Development Of Faults Research Articles

Active tectonics and fault evolution in the Western Balkans

SUMMARY The western Balkans occupy a region influenced by two major active tectonic processes: the collision between the Adriatic Region and the Dinarides in the west, and the extension of the Aegean Region and its surroundings as they move towards the Hellenic Trench. An understanding of the kinematics and dynamics of the western Balkans has significance for our understanding of continental tectonics in general, and is the object of this paper. The region is rich in observational data, with many well-studied earthquakes, good geodetic coverage by GNSS (Global Navigation Satellite System) and abundant exposure of active faulting and its associated geomorphology, especially within the Mesozoic carbonates that cover large sectors of the extensional areas. We first use such observations to establish the regional kinematic patterns, by which we mean a clarification of how active faulting achieves the motions observed in the deforming velocity field obtained from GNSS measurements. We then use geomorphological observations on the evolution of drainage systems to establish how kinematic and faulting patterns have changed and migrated during the Late Neogene-Quaternary. The kinematics, and its evolution, can then be used to infer characteristics of the dynamics, by which we mean the origin and effect of the forces that control the overall deformation. The principal influences are: (i) the distribution and evolution of gravitational potential energy (GPE) contrasts arising from crustal thickness variations and elevation, in particular the growth of topography by shortening in the Albanides–Hellenides mountain ranges and the high elevation of mainland Greece relative to the Mediterranean seafloor and (ii) the ability of the boundaries of the region, along the Adriatic coast and in the Hellenic Trench, to support the forces arising from those GPE contrasts. The evolution in space and time indicates an interaction between the anisotropic strength fabric of the upper crust associated with faulting, and the more distributed and smoother patterns of flow that are likely to characterize the ductile deformation of the lower, aseismic part of the lithosphere—both of which influence the deformation on the scale of 100–200 km. The persistent argument about whether continental deformation is best described by a continuum or by rigid-block motions is largely a matter of scale and particular location: both are influential in establishing the patterns we see.

Sediment provenance in the Murchison and Maruia basins, Aotearoa/New Zealand: a record of Neogene strike-slip displacement, convergence, and basement exhumation along the Australian–Pacific plate boundary

ABSTRACT The Murchison and Maruia basins are situated on the Australian Plate adjacent the Alpine Fault, an ideal place to study Cenozoic Australian–Pacific plate boundary evolution. Sandstone provenance was investigated using petrographic and detrital zircon U–Pb geochronologic methods and primarily varies geographically. Secondary up-section variation tracks spatiotemporal changes in basement exhumation. Eocene–middle Miocene western Murchison Basin sandstone is arkosic, derived locally from Devonian–mid-Cretaceous granitoids. Early Miocene–?Pliocene eastern Murchison and Maruia basin sandstone is lithic-/plagioclase-rich, reflecting a mixed provenance: proximal Carboniferous–mid-Cretaceous granitoids, and distal mid-Cretaceous Median Batholith and Permian–Triassic Eastern Province metasedimentary sources in the Pacific Plate. This confirms early Miocene Pacific Plate exhumation during initial Alpine Fault evolution began in northern Fiordland/western Otago but the contrast between eastern and western Murchison Basin indicates limited westward sediment dispersal. Higher proportions of Brook Street Terrane (BST) detrital zircon in middle Miocene eastern Murchison Basin sandstone suggests accelerated Pacific Plate exhumation at c. 15 Ma. By c. 10 Ma, the eastern Murchison Basin BST source had switched to the Australian Plate due to Waimea–Flaxmore fault reverse reactivation and dextral plate boundary strike-slip displacement, which by the late Miocene/Pliocene led to Rakaia Terrane-affinity Haast Schist replacing Caples Terrane as the main Maruia Basin sediment source.

