Secondary Faults Research Articles

Rupture Kinematics and Coseismic Slip Model of the 2021 Mw 7.3 Maduo (China) Earthquake: Implications for the Seismic Hazard of the Kunlun Fault

The 21 May 2021 Maduo earthquake was the largest event to occur on a secondary fault in the interior of the active Bayanhar block on the north-central Tibetan plateau in the last twenty years. A detailed kinematic study of the Maduo earthquake helps us to better understand the seismogenic environments of the secondary faults within the block, and its relationship with the block-bounding faults. In this study, firstly, SAR images are used to obtain the coseismic deformation fields. Secondly, we use a strain model-based method and steepest descent method (SDM) to resolve the three-dimensional displacement components and to invert the coseismic slip distribution constrained by coseismic displacement fields, respectively. The three-dimensional displacement fields reveal a dominant left-lateral strike-slip motion, local horizontal displacement variations and widely distributed near-fault subsidence/uplift deformation. We prefer a five-segment fault slip model, with well constrained fault geometry featuring different dip angles and striking, constrained by InSAR observations. The peak coseismic slip is estimated to be ~5 m near longitude 98.9°E at a depth of ~4–7 km. Overall, the distribution of the coseismic slip on the fault is highly correlated to the measured surface displacement offsets along the entire rupture. We observe the moderate shallow slip deficit and limited afterslip deformation following the Maduo earthquake, it may indicate the effects of off-fault deformation during the earthquake and stable interseismic creep on the fault. The occurrence of the Maduo earthquake on a subsidiary fault updates the importance and the traditional estimate of the seismic hazards for the Kunlun fault.

Seismicity at the Castor gas reservoir driven by pore pressure diffusion and asperities loading

The 2013 seismic sequence at the Castor injection platform offshore Spain, including three earthquakes of magnitude 4.1, occurred during the initial filling of a planned Underground Gas Storage facility. The Castor sequence is one of the most important cases of induced seismicity in Europe and a rare example of seismicity induced by gas injection into a depleted oil field. Here we use advanced seismological techniques applied to an enhanced waveform dataset, to resolve the geometry of the faults, develop a greatly enlarged seismicity catalog and record details of the rupture kinematics. The sequence occurred by progressive fault failure and unlocking, with seismicity initially migrating away from the injection points, triggered by pore pressure diffusion, and then back again, breaking larger asperities loaded to higher stress and producing the largest earthquakes. Seismicity occurred almost exclusively on a secondary fault, located below the reservoir, dipping opposite from the reservoir bounding fault.

Geochemical Characteristics and Migration Pathways of Ordovician Carbonate Oil Reservoirs in the Tuoputai Area, Tarim Basin, Northwestern China

AbstractExploration potential is huge and the oil resources are rich in the Ordovician reservoirs of the Tarim Basin. However, the mechanism of hydrocarbon accumulation is complex and not yet fully understood. In the Tuoputai area, the hydrocarbon migration pathways and characteristics of deep hydrocarbon accumulation are revealed through analyses of the physical data of rich oil and gas, the geochemical parameters of oil, and fluid inclusions. The results show that the Ordovician oils in the Tuoputai area have the same geochemical characteristics as the mixed oil from the Lower Cambrian source rock and the Middle–Upper Ordovician source rock. The Ordovician reservoirs have been charged three times: in the late Caledonian, late Hercynian, and Himalayan stages. Oil charging occurred in the Hercynian stage, in particular, as it is the main filling period of hydrocarbon. The north‐northeast (NNE)‐trending TP12CX major fault, active in in these times and is dominant migration channel of hydrocarbon, but there is segmentation affected by the difference of activities. Oil maturity is higher in the south than in the north and is abnormally high near the major fault. Parameters related to migration indicate that oil migrated northeastward along the NNE‐trending TP12CX major fault and adjusted laterally along the secondary faults and weathering crust, forming the present characteristics of oil and gas distribution.

