Basement faults evolve from multiscale distributed damage to localized shear, yet there remains a limited understanding of key controls on their internal structure leading to shear localization. We investigate the Off-Road Fault Zone (ORFZ), a similar to 260-m wide immature fault exposed in the texturally homogenous granitic basement of southern Oklahoma. We utilize multiscale remote sensing and field mapping to characterize the multiple fault-fracture systems in the fault zone, and 2-D electrical resistivity imaging to investigate its down-dip structure. It was found that ORFZ hosts steep NW-dipping, NE-striking fracture clusters with predominantly tensile fractography, en-echelon segmentation, horizontally striated slickensided surfaces, hematite- and epidote veins, and distributed gouge-lenses. Scan-line fracture mapping revealed systematic fracture intensity zonation: a. >10 m(-1) intensities, interpreted as the core-cluster (CC); b. 1 - 9.99 m(-1), and 0.1 - 0.99 m(-1) intensities, regarded as the inner cluster and outer cluster of the damage zone; and c. <0.1 m(-1) intensities represent the background, country rocks. The CCs occur across the fault zone but are most predominant and densely packed in the southeastern margin. Also, the gouge lenses and slickensided fracture surfaces are localized in the CCs, indicating increasing shear deformation concurrently with increasing fracture saturation. The resistivity tomography image shows the principal slip zone as a narrow similar to 70 degrees NW-dipping conductor located at the southeastern margin hosting the widest CC and thick gouge lenses. The mapped deformation field presents a hanging wall-directed damage asymmetry and margin-confinement of highest strain zone, exemplifying dip-controlled early evolution of strike-slip faults in the crystalline crust.

Oklahoma drew a significant amount of interest in the past years due to an increase in induced seismicity, which has been associated with the injection of wastewater into the sedimentary strata overlying the basement. Most of these seismogenic faults were unmapped and absent from the Oklahoma Geological Survey fault database until their reactivation revealed their existence. More interestingly, the seismicity reported was at basement depth, indicating that the faults reactivated were basement faults. Evidently, correctly knowing fault presence, orientation, and geometry, as well as the local stress field, is crucial for evaluating the reactivation potential of a fault and, therefore, the seismicity hazard associated. In this study, different geometric seismic attributes were analyzed and integrated using unsupervised machine-learning (ML) methods to identify potential basement-rooted faults and strike-slip-related structures in a seismic data set in northcentral Oklahoma. The ML results not only confirmed the existence of northeast-southwest faults that extended from the basement upward into the sedimentary section and that correlated with earthquake data but also the potential existence of other structurally controlled northeast-southwest features of antiform shape. Through a fault slip potential analysis, we also found that some of the basement-rooted faults interpreted have strikes that are favorable for reactivation if the conditions of pore pressure change were met.

Analyzing amplitude anomalies in seismic data requires a comprehensive understanding of the geologic context and the accuracy of the seismic image. Over the past four decades, numerous surveys in mature basins such as the U.S. Gulf of Mexico have undergone reprocessing and merging to enhance imaging quality. The merging of seismic data volumes demands careful attention during processing, as the different volumes are often acquired at different times with different hardware, acquisition geometries, and exploration objectives. If insufficient care is taken, significant differences in the amplitude and spectra of the merged survey components can pose challenges when used as input for machine-learning techniques or seismic attribute interpretation and studies. We implement spectral balancing followed by structure-oriented filtering (SOF) to address the previously mentioned discrepancies in a merged survey. Spectral balancing equalizes high and low frequencies, creating a more uniform frequency spectrum. SOF eliminates random and cross-cutting coherent noise while preserving structural and stratigraphic features. This workflow ameliorates the discrepancies between the areas covered by the individual surveys, resulting in a more consistent interpretation across the seam between the two surveys. This study finds that these two processes improved the vertical resolution and lateral delineation of fault and stratigraphic edges. However, we also observe in our data that increasing the spectrum runs the risk of increasing the effect of low- and high-frequency noise, including acquisition footprint. Surprisingly, we find that spectral balancing can diminish the appearance of stratigraphic edges that are fortuitously imaged by the original narrowband data volume. Finally, because spectral balancing and SOF are set to not damage relative amplitudes, we need to apply amplitude gain control to balance them on the shallower parts of the merged survey.