High-resolution crustal and upper mantle shear-wave velocity structure beneath the central-southern Tanlu fault: Implications for its initiation and evolution

The Tanlu fault is a well-known lithosphere-cutting, strike-slip fault in eastern China and it has played an important role in regional plate tectonics since the middle Mesozoic. However, the initiation mechanisms and tectonic evolution of the Tanlu fault remain controversial, in part due to the absence of constraints from deep structures. In this study, we inverted 5–150 s surface-wave dispersion data collected from 253 permanent stations and 111 temporary stations in the vicinity of the central-southern Tanlu fault and obtained both isotropic and azimuthally anisotropic shear-wave velocity (Vs) models in the crust and upper mantle simultaneously. The new Vs models reveal unprecedented multiple patterns of anomalies. There is, for example, an arc-shaped pattern of fast directions found in the South China plate (SCP), providing direct evidence of the sudden termination of the Tanlu fault at its southern end; orogen-parallel fast directions and high-velocity anomalies were detected beneath the Dabie and Sulu orogens, which are believed to be the residue of the delaminated lithosphere. Based on the evidence collected, we propose a four-stage tectonic model for the Tanlu fault. The tectonic model suggests that the area has been subjected to multiple geologic processes since the Early Mesozoic, including oceanic-continental collision, continental-continental collision, break-off of oceanic slabs, lithospheric delamination, and convective erosion resulting from corner flow. As such, the proposed tectonic model reconciles the newly discovered Vs anomalies as well as various previous findings, providing profound insight into regional deformations and the evolution of the Tanlu fault and its adjacent areas.

Discrete Fault Models

Fault surfaces are characterized by an inhomogeneous friction distribution, that can be represented with asperity models. Fault mechanics is dominated by asperities, so that a fruitful approach is to use discrete models, where asperities are the basic elements and the state of the fault is described by the average values of stress, friction and slip on each asperity. Under reasonable assumptions, the equations of motion can be solved analytically, with a deeper understanding of the behavior of the system. Fault dynamics has a sticking mode, where asperities are stationary, and a number of slipping modes, corresponding to the separate or simultaneous motion of asperities. Any seismic event is a sequence of slipping modes and a large variety of source functions is possible. Many large earthquakes are observed to be the consequence of the failure of two asperities: a discrete two-asperity model shows a rich dynamics and allows a detailed study of interaction between asperities. In this framework, fault evolution during coseismic and interseismic intervals can be calculated in terms of fault slip, stress state, energy release and seismic spectrum, including viscoelastic relaxation, fault creep and stress perturbations from other faults. Discrete models may include interaction between neighboring faults, allowing to assess conditions for the occurrence of seismic sequences in a fault system. A review of recent work on this subject is presented with applications to real earthquakes.

The control effect of normal faults and caprocks on hydrocarbon accumulation: A case study from the Binhai fault nose of the Huanghua Depression, Bohai Bay Basin, China

An exploration breakthrough was made in the Paleogene strata in the Binhai fault nose of the Huanghua Depression, but the distribution of hydrocarbons remained insufficient to understand. A series of fault-controlled traps were formed around the Gangdong fault, especially a large number of fault-block traps, which gave us a unique opportunity to use seismic data to study the distribution of the hydrocarbons under the control of normal fault and caprocks. By analysing the vertical and lateral changes of the fault throws (T-x and T-z plots), combined with the expansion index (EI), the characteristics of the Gangdong fault were studied and the evolution process of the fault was reconstructed. The fault has undergone the evolution process of lateral and dip linkage, and finally, the Gangdong fault was formed. The reconstruction of the evolution process and determination of charging stages found that the Gangdong fault was formed dip linkage just before late Neogene, providing an excellent vertical pathway for hydrocarbon migration. Besides, when the fault throw exceeds than 39 m, hydrocarbons were found near the fault, indicating a lower limit of fault throw. However, there were differences in the spatial distribution of hydrocarbons in the study area, which may be related to the integrity of the caprock. A lower thickness limit was found by analysing the relationship between the difference in hydrocarbon distribution above and below the regional caprock and the effective caprock thickness. When the effective caprock thickness is greater than this lower thickness limit, hydrocarbons can only accumulate below the caprock. When the effective caprock thickness is less than this lower limit, there is hydrocarbon accumulation above the caprock. This work highlights the evolution of normal fault and the control effect of fault-caprocks on hydrocarbon accumulation and further understands the spatial distribution of petroleum near the fault.

