Advances in seismological methods for characterizing fault zone structure

Large earthquakes frequently occur along complex fault systems.Understanding seismic rupture and long-term fault evolution requires constraining the geometric and material properties of fault zone structures.We provide a comprehensive overview of recent advancements in seismological methods used to study fault zone structures,including seismic tomography,fault zone seismic wave analysis,and seismicity analysis.Observational conditions limit our current ability to fully characterize fault zones,for example,insufficient imaging resolution to discern small-scale anomalies,incomplete capture of crucial fault zone seismic waves,and limited precision in event location accuracy.Dense seismic arrays can overcome these limitations and enable more detailed investigations of fault zone structures.Moreover,we present new insights into the structure of the Anninghe-Xiaojiang fault zone in the southeastern margin of the Qinghai-Xizang Plateau based on data collected from a dense seismic array.We found that utilizing a dense seismic array can identify small-scale features within fault zones,aiding in the interpretation of fault zone geometry and material properties.

Microearthquake reveals the lithospheric structure at midocean ridges and oceanic transform faults

Mid-ocean ridge and oceanic transforms are among the most prominent features on the seafloor surface and are crucial for understanding seafloor spreading and plate tectonic dynamics,but the deep structure of the oceanic lithosphere remains poorly understood.The large number of microearthquakes occurring along ridges and transforms provide valuable information for gaining an indepth view of the underlying detailed seismic structures,contributing to understanding geodynamic processes within the oceanic lithosphere.Previous studies have indicated that the maximum depth of microseismicity is controlled by the 600-℃isotherm.However,this perspective is being challenged due to increasing observations of deep earthquakes that far exceed this suggested isotherm along mid-ocean ridges and oceanic transform faults.Several mechanisms have been proposed to explain these deep events,and we suggest that local geodynamic processes(e.g.,magma supply,mylonite shear zone,longlived faults,hydrothermal vents,etc.)likely play a more important role than previously thought.

Cooperative structure of Li/Ni mixing and stacking faults for achieving high-capacity Co-free Li-rich oxides

Co-free Li-rich layered oxides(LLOs)are emerging as promising cathode materials for Li-ion batteries due to their low cost and high capacity.However,they commonly face severe structural instability and poor electrochemical activity,leading to diminished capacity and voltage performance.Herein,we introduce a Co-free LLO,Li_(1.167)Ni_(0.222)Mn_(0.611)O_(2)(Cf-L1),which features a cooperative structure of Li/Ni mixing and stacking faults.This structure regulates the crystal and electronic structures,resulting in a higher discharge capacity of 300.6 mA h g^(-1)and enhanced rate capability compared to the typical Co-free LLO,Li_(1.2)Ni_(0.2)Mn_(0.6)O_(2)(Cf-Ls).Density functional theory(DFT)indicates that Li/Ni mixing in LLOs leads to increased Li-O-Li configurations and higher anionic redox activities,while stacking faults further optimize the electronic interactions of transition metal(TM)3d and non-bonding O 2p orbitals.Moreover,stacking faults accommodate lattice strain,improving electrochemical reversibility during charge/discharge cycles,as demonstrated by the in situ XRD of Cf-L1 showing less lattice evolution than Cf-Ls.This study offers a structured approach to developing Co-free LLOs with enhanced capacity,voltage,rate capability,and cyclability,significantly impacting the advancement of the next-generation Li-ion batteries.