The formation of folds often leads to the emergence of subsidiary faults, thereby creating intricate fault-fold systems with fractures. While existing literature on fault-fold systems predominantly relies on field observations, there has been scant research focusing on their subsurface structures. Utilizing three-dimensional seismic data, this study endeavors to identify and quantify the principal fault-fold systems within the No. 3 coal seam of the Shanxi Formation and the No. 15 coal seam of the Taiyuan Formation, in the southern Qinshui Basin, China. The findings reveal: (1) The presence of five principal fault-fold systems, with four exhibiting a North-South orientation and one aligning East-West; (2) The establishment of an asymmetric model for the fault-fold system through a quantitative analysis of seismic attributes, particularly focusing on the high-angle normal faults along the folds' limbs; (3) The asymmetrical fault damage zone width (No. 3 fault-fold system) is quantitatively measured at approximately 200 meters on the west side, in contrast to the east side where widths range from 50 to 500 meters. These initial assessments show the great potential of an attribute-enhanced geological model, which may provide insights for analyses of the continuity of coal seams, the propagation of fractures, and the migration of gas within fractured reservoirs.#xD;

The competition between fault healing (i.e., re-strengthening) and fault loading determines the timing and magnitude of fault failure within the seismic cycle. Repeating earthquakes can give observational estimates of fault healing rates, however, it is difficult to link laboratory studies of frictional healing and observed healing rates from repeating earthquakes in part because of uncertainty in lithology at depth. Due to well-constrained and relatively simple geology, earthquakes in Oklahoma can be linked to the granitic basement rock and to the Arbuckle Group, which is primarily composed of dolomite at earthquake depths. Here, we conduct friction experiments to measure healing rates of the two earthquake-bearing lithologies at confining pressures representative of earthquake depths and pore pressures ranging from 0% to 80% of the confining pressure. We measure frictional healing by executing slide-hold-slide tests with hold times ranging from 3 s to 3000 s. The friction experiments on the Troy Granite indicate that pore fluid pressure does not greatly affect healing rate. On the other hand, the dolomite of the Arbuckle Group exhibits decreased healing with increased pore fluid pressure, with weakening at the highest pore pressure. We hypothesize that this is due to an increase in dissolution of dolomite at high pore pressures/low effective normal stress. These healing rates are used in the companion paper to understand the moment-recurrence time behavior of repeating earthquakes in Prague, Oklahoma. This work has implications for possible enhanced dissolution and weakening behavior of the Arbuckle Group during wastewater injection activities.

Analyzing amplitude anomalies in seismic data requires a comprehensive understanding of the geological context and the accuracy of the seismic image. Over the past four decades, numerous surveys in mature basins like the US Gulf of Mexico have undergone reprocessing and merging to enhance imaging quality. The merging of seismic data volumes demands careful attention during processing, as the different volumes are often acquired at different times with different hardware, acquisition geometries, and exploration objectives. If insufficient care is taken, significant differences in the amplitude and spectra of the merged survey components can pose challenges when used as input for machine learning techniques or seismic attribute interpretation and studies. We implemented spectral balancing followed by structure-oriented filtering to address the abovementioned discrepancies in a merged survey. Spectral balancing equalizes high and low frequencies, creating a more uniform frequency spectrum. Structure-oriented filtering eliminates random and cross-cutting coherent noise while preserving structural and stratigraphic features. This workflow ameliorates the discrepancies between the areas covered by the individual surveys, resulting in a more consistent interpretation across the seam between the two surveys. This study found that these two processes improved vertical resolution and lateral delineation of fault and stratigraphic edges. However, we also observed in our data that increasing the spectrum runs the risk of increasing the effect of both low and high-frequency noise, including acquisition footprint. Surprisingly, we found that spectral balancing can diminish the appearance of stratigraphic edges that were fortuitously imaged by the original narrowband data volume. Finally, because both spectral balancing and structure-oriented filtering are set to not damage relative amplitudes, we need to apply amplitude gain control to balance them on the shallower parts of the merged survey.