Climate-driven stress changes and normal fault behavior in the Lake Malawi (Nyasa) Rift, East Africa

Climate-triggered fluctuations of surface masses, including ice and water, can cause transient stress in the Earth's crust, further affecting the slip behavior of faults over different temporal and length scales. In particular, lakes developed within active continental rifts may modulate the stress states and slip rates of rift border faults and intrarift faults. Here, we utilize a numerical model in a case study of the Malawi (Nyasa) Rift to understand the response of faults to mass fluctuations on the Earth's surface. The water level of Lake Malawi rose 600 m over the last 150 kyr, and significantly influenced the stress state of faults in rift valley. We find that such water load fluctuations can exert 4.6 MPa normal stress on fault planes and produce a negative Coulomb stress (down to −2.0 MPa) on fault planes as well as a pronounced reduction of slip (∼2 m) on fault planes within the rift. Moreover, along-strike differences in fault geometries and their position relative to the center of the water column load resulted in variable along-strike stress and slip changes. These results suggest that lakes that develop within continental rifts play an important role in the evolution of extensional faulting. Our case study provides a basis for evaluating the relationship between climate-driven surface mass variations and the subsurface stress state of fault planes and associated seismic potentials.

Fault Zones and Stress Fields in the Sedimentary Fill of Lake Baikal: Tectonophysical Approach for Seismic and Hydroacoustic Data Interpretation

Abstract —This paper presents a schematic summary of comprehensive analysis of seismic, reflection profiling, and hydroacoustic data on faults which caused sediment deformation in the central segment of the Central Baikal basin. According to the tectonophysical analysis results, the fault pattern within sediment fill has been recognized as zone-block, i.e., it represents a network of high-density fracture zones limiting weakly deformed blocks. The structure of large NE-trending fault zones (Olkhon, Beregovoy, Gydratny, and Svyatoy Nos) is controlled by main fault planes (or their segments) bounded by subsidiary faults. Geomorphic expression of NW cross faults in the sedimentary cover as broad zones of smaller-scale fractures accounts for early stages of the evolution of basement faults. In a longitudinal direction, they divide the basin into large fragments. The zone–block structure of the sedimentary strata was developed in different stress regimes: strike-slip and extension at the early and late orogenic rifting stages, respectively. At the modern stage of tectogenesis, the established network of fault zones controls the gaseous (including hydrate formation) and seismic activity expression in the subsurface. Hydrate-bearing mud volcanoes and seeps are confined to major faults, while earthquake epicenters are confined to fault zones and form clusters at junctions of large NE-trending faults with NW-oriented extension zones and E–W left-lateral strike-slip faults.

Comprehensive diagnosis and analysis of spur gears with pitting-crack coupling faults

As an important part of power transmission in mechanical system, the health status of gear needs to be judged accurately. However, most of researchers focus on single fault gear, and very few papers are reported on the performance of multiple faults. So the gear mathematical model with pitting-crack coupling faults is derived in this study, and it is validated by a three-dimensional finite element model. Furthermore, several types of fault combinations from health to severity are presented to investigate the effect of coupling fault evolution on gear time-varying meshing stiffness. The stiffness excitation is applied into an 8 degrees of freedom model to obtain the dynamic characteristics of the gear-rotor system in terms of displacement and acceleration, and a reasonable diagnosis of the gear status can be made by analyzing the dynamic characteristics in time domain and frequency domain. In the next step of research, the statistical indicators are applied to further reveal the degree of coupling faults, which provides effective reference on the diagnosis of coupling fault gears.