Fault Identification for Shear-Type Structures Using Low-Frequency Vibration Modes

Shear-type structures are common structural forms in industrial and civil buildings,such as concrete and steel frame structures.Fault diagnosis of shear-type structures is an important topic to ensure the normal use of structures.The main drawback of existing damage assessment methods is that they require accurate structural finite element models for damage assessment.However,for many shear-type structures,it is difficult to obtain accurate FEM.In order to avoid finite elementmodeling,amodel-freemethod for diagnosing shear structure defects is developed in this paper.This method only needs to measure a few low-order vibration modes of the structure.The proposed defect diagnosis method is divided into two stages.In the first stage,the location of defects in the structure is determined based on the difference between the virtual displacements derived from the dynamic flexibility matrices before and after damage.In the second stage,damage severity is evaluated based on an improved frequency sensitivity equation.Themain innovations of this method lie in two aspects.The first innovation is the development of a virtual displacement difference method for determining the location of damage in the shear structure.The second is to improve the existing frequency sensitivity equation to calculate the damage degree without constructing the finite elementmodel.Thismethod has been verified on a numerical example of a 22-story shear frame structure and an experimental example of a three-story steel shear structure.Based on numerical analysis and experimental data validation,it is shown that this method only needs to use the low-order modes of structural vibration to diagnose the defect location and damage degree,and does not require finite element modeling.The proposed method should be a very simple and practical defect diagnosis technique in engineering practice.

Structural Style and Hydrocarbon Prospectivity of the Growth Faults Related Structures in the Bengal Basin

The structural and tectonic evolution of the Bengal Basin is characterized by a complex interplay of factors, including sedimentation, the rise of the Himalayan Mountains, and the movements of Jurassic syn-rift faults. This study aims to comprehend the progression of growth faults inside the basin by examining fault geometry, basin development, and structural relief patterns. We used high-quality 2D seismic lines from the PK-MY-8403, classical seismic interpretation techniques and modeling were carried out to reveal the plate tectonic conditions, stratigraphy, and sedimentation history of the basin. The break-up unconformity, Paleocene and Eocene submerged conditions, and crucial geological formations including the Sylhet Limestone, Barail Group, and Surma Group were among the notable features recognized in seismic section. With an emphasis on growth strata and pre-growth strata, significant variations in layer thickness and relief were remarked in different stratigraphic levels. Basin development events like the evolution of the Miocene remnant ocean basin, sedimentation in Oligocene, Eocene Himalayan collision, and the Pliocene reverse fault development are analyzed. In the early the Pliocene compressional forces outpaced sedimentation rates and syn-depositional normal faults of Oligocene time began to move in opposite direction. Syn-depositional growth faults may have formed in the Bengal Basin as a result of this reversal. This research provides a detailed comprehensive knowledge of growth fault development in the Bengal Basin following the seismic interpretation, modelling, and thickness/relief analysis. The outcomes point to a substantial hydrocarbon potential, especially in regions like the Eocene Hinge Zone, where the prospectivity of the area is enhanced by carbonate reefs and Jalangi shale. However, the existence of petroleum four-way closure in the investigated region requires further investigation.

Three-dimensional structural models,evolution and petroleum geological significances of transtensional faults in the Ziyang area,central Sichuan Basin,SW China

With drilling and seismic data of Transtensional(strike-slip)Fault System in the Ziyang area of the central Sichuan Basin,SW China plane-section integrated structural interpretation,3-D fault framework model building,fault throw analyzing,and balanced profile restoration,it is pointed out that the transtensional fault system in the Ziyang 3-D seismic survey consists of the northeast-trending F_(I)19 and F_(I)20 fault zones dominated by extensional deformation,as well as 3 sets of northwest-trending en echelon normal faults experienced dextral shear deformation.Among them,the F_(I)19 and F_(I)20 fault zones cut through the Neoproterozoic to Lower Triassic Jialingjiang Formation,presenting a 3-D structure of an“S”-shaped ribbon.And before Permian and during the Early Triassic,the F_(I)19 and F_(I)20 fault zones underwent at least two periods of structural superimposition.Besides,the 3 sets of northwest-trending en echelon normal faults are composed of small normal faults arranged in pairs,with opposite dip directions and partially left-stepped arrangement.And before Permian,they had formed almost,restricting the eastward growth and propagation of the F_(I)19 fault zone.The F_(I)19 and F_(I)20 fault zones communicate multiple sets of source rocks and reservoirs from deep to shallow,and the timing of fault activity matches well with oil and gas generation peaks.If there were favorable Cambrian-Triassic sedimentary facies and reservoirs developing on the local anticlinal belts of both sides of the F_(I)19 and F_(I)20 fault zones,the major reservoirs in this area are expected to achieve breakthroughs in oil and gas exploration.

