Distribution Of Faults Research Articles

A novel sparse Bayesian learning and its application to fault diagnosis for multistation assembly systems

This article addresses the problem of fault diagnosis in multistation assembly systems. Fault diagnosis is to identify process faults that cause excessive dimensional variation of the product using dimensional measurements. For such problems, the challenge is solving an underdetermined system caused by a common phenomenon in practice; namely, the number of measurements is less than that of the process errors. To address this challenge, this article attempts to solve the following two problems: (i) how to utilize the temporal correlation in the time series data of each process error and (ii) how to apply prior knowledge regarding which process errors are more likely to be process faults. A novel sparse Bayesian learning method is proposed to achieve the above objectives. The method consists of three hierarchical layers. The first layer has parameterized prior distribution that exploits the temporal correlation of each process error. Furthermore, the second and third layers achieve the prior distribution representing the prior knowledge of process faults. Since posterior distributions of process faults are intractable, this article derives approximate posterior distributions via Variational Bayes inference. Numerical and simulation case studies using an actual autobody assembly process are performed to demonstrate the effectiveness of the proposed method.

Implications of Geological Conditions on Gas Contents: A Case Study in the Pingdingshan Coalfield

Coalbed methane occurrence and its geological control factors are important for coal and gas co-mining. In recent years, more than 50% of the outburst accidents occurred near the faults and the thickening strips in Chinese mines. Therefore, studying the gas occurrence and its controlling factors is vital to prevent gas disasters in outburst mines with complex geology. In this paper, the distributions of faults, coal thickness, and gas content were characterized and analyzed based on fractal theory and geostatistics. Then, finer coal thickness inverted by the cross-layer boreholes for gas extraction was analyzed at a single working face. The geological control characteristics of gas contents were finally studied. The results show that coal thickness, burial depth, and fault complexity are the geological factors controlling gas contents from a regional to local scale. The sedimentary environment determines the regional coal thickness distribution and even stratification, which leads to higher gas content in the eastern thick-coal region than in the west. And the gas content varies linearly with burial depth in the same geological zonation. The fault fractal dimension is a quantitative representation of fault complexity. The dense distribution of minor faults is why the sizable fractal dimension in the local region is crucial in controlling the uneven enrichment of gas content. Therefore, more refined geological detection and characterization is the way to gas precision control in the future.

Dynamic rupture simulations based on interseismic locking models—taking the Suoerkuli section of the Altyn Tagh fault as an example

SUMMARY For simulating the dynamic rupture process in earthquake scenarios, the stress distribution along the fault remains unclear owing to a lack of direct measurements. Regional stress fields are often resolved onto the fault plane to determine the stress distribution along it. To overcome this limitation, we considered different interseismic locking models to better constrain the actual stress distribution. Specifically, we took the Suoerkuli section in the middle of the Altyn Tagh fault, China, and conducted dynamic rupture simulations to obtain possible earthquake scenarios. The surface rupture length and moment magnitude obtained from the simulations were consistent with those of historical earthquakes. Compared with the traditional stress field resolution method, our approach led to better constrained fault rupture extent and distribution characteristics of regional intensity, thereby avoiding overestimations of earthquake damage. We conclude that examining regional seismic hazards and risks based on seismic dynamic rupture simulations that account for the locking ratio of the fault plane is advantageous, and should be encouraged.

The 2021 Ms 6.0 Luxian (China) Earthquake: Blind Reverse‐Fault Rupture in Deep Sedimentary Formations Likely Induced by Pressure Perturbation From Hydraulic Fracturing

AbstractTo resolve the occurrence mechanism of the Luxian earthquake occurred near an active hydraulic fracturing well pad on 15 September 2021, we first use seismic waveforms to invert the focal mechanism solution and centroid depth, and then utilize Sentinel‐1 Synthetic Aperture Radar images and Global Navigation Satellite System observations to determine the seismogenic fault and slip distribution. Our results show that the Luxian event ruptured a previously‐unmapped southwest‐dipping reverse fault intersecting with one horizontal well of the well pad. Major slip occurred below the shale gas bed (∼4 km deep) but above the crystalline basement (∼7 km deep). Further analyses on preseismic surface deformation initiated in the northeast of the event reveal that pore pressure near the hypocenter was increased by ∼4.5 MPa. Consequently, fracking fluid injected through the horizontal well and other wells of nearby pads likely flowed directly into the fault zones and prompted the occurrence of the Luxian earthquake.