Sandbox Modeling of Transrotational Tectonics With Changeable Poles: Implications for the Yinggehai Basin

The main formation of the Yinggehai Basin has been related to the rotation of the Indochina block, resulting in large-scale strike-slip motion along the Red River Fault Zone (RRFZ). Transrotational tectonics played a key role in the evolution of the Yinggehai Basin. In this study, we present analog experiments with a preexisting basal velocity discontinuity boundary, rotation of crustal blocks concerning vertical axes, and syntectonic sedimentations to evaluate how the transrotational tectonics controls the evolutionary process of the Yinggehai Basin. Particle image velocimetry (PIV) was used to monitor the deformation of the model surface. Four successive poles of rotation have been applied to the model. The basin evolution underwent two phases. An early phase of deformation is characterized by the nucleation of the main internal faults above the velocity discontinuity boundary and segmented en echelon border fault systems. In the early phase, the internal and boundary faults mainly accommodated large-scale strike-slip displacement. During progressive extension, the main internal faults deactivated, and tectonic activity is localized along the boundary and secondary internal faults in the late phase. The boundary faults in the rotating block play a dominant role in the widening and deepening of the rift zone at an accelerating rate. The model surface morphology shows similarities to the Yinggehai Basin, which is wide in the middle and converges toward the northwest and southeast. In addition, experimental profiles have been compared with seismic profiles in the Yinggehai Basin. The model results also indicate that the rotation of the Indochina block combines with strong strike-slip motion. The similarities between modeling and nature provide support for ∼250 km sinistral displacement along the RRFZ between ∼32 and ∼21 Ma.

The 2019 Ridgecrest, California earthquake sequence: Evolution of seismic and aseismic slip on an orthogonal fault system

Cascade-up and/or slow-slip processes are commonly believed to control interactions between foreshocks, mainshocks and aftershocks, but their relative contributions remain poorly resolved. Discrimination between these processes will shed light on the understanding of earthquake physics, which requires exceptional observations of earthquake sequences. The well-recorded July 2019 Ridgecrest, California foreshock-mainshock-aftershock earthquake sequence provides such an opportunity. We perform simultaneous inversion of the July 4th MW 6.4 foreshock and July 5th MW 7.1 mainshock kinematic rupture models using SAR, strong motion, and GPS data. We also invert for afterslip models following the MW 6.4 foreshock and the mainshock, respectively, by developing an inversion method that utilizes strainmeter, SAR and daily GPS time series. The inversion results show that the overall sequence involves no less than six fault segments, which include a main northwest-trending fault and secondary faults with sub-parallel and orthogonal geometry to the main fault. Co-seismic slip and afterslip have complementary patterns on the faults. During the early post-seismic period following the MW 6.4 foreshock and the mainshock, moment release on the southwest-trending fault is dominated by aseismic slip, in contrast to the predominantly seismic slip on the northwest-trending fault. The mainshock appears to be triggered by a cascade migration of foreshocks on a northwest-trending fault. Slip on the southwest-trending fault migrates from the fault junction at the northeast end (following the MW 6.4 foreshock) to the southwest end (following the mainshock) during the afterslip interval. The dual-mode (seismic versus aseismic) slip phenomena appear to be driven by co-seismic stress changes produced by the major events.

Genesis of thermal waters from the Taşkesti-Sarıot geothermal prospect in Mudurnu (Bolu, NW Turkey)

The Taşkesti–Sarıot study area is located in northwest Turkey, about 23 km NW of Mudurnu town in the Bolu province. The thermal waters of the Taşkesti–Sarıot were investigated by means of field measurements, chemical analyses and isotope investigations. An area of 20 km2 was geologically mapped around the spa and characteristics of thermal and cold-waters were determined. The Taşkesti-Sarıot thermal waters, (T °C = 63, and flowrate of 1.70 L/sec) emanates along a secondary fault in the North Anatolian Fault Zone (NAFZ). Geothermal water reservoirs are present within fractured limestone, micaschists, diorite, tonalite, serpentinite, gabbropegmatites and graywacke which have the secondary porosity and permeability. Based on the main consitituents, the thermal waters can be classfied as Na(Ca)SO4 types, whereas the cold and stream waters were characterized as a Ca(Mg)HCO3 type waters. Geochemical processes responsible for the genesis of the hydrochemical features of the waters include dissolution, mixing, oxidation and loss of energy by heat conduction. Chemical geothermometers suggest deep temperatures close to 100 °C for the deepest geothermal well (SK-1: 63 °C at the surface) water in the region and thus the Taşkesti-Sarıot geothermal system can be classified as a low temperature resource.These thermal waters are of meteoric origin that circulate and restores heat through the fault zone due to the geothermal gradient and discharge to the surface. The thermal waters are derived from advective flow as indicated by the δ2H and 18O isotope data, which plot on the meteoric water line showing a significant downward shift if compared with a local reference point thus indicating recharge by infiltration derived from a high standing (colder) terrain. The recharge area for the thermal waters is estimated to be nearly 1000 – 1600 m from the northeast part of the study area. Moreover, there is no evidence for isotope exchange between hot waters and reservoir rock. Tritium data confirm the deep origin of the thermal waters. Finally, a conceptual geochemical model of the geothermal system is proposed.