Determination of the in-situ stress orientations in the subsurface is key to understanding crustal behavior. For example, in Oklahoma and Kansas a surge in seismic activity occurred between 2010 and 2019 with the vast majority of hypocenters located in the crystalline basement. This prompted significant interest in characterizing the stress state in this region through indirect geophysical methods, such as shear-wave anisotropy, which is a technique used to identify the principal stress directions through identification of seismic anisotropy. The interpretation of apparent anisotropy from regional-scale seismic measurements can be somewhat limited due to assumptions regarding the physical mechanism for the observed S-wave velocity polarizations and the difficulty in separating the intrinsic anisotropy from other factors. In this work we have investigated the intrinsic velocity anisotropy of crystalline basement rocks from Oklahoma and Kansas using direct laboratory velocity measurement techniques. Two sets of tests were conducted to measure the horizontal and vertical velocities of each rock sample. Tests were conducted under hydrostatic conditions so that the intrinsic rock properties would be the dominant factor in the observed velocity anisotropy. Stereologic techniques were used to quantify the microstructural variation and relate it to both the laboratory and field observations. The results indicate that there is a non-trivial degree of velocity anisotropy in both the horizontal and vertical directions, varying for rocks from different locations. Microstructural observations of fractures show that horizontal fractures orientations dominate the samples, coinciding with the strike-slip regime of the region. However, velocity polarization and fracture orientations do not always align well. The results indicate a clear intrinsic anisotropy in the basement rocks of Oklahoma and Kansas and our work highlights the need for a suite of other measurements (i.e. borehole breakouts, stress inversion, or others) to aid in determining the stress orientations, aside from relying solely upon shear-wave polarization to determine subsurface relative stress orientations.

Knowledge of the midcontinent crustal structure of North America is crucial for understanding the evolutionary history of the ancient North American craton as Laurentia grew through accretion similar to 1.5 Ga to 1 Ga. Although Oklahoma has been recognized as a tectonically stable region since the Phanerozoic, its crustal structure records the earlier formation of the Mazatzal and southern Granite-Rhyolite provinces 1.6 Ga to 1.4 Ga. We present results from teleseismic receiver function analysis applied to 221 events recorded on 169 broadband stations in central Oklahoma. Our findings include a Moho depth map of central Oklahoma based on stacked and depth-converted teleseismic P receiver functions. The results are interpreted together with gravimetric and magnetic datasets and a recently established seismic velocity model of the crust. The Moho map shows a generally flat crust-mantle boundary in central Oklahoma with an average depth of 43.5 km while we observe a sudden thickening on the crust of the northwestern part of Oklahoma where the Moho deepens to over 50 km depth. We also find a Mid-lithosphere discontinuity at the upper-most mantle in north-central Oklahoma, presented as a negative phase deepening southeastward from 60 km to 80 km. We further observe an intracrustal discontinuity at the Nemaha uplift and Anadarko shelf regions in a depth range of 17-30 km. The hypothesis of the Mid-continent Rift (MCR) extending into Oklahoma is examined in terms of the crustal structure and Moho depth variation revealed by receiver functions. We do not find evidence of Moho structure or lower-crustal underplay characteristics similar to what has been discovered in the northern part of MCR, but the intracrustal discontinuity that deepens towards the hypothesized MCR region suggests upper-crustal volcanics potentially caused by the extended expansion regime of the failed rift near the south-most termination.

We integrate new high-resolution aeromagnetic data with seismic reflection data, well logs, satellite remote sensing, and field observations to provide a regional view of buried and exposed structures in the Southern Oklahoma Aulacogen and to assess their potential for future seismicity. Trends ranging from NW-SE to similar to E-W, peaking at 330 degrees +/- 4.5 degrees and 280 degrees +/- 3 degrees, dominate the magnetic lineaments of the Southern Oklahoma Aulacogen, reflecting basement contacts, dikes, and faults, including a previously unmapped similar to 100-km-long basement fault, which is herein referred to as the Willow fault. The fault disrupts, truncates, and vertically offsets basement-related seismic reflectors and overlying Paleozoic strata up through the Permian reflectors. Surface deformation along the trend includes fault-parallel monoclinal folds, pervasive fractures, and fracture-hosted mud dikes in Permian evaporite units. These structures indicate a Permian or post-Permian reactivation of the fault. Along-strike, the Willow fault connects to the NW-trending, seismically active Meers Fault to comprise the similar to 180-km-long Meers-Willow fault system, which potentially represents a major seismic hazard along the Southern Oklahoma Aulacogen. Fault slip potential analyses of the mapped potential fault traces show that seismic hazards are elevated where faults have steeper dips. Given some uncertainty in the regional stress state, we also show that hazards along the NW-SE to E-W trending faults vary considerably within the uncertainty range. We propose that the Meers-Willow fault system originated as a Cambrian aulacogen-scale, basement-rooted fault that was later reactivated as a left-lateral strike-slip fault (with similar to 40 km displacement) during the late Paleozoic Ancestral Rocky Mountain orogeny, highlighting that lateral offset accommodated a major component of deformation during the orogen.