Characteristics of geological structures in Shiling and Zhuanshanhu areas of Yehe Uplift,NE China

The basin marginal fault system is the key to understand the formation and evolution of Songliao Basin.In order to investigate the influence of marginal fault system on the structural evolution of Songliao Basin,a comprehensive study was conducted on Shiling Town and Zhuanshanhu area of Yehe Town in Siping City of Jilin Province,where is the southeastern margin of the Songliao Basin and there are a series of well-exposed fault,fold and intrusive bodies belonging to the main marginal fault system of the Songliao Basin known as the Jiamusi-Yitong(Jia-Yi)fault zone.Through profile measurement and field investigation,samples with various lithologies and distinctive features were collected.Detailed field and laboratory works include component and microstructure analysis of these samples,rock-rock contact analysis,main strike measurement and statistics analysis.These data reveal the structural characteristics of the fold,fault and intrusive bodies in the study area.The research results show that the folds are distributed in the Mesozoic strata near the main fault of the eastern branch of the Jia-Yi fault zone,and the folded strata involve the Cretaceous Denglouku and Quantou formations.In addition,the section is dominated by high-angle strikeslip thrust faults.Light-colored veins and dark-colored veins are extensively distributed in the exposed granites.Statistical analysis of joint and fault attitudes in the study area reveals a right-lateral strike-sliping along the main fault.The large-scale right-lateral strike-slip and thrust fault system in Shiling Town occurred in right-lateral transpressive stage in Late Cretaceous.Based on the results above,tectonic evolution sequence in Shiling section of the Jia-Yi fault zone during the Mesozoic can be divided into five stages:Middle Jurassic left-lateral ductile strike-slip stage,Late Jurassic compression stage,Early Cretaceous tension stage,Early Cretaceous extension stage and Late Cretaceous right-lateral transpressive stage.These may have important constraint on understanding the Mesozoic evolution of the Songliao Basin.

Detailed sedimentary structure of the Mianning segment of the Anninghe fault zone revealed by H/V spectral ratio

The Anninghe fault is a major left-lateral strike-slip fault in southwest China and a seismic gap with a potential earthquake larger than MW 7.0 lies in the Mianning-Xichang segment according to recent observations.The shallow structure of this region can offer a glimpse into the geometry of the fault,which plays an important role in earthquake hazard mitigation.To further investigate the sedimentary structure of the Anninghe fault zone,two dense linear arrays with a station spacing of around 80 m were deployed across the fault.In this study,the H/V spectral ratio(HVSR),together with its peak frequency at each station site,was obtained by applying the Nakamura method.Our findings demonstrate that the peak frequency behaves in high correlation with lithology and is controlled by topography.HVSR in foothills or regions with magmatic intrusion shows a single peak at about 2–3 Hz.In locations with abundant Quaternary sedimentation,such as Anninghe valleys and fracture zones,another low-frequency peak around 0.4 Hz can be noticed in HVSR.By using the empirical relationship,the thickness of the sedimentary layer around the fault fracture zone is estimated to be 300–600 m.Furthermore,the sedimentary interface shows a downward dip to the east,possibly influenced by the east-west extrusion stress.Considering the resonance effect,buildings with 6–9 stories in the valley area of the Anninghe require additional attention in earthquake hazard prevention.