Basin progress: active deformation analysis by tectonostratigraphic elements and geophysical methods on North Anatolian Fault System (Eastern Marmara Region, Turkey)

The Northern Branch of the North Anatolian Fault System controls and deforms the Izmit Basin and the Sapanca Lake Basin in the study area. Unlike the Sapanca Lake Basin, the oblique normal faults with WNW–ESE trending with maximum length of 5 km in the south of the basin have contributed to the deformation process in the formation of Izmit Basin. The fault sets mainly incline to the north. The N-S width of the dextral strike-slip active deformation was determined as 9 km at Izmit basin and 3.8 km at Sapanca Lake basin. Further, the minimum principal stress axes (σ3) vary in the trending ranges of N11°–74°E, which are caused by the transtensional stresses associated with strike-slip faulting in the Izmit Basin by a different tectonic source than the Sapanca Lake Basin. Besides, the crust depth of main strand of NAFS-NB was determined up to 1112 m by magnetic method. The secondary faults were determined by both magnetic and resistivity methods up to a depth of 110 m. The depression area between Izmit bay and Sapanca Lake on the northern Anatolian fault is an integrated basin with two dextral strike-slip tectonic origins. Thus, the Izmit Basin, along with the main strike-slip faulting, has been developed in the asymmetric negative flower structure, where only the southern boundary has become a fault. The Sapanca Lake Basin is a lazy-Z-shaped pull-apart system formed by the E–W trending fault as a releasing bend. A simple shear deformation ellipsoid with a long axis of approximately 35 km on the Northern Branch of the North Anatolian Fault System is defined for the Izmit–Sapanca integrated basin. Therefore, intra-basin deposits have different depths estimated from the gravity data in the Izmit–Sapanca integrated basin, and the maximum sediment thickness estimated is 2200 m in the middle of the Izmit Basin.

Numerical investigation of secondary-fault rupture propagation through sandy deposits

The increasing urban development in seismic-prone regions, in conjunction with the continuous construction of large-scale lifelines (i.e., road and railway networks, pipelines, etc.) has increased the risk of potential damages due to permanent displacements at the ground surface that can be caused by an earthquake fault rupture. Several recent earthquakes have revealed this risk. Therefore, the problem of fault rupture propagation of a single fault has been thoroughly investigated with field studies, as well as experimental tests and numerical models. Nevertheless, the presence of parallel or intersecting secondary fault ruptures is usually observed in the field due to stress redistributions and/or rock heterogeneities. The aim of the current study is to examine the rupture patterns and surface displacements caused by the contemporaneous rupture of a main fault and a perpendicular secondary fault. A three-dimensional numerical model has been developed utilizing the finite-element method in order to examine this complex phenomenon in sandy deposits. The soil behavior is represented quite accurately via an elastoplastic Mohr-Coulomb constitutive model with isotropic strain softening, which is initially validated with experimental results obtained by centrifuge tests in case of a single fault. Subsequently, a detailed parametric study has been performed, investigating different fault types and dip angles, as well as sandy layer thickness and material properties, to highlight various important aspects regarding the development and propagation of secondary fault ruptures and the resulting zones of excessive surface displacements.

