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.

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.

Crust-mantle structure feature and the seismic activity of the main tectonic units in the North Tanlu fault zone

Using recent data of geoscience transaction in Northeast China, the author analyses and studies the crust-upper mantle structure feature of the North Tanlu fault zone. The result shows the crust-mantle structure are obvious difference at both sides of the North Tanlu fault zone. The fault activity and segmentation are closely related with abruptly change zone of the crust-upper mantle structure. There is a clear mirror image relationship between the big geomorphic shape and asthenosphere undulate, the former restricts tectonic stability and tectonic style of dif- ferent crustal units. The significantly strengthening seismicity of north set and south set in the North Tanlu fault zone just correspond to the low-velocity and high conductivity layer of crust-upper mantle. In the North Tanlu fault zone, the main controlling structure of the mid-strong seismic generally consists of the active fault sectors, whose crust-mantle structure is more complicated in rigidity massif.

Structure and Properties of TiB_2 Thin Films Deposited at Low Temperatures Using RF Magnetron Sputtering

The TiB2 thin films were deposited on steel substrates using RF magnetron sputtering technique with the low normalized substrate temperature （0.1〈Ts/Tm〈0.2）. Microstructure of these films was obtained by field emission scanning electron microscope （FESEM） and the grazing incidence X-ray diffraction （GIXRD） characterization, while the composition of films was obtained using Auger emission spectroscopy （AES） analysis. It was found that the TiB2 thin films were overstoichiometric with the B/Ti ratio at 2.33 and the diffusion of Ti and B atoms on the substrate surface was greatly improved at 350 ℃. Moreover, a new dense structure, named ＂equiaxed＂ grain structure was observed by FESEM at this substrate temperature, Combined with FESEM and AES analysis, it was suggested that the ＂equiaxed＂ grain structure was located in Zone 2 at the normalized substrate temperature as low as 0.18.

Recent advances in imaging crustal fault zones: a review

Crustal faults usually have a fault core and surrounding regions of brittle damage, forming a low-velocity zone （LVZ） in the immediate vicinity of the main slip interface. The LVZ may amplify ground motion, influence rupture propagation, and hold important information of earthquake physics. A number of geophysical and geodetic methods have been developed to derive high-resolution structure of the LVZ. Here, I review a few recent approaches, including ambient noise cross-correlation on dense across-fault arrays and GPS recordings of fault-zone trapped waves. Despite the past efforts, many questions concerning the LVZ structure remain unclear, such as the depth extent of the LVZ. High-quality data from larger and denser arrays and new seismic imaging technique using larger portion of recorded waveforms, which are currently under active development, may be able to better resolve the LVZ structure. In addition, effects of the alongstrike segmentation and gradational velocity changes across the boundaries between the LVZ and the host rock on rupture propagation should be investigated by conducting comprehensive numerical experiments. Furthermore, high-quality active sources such as recently developed large-volume airgun arrays provide a powerful tool to continuously monitor temporal changes of fault-zone properties, and thus can advance our understanding of fault zone evolution.

Effect of Sand Body Enrichment Under the Restriction of a Tectonic Transfer Zone: A Case Study on the Pinghu Formation in the Kongqueting Region on the Pinghu Slope

Results of long-term explorations in the Kongqueting region,located in an East China Sea depression,suggest that the strong fault activity during the sedimentary period of the Pinghu formation significantly influenced the development of the sedimentary system.However,the aggregation and enrichment of the sand body under a tectonic background has become a problem that requires an immediate solution.Considering research outcomes of previous studies,this study used three-dimensional seismic and logging data to identify Y-or H-type and the en echelon distribution patterns of the fault plane,as well as identify the locations wherein the fault growth index value is greater than 1 in the study region,indicating the tectonic background of the fault transfer zone in the region.Second,the development type of the fault transfer zone was studied,and the sand body enrichment site was identified based on seismic inversion data and the development position of the fault transfer point.This helps clarify the evolution of sedimentary facies of the Pinghu formation combined with the sedimentary environment of the braided-river delta.Finally,after summarizing the coupling relationship between the synsedimentary fault systems and the sand body enrichment patterns,three sand-control models were determined,namely,the flexural-parallel,the en echelon collinear,and the torsional-reformed superimposed transfer zones.The findings of this study lay a foundation for the subsequent search of tectonic lithologic oil and gas reservoirs.

