of the DXFZ,including the FAZ between large-scale faults.During the E_(s)^(2)sedimentary period,the EW-trending symmetric with opposite dipping normal faults and the NE-SW trending faults with large scale were furtherly developed.The junction area of two secondary normal faults were prone to be ruptured,performing significant period for inheriting and developing characteristics of fault accommodation zones.During the Es1 sedimentary period,the high-order faults in the DXFZ exhibited the obvious fault depressions and strike-slip activity,and the fault accommodation zones were furtherly inherited and developed.This stage was the molded and formative period of the FAZ,the low-order faults,and the depression in the DXFZ.

Seismic analysis of the active character of the Taihang Mountain piedmont fault

The Taihang Mountain piedmont fault is a large-scale structure zone in north and east China which cross Beijing,with the NE-NNE extent spans approximately 620 km.It is very important to determine the fault zone activity due to the close relation of active structures and earthquakes.Regarding the fault activity,there are three different opinions：1） it is a large deep fault zone;2） it is an active fault zone and an earthquake structure belt;and 3） it is not an earthquake structure belt.In order to ascertain the active character of the fault,the deep tectonic setting and the activity since the Quaternary were investigated using recent seismic and drilling data to make a joint interpretation.The investigation results show that the Taihang Mountain piedmont fault is not a large lithospheric fault because the early middle Pleistocene（Q（P2）） layers are offset by the fault and the late middle Pleistocene（Q（P2）） and late Pleistocene layers are not offset by the fault.We determine that the Taihang Mountain piedmont fault in the area is not an active fault and is also not a large lithospheric fault.This study result provides important geological and geophysical data for city planning and construction in Hebei province and, especially,has great significance for seismic hazard assessment of the capital area.

The numerical simulation and inversion fitting of radon concentration distribution in homogeneous overburden above active fault zones

Based on the convection and diffusion mechanisms of radon migration, in this paper we deduce the two-dimensional differential equation for radon transportation in the overburden above active fault zones with an unlimited extension along the strike. Making use of the finite difference method, the radon concentration distribution in the overburden above active faults is calculated and modeled. The active fault zone parameters, such as the depth and the width of the fault zone, and the value of radon concentration, can be inverted from the measured radon concentration curve. These realize quantitative interpretation for radon concentration anomalies. The inversion results are in good agreement with the actual fault zone parameters.

Active Faulting Pattern,Present-day Tectonic Stress Field and Block Kinematics in the East Tibetan Plateau

This paper examines major active faults and the present-day tectonic stress field in the East Tibetan Plateau by integrating available data from published literature and proposes a block kinematics model of the region. It shows that the East Tibetan Plateau is dominated by strike-slip and reverse faulting stress regimes and that the maximum horizontal stress is roughly consistent with the contemporary velocity field, except for the west Qinling range where it parallels the striking of the major strike-slip faults. Active tectonics in the East Tibetan Plateau is characterized by three faulting systems. The left-slip Kunlun-Qinling faulting system combines the east Kunlun fault zone, sinistral oblique reverse faults along the Minshan range and two major NEE-striking faults cutting the west Qinling range, which accommodates eastward motion, at 10--14 mm/a, of the Chuan-Qing block. The left-slip Xianshuihe faulting system accommodated clockwise rotation of the Chuan-Dian block. The Longmenshan thrust faulting system forms the eastern margin of the East Tibetan Plateau and has been propagated to the SW of the Sichuan basin. Crustal shortening across the Longmenshan range seems low （2-4 mm/a） and absorbed only a small part of the eastward motion of the Chuan-Qing block. Most of this eastward motion has been transmitted to South China, which is moving SEE-ward at 7-9 mm/a. It is suggested from geophysical data interpretation that the crust and lithosphere of the East Tibetan Plateau is considerably thickened and theologically layered. The upper crust seems to be decoupled from the lower crust through a decollement zone at a depth of 15-20 kin, which involved the Longmenshan fault belt and propagated eastward to the SW of the Sichuan basin. The Wenchuan earthquake was just formed at the bifurcated point of this decollement system. A rheological boundary should exist beneath the Longmenshan fault belt where the lower crust of the East Tibetan Plateau and the lithospheric mantle of the Yangze block are juxtaposed.