Enrichment Mechanism and Prospects of Deep Oil and Gas

AbstractWith the deepening of oil and gas exploration, the importance of depth is increasingly highlighted. The risk of preservation of storage space in deep reservoirs is greater than that in shallow and medium layers. Deep layers mean older strata, more complex structural evolution and more complex hydrocarbon accumulation processes, and even adjustment and transformation of oil and gas reservoirs. This paper systematically investigates the current status and research progress of deep oil and gas exploration around the world and looks forward to the future research focus of deep oil and gas. In the deep, especially the ultra‐deep layers, carbonate reservoirs play a more important role than clastic rocks. Karst, fault‐karst and dolomite reservoirs are the main types of deep and ultra‐deep reservoirs. The common feature of most deep large and medium‐sized oil and gas reservoirs is that they formed in the early with shallow depth. Fault activity and evolution of trap highs are the main ways to cause physical adjustment of oil and gas reservoirs. Crude oil cracking and thermochemical sulfate reduction (TSR) are the main chemical modification effects in the reservoir. Large‐scale high‐quality dolomite reservoirs is the main direction of deep oil and gas exploration. Accurate identification of oil and gas charging, adjustment and reformation processes is the key to understanding deep oil and gas distribution. High‐precision detection technology and high‐precision dating technology are an important guarantee for deep oil and gas research.

An Industrial Fault Diagnostic System Based on a Cubic Dynamic Uncertain Causality Graph.

This study presents an industrial fault diagnosis system based on the cubic dynamic uncertain causality graph (cubic DUCG) used to model and diagnose industrial systems without sufficient data for model training. The system is developed based on cloud native technology. It contains two main parts, the diagnostic knowledge base and the inference method. The knowledge base was built by domain experts modularly based on professional knowledge. It represented the causality between events in the target industrial system in a visual and graphical form. During the inference, the cubic DUCG algorithm could dynamically generate the cubic causal graph according to the real-time data and perform the logic and probability calculations based on the generated cubic DUCG models, visually displaying the dynamic causal evolution of faults. To verify the system’s feasibility, we rebuild a fault-diagnosis model of the secondary circuit system of No. 1 at the Ningde nuclear power plant based on the new system. Twenty-four fault cases were used to test the diagnostic accuracy of the system, and all faults were correctly diagnosed. The results showed that it was feasible to use the cubic DUCG platform for fault diagnosis.

Physical simulation experiments of structural deformation and hydrocarbon accumulation in piggyback thrust wedges

The piggyback thrust wedge is a common structural style in thrust belts, which controls the lateral arrangement of hydrocarbon distribution. This study conducted physical simulation experiments of structural deformation and hydrocarbon accumulation by using the piggyback thrust wedge as the geological model. According to the experimental results, hydrocarbon accumulation patterns were obtained by investigating the evolutionary history of the fault-sealing performance while inverting the coupling relationship between the fault evolution and hydrocarbon accumulation. The structural deformation experiment showed that the evolution of the fault displacement and dip angle was characterized by gradual and staged progress. The kaolin smear continuity deteriorated with fault evolution. The soybean oil accumulation experiment demonstrated that the fault-sealing performance in the rear of the thrust wedge was inferior to that in the front. Hydrocarbon migration was mostly lateral in the front of the thrust wedge and mainly vertical in the rear. Quantitative analysis showed that the fault-sealing performance had three closed, partially closed, and open stages, which gradually deteriorated with the structural evolution. Three hydrocarbon accumulation patterns were identified in the piggyback thrust wedge: synchronized, adjustment, and non-adjustment patterns. The evolution of the structural deformation and faults-sealing performance resulted in spatio-temporal differences in hydrocarbon accumulation in the thrust belts of central-western China. The front of the thrust wedge had a higher exploration potential than the rear.