Relationship between gravitational flap structures in the backlimb of anticlinal breakthrough Fault-Propagation Folds:case study of the Southern-Central Tunisian Atlas

The development of orogenic belts structures in the Southern-Central Tunisian Atlas is influenced by the evolution of tectonic activities during different phases,which are also closely linked to the formation of gravitational collapse structure.The typical example is that of the northern flank of the Jebel Orbata particularly the Ben Zannouch fold.It is an asymmetrical anticline interpreted by the model of“Fault Propagation Folds”.The development of the Ben Zannouch structures is resulted from landslides,scree falls and inverted layers plunging to the south.The direction of resulted gravitational structure is parallel to the main thrust direction of the Bou Omrane anticline.The thrust activity of Bou Omrane fault is associated to the important paleo-slope facing south and plastic lithology(incompetent marl layers)of outcropped series,facilitates the development of the Ben Zannouch Flap structure.The definition of gravitational collapse structures for the first time in Tunisia particularly in the northern flank of the Jebel Orbata is controlled by many principal structural conditions:fragmentation of the landslide surfaces,rheology and topography.Other regional factors can be distinguished in the Southern-Central Tunisian Atlas as the seismic activity of the pre-existing Gafsa fault reactivated during compressive phases and the weather conditions during the postglacial period.

Fault Analysis and Structure Optimization of Traveling Transmission System of Shuttle Car

This paper firstly introduces the common faults of traveling transmission system of shuttle car.Secondly,by analyzing the characteristics of shuttle car structure,the layout of traveling transmission system and the common faults on shuttle car,this paper concludes that"internal holding torque"is the main cause of faults.Finally,this paper proposes a corresponding optimization design scheme to reduce the impact of"internal torque",and calculates the relevant results through the finite element simulation analysis method.Through these analyses and calculations,it is shown that the method can effectively reduce the probability of failure of traveling transmission system of shuttle car.

Internal structure of Longmenshan fault zone at Hongkou outcrop,Sichuan,China,that caused the 2008 Wenchuan earthquake

This paper reports the internal structures of the Beichuan fault zone of Longmenshan fault system that caused the 2008 Wenchuan earthquake, at an outcrop in Hongkou, Sichuan province, China. Present work is a part of comprehensive project of Institute of Geology, China Earthquake Administration, trying to understand deformation processes in Longmenshan fault zones and eventually to reproduce Wenchuan earthquake by modeling based on measured mechanical and transport properties. Outcrop studies could be integrated with those performed on samples recovered from fault zone drilling, during the Wenchuan Earthquake Fault Scientific Drilling （WFSD） Project, to understand along-fault and depth variation of fault zone properties. The hanging wall side of the fault zone consists of weakly-foliated, clayey fault gouge of about 1 m in width and of several fault breccia zones of 30-40 m in total width. We could not find any pseudotachylite at this outcrop. Displacement during the Wenchuan earthquake is highly localized within the fault gouge layer along narrower slipping-zones of about 10 to 20 mm in width. This is an important constraint for analyzing thermal pressurization, an important dynamic weakening mechanism of faults. Overlapping patterns of striations on slickenside surface suggest that seismic slip at a given time occurred in even narrower zone of a few to several millimeters, so that localization of deformation must have occurred within a slipping zone during coseismic fault motion. Fault breccia zones are bounded by thin black gouge layers containing amorphous carbon. Fault gouge contains illite and chlorite minerals, but not smectite. Clayey fault gouge next to coseismic slipping zone also contains amorphous carbon and small amounts of graphite. The structural observations and mineralogical data obtained from outcrop exposures of the fault zone of the Wenchuan earthquake can be compared with those obtained from the WFSD-1 and WFSD-2 boreholes, which have been drilled very close to the Hongkou outcrop. The presence of carbon and graphite, observed next to the slipping-zone, may affect the mechanical properties of the fault and also provide useful information about coseismic chemical changes.