Upper Paleozoic total petroleum system and geological model of natural gas enrichment in Ordos Basin, NW China

Based on the analysis of Upper Paleozoic source rocks, source-reservoir-caprock assemblage, and gas accumulation characteristics in the Ordos Basin, the gas accumulation geological model of total petroleum system is determined. Then, taking the Carboniferous Benxi Formation and the Permian Taiyuan Formation and Shanxi Formation as examples, the main controlling factors of gas accumulation and enrichment are discussed, and the gas enrichment models of total petroleum system are established. The results show that the source rocks, faults and tight reservoirs and their mutual coupling relations control the distribution and enrichment of gas. Specifically, the distribution and hydrocarbon generation capacity of source rocks control the enrichment degree and distribution range of retained shale gas and tight gas in the source. The coupling between the hydrocarbon generation capacity of source rocks and the physical properties of tight reservoirs controls the distribution and sweet spot development of near-source tight gas in the basin center. The far-source tight gas in the basin margin is mainly controlled by the distribution of faults, and the distribution of inner-source, near-source and far-source gas is adjusted and reformed by faults. Generally, the Upper Paleozoic gas in the Ordos Basin is recognized in four enrichment models: inner-source coalbed gas and shale gas, inner-source tight sandstone gas, near-source tight gas, and far-source fault-transported gas. In the Ordos Basin, inner-source tight gas and near-source tight gas are the current focuses of exploration, and inner-source coalbed gas and shale gas and far-source gas will be important potential targets in the future.

Characteristics and Controlling Role in Hydrocarbon Accumulation of Strike-Slip Faults in the Maigaiti Slope

The Maigaiti Slope is a significant oil-gas-bearing field in the Tarim Basin. Based on 3D and 2D seismic data, systematic interpretation, stage sorting and genetic analysis of strike-slip faults in the Maigaiti Slope were carried out for the first time. The relationship between strike-slip faults and hydrocarbon accumulation was studied in combination with the fine dissection of hydrocarbon reservoirs. The study suggested that: (1) Staging and segmentation characteristics of strike-slip faults are evidently presented in the Maigaiti Slope. According to active periods, strike-slip faults can be divided into early Caledonian period, late Caledonian period, Hercynian period, and Himalayan period. According to plane distribution characteristics, strike-slip faults can be divided into the west Maigaiti Segment, mid-Maigaiti Segment, Madong Segment, and Bachu Segment. The main active periods and plane distribution of strike-slip faults in different sections are remarkably different. This analysis suggests that it is the response to multi-period and multi-directional tectonic movements, which are primarily dominated by the migration and evolution of the Hetian paleo-uplifts. (2) The coupling relationship between the active period of strike-slip faults and the trap forming period is the key to hydrocarbon accumulation in the Carboniferous–Ordovician, which determines the petroleum properties and enrichment horizon of the Cambrian post-salt system; medium-heavy oil is in the Caledonian period, light oil in the Indosinian period, and dry gas in the Himalayan period.

An Aftershock Deletion Method Based on Fault Buffer Zone

The existence of aftershocks in an earthquake sequence can impact the analysis of the mainshock. In this study, we present a method for deleting an aftershock sequence based on the spatial relationship between earthquakes and faults. This method improves the performance of space window selection in the classical K-K method by eliminating aftershocks with an ideal fault buffer zone. The determination of fault buffer zones is based on a trial-and-error analysis of 69,714 earthquake records from the China Seismic Network Center (CENC) collected between 1980 and 2020. We selected 20 typical big earthquakes (ML7.0–8.0 or ~Ms6.6–8.0; for earthquakes above magnitude Ms7 or ML7.2, ML is approximately equal to Ms) as the mainshocks to establish the fault buffer zones. We also propose an empirical formula to determine the distance of the fault buffer zone by counting the aftershock deletion effect at different buffer distances. Compared with the classical K-K method, our method considers the correlation between the spatial distribution of aftershocks and faults, eliminates earthquake groups that are not related to the mainshock, greatly reduces the spatial range of aftershocks, improves the performance of deleting aftershocks of different magnitudes, and provides a new rule and reference for aftershock deletion.