Characteristics of fault zones and their control on remaining oil distribution at the fault edge: a case study from the northern Xingshugang Anticline in the Daqing Oilfield, China

Most major oil zones in the Daqing Oilfield have reached a later,high water cut stage,but oil recovery is still only approximately 35%,and 50%of reserves remain to be recovered.The remaining oil is primarily distributed at the edge of faults,in poor sand bodies,and in insufficiently injected and produced areas.Therefore,the edge of faults is a major target for remaining oil enrichment and potential tapping.Based on the dynamic change of production from development wells determined by the injection-recovery relationship at the edge of faults,we analyzed the control of structural features of faults on remaining oil enrichment at the edge.Our results show that the macroscopic structural features and their geometric relationship with sand bodies controlled remaining oil enrichment zones like the edges of NNE-striking faults,the footwalls of antithetic faults,the hard linkage segments（two faults had linked together with each other to form a bigger through-going fault）,the tips of faults,and the oblique anticlines of soft linkages.Fault edges formed two types of forward microamplitude structures：（1） the tilted uplift of footwalls controlled by inverse fault sections and（2） the hanging-wall horizontal anticlines controlled by synthetic fault points.The remaining oil distribution was controlled by microamplitude structures.Consequently,such zones as the tilted uplift of the footwall of the NNW-striking antithetic faults with a fault throw larger than 40 m,the hard linkage segments,the tips of faults,and the oblique anticlines of soft linkage were favorable for tapping the remaining oil potential.Multi-target directional drilling was used for remaining oil development at fault edges.Reasonable fault spacing was determined on the basis of fault combinations and width of the shattered zone.Well core and log data revealed that the width of the shattered zone on the side of the fault core was less than 15 m in general;therefore,the distance from a fault to the development target should be larger than 15 m.Vertically segmented growth faults should take the separation of the lateral overlap of faults into account.Therefore,the safe distance of remaining oil well deployment at the fault edge should be larger than the sum of the width of shattered zone in faults and the separation of growth faults by vertical segmentation.

Structural formation and evolution mechanisms of fracture plugging zone

A coupled CFD-DEM method is used to simulate the formation process of fracture plugging zone.A photo-elastic system characterizing mesoscale force chain network developed by our own is used to model the pressure evolution in fracture plugging zone to reveal the evolution mechanism of the structure of fracture plugging zone.A theoretical basis is provided for improving the lost circulation control effect in fractured reservoirs and novel methods are proposed for selecting loss control materials and designing loss control formula.CFD-DEM simulation results show that bridging probability is the key factor determining the formation of fracture plugging zone and fracture plugging efficiency.Critical and absolute bridging concentrations are proposed as the key indexes for loss control formula design.With the increase of absolute bridging concentration,the governing factor of bridging is changed from material grain size to the combination of material grain size and friction force.Results of photo-elastic experiments show that mesoscale force chain network is the intrinsic factor affecting the evolution of pressure exerting on the fracture plugging zone and determines the macroscopic strength of fracture plugging zone.Performance parameters of loss control material affect the force chain network structure and the ratio of stronger force chain,and further impact the stability and strength of fracture plugging zone.Based on the study results,the loss control formula is optimized and new-type loss control material is designed.Laboratory experiments results show that the fracture plugging efficiency and strength is effectively improved.

