The Dihedral Angle and Intersection Processes of a Conjugate Strike-Slip Fault System in the Tarim Basin, NW China

Recent studies, focused on dihedral angles and intersection processes, have increased understandings of conjugate fault mechanisms. We present new 3-D seismic data and microstructural core analysis in a case study of a large conjugate strike-slip fault system from the intracratonic Tarim Basin, NW China. Within our study area, ＂X＂ type NE and NW trending faults occur within Cambrian- Ordovician carbonates. The dihedral angles of these conjugate faults have narrow ranges, 19~ to 62~ in the Cambrian and 26~ to 51~ in the Ordovician, and their modes are 42~ and 44~ respectively. These data are significantly different from the ~60~ predicted by the Coulomb fracture criterion. It is concluded that： （1） The dihedral angles of the conjugate faults were not controlled by confining pressure, which was low and associated with shallow burial; （2） As dihedral angles were not controlled by pressure they can be used to determine the shortening direction during faulting; （3） Sequential slip may have played an important role in forming conjugate fault intersections; （4） The conjugate fault system of the Tarim basin initiated as rhombic joints; these subsequently developed into sequentially active ＂X＂ type conjugate faults; followed by preferential development of the NW-trending faults; then reactivation of the NE trending faults. This intact rhombic conjugate fault system presents new insights into mechanisms of dihedral angle development, with particular relevance to intracratonic basins.

Neotectonics of the Eastern Margin of the Tibetan Plateau: New Geological Evidence for the Change from Early Pleistocene Transpression to Late Pleistocene-Holocene Strike-slip Faulting

We present in this paper some new evidence for the change during the Quaternary in kinematics of faults cutting the eastern margin of the Tibetan Plateau. It shows that significant shortening deformation occurred during the Early Pleistocene, evidenced by eastward thrusting of Mesozoic carbonates on the Pliocene lacustrine deposits along the Minjiang upstream fault zone and by development of the transpressional ridges of basement rocks along the Anninghe river valley. The Middle Pleistocene seems to be a relaxant stage with local development of the intra-mountain basins particularly prominent along the Minjiang Upstream and along the southern segment of the Anninghe River Valley. This relaxation may have been duo to a local collapse of the thickened crust attained during the late Neogene to early Pleistocene across this marginal zone. Fault kinematics has been changed since the late Pleistocene, and was predominated by reverse sinistral strike-slip along the Minshan Uplift, reverse dextral strike-slip on the Longmenshan fault zone and pure sinistral strike-slip on the Anninghe fault. This change in fault kinematics during the Quaternary allows a better understanding of the mechanism by which the marginal ranges of the plateau has been built through episodic activities.

Characteristics of the Late Quaternary right-lateral strike-slip movement of Bolokenu-Aqikekuduk fault in northern Tianshan Mountains,NW China

The characteristics of the Bolokenu-Aqikekuduk（Bo-A） fault,a right-lateral strike-slip fault that runs for more than 700 km long and obliquely cuts North Tianshan Mountains,are evaluated here based on remote sensing data,and through an analysis of the results from field investigations as well as climate-geomorphic events. The fault is composed of a western segment with a NW strike and an eastern segment with a NWW strike.The western segment is nearly 250 km long,extending northwestward into Kazakhstan with a right-lateral strike-slip rate of 5 mm/a.This domain consists of 4-5 rupture sections,with 3-4 deformation belts,caused by ancient or historical earthquakes,and suggesting the potential for the occurrence of further strong earthquakes（with M≈7.5） in future. The eastern segment of the fault shows a right-lateral strike-slip rate of 1-1.4 mm/a,with the development of 3-4 deformation belts caused by ancient or historical earthquakes,and with a potential for future strong earthquake with M≈7.0. A typical strain partitioning style in the compression area has developed between the intermontane BoA fault and the piedmont thrust structures of Northern Tianshan Mountains,under the effect of oblique compression,as indicated by the piedmont thrust structure and the strike-slip fault in the mountains.

LARGE-SCALE STRIKE SLIP FAULT: THE MAJOR STRUCTURE OF INTRACONTINENTAL DEFORMATION AFTER COLLISION

Intracontinental deformation is one of the most interesting problems in tectonics. But so far little attention has been paid to rock deformation, metamorphism and magmatism related with large-scale displacement and rotation of these blocks. In this note, we take the Ailaoshan-Red River fault (ARF)zone in western Yunnan as an example and discuss the kinematics and dynamics of the fault With its neighbouring blocks in the Tertiary.