The Magnitude 4.5 Earthquake in the Karst Area of Guizhou on 21 August 2021: An Extremely Shallow Earthquake with a Closing-Crack Source

AbstractGuizhou province is located in a karst development area in China, and there are many moderate earthquakes, among which extremely shallow earthquakes are likely to cause damage to buildings, transportation lines, and other engineering facilities. Accurate focal depth and moment tensor can provide vital information for earthquake disaster assessment and karst collapse monitoring in karst areas. The network in the study area is relatively sparse, and the velocity structure is complex. For shallow earthquakes, the shallow velocity structure may cause certain errors in the inversion of the focal depth and mechanisms. In this study, based on the surface-wave information of regional stations, the shallow velocity structure is inverted. Based on the updated velocity model, we obtain the focal depth and mechanism of the Mw 4.5 earthquake on 21 August 2021 in Guizhou province. The results show that the optimal focal depth is about 2 km, and the moment of horizontal closing crack (M​crack) accounts for about 31% of the full moment tensor. The first motions of the P wave at the near-seismic stations of the earthquake are negative, similar to the typical collapses. However, compared to mining collapse earthquakes, the proportion of closing-crake components is relatively low. The dominant double-couple source of the earthquake is a thrust fault, which is consistent with the distribution of faults in the study area. It is speculated that a collapse in the karst area, resulting in negative P-wave polarities and about 31% closing-crake source, induced the shallow earthquake.

Slurry Leakage Channel Detection and Slurry Transport Process Simulation for Overburden Bed Separation Grouting Project: A Case Study from the Wuyang Coal Mine, Northern China

The 8006 working face at the Wuyang Coal Mine adopts grout injection into bed separation technology for surface subsidence control. Surface grout leakage occurred during the grout injection into the bed separation process of this working face. Grout leakage has adverse effects on the grouting filling effect, grouting cost and the environment. To determine the grout leakage channels and the slurry transport process, and to provide a theoretical basis for slurry leakage prevention and control, this paper first used 3D seismic exploration technology to identify the fault distribution characteristics of the study area, and then used COMSOL Multiphysics to carry out the numerical simulation of the grout transport process. The conclusions are as follows. Fifteen normal faults were identified in the vicinity of the 8006 working face. Among all the faults, the F1, F11, F18, F19 and F27 faults penetrate the surface and are the main channels for the grout to run to the surface. Based on the distribution characteristics of the faults and the spatial location relationship among the bed separation, faults and grout leakage points, the theoretical analysis of the leakage causes of each grout leakage point was carried out, and the main leakage channels of the grout injection into bed separation were proposed to be the bed separation and faults. The results of the numerical simulation of grout transport show that, as the permeability of the bed separation space and fault is much better than that of the surrounding rock, during the grout injection process the grout diffuses through the bed separation and fault in turn, and finally to the surface, where leakage occurs. The simulation results confirm that the main leakage channels for the grout are bed separation and faults.

Preliminary Estimation of Geological Structure Based on Relocated Hypocenter of Microearthquake: Case Study at “X” Geothermal Field