Field structure at mode Ⅲ dynamically propagating crack tip in elastic-viscoplastic materials

An elastic-viscoplastic mechanics model is used to investigate asymptotically the mode Ⅲ dynamically propagating crack tip field in elastic-viscoplastic materials. The stress and strain fields at the crack tip possess the same power-law singularity under a linear-hardening condition. The singularity exponent is uniquely determined by the viscosity coefficient of the material. Numerical results indicate that the motion parameter of the crack propagating speed has little effect on the zone structure at the crack tip. The hardening coefficient dominates the structure of the crack-tip field. However, the secondary plastic zone has little influence on the field. The viscosity of the material dominates the strength of stress and strain fields at the crack tip while it does have certain influence on the crack-tip field structure. The dynamic crack-tip field degenerates into the relevant quasi-static solution when the crack moving speed is zero. The corresponding perfectly-plastic solution is recovered from the linear-hardening solution when the hardening coefficient becomes zero.

Investigating the Stratigraphy and the Gender of Nano-Fossils in the Lower Part of the Abtalkh Formation in Kopet Dagh Zone

A structural-sediment zone of Kopet Dagh is one of the geological units. The southern Kopet Dagh zone is limited to Binalood and the northern limit is with the Turan plateau fault and is created as sediment (Trough) in the late Triassic. The main fault zones are divided into two groups of foundation faults and overthrust. Kopet Dagh is a giant gas field between Turkmenistan, Iran and Afghanistan. Most areas of the region have a temperate climate so cold. From the middle Cambrian to the present, five phases of orogeny have occurred in the region. The geographic location of the study area is 37°43'03"N latitude and 55°35'47"E. In terms of stratigraphic formations in the Cretaceous period, Kopet Dagh area, respectively, is from old to new, including: Shurijeh, Zard, Tiregan, Sar Cheshmeh, Sanganeh, Aitamir, Abderaz, Abtalkh, Neyzar and Kalat. Abtalkh formation is one of the most important rock units in the late Cretaceous in the Kopet Dagh Basin. Abtalkh formation is 489 m and its stratigraphic units are 80 meters of dark grayshale, 20 km dark grayshale with calcareous layers with Inoseramus, 50 m gray marl tend to bluish with Siliceous limestone interlayers, 19 meters of gray-blueshale, 320 meters of light gray shale withthinlayer limestone interlayers. To take pictures of the samples, 100× objective lens and digital camera were used. In the course of this study, the lower part of Abtalkh formation was in Itamir cutting of the study and 9 genera were identified. Recognized calcareous Nannofossil had diversity and abundance. In general, in the greater thickness of the study, samples have moderate preservation. In some cases, the impact of dissolution phenomenon was so great that the main part of the species were corroded. Paying attention to the range of the rise and fall of index species and fossil assemblages, 4 biozones were identified for cutting according to the zones (CC18-CC21) of Sysyngzoning, 1977.

Estimation of main rheological parameters for Pangxidong-Jinkeng structural fracture zone and Qinzhou-Hangzhou metallogenetic belt in South China

The mylonites occurred in the fracture zones are studied by dynamically recrystallized quartz grains.The natural microstructures in mylonites are simulated and the deformation conditions of mylonitization are estimated by fractal analysis,recrystallized grain size paleopiezometer and flow laws of quartzite.Depending on fractal analysis,the deformation temperature of mylonitization is approximately 600℃,which presents high greenschist facies to low amphibolite facies.The mylonitization occurred at differential stresses of 9.1--10.7MPa(lower limits).Compared with extrapolation of quartzite flow laws and estimates of fractal analysis,the strain rate of mylonitization is under 10-13.8/s.

Study on the characteristics of crust－mantle transition zone in Western Yunnan Province

In this paper the fine structure of crust mantle transition zone in Western Yunnan Province is analysed and discussed based on the reflection phases from Moho discontinuity in Project Western Yunnan 86～87. It shows that in two points: in the north 27.64 km from shot point Jinggu and south 58.74 km from shot point Zhiti, there are transition zones of group of thin layers with inverse velocity.These two reflection points are both situated in the lower velocity anomaly zone in the top of upper mantle. The crust of this region is more seismicity. Maybe the unusual structure of this transition zone is related with the characteristics of this region. This paper discusses the possible geological interpretation model for this transition zone, and also makes suggestion about its application in earthquake prediction.