Strain analysis of buried steel pipelines across strike-slip faults

Existing analytical methods of buried steel pipelines subjected to active strike-slip faults depended on a number of simplifications.To study the failure mechanism more accurately,a refined strain analytical methodology was proposed,taking the nonlinear characteristics of soil-pipeline interaction and pipe steel into account.Based on the elastic-beam and beam-on-elastic-foundation theories,the position of pipe potential destruction and the strain and deformation distributions along the pipeline were derived.Compared with existing analytical methods and three-dimensional nonlinear finite element analysis,the maximum axial total strains of pipe from the analytical methodology presented are in good agreement with the finite element results at small and intermediate fault movements and become gradually more conservative at large fault displacements.The position of pipe potential failure and the deformation distribution along the pipeline are fairly consistent with the finite element results.

On the faults of western Hexi Corridor and its nearby regions, northwestern China: Thrust faults and strike-slip faults of Late Cenozoic

The structural analysis based on the explanation of seismic profiles indicates that a lot of thrust faults and strike-slip faults of Late Cenozoic occur in western Hexi Corridor and its nearby regions. They can be divided into two types. One is thrust faults dipping southwards and extending NWwards, which was mainly correlated with the thrusting of northern Qilianshan and located at the NE margin of Qilianshan and the southwestern Hexi Corridor, the other is thrust faults and strike-slip faults that were related to the strike-slipping of Altun fault and located mainly at the regions of Hongliuxia, Kuantaishan, and Helishan that are close to the Altun fault. All these faults, which were related to the remote effects of collision between the two continents of India and Tibet during the Late Eocene and later, started to develop since the Late Tertiary and presented the features of violent thrust or strike-slip movement in Quaternary. Many of them are still active up to now and thus belong to the active faults that are the potential inducement of earthquakes in the Hexi Corridor. Moreover, a lot of intense structural deformation and many morphology phenomena such as tectonic terrace and river offset were formed under the control of these faults in Quaternary.

Decadal Seismicity before Great Earthquakes—Strike-Slip Faults and Plate Interiors: Major Asperities and Low-Coupling Zones

Decadal forerunning seismic activity is examined for very large, shallow earthquakes along strike-slip and intraplate faults of the world. It includes forerunning shocks of magnitude Mw ≥ 5.0 for 21 mainshocks of Mw 7.5 to 8.6 from 1989 to 2020. Much forerunning activity occurred at what are interpreted to be smaller asperities along the peripheries of the rupture zones of great mainshocks at transform faults and subduction zones. Several great asperities as ascertained from forerunning activity agree with the areas of high seismic slip as determined by others using geodetic, mapping of surface faulting, and finite-source seismic modeling. The zones of high slip in many great earthquakes were nearly quiescent beforehand and are identified as the sites of great asperities. Asperities are strong, well-coupled portions of plate interfaces. Different patterns of forerunning activity on time scales of up to 45 years are attributed to the sizes and spacing of asperities (or lack of). This permits at least some great asperities along transform faults to be mapped decades before they rupture in great shocks. Rupture zones of many great mainshocks along transform faults are bordered either along strike, at depth or regionally by zones of lower plate coupling including either fault creep forerunning activity, aftershocks and/or slow-slip events. Forerunning activity to transforms in continental areas is more widespread spatially than that adjacent to oceanic transforms. The parts of the San Andreas fault themselves that ruptured in great California earthquakes during 1812, 1857 and 1906 have been very quiet since 1920;moderate to large shocks have been concentrated on their peripheries. The intraplate shocks studied, however, exhibited few if any forerunning events, which is attributed to the short period of time studied compared to their repeat times. The detection of forerunning and precursory activities for various time scales should be sought on the peripheries of great asperities and not just along the major faults themselves. This paper compliments that on decadal forerunning activity to great and giant earthquakes along subduction zones.