Quaternary Geology and Faulting in the Damxung-Yangbajain Basin

The detailed geological mapping, conducted in the Damxung-Yangbajain basin, shows that there are many types of deposits formed since the Pliocene. The oldest sediments are formed during the Pliocene. The most prominent sediments are three sets of moraines and fluvioglacial deposits. The ESR, U-series and OSL dates indicate they are formed about 700-500 ka B.P., 250-125 ka B.P. and 75-12 ka B.P. respectively and indicate that there are three glacial periods since the mid-Pleistocene in the Nyainqentanglha Range. Along the southeast side of the Nyainqentanglha Range, the main southeast dipping fault zone which bounds the Damxung-Yangbajain Graben on its western edge was mapped. The fault zone consists of three secondary fault zones and their initiation ages that the fault zones became active gradually decrease southeastward. Prominent faulting occurred in about 700-500 ka B.P., 350-220 ka B.P., -140 ka B.P. and 70-50 ka B.P. since the mid-Pleistocene. The height of fault scarps which offset the sediments formed since the mid-Pleistocene suggest that the vertical slip rates change between 0.4 -2 mm/a and the cumulative average vertical movement at rates of 1.1±0.3 mm/a during the Quaternary period and the Holocene vertical throw rate is 1.4±0.6 mm/a along the fault zones on the western side of the Damxung-Yangbajain Graben.

Distribution patterns of rock mass displacement in deeply buried areas induced by active fault creep slip at engineering scale

Active fault creep slip induces deformation of rock mass buried deeply in fault zones that significantly affect the operational safety of long linear projects passing through it.Displacement distribution patterns of rock masses in active fault zones which have been investigated previously are the key design basis for such projects.Therefore,a discrete element numerical model with different fault types,slip time,dip angles,and complex geological features was established,and then the creep slip for normal,reverse,and strike-slip faults were simulated to analyze the displacement distribution in the fault rock mass.A disk rotation test system and the corresponding laboratory test method were developed for simulating rock mass displacement induced by creep slippage of faults.A series of rotation tests for softand hard-layered specimens under combined compression and torsional stress were conducted to verify the numerical results and analyze the factors influencing the displacement distribution.An S-shaped displacement distribution independent of fault dip angle was identified corresponding to reverse,normal,and strike-slip faults.The results indicated that the higher the degree of horizontal extrusion,the softer the rock mass at the fault core,and the higher the degree of displacement concentration in the fault core;about 70%of the creep slip displacement occurs within this zone under 100 years of creep slippage.

Earthquake recurrence on whole active fault zones and its relation to that on individual fault-segments

Based on the earthquake data of 11 active intraplate fault zones of the Chinese mainland, we have studied the earthquake recurrence behaviors on entire active fault zones and their relations to those on individual fault-segments. The results show that the earthquake recurrence on entire active fault zones, each of them is made up of multiple segments, displays three types of behavior, i.e., the clustering behavior, the random behavior, and the poor quasi-periodic behavior. The major one is the sparse clustering behavior, its recurrence process often exhibits that clusters (active periods) and gaps (quiescent periods) occur alternatively in varying degrees. The recurrence intervals within and between clusters, the durations of individual clusters, the earthquake number and strength of every cluster are all variable. The recurrence process is non-linear, there is neither the strength-time dependence nor the time-strength dependence. However, the earthquake recurrence processes on individual fault-segments are much more simple, and mainly display either the quasi-periodic or the time-predictable behaviors. Also, this study further discovers that the temporal clustering in earthquake recurrence process on entire fault zones is mainly caused by the rupture 'contagion' on different fault-segments within relatively short periods of time. Along active fault zones, the degree and orientation of rupture 'contagion' may vary with different seismic cycles, and the 'contagion' seems to be able to jump over unbroken 'gaps' on the fault zones.

Earthquake probabilities and magnitude distribution (M≥6.7) along the Haiyuan fault, northwestern China

In recent years, some researchers have studied the paleoearthquake along the Haiyuan fault and revealed a lot of paleoearthquake events. All available information allows more reliable analysis of earthquake recurrence interval and earthquake rupture patterns along the Haiyuan fault. Based on this paleoseismological information, the recur- rence probability and magnitude distribution for M≥6.7 earthquakes in future 100 years along the Haiyuan fault can be obtained through weighted computation by using Poisson and Brownian passage time models and consid- ering different rupture patterns. The result shows that the recurrence probability of MS≥6.7 earthquakes is about 0.035 in future 100 years along the Haiyuan fault.