Generally, analysis of geological structure in the geothermal field is carried out using remote sensing methods, geological mapping, and gravity analysis. These methods can provide the distribution of geological structure on the surface but cannot provide information on whether the structure is active or not. This study aims to utilize improved hypocenter location which can be used to delineate the distribution of active faults. This is useful for obtain a better interpretation of geological structures in geothermal areas. Hypocenter locations are determined by picking the arrival time of the P-wave and S-wave. This method sometimes leads to uncertainty of hypocenter location due to subjectivity of picking arrival time. The double-difference method is applied with additional input pairing events from waveform cross-correlation (WCC) to overcome the uncertainty of hypocenter location. The result shows 3 microearthquake clusters formed in the western, central, and eastern parts of the “X” Geothermal Field. The cluster formed in the western area shows that there are two orientations of conjugated hypocenter distribution with the orientation of NW-SE and NE-SW. These hypocenters reveal the presence of geological structures which provide permeability pathways for fluids rising in the western part of the geothermal field. Multiplet-clustering analysis in the middle cluster which coincides with the reservoir zone shows two different sub-clusters indicating the possibility of two different sources mechanism working in the area. By integrating all the analysis and hypocenter distribution, these methods provide a better interpretation of structure’s distribution in the “X” Geothermal Field.

Оперативная оценка технического состояния стальных канатов по данным магнитной дефектоскопии

A combined approach to the prompt analysis of technical condition of steel wire ropes of various functions is proposed. It is based on the bearing capacity (strength) criterion and the magnetic testing results. The principals are stated related to the strength assessment of degraded rope with measured local wire breaks and loss of metallic area due to corrosion (abrasion). After processing the received diagnostic charts the strength analysis is performed by means of appropriate mechanical model in terms of weak element hypotheses used in structure mechanics. Stress analysis gives the conservative strength estimates which will be referred to reliability margin. The stress safety factor is evaluated regarding the steady and cyclic loading. Because the measured data are of random nature and do not account for the distribution of faults at cross-section the statistical modeling of wear location over wires is performed. The total strength decrease is determined by superposition of strength reduction due to metallic area loss, and due to the wire breaks. Thus, the stress safety factor is considered as a probabilistic indicator of the state of the rope strength. The rope in service should be discarded if its stress safety factor becomes less than the empirical allowable strength factor which defines the rope margin of survival capability as a partially worn-out structure. Adjusted for regulatory disposal rules, three categories of worn rope condition are considered: serviceable, with a limited service life, and inoperative. These categories are presented by the green-yellow-red ranges at so-called «rope status map» in specified coordinates «Number of wire breaks — Loss of metallic section». The rope bearing capacity is promptly assessed by placing two mentioned testing data in corresponding position at the status map. An example is given related to the assessment of the status map for the load-carrying cable rod of the well pumping unit. Based on the obtained results the recommendations are formulated for application of the rope status maps as the templates for service personnel concerning further operation.

On comprehensive application of seismic reflection and MASW method for investigation of urban subsurface active faults and underneath structures: A case study in Haikou city of Hainan province, China

Tectonically, northeast of Hainan Island belongs to the south part of Lei-Qiong sag, and experienced a great subsidence process during the Cenozoic. It is likewise the strongest earthquake activity area on Hainan Island. In 1605, an M7.5 earthquake occurred in the northeast of Hainan Island, which caused a large area of land subsidence into the sea, and initially formed the present pattern of Dongzhaigang Bay in northeast Hainan Island. Previous studies have shown that the seismogenic fault of this earthquake was the Maniao-Puqian fault. About this fault, there has been a lack of in-depth research on the fault activity, the controlled subsidence process, and the state of the underground structure in this area since the late Cenozoic. To investigate the latest active age and the specific location distribution of the Maniao-Puqian fault, and the influence of its normal fault on the subsidence of the Dongzhaigang area, detailed investigation work has been done on this fault area, through the near-surface seismic reflection and Multichannel Analysis of Surface Wave (MASW) method. The results of near-surface seismic exploration showed that the Maniao-Puqian Fault belt is composed of a group of north-dipping normal faults with a near east-west distribution, which was named Maniao-Luodou fault, Guilingyang-Qiaotoucun fault, and Xixiu-Puqian fault. This differs from previous research that the Maniao-Puqian Fault belt is an en echelon type fault. This work redefines the nature and distribution of active faults in Haikou City, which can provide important technical support for the site selection of critical infrastructure construction in the Jiangdong New district of Haikou City.