Uniform Strike-Slip Rate along the Xianshuihe-Xiaojiang Fault System and Its Implications for Active Tectonics in Southeastern Tibet

Recent studies on the Xianshuihe-Xiaojiang fault system suggest that the Late Quaternary strike-slip rate is approximately uniform along the entire length of the fault zone, about 15±2 mm/a. This approximately uniform strike slip rate strongly supports the clockwise rotation model of the southeastern Tibetan crust. By approximating the geometry of the arc-shaped Xianshuihe-Xiaojiang fault system as a portion of a small circle on a spherical Earth, the 15±2 mm/a strike slip rate corresponds to clockwise rotation of the Southeastern Tibetan Block at the （5.2±0.7）×10^-7 deg/a angular velocity around the pole （21°N, 88°E） relative to the Northeast Tibetan Block. The approximately uniform strike slip rate along the Xianshuihe-Xiaojiang fault system also implies that the Longmeushan thrust zone is not active, or at least its activity has been very weak since the Late Quaternary. Moreover, the total offset along the Xiaushuihe-Xiaojiang fault system suggests that the lateral extrusion of the Southeastern Tibetan Block relative to Northeastern Tibetan Block is about 160 km and 200-240 km relative to the Tarim-North China block. This amount of lateral extrusion of the Tibetan crust should have accommodated about 13-24% convergence between India and Eurasia based on mass balance calculations. Assuming that the slip rate of 15±2 mm/a is constant throughout the entire history of the Xianshuihe-Xiaojiang fault system, 11±1.5 Ma is needed for the Xianshuihe-Xiaojiang fault system to attain the 160 km of total offset. This implies that left-slip faulting on the Xianshuihe-Xiaojiang fault system might start at 11±1.5 Ma.

Superimposed characteristics and genetic mechanism of strike-slip faults in the Bohai Sea, China

Based on the 3 D seismic structure interpretation of Bohai Sea, combined with physical modeling of structure, structural style analysis and apatite fission track simulation, the structural characteristics and genetic mechanism of the Cenozoic strike-slip faults in Bohai Sea were investigated. The results show that Tanlu strike-slip fault experienced three stages of strike-slip activities in the Cenozoic,and the transition from left-lateral strike to right-lateral strike-slip was completed at the end of the fourth member of the Shahejie Formation. The strike-slip faults in the Bohai Sea have the characteristics of multi-stage and multi-strength stress superposition. According to the superimposed forms of different strengths, different properties and different ratios, they can be divided into three major genetic types,extension and strike-slip superimposition, extension and extrusion superimposition, extrusion and strike-slip superimposition, and fifteen typical structure patterns. Affected by multiple changes in the direction and rate of subduction of the Cenozoic Pacific plate, the difference between the Cenozoic extension and the strike-slip in the Bohai Sea area leads to the diversity of the fault system and the zoning of the depression structure. According to superimposition features of faults, the Bohai Sea area can be divided into the Liaoxi S-type weak strike-slip zone, Liaodong braided strong strike-slip zone, Boxi conjugated medium strike-slip zone, Bodong brush structure medium strike-slip zone and Bonan parallel strong strike-slip zone. These zones differ in oil and gas accumulation features.

Characteristics of strike-slip inversion structures of the Karatau fault and their petroleum geological significances in the South Turgay Basin,Kazakhstan

The Karatau fault is one of the important strike-slip faults in central Asia,and the South Turgay Basin is located towards its northern end.Detailed seismic interpretation indicated that the strikeslip tectonism of the Karatau fault weakened gradually from west to east in the South Turgay Basin.Typical flower structures developed on the section,and strike-slip faults showed an echelon pattern on planar view.The Karatau strike-slip fault affected the South Turgay Basin in two periods：（1） The South Turgay strike-slip pull-apart rift basin formed as a result of regional extensive stress in the Early-Middle Jurassic,characterized by the juxtaposition of horsts and grabens.The formation of horsts provided favorable reservoir spaces for later hydrocarbon accumulation,and different filling stages of grabens controlled different reservoir-forming factors in grabens.（2） Two stages of tectonic inversion occurred in the Late Jurassic and Late Cretaceous and played a crucial role in the final shape of the structure in the South Turgay Basin.The oil and gas migrated to form reservoirs and mainly concentrated in the horsts,graben slopes and in both sides of the strike-slip fault zone.In the case of the degree of accumulation of petroleum,the factor explaining why horsts are better than grabens is the strike-slip pull-apart of the South Turgay Basin,and the structure inversion of the South Turgay Basin explains why the west graben is better than the east one.Overall,the Karatau strike-slip fault played a very important role in the formation of the South Turgay Basin and its hydrocarbon accumulations.