SUMMARY Active or man-made seismic sources are often used to delineate subsurface geological structures via seismic imaging techniques. Although conventional controlled seismic sources have provided high-resolution subsurface images, the high cost of data acquisition necessitates improved use of cheaper alternative seismic sources for subsurface imaging, such as traffic noise, quarry blasts and earthquakes. Here, we explore the potential use of quarry blasts as an active seismic source for subsurface imaging. The goal of our study is to demonstrate the utility of quarry blasts as seismic sources for investigating subsurface structure with a field experiment in Mill Creek, southern Oklahoma. We deployed a 7455-m-long receiver line of 72 receivers (105 m spacing) extending away from a quarry, with a recording time of 28 d. We analyse similarities between blasts, wave types, origin time and excitation location of quarry blasts, which is important information for using such signal as an active source. Given a relative homogeneous geological condition in the study area, we could not observe clear reflected waves. However, the use of P- and S-wave velocities led to the delineation of a major basement damage zone in the study area, which further demonstrates the viability of quarry blasts as a useful seismic source for subsurface geological imaging.

We investigate the spatiotemporal patterns of strain accommodation during multiphase rift evolution in the Shire Rift Zone (SRZ), East Africa. The NW-trending SRZ records a transition from magma-rich rifting phases (Permian-Early Jurassic: Rift-Phase 1 (RP1), and Late Jurassic-Cretaceous: Rift-Phase 2 (RP2)) to a magma-poor phase in the Cenozoic (ongoing: Rift-Phase 3 (RP3)). Our observations show that although the rift border faults largely mimic the pre-rift basement metamorphic fabrics, the rift termination zones occur near crustal-scale rift-orthogonal basement shear zones (Sanangoe (SSZ) and the Lurio shear zones) during RP1-RP2 period. In RP3, the RP1-RP2 sub-basins were largely abandoned, and the rift axes migrated northeastward (rift-orthogonally) into the RP1-RP2 basin margin, and northwestward (strike-parallel) ahead of the RP2 rift-tip. The northwestern RP3 rift-axis side-steps across the SSZ with a rotation of border faults across the shear zone, and terminates farther northwest at another regional-scale shear zone. We suggest that over the multiple pulses of tectonic extension and strain migration in the SRZ, pre-rift basement fabrics acted as: 1) favorably-oriented zones of mechanical strength contrast that localized the large rift faults, and 2) mechanical 'barriers' that refracted and possibly, temporarily halted the lateral propagation of the rift zone. Further, the cooled RP1-RP2 mafic dikes localized later-phase deformation in the form of border fault hard-linking transverse faults that exploited strength con-trasts within the dike clusters and served as mechanically-strong zones that arrested some of the RP3 fault-tips. Overall, we argue that during pulsed rift propagation, inherited crustal strength anisotropies may serve as both strain-localizing, refracting, and 'strain barrier' tectonic structures.

Understanding fault characteristics and geometry is key to elucidating the deformation history of an area and any structural effects on subsurface fluid flow. In this paper, we use experimental models in determining fault geometry, shape, and other properties associated with the formation of transfer zones particularly for convergent fault systems. Clay experiments show the lithological impact on fracturing using brittle and ductile layers with variations in fracture density, orientation, distribution, and growth mechanism. Comparing those experimental results with natural examples from outcrops and seismic data shows similarity in terms of style and observations and highlights the impact that lithology and pre-existing conditions can play on structural deformation and the potential for hydrocarbon storage.