Shallow crustal velocity structures revealed by active source tomography and fault activities of the Mianning–Xichang segment of the Anninghe fault zone, Southwest China

The Anninghe fault is a large left-lateral strike-slip fault in southwestern China. It has controlled deposition and magmatic activities since the Proterozoic, and seismic activity occurs frequently. The Mianning-Xichang segment of the Anninghe fault is a seismic gap that has been locked by high stress. Many studies suggest that this segment has great potential for large earthquakes(magnitude >7). We obtained three vertical velocity profiles of the Anninghe fault(between Mianning and Xichang) based on the inversion of P-wave first arrival times. The travel time data were picked from seismograms generated by methane gaseous sources and recorded by three linearly distributed across-fault dense arrays. The inversion results show that the P-wave velocity structures at depths of 0-2 km corresponds well with the local lithology. The Quaternary sediments have low seismic velocities, whereas the igneous rocks,metamorphic rocks, and bedrock have high seismic velocities. We then further discuss the fault activities of the two fault branches of the Anninghe fault in the study region based on small earthquakes(magnitudes between ML 0.5 and ML 2.5) detected by the Xichang array.The eastern fault branch is more active than the western branch and that the fault activities in the eastern branch are different in the northern and southern segments at the border of 28°21′N. The high-resolution models obtained are essential for future earthquake rupture simulations and hazard assessments of the Anninghe fault zone. Future studies of velocity models at greater depths may further explain the complex fault activities in the study region.

Features of the fault system and its relationship with migration and accumulation of hydrocarbon in Liaodong Bay

The fault system of Liaodong Bay developed extensively under the control of the Tanlu Fault. The fault system can be grouped into strike-slip faults of grade Ⅰ, trunk faults of grade Ⅱand branch faults （induced faults） of grade Ⅲ respectively based on its developmental scale. The faults of grade Ⅰ and Ⅱwere deep, early and large while the faults of grade Ⅲwere shallow, late and small. The formation, evolution and distribution features played a significant role in controlling the migration of oil and gas in both horizontal and vertical directions. The fluid transfer in the fault system occurred in the process of faulting. The strike-slip and trunk faults moved actively forming predominant pathways for oil and gas migration. The branch faults, with weak activity, generally controlled the development of traps and were beneficial for the accumulation and preservation of oil and gas. The faults of grade Ⅰ and Ⅱ formed the major migration pathways for oil and gas, but their fault activity rates appeared to vary along their strikes. The zones with a relatively low fault activity rate might be favorable for oil and gas accumulation. When the activities of strike-slip, trunk, and branch faults came to a halt, the fault seal behavior had a vitally important effect on the accumulation of oil and gas. The controlling role of the fault over fluid distribution was further analyzed by calculating the fault activity quantitatively.

Main active faults and seismic activity along the Yangtze River Economic Belt:Based on remote sensing geological survey

The Yangtze River Economic Belt(YREB)spans three terrain steps in China and features diverse topography that is characterized by significant differences in geological structure and presentday crustal deformation.Active faults and seismic activity are important geological factors for the planning and development of the YREB.In this paper,the spatial distribution and activity of 165 active faults that exist along the YREB have been compiled from previous findings,using both remote-sensing data and geological survey results.The crustal stability of seven particularly noteworthy typical active fault zones and their potential effects on the crustal stability of the urban agglomerations are analyzed.The main active fault zones in the western YREB,together with the neighboring regional active faults,make up an arc fault block region comprising primarily of Sichuan-Yunnan and a“Sichuan-Yunnan arc rotational-shear active tectonic system”strong deformation region that features rotation,shear and extensional deformation.The active faults in the central-eastern YREB,with seven NE-NNE and seven NW-NWW active faults(the“7-longitudinal,7-horizontal”pattern),macroscopically make up a“chessboard tectonic system”medium-weak deformation region in the geomechanical tectonic system.They are also the main geological constraints for the crustal stability of the YREB.