The brittle evolution of Western Norway – A space-time model based on fault mineralizations, K–Ar fault gouge dating and paleostress analysis

Basement fracture and fault patterns on passive continental margins control the onshore landscape and offshore distribution of sediment packages and fluid pathways. In this study, we decipher the spatial-temporal evolution of brittle faults and fractures in the northern section of the passive margin of Western Norway by combining field observations of fault mineralizations and K–Ar fault gouge dating with different paleostress approaches, resulting in the following model: (1) High-T fault mineralizations indicate Silurian NW-SE compression followed by NW-SE extension in the Early to Mid-Devonian. (2) Epidote, chlorite and quartz fault mineralizations indicate a dominant strike-slip stress field in the Late Devonian to early Carboniferous. (3) E-W extensional stress fields which could be related to Permo-Triassic or Late Jurassic rifting are not prominent in our data set. (4) K–Ar fault gouge ages indicate two extensive faulting events under a WNW-ESE transtensional stress regime with related precipitation of zeolite and calcite in the mid (123-115 Ma) and late (86-77 Ma) Cretaceous. Our results show that the brittle architecture of the study area is dominated by reactivation of ductile precursors and newly formed strike-slip faults, which is different from the dip-slip dominated brittle architecture of the southern section of the West Norway margin.

Main Factors of Mesozoic Tectonic Deformation in the Erlian Basin, Inner Mongolia, China: Insights from Physical Modelling

Erlian Basin is a Mesozoic oil and gas-bearing basin in northeast of China. The extension rate, extension direction, and stratum thickness of this rift basin have a clear control on its shape and extension. In this study, we design three sandbox models of the Erlian Basin to represent the effects of changing these three factors. The extension rate controls the timing of secondary fault formation inside the rift basin; a high extension rate promotes faster deformation inside the rift. The extension direction controls the strike of the fault inside the rift; a greater angle between the extension direction and the normal direction of the strike of the rift favors rapid evolution of internal secondary faults. The stratum thickness represents the control of sedimentation on the rift basin; the thinner the brittle layer, the wider the rift. The simulation results also show that the extension direction is the major factor controlling tectonic deformation in the basin. Stratum thickness and extension rate are secondary controlling factors. Additionally, according to geometric and kinematic similarities between typical Mesozoic rift basins in eastern and adjacent areas of China, we suggest that southeastward extension is a possible kinematic mechanism for basin formation.

Looking Into the Entanglement Between Karst Landforms and Fault Activity in Carbonate Ridges: The Fibreno Fault System (Central Italy)

The entanglement between active tectonics and karst systems is well-known in the literature. Karst systems are sound recorders of continental deformation in terms of brittle structures and seismic features and have been successfully used as markers for reconstructing tectonic stresses and assessing preferential directions of increased permeability in oil and gas fields. Karst systems could also be exploited to evaluate the past activity of faults bounding karst hydrostructures, thus providing useful data for the assessment of the seismic hazard of a specific area. In this work, we look into the complex relationship among karst development, recent tectonics and groundwater flow, which appear to be strongly interconnected with each other, to assess the activity of faults bounding karst hydrostructures. We focused our attention on an active karst area located in the Mesozoic and Cenozoic carbonate reliefs of the Italian central Apennines. In this context, the morphological and morphometric features of the karst landforms (dolines, dry valleys, and cave entrances), identified with geomorphological surveys, and their mutual relationship with fractures and fault segments, identified employing geostructural analysis, document stasis and deepening events in karst evolution. Such events are related to changes in the groundwater table and the consequent variation of the paleokarst base level associated with the Quaternary fault activity. A comprehensive evaluation of the evolution of karst systems at local and regional scales, considering the hydrogeological influence on base levels, allows us to use karst landforms as a proxy to unravel fault activity and evolution in Italy and in other similar karst environments.

A Fault Diagnosis System for a Pipeline Robot Based on Sound Signal Recognition.