SUMMARYObservations of slow earthquakes and tremor have raised fundamental questions about the physics of quasi-dynamic rupture and the underlying fault zone processes. The presence of serpentinite at P-T conditions characteristic of deep tremor and slow earthquakes suggests that it plays an important role in controlling complex fault slip behaviour. Here, we report on experiments designed to investigate the frictional behaviour of serpentinite sampled from outcrop exposures (SO1 and SO2) of altered ultramafic rocks present at depth, and recovered from the SAFOD borehole (G27). XRD analyses reveal the presence of chrisotyle, lizardite, kaolinite, talc in SO1; lizardite, clinochlore and magnetite in SO2; and lizardite, quartz and calcite in G27. We sheared fault gouge in a double-direct shear configuration using a true triaxial deformation apparatus. The effective normal stress was varied from 2 to 40 MPa. We conducted velocity stepping tests and slide-hold-slide (SHS) tests in each experiment to characterize frictional stability and healing. At the end of each experiment, post-shear permeability was measured and the samples were recovered for microstructural analysis. The steady-state friction coefficient was μ = 0.17 for SO1, μ = 0.33 for SO2 and μ = 0.53 for G27. Overall, the gouges exhibit velocity strengthening behaviour, and become nearly velocity neutral at 40 MPa effective normal stress. SHS tests show positive healing rates for SO2 and G27, whereas SO1 exhibits zero or negative healing rates. Permeability decreases with increasing σn’, with SO1 (k = 10–20 m2) showing the lowest values. Microstructural observations reveal a well-developed R-Y-P fabric in SO1, which is not observed in SO2 and G27. We posit that the development of shear fabric controlled by mineralogy governs frictional and hydrological properties. In this context, when serpentinite is associated with other weak phyllosilicate minerals, frictional stability and hydrological properties can vary greatly, with a potential control on the mode of fault failure.

The formation of frictional melt likely impacts the coseismic and, when solidified (pseudotachylyte), the interseismic strength of faults. Here we investigate these effects through experiments using a new energy‐controlled rotary shear machine (ECoR) on simulated faults made of a transparent rock analog material (polymethyl‐methacrylate). As in nature, ECoR allows (a) elastic strain energy to accumulate at different loading rates and (b) the spontaneous nucleation of slip events. ECoR is equipped with a high‐speed camera, thermocouples, and transducers to monitor the surface, temperature, and acoustic emissions (AEs), respectively. We perform experiments at normal stresses of ∼3.5 MPa across loading rates from 0.15 MPa/s, phase A, to 2.5 MPa/s, phases B‐C‐D. In phase A, the temperature remains constant, and slip events occur without visible melting every 3.3–6.4 s with 0.5–0.7 MPa stress drops and 3–7 mm displacements. In phases B‐C, slip events occur in the presence of melts every 0.5–0.9 s, and the bulk temperature increases progressively. Melt solidification increases static friction yielding slip events with stress drops up to 5 MPa and displacements up to 3 cm. Samples produce high‐frequency AEs during slip acceleration and deceleration. Once the bulk temperature reaches ∼110°C, a “final” and silent long displacement event occurs in the presence of melts (phase D). Experimental observations suggest that melt formation modulates the coseismic (flash melting, melt lubrication, and viscous braking) and interseismic (welding) stages. Furthermore, AEs associated with coseismic fault weakening and strengthening may have their natural equivalent and could be observed in seismograms through near‐fault instrumentation.

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.

To better understand relationships among crustal anisotropy, fracture orientations, and the stress field in Oklahoma and southern Kansas, we conduct shear-wave splitting analysis on the last 9 yr of data (2010-2019) of local earthquake observations. Rather than a predominant fast direction (o), we find that most stations have a primary fast direction of polarization (opri) and a secondary fast direction of polarization (osec). At most stations, either the primary fast direction of polarization (opri) or the secondary fast direction of polarization (osec) is consistent with the closest estimated maximum horizontal stress (sigma H max) orientation in the vicinity of the observation. The general agreement between fast directions of polarization (o) and the maximum horizontal stress orientations (sigma H max) at the regional level implies that the fast polarization directions (o) are extremely sensitive to the regional stress field. However, in some regions, such as the Fairview area in western Oklahoma, we observe discrepancies between fast polarization directions (o) and maximum horizontal stress orientations (sigma H max), in which the fast directions are more consistent with local fault structures. Overall, the primary fast direction of polarization (opri) is mostly controlled and influenced by the stress field, and the secondary fast direction of polarization (osec) likely has some geologic structural control because the secondary direction is qualitatively parallel to some mapped north-striking fault zones. No significant changes in fast directions over time were detected with this technique over the 5 yr (2013-2018) of measurements, suggesting that pore pressure may not cause a significant enough or detectable change above the magnitude of the background stress field.