TECTONIC-GEOMORPHIC FEATURES OF THE STRIKE-SLIP FAULT ZONE IN EASTERN HUNAN AND WESTERN JIANGXI

Eastern Hunan-western Jiangxi, the main distribution domain of the Luoxiao MountainRange, is one of the key districts of the Circum-Pacific tectonically active belt in China, in whichNNE-trending en echelon strike-slip faulting since Cenozoic time has obviously controlled thefundamental framework of the modern land forms. Based on the study of tectonic evolution and ac-tive strike-slip faults, this paper discusses the forms, types and combinations of the modern tec-tonic land forms in this region.

An Inhomogeneous Distribution Model of Strong Earthquakes along Strike-Slip Act ive Fault Segments on the Chinese Continent and Its Implication in Engineering Seismology

Through the statistical analysis of earthquake distribution along 51 strike-sli p active fault segments on the Chinese continent, we found that strong earthquak e distribution along the seismogenic fault segments is inhomogeneous and the dis tribution probability density p(K) can be stated as p(K)=1.1206e -3.947K in which K=S/(L/2), S refers to the distance from earthquake epicenter to the center of a fault segment, L is the length of the fault segment. The above model can be utilized to modify the probability density of earthquake occurrence of t he maximum magnitude interval in a potential earthquake source. Nevertheless, it is only suitable for those potential earthquake sources delineated along a sing le seismogenic fault. This inhomogeneous model has certain effects on seismic risk assessment, especia ll y for those potential earthquake sources with higher earthquake reoccurrence rat es of the maximum magnitude interval. In general, higher reoccurrence rate of th e maximum magnitude interval and lower exceeding probability level may bring lar ger difference of the results in seismic risk analysis by adopting the inhomogen eous model, the PGA values increase inner the potential earthquake source, but r educe near the vicinity and out of the potential earthquake source. Taking the T angyin potential earthquake source as an example, with exceeding probability of 10% and 2% in 50 years, the difference of the PGA values between inhomogeneous m odel and homogenous models can reach 12%.

Geomorphic Evidence for and Rate of Sinistral Strike-slip Movement Along Northwest-trending Faults in Chaoshan Plain

Two sets of active faults,northwest-and northeast-trending faults,are developed in the Chao-shan Plain of East Guangdong.After detailed interpretation of aerophotos,we have found outthat there is the clear phenomenon of sinistral dislocation of drainage system on the Huang-gang-shui fault and part of Fengshun-Shantou fault.Field investigation confirmed that the geo-morphic bodies along the two faults have undergone displacement.Large-scale topographicmapping was made at three displaced sites and samples for age dating were collected from thegeomorphic booies.Calculation indicates that the average rate of sinistral strike-slip movementin the Holocene time amounts to 1.11±0.09～2.69±0.24mm/a along the Huanggangshuifault and 3.26±0.26mm/a along the Fengshun-Shantou fault.These two more active NW-trending faults extend into sea area,where they intersect the NE-trending strongly active Nius-han Island-Xiongdi Isle-Nanpeng Isles fault at a depth of 40～50m in water.The intersection isa location favorable

CENOZOIC LARGE-SCALE STRIKE-SLIP FAULT IN WEST YUNNAN, CHINA

During the collision between India and Eurasia, the continental compression and shorten is thought to be absorbed by the way of thickening of the Tibetan plateau crust and strike\|slip extrusion outwardly of blocks surrounding the Tibetan plateau. A series of models have been proposed recently, of which the most typical one is continental blocks extrusion by Tapponnier et al.. Virtually previous studies show that the Red River—Ailaoshan fault is the eastern boundary of extrusion Indochina displaced southward relative to South China about 23 Ma ago, and more, the western boundary of extrusion blocks is inferred to be Sijie fault in the eastern Burma. But the movement age of Sijie fault is around 13 Ma inferred from the age of Andeman Sea formation and different from that of the Red River—Ailaoshan fault. It is an important scientific problem where the western boundary of extrusion blocks is.

STRUCTURAL ORIGIN OF THE FAULTED BROWN COAL BASIN IN YUNNAN, CHINA──The role of strike-sliping in basin formation and inversion of Xianfeng coal basin

Based on the analysises of regional structural setting, basin formation and deformation, this paper demonstrates that the Xianfeng basin has been formed and inverted under the strike-slip regime. The article is a partial result of the whole research.