Timely and accurate identification of fault types at the early stage of minor faults is significant for cutting off fault evolution. In order to have a clear understanding of the pipeline robot’s own situation in the pipeline, this paper proposes a fault diagnosis system for pipeline robots based on sound signal recognition. This can effectively reduce the probability of serious faults such as shutdown and loss of control in the pipeline without affecting the safe operation of the pipeline robot, which is a key issue to improve the reliability of the pipeline robot. The system consists of a combination of three parts: hardware, software, and algorithm. On the one hand, Raspberry Pi is the core module, while on the other hand, it is also responsible for the data transmission between the various modules, including storing the original sound signals collected by the sensors and transmitting the diagnosis results to the upper computer software interface. The proposed system is validated on the dataset collected by the data experimentation platform. The experimental results show that the proposed fault prediction method obtains advanced results on this dataset, verifying the effectiveness and stability of the proposed fault diagnosis system for pipeline robots based on sound signal recognition.

A high-entropy alloy with dislocation-precipitate skeleton for ultrastrength and ductility

The introduction of dislocations and precipitates has proven to be the effective methods to improve the mechanical properties of metallic materials and break strength-ductility trade-off. However, it is difficult to obtain a suitable combination of both strategies in the metal materials, that is, the coexistence of high-density dislocations and high-volume-fraction precipitates. Here, utilizing a three-dimensional (3D) printing technique, we have successfully achieved a combination of high-density dislocation structures and high-volume-fraction ductile nano-precipitates in a high-entropy alloy (HEA). This 3D-printed HEA, with a novelty dislocation-precipitate skeleton (DPS) architecture and high-density ductile nano-precipitations wrapped in the DPS, has an ultra-high tensile strength of ∼ 1.8 GPa together with the maximum elongation of ∼ 16%. The ultra-high strength mainly comes from dislocation-precipitation synergistic strengthening, while the large ductility mainly originates from an evolution of multiple stacking fault (SF) structures. The DPS can not only slow down the dislocation movement during the strain process without completely hindering its motion, but more importantly, the DPS still has good structural stability during the deformation, which avoids any premature failure due to stress concentrations at the boundary. The DPS formation promotes the development of the metal-based 3D printing technique in the preparation of the high-performance materials, and it can provide an efficient pathway for further enhancement of the alloy properties.

Multi-lag and multi-type temporal causality inference and analysis for industrial process fault diagnosis

Causality analysis methods play an increasingly crucial role in revealing the underlying mechanisms and evolution of process faults in industry. Indeed, in modern complex and integrated industrial systems, causation among various components usually have multi-lag and multi-type characteristics, which means that the time-delay of fault propagation between various process variables is multiple, and there exist both linear and nonlinear causal relations. Such characteristics make conventional causal inference tools ineffective. In this study, a systematic root cause diagnosis strategy is proposed. First, a modular neural network structure, termed Sparse Causal Residual Neural Network(SCRNN) is designed to concurrently extract multi-lag linear and nonlinear causal relations. By optimizing a multivariate time series forecasting objective with hierarchical sparsity constraints, the integral causal structure can be interpreted by checking the parameters of the SCRNN model. This causal structure represents the topology of fault propagation. Furthermore, an R-value metric is devised to quantify the position of each faulty variable and hence pinpoint the root cause accordingly. A numerical case, a benchmark process and a real industrial process illustrate the practicability and superiority of the proposed method.

Structural Formation, Evolution, and Genetic Mechanisms of Fault in Controlling Hydrocarbon Migration of Unconventional Rocks: A Case Study of Zhuangnan Fault