Fault Detection Algorithm for Multiple-Simultaneous Refrigerant Charge and Secondary Fluid Flow Rate Faults in Heat Pumps

The detection and diagnosis of faults is becoming necessary in ensuring energy savings in heat pump units. Faults can exist independently or simultaneously in heat pumps at the refrigerant side and secondary fluid flow loops. In this work, we discuss the effects that simultaneous refrigerant charge faults and faults associated with the flow rate of secondary fluids have on the performance of a heat pump operating in summer season and we developed a correlation to detect and diagnose these faults using multiple linear regression. The faults considered include simultaneous refrigerant charge and indoor heat exchanger secondary fluid flow rate faults (IFRFs), simultaneous refrigerant charge and outdoor heat exchanger secondary fluid flow rate faults (OFRFs) and simultaneous refrigerant charge, IFRF and OFRF. The occurrence of simultaneous refrigerant charge fault, IFRF and OFRF caused up to a 5.7% and 8% decrease in cooling capacity compared to simultaneous refrigerant charge and indoor heat exchanger secondary fluid flow rate faults, and simultaneous refrigerant charge and outdoor heat exchanger secondary fluid flow rate faults, respectively. Simultaneous refrigerant charge fault, IFRF and OFRF resulted in up to an 11.6% and 5.9% decrease in COP of the heat pump unit compared to simultaneous refrigerant charge fault and IFRF, and simultaneous refrigerant charge fault and OFRF, respectively. The developed FDD correlations accurately predicted the simultaneous refrigerant charge and faults in the flow rate of the secondary fluid within an error margin of 7.7%.

New insights on the geometry and kinematics of the Shunbei 5 strike-slip fault in the central Tarim Basin, China

Integrated geological-geophysical methods have been used to depict the geometric characteristics and kinematic evolution of the Shunbei 5 (SB5) and adjacent Shunbei1 (SB1) strike-slip faults in the central Tarim Basin, China. Geometric evidence for strike-slip faulting includes the occurrence of positive and negative flower structures in stepover zones, oblique secondary splay faults, en echelon folds, and adjacent secondary faults. The multi-humped along-strike and along-dip displacement variations of the SB5 fault provide insights into the initial segmentation, interaction and polycyclic growth of the fault zones both in plan and section views: The SB5 fault initiated as an apparent “X-type” conjugate pure shear fault system in the north and a simple shear fault system in the south respectively. At depth (mainly in Cambrian to Middle Ordovician rocks), the northern and southern parts of the SB5 fault exhibit a typical dextral strike-slip architecture consisting of multiple fault segments connected via transpressional push-up or transtensional pull-apart stepovers or bends. The southern part has a linear, narrow sinistral ridge system. At shallower depths (in Upper Ordovician to Middle Devonian rocks), the lower subvertical faults propagated upwards as en echelon normal faults in the north, and as a two-phase, partitioned system consisting of boundary grabens and en echelon normal faults that dissected the early-formed border grabens in the south. With progressive deformation, the northern and southern parts of the SB5 fault reactivated and transferred into one large, sinistral fault in Upper Devonian to Permian rocks. Four major tectonic phases matching the kinematic evolutions of regional fault systems and uplifts in the study region, have also been recognized in the Middle Ordovician to Cretaceous. The pull-apart stepover and single fault zones developed in Middle Ordovician rocks are favorable fracture-related reservoirs.

Synthetic transfer zone characterization using seismic attributes: An example from the Parihaka fault system in the Taranaki Basin, New Zealand