Crustal structure in Xiaojiang fault zone and its vicinity

Based on the integrative interpretation of travel-time data and amplitude information obtained from the deep seismic sounding experiment on the Chuxiong-Luoping profile, eastern Yunnan province, carried out in January of 2005, we present a 2-D P wave velocity structure along the profile. The crustal structure shows remarkable contrasts between the two sides of the Xiaojiang fault zone, although the whole profile is situated within the Yangtze platform. The average P wave velocities of the crust on the west and east sides of the fault zone are 6.21 km/s and 6.32 km/s, respectively, and the crustal thicknesses are 41 km and 45 km, respectively. These results imply that the crust to the east of the Xiaojiang fault zone presents characteristics of crustal structure in a stable platform, while the crust to the west is complicated with a lower velocity zone in middle of the upper crust. The average velocity of 6.21 km/s is lower than the global continental crustal average （6.30 km/s）, indicating that the region is tectonically active. According to the lateral variation of velocity and depth of interfaces （including the Moho）, it is inferred that the Xiaojiang fault zone has cut through the whole crust. It is also deduced that existence of low velocity zone in middle of the upper crust is conducive to the south-southeastern sliding of the Sichuan- Yunnan （Chuan-Dian） rhombus block.

Rock Damage Structure of the South Longmen-Shan Fault in the 2008 M8 Wenchuan Earthquake Viewed with Fault-Zone Trapped Waves and Scientific Drilling

This article is to review results from scientific drilling and fault-zone trapped waves （FZTWs） at the south Longman-Shan fault （LSF） zone that ruptured in the 2008 May 12 M8 Wenchuan earthquake in Sichuan,China.Immediately after the mainshock,two Wenchuan Fault Scientific Drilling （WFSD） boreholes were drilled at WFSD-1 and WFSD-2 sites approximately 400 m and 1 km west of the surface rupture along the Yinxiu-Beichuan fault （YBF）,the middle fault strand of the south LSF zone.Two boreholes met the principal slip of Wenchuan earthquake along the YBF at depths of 589-m and 1230-m,respectively.The slip is accompanied with a 100-200-m-wide zone consisting of fault gouge,breccia,cataclasite and fractures.Close to WFSD-1 site,the nearly-vertical slip of ～4.3-m with a 190-m wide zone of highly fractured rocks restricted to the hanging wall of the YBF was found at the ground surface after the Wenchuan earthquake.A dense linear seismic array was deployed across the surface rupture at this venue to record FZTWs generated by aftershocks.Observations and 3-D finite-difference simulations of FZTWs recorded at this cross-fault array and network stations close to the YBF show a distinct low-velocity zone composed by severely damaged rocks along the south LSF at seismogenic depths.The zone is several hundred meters wide along the principal slip,within which seismic velocities are reduced by ～30-55％ from wall-rock velocities and with the maximum velocity reduction in the ～200-m-wide rupture core zone at shallow depth.The FZTW-inferred geometry and physical properties of the south LSF rupture zone at shallow depth are in general consistent with the results from petrological and structural analyses of cores and well log at WFSD boreholes.We interpret this remarkable low-velocity zone as being a break-down zone during dynamic rupture in the 2008 M8 earthquake.We examined the FZTWS generated by similar earthquakes before and after the 2008 mainshock and observed that seismic velocities within fault core zone was reduced by ～10％ due to severe damage of fault rocks during the M8 mainshock.Scientific drilling and locations of aftershocks generating prominent FZTWs also indicate rupture bifurcation along the YBF and the Anxian-Guangxian fault （AGF）,two strands of the south LSF at shallow depth.A combination of seismic,petrologic and geologic study at the south LSF leads to further understand the relationship between the fault-zone structure and rupture dynamics,and the amplification of ground shaking strength along the low-velocity fault zone due to its waveguide effect.