Earth and Space Science Open Archive This is a preprint and has not been peer reviewed. ESSOAr is a venue for early communication or feedback before peer review. Data may be preliminary.Learn more about preprints preprintOpen AccessYou are viewing the latest version by default [v1]New data on the stick-slip mechanics of seismogenic faults from rotary shear experimentsAuthorsEthanConradiDNicolaTisatoGiulioDi ToroBrettCarpenterClaudioFaccennaSee all authors Ethan ConradiDCorresponding Author• Submitting AuthorJackson School of Geosciences: The University of Texas at AustiniDhttps://orcid.org/0000-0002-4958-7274view email addressThe email was not providedcopy email addressNicola TisatoJackson School of Geosciences: The University of Texas at Austinview email addressThe email was not providedcopy email addressGiulio Di ToroUniversity of Padovaview email addressThe email was not providedcopy email addressBrett CarpenterUniversity of Oklahoma Norman Campusview email addressThe email was not providedcopy email addressClaudio FaccennaUniversity Roma TREview email addressThe email was not providedcopy email address

Caprocks are nearly impermeable rocks that inhibit the migration of hydrocarbons. Caprock efficiency at sealing hydrocarbon reservoirs is contingent upon maintaining its integrity, or the absence of features that enhance fluid flow such as fractures/faults. Caprock lithology is an important factor in sealing efficiency, as it controls caprock mechanical behavior and brittleness. Evaluating caprock failure due to chemo-thermo- mechanical forces requires an understanding of the deformation and failure properties consistent with effective caprocks. Core samples of caprocks from the northeast Sichuan Basin – primarily evaporites, limestones and dolostones – were tested under laboratory conditions to determine the relationships between lithology and geomechanical properties of different caprocks. The results of hardness, ultrasonic velocity, and axial deformation tests of the caprock samples indicate that caprock brittleness is strongly correlated with high values of hardness, peak and yield strength, Young’s modulus and coefficient of internal friction. Lithologic heterogeneity in caprocks is found to enhance sample failure in most cases, though the inclusion of minor phyllosilicate and evaporite minerals may conversely decrease caprock brittleness. Evaporites and dolostones consistently exhibit the least and most brittle characteristics, respectively, though individual mechanical properties can indicate contradictory caprock behavior. These results suggest evaluation of the geomechanical-risk to caprocks can thus be enhanced by combining mechanical properties to map trends in caprock effectiveness. When combined with accurate in- situ conditions, the mechanical properties of a caprock allow for a quantitative interpretation of caprock integrity.

The structure of subsurface fault networks, which has a significant effect on hydrocarbon migration, is inherently difficult to recognize and map. 3D seismic surveys provide an opportunity to map the fault system within a carbonate reservoir of Xinchang in the western Sichuan Basin, China. We calculated attributes from the seismic reflection data that covers an area of 1330 km(2), including variance, edge detection, dip-magnitude and dip azimuth. We focused on the Triassic Leikoupo Formation of dolostone, at similar to 6 km depth, adjacent to the Longmen Shan thrusting range. The mapped attributes display (1) a primary network of faults in an orthogonal pattern in the anticline, striking East-West and North-South, and (2) a secondary, conjugate fault set in the fold limb, striking Northeast and Northwest with a length range of 1-10 km. The latter set of conjugate faults are confined to a 300 m-thick layer of dolostone, diminishing into underlaying unit of anhydrite. We envision that the conjugate fault networks and associated fractures enhance gas charging and reflect a model of self-sourced migration and accumulation in the Leikoupo Formation. These results are significant for sweet-spot evaluation of carbonate reservoirs in the Sichuan Basin, and provide insights for understanding the migration of subsurface fluids.