Synthetic transfer zones develop between fault segments that dip in the same direction, with relay ramps connecting the fault blocks separated by the different fault segments. The characteristics of the transfer zones are controlled by the lithology, deformation conditions, and strain magnitude. The Parihaka fault is a northeast–southwest-trending set of three major en echelon faults connected by relay ramps in the Taranaki Basin, New Zealand. The structure in the basin is defined by extension during two episodes of deformation between the late Cretaceous and Paleocene and between the late Miocene and recent. To better understand the evolution of a synthetic transfer zone, we studied the geometry and secondary faulting between the individual fault segments in the Parihaka fault system using structural interpretation of 3D seismic data and seismic attributes. This interpretation allows for a unique application of seismic attributes to better study transfer zones. Seismic attributes, such as coherence, dip, and curvature, are effective tools used to understand the detailed geometry and variation in displacement on the individual faults, the nature of secondary faulting along the transfer zones, and the relationship between the faults and drape folds. The seismic characterization of the fault system of Miocene to Pliocene age horizons highlights variations in the degree of faulting, deformation, and growth mechanism associated with different stages of transfer zone development. The coherence, dip, and curvature attributes indicate a direct correlation with structural parameters such as deformation, folding, and breaching of relay ramps. All three attributes enhance the visualization of the major and associated secondary faults and better constrain their tectonic history. The observed correlation between the seismic attributes and structural characteristics of transfer zones can significantly improve the structural interpretation and exploration workflow.

Distributed secondary consensus fault tolerant control method for voltage and frequency restoration and power sharing control in multi-agent microgrid

This paper proposes a distributed secondary consensus fault-tolerant control (FTC) method for the multi-agent microgrid (MG). The proposed controller is applied to compensate for the errors in the system frequency and voltage profiles in the presence of MG faults. The proposed controller also enables the system to ensure an accurate sharing of the active and reactive power among the connected distributed generations (DGs) in MG. The consensus-based controller depends on the information transferring between MG neighbor agents through a graph communication network. The proposed secondary controller improves the primary controllers' performance, including droop control and inner voltage and current controllers. The proposed controller has been verified using a hypothetical multi-agent MG system in MATLAB/Simulink environment. A comparative analysis between the results obtained from applying the proposed controller and the primary droop control method (DCM). The proposed controller's performance is evaluated using the controller response time, the maximum frequency deviation, and the steady-state restoration time. The results show the proposed secondary FTC method's effectiveness in mitigating the faults' effect in multi-agent MG.

Geometric and Dynamic Patterns of the Golmud Segment in the Southern Marginal Fault of the Qaidam Basin

The southern marginal fault of the Qaidam Basin (SMQBF) is a block-bounding border fault that has played a key role in the structural evolution of the Kunlun Fault. However, its geometric and dynamic deformation patterns since the Late Pleistocene have not been clearly observed. Field investigations, combined with high-resolution imagery and shallow seismic profiles, show that the SMQBF is a thrust fault with a sinistral strike-slip component composed of several secondary faults. Its Late Quaternary deformation pattern is characterized by piggyback thrust propagation, and the frontal fault may not be exposed to the surface. Due to the flexural slip of the hanging strata of the secondary fault, sub-parallel faults with widths of thousands of meters have formed on high terraces; these are important when assessing the seismic hazard of this area. Based on high-resolution topographic data obtained using an unmanned erial vehicle and optically stimulated luminescence chronology, the slip rates of several secondary faults were obtained. The vertical and strike-slip rates of the SMQBF were determined to be 0.96 ± 0.33 mm/a and 2.66 ± 0.50 mm/a, respectively, which may be the minimum rates for the fault. Considering that the SMQBF is composed of several secondary faults, these rates possibly correspond to minimum deformation only. The evident sinistral strike-slip of the SMQBF indicates that although the sinistral slip of the Kunlun Fault system is concentrated in main fault of this system, the branch faults have a significant influence on the lateral extrusion of the Qinghai-Tibet Plateau.

Evolution of prototype basin and analysis of lithofacies paleogeography in Hongqi depression

Based on the analysis of three-dimensional seismic data in Hongqi sag, it is clear that the structure of the depression is controlled by volcanic mechanism, controlled subsidence fault and secondary fault. The structure is complex. The structural framework of the residual basin changed greatly due to the multi-stage tectonic movements. It is not conducive to the understanding of the prototype and lithofacies paleogeography of the depression. Through the study of the recovery of the prototype basin in the key period, the basin prototype of different construction and transformation periods is constructed. The paleogeographic characteristics of lithofacies in different periods are determined. Then, combined with the analysis of single well facies, lake water advance and retreat and sediment supply conditions, the lithofacies paleogeographic characteristics of different periods are determined. The sedimentary period of Tamulangou formation developed a lithofacies paleogeographic pattern of coexistence of volcanic rocks, fan delta and lakes. During the sedimentary period of Tongbomiao formation, the lake basin develops. But the water body is shallow. The material source is sufficient. The fan delta shallow lake sedimentary assemblage is developed. During the deposition period of Nantun formation, the lake basin further expanded rapidly. The water body became deeper. The lake basin became larger. The fan delta shrank. It is fan delta lacustrine sedimentary assemblage. The sedimentary period of Damoguaihe - Yimin formation is a fan delta lacustrine sedimentary assemblage dominated by lacustrine deposits.