Development characteristics of the fault system and its control on basin structure, Bodong Sag, East China

The Bodong Sag,located in the Bohai Sea,offshore China,is one of the most petroliferous basins in China.Based on three dimensional seismic reflection data and time slice data,we analyze the fault system of the Bodong area in detail,establish the fault structure pattern of different types and summarize the distribution of the fault system.It is concluded that the development characteristics of the Cenozoic fault system are in accordance with the dextral stress field of the Tanlu Fault,which displayed a brush structure with NNE strike-slip faults as its principal faults,NE-trending extensional faults as secondary faults and EW-trending faults as minor faults.Faults can be divided into （1） strike-slip type,（2） extensional type,（3） strike-slip extensional type and （4） extensional strike-slip type.The spatial structures of different faults have obvious differences because of the fault properties and activity intensity.The fault system at different stages shows tremendous differences because of the transition of the Tanlu Fault from sinistral strike-slip to dextral strike-slip,the transition between extension and strike-slip,and the transition from mantle upwelling to thermal subsidence.According to the controlling effect of faults on basin structure,the Cenozoic basin experienced four evolutionary stages,（a） transition stage from sinistral strike-slip to dextral strike-slip,（b） strike-slip extensional faulted stage,（c） extensional strike-slip faulted stage and （d） strike-slip depression stage.The identification of temporal and spatial differences of faults could be used as a significant guideline for oil and gas exploration in the Bodong area.

Sensor fault diagnosis of nonlinear processes based on structured kernel principal component analysis

A new sensor fault diagnosis method based on structured kernel principal component analysis （KPCA） is proposed for nonlinear processes. By performing KPCA on subsets of variables, a set of structured residuals, i.e., scaled powers of KPCA, can be obtained in the same way as partial PCA. The structured residuals are utilized in composing an isolation scheme for sensor fault diagnosis, according to a properly designed incidence matrix. Sensor fault sensitivity and critical sensitivity are defined, based on which an incidence matrix optimization algorithm is proposed to improve the performance of the structured KPCA. The effectiveness of the proposed method is demonstrated on the simulated continuous stirred tank reactor （CSTR） process.

Fault detection and accommodation via neural network and variable structure control

This paper proposes a novel idea that classifies faults into two different kinds： serious faults and small faults, and treats them with different strategies respectively. A kind of artificial neural network （ANN） is proposed for detecting serious faults, and variable structure （VS） model-following control is constructed for accommodating small faults. The proposed framework takes both advantages of qualitative way and quantitative way of fault detection and accommodation. Moreover, the uncertainty case is investigated and the VS controller is modified. Simulation results of a remotely piloted aircraft with control actuator failures illustrate the performance of the developed algorithm.

Using structure restoration maps to comprehensively identify potential faults and fractures in compressional structures

Faults and fractures of multiple scales are frequently induced and generated in compressional structural system. Comprehensive identification of these potential faults and fractures that cannot be distinguished directly from seismic profile of the complex structures is still an unanswered problem. Based on the compressional structural geometry and kinematics theories as well as the structural interpretation from seismic data, a set of techniques is established for the identification of potential faults and fractures in compressional structures. Firstly, three-dimensional(3D) patterns and characteristics of the faults directly interpreted from seismic profile were illustrated by 3D structural model. Then, the unfolding index maps, the principal structural curvature maps, and tectonic stress field maps were obtained from structural restoration. Moreover, potential faults and fractures in compressional structures were quantitatively identified relying on comprehensive analysis of these three maps. Successful identification of the potential faults and fractures in Mishrif limestone formation and in Asmari dolomite formation of Buzurgan anticline in Iraq demonstrates the applicability and reliability of these techniques.

Electrical Structure and Fault Features of Crust and Upper Mantle beneath the Western Margin of the Qinghai-Tibet Plateau:Evidence from the Magnetotelluric Survey along Zhada-Quanshui Lake Profile