Deformation of a two-phase medium due to a long buried strike-slip fault

The aim of the present paper is to obtain the two-dimensional deformation of a two-phase elastic medium consisting of half-spaces of different ri- gidities in welded contact due to a buried long strike-slip fault. The solution is valid for arbitrary values of the fault-depth and the dip angle. The effect of fault-depth on the displacement and stress fields for different values of dip angle has been studied numerically. It is found that the displacement field varies significantly for a buried fault from the corresponding displacement field for an interface-breaking fault. The contour maps showing the stress field for various dip angles for buried and interface-breaking fault have been plotted. It has been observed that the stress field varies significantly for a buried fault from the corresponding stress field for an interface-breaking fault.

Yitong Graben:a Typical Petroliferous Strike-Slip Fault Depression of China

Although Yitong graben appears in a rift basin region of Eastern China , it is really not a rift basin but a strike-slip depression . Its features are as follows : (1 ) graben is controlled by both east and west boundary fauns without any relationship with Mono discontinuity figure ; (2 ) there is no alkalic or calc-alkalic igneous rocks in the layer of early and middle period of graben development ; (3 )west boundary fault is a typical strike-slip fault with some what of arc along the strike , and the fault depression locates in the concave of the arc . East boundary fault is a syndepostional normal fault with translational motion ; (4 ) graben has a long and narrow shape with four sags and three bulges alternating each other ; (5 ) the cross section of graben is asymmetric , high in the east and low in the west ; (6 )the lithofacies changes are quite fast in the cross section . Unconfonnities exist in some area of graben ; (7 )the angle between fault 2 and west boundary fault is a acute angle directing the opposite trend of the west side motion of boundary fault ; (8 )the extensional rate of graben is about 12% , less than the rate in Huabei (19%) and Liaohe (20 %)rift basin.

Sinistral strike slip of the Zhangjiakou-Penglai Fault and its control on hydrocarbon accumulation in the northeast of Shaleitian Bulge,Bohai Bay Basin,East China

The structural style, fault activity, strike-slip displacement, and the formation mechanism and hydrocarbon migration and accumulation in the center tectonic zone in the northeast Shaleitian Bulge of Zhangjiakou-Penglai Fault Zone were studied by seismic attribute analysis, structural geometric analysis, fault activity analysis, structure evolution history and simulation of hydrocarbon migration, based on 3-D seismic and drilling data. The main results are as follows:(1) The study area is a superimposed tectonic zone, which experienced early(Paleocene and Eocene) extension and late(Oligocene and Pliocene-Quaternary) strike-slip and pull-apart.(2) The sinistral strike slip of the northeast Shaleitian Bulge of Zhangjiakou-Penglai Fault Zone went through two periods, Oligocene and Pliocene-Quaternary, and the Bohai section was active earlier than the inland section.(3) The sinistral strike slip displacement of Zhangjiakou-Penglai Fault is 4 km since Cenozoic, including 1 km in the Oligocene, and 3 km in the Pliocene-Quaternary.(4) The strike-slip movements have resulted in the increase of fault activity and basin-mountain restructure in the fault zone, also contributed to the formation of the central tectonic belt and the conjugate evolution in north-east structural belt.(5) The conjugate strike slip of the Zhangjiakou-Penglai Fault Zone dominated the migration and accumulation of hydrocarbon in shallow formations by controlling the injection points and segments of hydrocarbon from the deep layers to shallow layers.

Sinistral Strike-slip Movement Along Western Terminal Segment of the Active Daqingshan Piedmont Fault, Inner Mongolia, China

There are 18 gullies displaying sinistral contortions to different degrees along the western terminal segment about 10 km long of the active Daqingshan piedmont fault near the Donghe District, Baotou City. The contortion amount of gullies ranges from 20 m to 300 m. The contortion and length of the gullies are in direct proportion. The relation between piedmont terraces and gullies indicates that the gullies with upper reaches of about 1 ～ 5 km long and those smaller than one kilometer were formed at the end of Late Pleistocene and Holocene.Meanwhile, sandy gravel layer of alluvial-proluvial sediment on the upthrown wall is directly in contact with yellow clayey sand of the downthrown wall. During the Holocene, the sinistral strike-slip rate along the western terminal segment of the active Daqingshan piedmont fault reached 5 mm/a from age data of dislocated sediments. The evolutional mechanism of the active Daqingshan piedmont fault is also discussed in the paper.