ANN에 기반한 3상 PWM 컨버터의 다중 스위치 개방고장 진단 방법

For single and double open-switch faults in three-phase PWM (Pulse Width Modulation) converters, there are 21 types of fault modes depending on faulty switches, causing secondary faults in peripherals. In this paper, for diagnosing those fault modes, two-step technique based on ANNs using dc and THDs (Total Harmonics Distortions) of phase currents is proposed. Those dc and THDs are obtained through an ADALINE (Adaptive Linear Neuron) in real-time. In the first step, the ANN categorizes fault modes into six sectors in the three-phase plane. In the second step, the ANN localizes fault modes in each sector. Especially, the fault modes of both switches in the same legs are localized by comparing the number of the sampled zero current of the fault currents. The proposed method allows a real-time diagnosis with a simple and an high accuracy for the multiple open-switch faults and operates online. Simulations and experiments for a 3.7kW three-phase PWM converter confirmed the validity of the proposed diagnostic method.

High-Resolution 3D Seismic Imaging of Fault Interaction and Deformation Offshore San Onofre, California

The Inner California Borderland (ICB) records a middle Oligocene transition from subduction to microplate capture along the southern California and Baja coast. The closest nearshore fault system, the Newport-Inglewood/Rose Canyon (NIRC) fault complex is a dextral strike-slip system that extends primarily offshore approximately 120 km from San Diego to Newport Beach, California. Holocene slip rates along the NIRC are 1.5–2.0 mm/year in the south and 0.5 mm/year along its northern extent based on trenching and well data. High-resolution 3D seismic surveys of the NIRC fault system offshore of San Onofre were acquired to define fault interaction across a prominent strike-slip step-over. The step-over deformation results in transpression that structurally controls the width of the continental shelf in this region. Shallow coring on the shelf yields a range of sedimentation rates from 0.27–0.28 mm/year. Additionally, a series of smaller anticlines and synclines record subtle changes in fault trends along with small step-overs and secondary splay faults. Finally, sedimentary units onlapping and dammed by the anticline, place constraints on the onset of deformation of this section of the NIRC fault system. Thickness estimates and radiocarbon dating yield ages of 560,000 to 575,000 years before present for the onset of deformation.

The Shear Deformation Zone and the Smoothing of Faults With Displacement

AbstractWe use high‐resolution earthquake locations to characterize the three‐dimensional structure of active faults in California and how it evolves with fault structural maturity. We investigate the distribution of aftershocks of several recent large earthquakes that occurred on continental strike slip faults of various structural maturity (i.e. various cumulative fault displacement, length, initiation age and slip rate). Aftershocks define a tabular zone of shear deformation surrounding the mainshock rupture plane. Comparing this to geological observations, we conclude that this results from the re‐activation of secondary faults. We observe a rapid fall off of the number of aftershocks at a distance range of 0.06‐0.22 km from the main fault surface of mature faults, and 0.6‐1.0 km from the fault surface of immature faults. The total width of the active shear deformation zone surrounding the main fault plane reaches 1.0‐2.5 km and 6‐9 km for mature and immature faults, respectively. We find that the width of the shear deformation zone decreases as a power law with cumulative fault displacement. Comparing with a dynamic rough fault model, we infer that the narrowing of the shear deformation zone agrees quantitatively with earlier estimates of the smoothing of faults with displacement, both of which are aspects of fault wear. We find that earthquake stress drop decreases with fault displacement and hence with increased smoothness and/or slip rate. This may result from fault healing or the effect of roughness on friction.