Structural Relationships along a Neoarchean Arc-Continent Collision Zone, North China Craton

The Archean North China Craton is composed of the Western Block,Eastern Block and the intervening Central Orogenic Belt.A 4-10 km wide and 85 km long tectonic mélange belt informally called the Zanhuang tectonic

Application of high-pressure water jet technology and the theory of rock burst control in roadway

This paper puts forward using high-pressure water jet technology to control rock burst in roadway, and analyzes the theory of controlling rock burst in roadway by the weak structure zone model. The weak structure zone is formed by using high-pressure water jet to cut the coal wall in a continuous and rotational way. In order to study the influence law of weak structure zone in surrounding rock, this paper numerically analyzed the influence law of weak structure zone, and the disturbance law of coal wall and floor under dynamic and static combined load. The results show that when the distance between high-pressure water jet drillings is 3 m and the diameter of drilling is 300 mm, continuous stress superposition zone can be formed. The weak structure zone can transfer and reduce the concentrated static load in surrounding rock, and then form distressed zone. The longer the high-pressure water jet drilling is, the larger the distressed zone is. The stress change and displacement change of non-distressed zone in coal wall and floor are significantly greater than that of distressed zone under dynamic and static combined load. And it shows that the distressed zone can effectively control rock burst in roadway under dynamic and static combined load. High-pressure water jet technology was applied in the haulage gate of 250203 working face in Yanbei Coal Mine, and had gained good effect. The study conclusions provide theoretical foundation and a new guidance for controlling rock burst in roadway.

Tectonic Units and Their Fundamental Characteristics on the Northern Margin of the Alxa Block

The northern margin of the Alxa block is the junction of a tectonic units. Four first-order tectonic units are distinguished: 1. the Yagan structural zone characteristic of an immature island arc; 2. the Zhusileng-Hangwula structural zone, which was a passive continental margin in the Early Palaeozoic and was transformed into an active continental margin in the Late Palaeozoic;3. the Shalazha structural zone characteristic of a mature island arc; 4. the Nuru-Langshan structural zone, which was a Proterozoic orogenic belt and later evolved into an extensional transtional crust in the Palaeozoic. The above-mentioned tectonic units differ remarkably in sedimentary formations, magmatic rock associations, metamorphism and geochemistry and are bounded by faults between one another.

Ore Zoning as Self-Organization of Geochemical Dynamic Systems

Zoning in ore bodies, ore deposits and ore regions are recognized as temporal-spatial structures generated by the dynamics of ore- forming processes. Viewed from the theory of dissipative structures, ore zoning is a kind of self-organization phenomenon occurring in far from-equilibrium geochemical dynamic systems. Therefore,kinetic and dynamic approaches must be taken to reveal the mechanisms of ore zoning. Two dominant coupling processes leading to ore zoning——reaction-transport feedbacks and double-diffusive convection——are discussed.

Determining the Gender of Nano-Fossils in the Lower Part of the Abtalkh Formation (150 M Primary)