Offshore Fault-related Fold along the Eastern Marginal Zone of Ishikari Lowland, Hokkaido, Japan

Distributions, characteristics, and activities of offshore fault-related folds which comprise the southern part of the Eastern Boundary Fault Zone of Ishikari Lowland (EBFIL) are clarified by conducting a high-resolution multi-channel seismic reflection survey. To determine termination point of the fault zone, we placed seven survey lines perpendicular to the fault-related folds with a total line length of 107.5 km. We choose a compact water gun (15 cubic inch) as the seismic source to obtain high-resolution imagery of the Late Quaternary and investigate activity of the fault zone. Based on seismic facies, we distinguished packages of offshore sediment (unit 2, 3 and 4, in descending order), which separated by downlap surfaces and correlated to the Middle to the Late Pleistocene. They are progressively deformed by the active fault and compose series of fault-related folds (Fo1, Fo2 and Fo3). Traces of these folds are figured out from the seismic sections obtained by this study and existing surveys. Deformation related to these folds are clearly recognized in the topography of the unit 4 base. The reliefs of strata indicate that the Fo2 fold should have uplifted seafloor at a rate of 0.09-0.20 m/ky since 300 ka. The structures, spatial distributions and growth-rates of the folds suggest that Fo1 and Fo2 should compose series of anticline developing at the front of EBFIL. Besides, Fo2 fold would compose the southern termination of the fault zone. This study has successfully demonstrated that densely operated high-resolution seismic survey can figure out distribution and activity of offshore active faults in the Late Quaternary, even at the outside of shelf.

Geophysical Characterisation and Oil–Gas Resource Analysis of the Southern Huaying Mountain Fault Zone, Sichuan Basin, China

As the west rim of an ejective fold zone, the Huaying Mountain fault zone (HMFZ) in the eastern Sichuan Basin (SB) plays an important role in the tectonic evolution of the SB. The distribution and characteristics of HMFZ are strongly associated with tectonic activities and have greatly impacted the distribution of oil and gas reservoirs. However, its distribution and characteristics have remained poorly understood due to a lack of geophysical data, especially areal gravity survey and magnetotellurics (MT) survey, which are admittedly advantageous for detecting the edges of geological structures. Therefore, we carried out the ground geophysical surveys that areal gravity survey and MT survey, and acquired 1:250,000-scale real gravity data and MT data for the first time in this area. Optimized edge-detection methods were adopted to process the areal gravity data, allowing us to characterize the planar distribution of faults more reliably and convincingly. We found that the southern HMFZ is well developed and primarily trends in NNE and NE, whereas the subordinate faults trend in N-S and W-E. Vertical information for the faults extracted using the improved depth from the extreme points method revealed that the fault dominantly dipped to the SE, which was consistent with the results of MT inversion. Based on the spatial distribution of the faults, we further discussed the gravity anomaly, fault distribution, Luzhou palaeo uplift, and the distribution and characteristics of oil-gas resources, and found the convincing evidence to analysis the distribution of oil and gas resources in this region.

Optimization design of multi-layer metal box-type pre-insertion resistance for VSCUHVDC

In a ±800kV VSC-UHVDC transmission project, due to the uneven voltage distribution of multi-layer metal box-type preinsertion resistance, several breakdown and flashover faults occurred in type and debugging tests. The paper studies the overvoltage characteristic of two types of multi-layer metal box-type resistances. Firstly, for A-type pre-insertion resistance, the voltage distribution without stray capacitance is preliminarily analyzed based on PSCAD. The preliminary analysis shows that the recommended voltage non-uniformity coefficient for VSC-UHVDC pre-insertion resistance is 1.3, and the optimization method for A-type is proposed. Then, the difference of B-type is analyzed on the basis of the research on A-type. The electrostatic field solver is used to calculate B-type stray capacitance, and the PSCAD circuit model with stray capacitance is built. The uneven voltage distribution is obtained by simulation calculations and experiments. The results show that the terminal voltage of resistance unit is significantly higher than the average voltage, and withstand voltage reference values of the mica rod and the wall bushing are also calculated. Based on practical engineering problems, this paper combines theoretical calculations with simulations and experiments. The research results can provide some research directions and data references for the insulation optimization design of VSC-UHVDC pre-insertion resistance.