The magnetotelluric （MT） survey along the Zhada （札达）-Quanshui （泉水） Lake profile on the western margin of the Qinghai （青海）-Tibet plateau shows that the study area is divided into three tectonic provinces by the Yalung Tsangpo and Bangong （班公）-Nujiang （怒江） sutures. From south to north these are the Himalayan terrane, Gangdise terrane, and Qiangtang （羌塘） terrane. For the study area, there are widespread high-conductivity layers in the mid and lower crust, the top layers of which fluctuate intensively. The high-conductivity layer within the Gangdise terrane is deeper than those within the Qiangtang terrane and the Himalaya terrane, and the deepest high-conductivity layer is to the south of the Bangong-Nujiang suture. The top surface of the high-conductivity layer in the south of the Bangong-Nujiang suture is about 20 km lower than that in the north of it. The high-conductivity layer within the Gangdise terrane dips toward north and there are two high-conductivity layers within the crust of the southern Qiangtang terrane. In the upper crust along the profile, there are groups of lateral electrical gradient zones or distortion zones of different scales and occurrence indicating the distribution of faults and sutures along the profile. According to the electrical structure, the structural characteristics and space distribution of the Yalung Tsangpo suture, Bangong.Nujiang suture, and the major faults of Longmucuo （龙木错） and Geerzangbu are inferred.

Fractal Characteristics of Fault Structures and Their Use for Mapping Ore-prospecting Potential in the Qitianling Area, Southern Hunan Province, China

Quantitative analyses of the spatial distribution of fault structures can provide a theoretical basis for forecasting prospective ore deposits. Characteristics and complexity of fault structure distribution in the Qitianling area, Southern Hunan Province, China, were quantitatively calculated and appraised by fractal and multifractal methods to evaluate the relation between fault structures and ore-prospecting potential. The results show that the lengths of faults can be modeled as multifractals. Multifractal spectra evidently reflect the characteristics of the scaling of fault structures. The box- counting dimension value （D） of fault structures is equal to 1.656, as indicates complexity of the spatial distribution of faults and favorable structural conditions for the formation of ore deposits. Moreover, the D values of sub-regions were calculated and isopleths of their fractal dimension values were plotted accordingly. Overlay analyses of isopleths of fractal dimension values and distributions of known ore deposits show that areas with the larger fractal dimension values of fault structures have more ore deposits. This spatial coupling relationship between D values and ore deposits can be used to forecast and explore other ore deposits. On the basis of complexity theory for ore-forming systems, three exploration targets with high D values were delineated as prospective ore deposits.

Internal structures and high-velocity frictional properties of Longmenshan fault zone at Shenxigou activated during the 2008 Wenchuan earthquake

This paper reports internal structures of a wide fault zone at Shenxigou,Dujiangyan,Sichuan province,China,and high-velocity frictional properties of the fault gouge collected near the coseismic slip zone during the 2008 Wenchuan earthquake.Vertical offset and horizontal displacement at the trench site were 2.8 m（NW side up）and 4.8 m（right-lateral）,respectively.The fault zone formed in Triassic sandstone,siltstone,and shale about 500 m away from the Yingxiu-Beichuan fault,a major fault in the Longmenshan fault system.A trench survey across the coseismic fault,and observations of outcrops and drill cores down to a depth of 57 m revealed that the fault zone consists of fault gouge and fault breccia of about0.5 and 250-300 m in widths,respectively,and that the fault strikes N62°E and dips 68° to NW.Quaternary conglomerates were recovered beneath the fault in the drilling,so that the fault moved at least 55 m along the coseismic slip zone,experiencing about 18 events of similar sizes.The fault core is composed of grayish gouge（GG） and blackish gouge（BG） with very complex slip-zone structures.BG contains low-crystalline graphite of about 30 %.High-velocity friction experiments were conducted at normal stresses of 0.6-2.1 MPa and slip rates of 0.1-2.1 m/s.Both GG and BG exhibit dramatic slip weakening at constant high slip rates that can be described as an exponential decay from peak friction coefficient lpto steadystate friction coefficient lssover a slip-weakening distance Dc.Deformation of GG and BG is characterized by overlapped slip-zone structures and development of sharp slickenside surfaces,respectively.Comparison of our data with those reported for other outcrops indicates that the high-velocity frictional properties of the Longmenshan fault zones are quite uniform and the high-velocity weakening must have promoted dynamic rupture propagation during the Wenchuan earthquake.