Faulting on the Anninghe fault zone,Southwest China in Late Quaternary and its movement model

The Anninghe fault is one of the significant earthquake-generating fault zones in the Southwest China. Local historical record shows that a M2≥7 strong earthquake occurred in the year of 1536. On the basis of the detailed air-photographic interpretation and field investigation, we have acquired the following knowledge： ① The average sinistral strike-slip rate since the Late Pleistocene is about 3～7 mm/a; ② There is important reverse faulting along the fault zone besides the main left-lateral strike-slip motion, and the shortening rate across the Anninghe fault zone due to the reverse faulting is about 1.7-4.0 mm/a. If the Xianshuihe fault zone is simply partitioned into the Anninghe and Daliangshan faults, we can also get a slip rate of 3-7 mm/a along the Daliangshan fault zone, which is the same as that on the Anninghe fault zone. Moreover, on the basis of our field investigation and the latest knowledge concerning the active tectonics of Tibetan crust, we create a dynamic model for the Anninghe fault zone.

A Comprehensive Investigation of an Offshore Active Fault in the Western Sagami Bay, Central Japan

Offshore active faults, especially those in the deep sea, are very difficultto study because of the water and sedimentary cover. To characterize the nature and geometry ofoffshore active faults, a combination of methods must be employed. Generally, seismic profiling isused to map these faults, but often only fault-related folds rather than fracture planes are imaged.Multi-beam swath bathymetry provides information on the structure and growth history of a faultbecause movements of an active fault are reflected in the bottom morphology. Submersible anddeep-tow surveys allow direct observations of deformations on the seafloor (including fracture zonesand microstructures). In the deep sea, linearly aligned cold seep communities provide indirectevidence for active faults and the spatial migration of their activities. The Western Sagami Bayfault (WSBF) in the western Sagami Bay off central Japan is an active fault that has been studied indetail using the above methods. The bottom morphology, fractured breccias directly observed andphotographed, seismic profiles, as well as distribution and migration of cold seep communitiesprovide evidence for the nature and geometry of the fault. Focal mechanism solutions of selectedearthquakes in the western Sagami Bay during the period from 1900 to 1995 show that the maximumcompression trends NW-SE and the minimum stress axis strikes NE-SW, a stress pattern indicating aleft-lateral strike-slip fault.

Analyses of active faults, seismic activities and sea floor unstable factors of the Zhujiang River Mouth Basin and its adjacent areas

-On the basis of the data of geophysics and seismic activities, the analyses of the active faults, seismic activities and the sea floor unstable factors of the Zhujiang River Mouth Basin have been made so as to study the characteristics of the compressional subactive continental margin of Cathaysian system, arc littoral strongly active fracture zone, the division of seismic subzone and seismic zone of the continental margin of northern South China Sea, the potential focal area, and to analyze the regional stability. We consider that the Zhujiang River Mouth Basin belongs to a stable or a moderately stable region.

Present-day Block Movement and Fault Activity on the Eastern Margin of the Tibetan Plateau

The geology and tectonics in the eastern margin of Tibetan Plateau are complex. The main tectonic framework is composed of blocks and faults. Using discontinuous global positioning system survey data for 2008–2014, the velocity field for the Eurasia reference framework was obtained. Based on the velocity field, the present-day velocities of the blocks and boundary faults were estimated. The results reveal that the movement rates of the Chuan-Qing, South China, Chuan-Dian and Indo-China blocks are（17.02±0.60） mm/a,（8.77±1.51） mm/a,（13.85±1.31） mm/a and（6.84 ± 0.74） mm/a, respectively, and their movement directions are 99.5°, 120.3°, 142.9° and 153.3°, respectively. All blocks exhibit clockwise rotation. The displacement rates of the Xianshuihe, Longmenshan, Anninghe, Zemuhe, Xiaojiang and Red River faults are（7.30±1.25–8.30±1.26） mm/a,（10.07±0.97–11.79±0.89） mm/a,（0.96±0.74–2.98±1.73） mm/a,（2.03±0.49–3.20±0.73） mm/a,（3.45±0.40–6.02±0.50） mm/a and（6.23±0.56） mm/a, respectively. The Xianshuihe, Anninghe, Zemuhe and Xiaojiang faults show leftlateral strike-slip movement, while the Longmenshan and Red River faults show right-lateral strikeslip. These characteristics of the blocks and faults are related to the particular tectonic location and dynamic mechanism.