In situ stress distribution law of fault zone in tunnel site area based on the inversion method with optimized fitting conditions

Tunnel construction in high geo-stress strata faces the risk of extreme natural disasters such as large squeezing deformation and rockburst. Therefore, it is of great significance to adopt a high-precision inversion method to investigate the distribution law of in situ stress in the tunnel site area. In this paper, the in situ stress inversion research was carried out based on a plateau tunnel with a buried depth of more than 1000 m. The idea of improving the inversion accuracy by unifying displacement constraints was proposed by aiming at the defects of the traditional method on the boundary conditions. Furthermore, the impact of the constant term in the regression model on the fitting accuracy was discussed. According to the inversion method with optimized fitting conditions, the in situ stress distribution characteristics in the tunnel site area were obtained, and the variation law of the in situ stress near the fault zone was discussed. The results showed that after unifying displacement constraints, the comprehensive inversion accuracy comprehensive indicator reflecting the inversion accuracy decreased from 15.291 to 12.895, indicating that the inversion error was effectively controlled. Whether the constant term should be retained had a random effect on the inversion accuracy, so it was recommended that this issue be independently verified when fitting the data. When approaching the inner side of the fault from the outer side, the in situ stress first increased slightly and then decreased significantly. Moreover, the wider the fault impact zone and the farther the fault distribution distance, the more significant the amplitude of stress change, e.g., the maximum amplitude of stress change reached 9.0 MPa. In addition, the in situ stress orientation near the fault can be significantly deflected. And the wider the fault impact zone, the more pronounced the deflection.

3D modeling of detachment faults in the Jiaodong gold province, eastern China: A Bayesian inference perspective and its exploration implications

The world-class Jiaodong gold province, which is located in the Jiaodong Peninsula, eastern North China Craton, hosts > 5,000 t of gold resources. The major gold mineralization in this area is mainly controlled by NE-NNE faults, such as the Zhaoping, Jiaojia, and Sanshandao faults. While intensive efforts have been devoted to the investigation of the architecture of the three detachment faults, the fault geometry at depth remains highly uncertain and hotly controversial due to the scarcity of observations, non-uniqueness of the geophysical inversion, and underutilization of the geological knowledge. Along these lines, the deep three-dimensional (3D) geometry of detachment faults from a Bayesian inference perspective is reconstructed in this work. In the Bayesian framework, the multi-source information and the prior geological knowledge are combined into an integrated probabilistic model and the posterior probability distribution of detachment faults is inferred. The resulting posterior distribution permits an estimation of the uncertainty (information entropy) of the 3D fault geometry and the expected shape undulations compared with a prior reference model. More specifically, it demonstrates that specific and detailed 3D models of faults could be inferred by tracking surfaces with maximum information entropy of the geological units. The reconstructed models exhibit detailed 3D geometry of the fault surfaces and their reliability is validated by a recent drill hole at ∼−2,300 m depth. In terms of the reconstructed 3D models, the dip variations are analyzed and the possible stress directions at deep zones of the three faults are discussed. The shape features of the reconstructed faults are also quantified, which indicates that the fault sections with a steep-to-gentle transition in dip angle are closely associated with the gold mineralization. The 3D gold prospectivity mapping with the spatial features as predictor variables, highlights seven deep prospecting targets, which are generally consistent with the gently dipping zones and beneath the known orebodies.