A structural zone of Dagh Kopet as sediment (Trough) has created in the late Triassic. There are two different views of Dagh Kopet zone: A) Eurasian theory;B) Gondwana theory. The main fault zones are divided into two groups of foundation faults and overthrust. Abtalkh formation is one of the most important Late Cretaceous rock units in the Kopet Dagh sediment Basin and the geographic location of the study area is "03'43°37 north latitude and "47'35°55 the east. The calcareous nannoplanktons are the first links in the food chain and are the main producers in the seas and oceans. The calcareous Nannoplankton is found in fine sediments such as shale and marl and for study and examination;the presence of trace amounts of sample is enough. The calcareous Lannoplankton is used to identify and introduce Nannofossils of Abtalkh in the bottom of the cut, to determine biozones available at the cutting zone and comparing it with the world standard, to determine their age. In the study section, Nannofossil is in glauconitic sandstone, conglomerate, siltstone, marl, shale, limestone, clay, marl and clay marl and Chuck. Their small size makes that a very small amount of samples are sufficient for the study. The most important method for sample preparation in this study is a smear slide method. In laboratory studies and identification of Nannofossil and counting them, the optical microscope and the object lens 50* and 100* are used. To take pictures of samples, 100× objective lens and digital camera were used. In the course of this study, for the lower part of Abtalkh, Aytamir cutting was studied and 12 genera were identified. The calcareous Nannofossils were recognized and have relatively good diversity and abundance. In general, the greater thickness of the study samples had an average preservation. In some cases, the impact of dissolution was so great that the wall or part of the main sections of the species was corroded.

Distribution and quantitative zonation of unloading cracks at a proposed large hydropower station dam Site

Rock mass unloading is an important rock engineering problem because unloading may impact the stability of a rock mass slope. Based on hydroelectric engineering principles, this study focuses on the classification of unloading zones to reflect the rock mass structure characteristics. Geological background and slope structure of the study region were considered to investigate the distribution and deformation of the unloading process. Quantitative indices were classified according to the formation mechanisms and the geological exhibition of unloading zones. The P-wave velocity(V_P), the ratio of the wave velocity(V_p) the ratio of the test P-wave velocity along the adit depth to the P-wave velocity of intact rock, the sum of joint openings every 2 meters(S_t), and the density of open joints(D_t) were calculated as quantitative indices for the rock mass unloading zone. The characteristics of the unloading zone of rock mass slopes at the dam site were successfully determined. The method of combining qualitative data with quantitative indices was found to be effective for the classification of slope unloading zones.

Paleo-temperature Evolution and Water Soluble Gas in Sinian Reservoir, Anpingdian-Gaoshiti Structural Zone, Central Sichuan Basin

The paleo-temperature evolution of Sinian reservoir of Anping （安平） 1 well was rebuilt by taking the method of apatite fission track and Easy%Ro model. The result of apatite fission track determines the accurate burial history and overcomes the flaw that the vitrinite reflectance is taken as paleo-temperature indicator simply. The authors used the laser Raman technique to analyze the methane present in the calcite and quartz fluid inclusions of Sinian reservoir, finding that the methane is water soluble gas. The authors also simulated the paleo-pressure of fluid inclusion by using PVTsim software and finally worked out the methane solubility in water.

Characterization of Fault Zones by Analysis of Aftershock Waveform Data

Large property contrasts between materials in a fault zone and the surrounding rock are often produced by repeating earthquakes. Fault zones are usually characterized by fluid concentration, clay-rich fault gouge, increased porosity, and dilatant cracks. Thus, fault zones are thought to have reduced seismic velocities than the surrounding rocks. In this article, we first investigated the synthetic waveforms at a linear array across a vertical fault zone by using 3D finite difference simulation. Synthetic waveforms show that when sources are close to, inside, or below the fault zone, both arrival times and waveforms of P-and S-waves vary systematically across the fault zone due to reflections and transmissions from boundaries of the low-velocity fault zone. The arrival-time patterns and waveform characteristics can be used to determine the fault zone structure. Then, we applied this method to the aftershock waveform data of the 1992 Landers M7.4 and the 2008 Wenchuan （汶川） M8.0 earthquakes. Landers waveform data reveal a low-velocity zone with a width of approximately 270-370 m, and P-and S-wave velocity reductions relative to the host rock of approximately 35%-60%; Wenchuan waveform data suggest a low-velocity zone with a width of approximately 220-300 m, and P-and S-wave velocities drop relative to the host rock of approximately 55%.