Quantitative prediction of multiperiod fracture distributions in the Cambrian-Ordovician buried hill within the Futai Oilfield, Jiyang Depression, East China

In the Futai carbonate oilfield of the Jiyang Depression, Bohai Bay Basin, oil enrichment is significantly related to fracture development during the oil production process. In this research, by methods of core observation and image logging interpretation, the tectonic fractures’ characteristics were distinguished. Numerically, through the elastoplastic mechanics method of finite element (FE) simulation, the three-dimensional (3-D) paleotectonic stress field (two key fracture-generating periods) and the current stress field in the Futai buried hill were quantitatively simulated. The equations between fracture parameters and tectonic stresses were deduced to predict the fracture distribution and development in various periods. Simultaneously, through the mechanical superposition algorithm, the fracture parameters under the present conditions were simulated by modifying the current stress field from preexisting fractures. The results indicated that: (1) The Yanshanian maximum principal stress ranged from −85 MPa to −435 MPa in the NWN-SES (344°) (343°–164°) direction. (2) The Himalayan minimum principal stress ranged from 5 to 30 MPa in the NWN–SES direction. (3) The fracture formation during the Yanshanian and Himalayan orogeny was primarily influenced by the regional stress field in the Jiyang Depression or the secondary stress field derived from the Tanlu fault zone, followed by the lithology. The current fracture porosity was primarily controlled by fold, followed by the large faults oriented by N–S direction and then by the secondary faults oriented by E-W direction. With successful calculations, the developed 3-D FE geomechanical modeling and fracture parameter calculation method holds great promise for characterizing fractures in other carbonate reservoirs.

Probing the Fault Complexity of the 2017 Ms 7.0 Jiuzhaigou Earthquake Based on the InSAR Data

On 8 August 2017, a surface wave magnitude (Ms) 7.0 earthquake occurred at the buried faults extending to the north of the Huya fault. Based on the coseismic deformation field obtained from interferometric synthetic aperture radar (InSAR) data and a series of finite fault model tests, we propose a brand-new two-fault model composed of a main fault and a secondary fault as the optimal model for the Jiuzhaigou earthquake, in which the secondary fault is at a wide obtuse angle to the northern end of the main fault plane. Results show that the dislocation distribution is dominated by sinistral slip, with a significant shallow slip deficit. The main fault consists of two asperities bounded by an aftershock gap, which may represent a barrier. In addition, most aftershocks are located in stress shadows and appear a complementary pattern with the coseismic high-slip regions. We propose that the aftershocks are attributable to the background tectonic stress, which may be related to the velocity-strengthening zones.

Physics‐Based Evaluation of the Maximum Magnitude of Potential Earthquakes Induced by the Hutubi (China) Underground Gas Storage

AbstractThe world's largest underground gas storage facility in Hutubi (HUGS), China, is a unique case where cyclic gas injection‐extraction induced both seismicity and ground deformation. To assess the potential for future induced seismicity, we develop a framework physically based on a well‐constrained hydro‐geomechanical model and on fully‐coupled poroelastic simulations. We first interpret the spatiotemporal distribution and focal mechanisms of induced earthquakes and take it as a key step and a premise to estimate the magnitude and location of the largest potential earthquake. The sharp increase in seismicity was controlled by poroelastic loading on secondary southwest‐dipping thrust faults with spatial scales too small to be resolved by 3D seismic surveys. Both operational and local geological factors affect the seismic productivity at the HUGS site, distinguishing it from most cases of seismicity induced by wastewater disposal and hydraulic fracturing. We then conduct slip tendency analyses for major faults imaged by the seismic data, including the largest reservoir‐bounding Hutubi fault hydraulically connected to injection wells. The reactivation potentials of these imaged faults are estimated to be extremely low. Accordingly, future seismicity would most likely occur on failure‐prone secondary faults in regions with positive stress perturbation due to poroelastic loading. The maximum magnitude likely depends on the spatial scales of the secondary faults. As the occurrence of detected earthquakes is spatially and temporally consistent with the simulated evolution of Coulomb stress perturbation, the location of the largest potential earthquake probably depends on the sizes of the poroelastic stressing regions.