Forecasting Earthquake Magnitude and Epicenter by Incorporating Spatiotemporal Priors Into Deep Neural Networks

Forecasting earthquake magnitude and epicenter is of great significance for disaster management and hazard mitigation. Existing machine learning-based earthquake forecasting has faced two shortcomings: limited historical earthquake samples for training and lack of explicit consideration of seismic prior knowledge. We propose a novel Spatio-Temporal Priors-Informed Deep Networks (STPiDN) that incorporates seismic spatio-temporal prior knowledge into deep neural networks using limited historical earthquake samples. In our method, a Physics-informed Recurrent Graph Network (PRGN) is developed to extract representations of observed earthquake precursor data in a physics-informed manner. In order to make prior-guided earthquake predictions, we develop seismic prior knowledge activation layers that combine earthquake event representations with prior knowledge (e.g. fault distribution) through activation gates. An adaptive multi-task loss function is proposed to achieve joint magnitude and epicenter forecasting with the consideration of alleviating the magnitude and epicenter imbalance problem. Our empirical evaluation results show that the proposed forecasting method outperforms several competing methods on a real-world earthquake dataset, proving that physics-informed prediction methods have the potential to capture complex earthquake patterns using limited training samples.

LATE QUATERNARY ACTIVITY OF THE HARAMACHI SEGMENT OF THE FUTABA FAULT IN NORTHEAST JAPAN THROUGH TOPOGRAPHIC ANAGLYPH IMAGES AND BOREHOLE CORE SEDIMENT ANALYSIS

The Haramachi Fault segment in the northeastern part of Honshu Island, Japan, has mainly sinistral fault movements with minor reverse component within the Futaba Fault Zone in the northeastern Japan arc. The 2011 Mw 9.0 earthquake occurred off the Pacific coast of Tohoku which caused large crustal deformations. Despite being the closest active fault to the epicenter, very limited investigation has been conducted on the Futaba Fault Zone. Previous studies used smaller scale topographic maps and fault activity was estimated only from trenching and borehole investigations in the central part of the Haramachi Fault segment. Thus, geometry, kinematic, and recent tectonic activity of the fault segment is not well identified, especially in northern part. In this study, we use a combination of high-resolution DEMs (2-m and 5-m mesh), several types of topographic anaglyph images (slope, negative and positive openness), and conducted field survey to confirm remote sensing interpretation. Subtle surface expression of deformation associated with active faulting, such as deformed terrace risers, deflected drainages, and small fault scarps can now be identified more clearly. Several new fault strands in the northern part of the segment were found supported by fault outcrops found in the field confirming the recent activity of the fault system. The new estimation of the total length of the Haramachi segment produced from the approach of this study yields 25 km, which is capable of producing Mw 6.5 – 7.0 or Mjma 7.2 earthquakes if ruptures were to occur altogether in the future. Moreover, a shallow borehole survey and radiocarbon dating from the soil organic material has revealed the minimal timing estimation of the most recent faulting in the Haramachi segment to be 3694 ± 24 BP. This research provides a revised understanding of active fault distribution and deformation associated with the Haramachi segment and validates the timing of the most recent faulting event more broadly.

Quantitative characterization of deep fault-karst carbonate reservoirs: A case study of the Yuejin block in the Tahe oilfield

The Ordovician reservoirs in the Tahe oilfield are dominated by fractured-vuggy carbonate reservoirs, of which fault-karst reservoirs are a hot topic in recent years. Fault-karst reservoirs feature high production, large burial depth, and strong heterogeneity under the control of faulting and karstification. Based on geological, logging, and seismic data, this study classified the Ordovician fault-karst reservoirs in the Yuejin block of the Tahe oilfield into three types, namely karst-cave, dissolved-vug, and fractured types, and established the integrated identification criteria of the three types of reservoirs. This study characterized karst caves, dissolved vugs, and multi-scale faults through seismic wave impedance inversion and frequency-domain detection of multi-scale faults. 3D geological models of different types of reservoirs were built using the combined deterministic and stochastic methods and characterized the spatial distribution of multi-scale faults, karst caves, dissolved vugs, and physical property parameters of reservoir. This study established the method for the geological modeling of fault-karst reservoirs, achieved the quantitative characterization and revealed the heterogeneity of fault-karst reservoirs. The karst-cave and dissolved-vug types are high in porosity and act as reservoirs, while the fractured type is high in permeability and act as flow pathway. This study lays the foundation for the development index prediction, well emplacement, and efficient development of the fault-karst carbonate reservoirs.