Zhuangnan fault zone was affiliated with Gubei subsag of the Zhanhua sag in Jiyang Depression, Bohai gulf basin. Zhuangnan fault zone has two functions as the main east-west strike-slip accommodation structure. That is, on the one hand, Zhuangnan fault zone inherited the rules of development of regional tectonic. On the other hand, the present structure framework of Zhanhua sag was reconstructed by Zhuangnan fault zone. In the study, there are four main seismic reflectors: T0, T1, T2, and T6. They are the basis for researching the planar and vertical features of Zhuangnan fault zone. The structural formation, evolution, and genetic mechanisms of Zhuangnan fault zone are studied from three aspects of geometry, kinematics, and dynamics. In geometry, by the closure interpretation of 43 south-north interpretation sections and 24 east-west interpretation sections, the result indicates that Zhuangnan fault zone has its special regularity and characteristic which has three-piece planar characterization (eastern part, middle part, and western part). Three types of plane combination forms are determined: arched, linear, and “S” curved type. The plane combination structure styles of the Zhuangnan fault zone mainly include feather row, horsetail, grid, diagonal, and parallel style. These planar structural features play an important role in indicating the fault zoning of Zhuangnan fault zone. Based on the plane and section structural styles of Zhuangnan fault zone and the analysis of dynamic evolution, it is found that Zhuangnan fault zone has a succession relationship between deep and shallow fault systems. From tectonic evolution and regional dynamic point of view, this paper discusses the activity law of the Zhuangnan fault zone and the boundary faults on the east and west sides of Jiyang Depression, which are Changdi fault, Wuhaozhuang fault, and Chengnan fault, respectively. This study provides a new and more reasonable explanation for the unique structural characteristics of Zhuangnan fault zone and further confirms the important role and regulation mechanism of Zhuangnan fault zone.

A combined deep learning model for damage size estimation of rolling bearing

The identification of damage sizes based on vibration monitoring data is significant in the study of fault evolution, prediction and diagnosis of rolling bearing. There are inherent restrictions in traditional identification models such as high dependence on prior knowledge and insufficient feature extraction, aiming at the limitation, a prediction method of rolling bearing damage size based on deep learning is proposed. In this paper, a combined model of deep convolutional long-short-term memory network is developed, which can sufficiently extract the multi-dimensional and time-series characteristics of bearing vibration signal, and realize the intelligent and efficient diagnosis of bearing fault. On the basis of theoretical analysis, the rolling bearing fault tests under various damage sizes and rotational velocities are carried out by using the accelerated fatigue testing machine for rolling bearings, and the traditional and novel methods are compared based on the test data. The results show that the prediction accuracy of the combined network can reach 99.94% and 98.67%, respectively under normal and noisy conditions, which is higher than the single deep convolution network, long-short-term memory network and other models. The comparison results amply demonstrate the superiority of the proposed method.

Structure and formation mechanism of the Pearl River Mouth Basin: Insights from multi-phase strike-slip motions in the Yangjiang Sag, SE China

• The Pearl River Mouth Basin experienced two stages of strike-slip motions along the ENE and WNW directions. • The partial reactivation of the intrabasement faults controlled the evolution of intrabasin faults. • The formation of the basin resulted from the joint effect of oblique Pacific-Eurasian subduction and the Indo-Eurasian collision. The Pearl River Mouth Basin (PRMB) experienced multi-phase rifting and complex tectono-sedimentary evolution during the Cenozoic, and is a topic of many studies regarding the basin-forming mechanism. In the present study, detailed seismic interpretation and tectonic analysis based on the 3D seismic reflection data of the Yangjiang Sag in the northwestern PRMB were carried out, to provide clues to its tectonic evolutionary history. The qualitative-quantitative analysis of fault strikes and migration of depocenter in the Yangjiang Sag indicated the dextral transtensional setting during the Paleocene to Miocene. Meanwhile, the horsetail and en echelon structures on plane view and negative flower structures in cross-section are exhibited, indicating the successive occurrence of strike-slip motions in ENE and WNW directions respectively after initial rifting combined with the structural analysis of Huizhou Sag and Baiyun Sag. In addition, thrust fault systems trending in WNW and ENE were identified in the basement. Their partial and selective reactivation in strike-slip character during the Cenozoic restricted the faults developed in the basin with differential properties. Geometrically, rhombic-shaped sags with cross-basin fault zones were formed, implying the formation of pull-apart structures along with multi-phase strike-slip motions. The pull-apart mechanism could be accounted due to the joint effect of the oblique Pacific-Eurasian subduction and the Indo-Eurasian collision during the Cenozoic.