Structural Analysis and Fractures Kinematics Using Seismic 2D and Geological Maps

Fault kinematics of the Magallanes-Fagnano fault system, southern Chile; an example of diffuse strain and sinistral transtension along a continental transform margin

<p>The European Variscan belt sharply changes its trend in easternmost Germany and western Poland, where the ENE- to NE-striking structures are replaced by the ESE- to SE-trending ones. The structures of still another, NNE-SSW strike, take the lead, however, along the SE margin of the Bohemian Massif. The Variscan belt seems, thus, to make nearly a U-turn, encircling the Bohemian Massif from the north. This has been explained for almost a century by assuming a 180° oroclinal loop, in which the Rhenohercynian and Saxothuringian tectonostratigraphic zones inarm the core of the Bohemian Massif. According to this classical view, the outermost tectonostratigraphic zone of the Variscan belt, the Rhenohercynian Zone, continues eastward in the deep substratum of the Permian-Mesozoic basin and reappears at the surface along the eastern rim of the Bohemian Massif.</p><p>Since the late 1970s an alternative view has gained an increasing attention that postulates a dextral transpressional regime during the final accretion of the Variscan terranes. This transpressional tectonic context is believed to have resulted from sublatitudinal, right-lateral displacements between Gondwana and Laurussia. Near the Carboniferous-Permian boundary, Gondwana decoupled from the newly formed European Variscan belt and proceeded westward, toward the southern edge of the Laurentian segment of Laurussia, owing to the development of the Appalachian subduction system. Concomitantly with the peak of the Alleghanian orogeny during early Permian, the European Variscan belt experienced a crosscut of its major tectonic zones along a set of dextral strike-slip faults.</p><p>In this study, we investigate directions and continuity of structural trends in the external zones of the Variscan orogen in Poland and map a foreland extent of Variscan deformations using seismic, gravimetric-magnetic and borehole data. These permit us testing the orocline- vs strike-slip concepts and develop an overall kinematic model for the NE Variscides.</p><p>Matched filtering of isostatic gravity, guided by results of spectral analysis, along with other derivatives of gravity and magnetic fields reveal a dominant WNW-ESE-trending pre-Permian structural grain in the external zones of the Variscan belt in Poland. This trend is confirmed by regional distribution of dips in Carboniferous and Devonian strata that were penetrated by boreholes beneath Permian-Mesozoic sediments. Seismic constraints on the position of the Variscan deformation front come from (1) the GRUNDY 2003 seismic experiment, combining wide-angle reflection-refraction measurements with the near-vertical reflection seismics in central Poland and (2) PolandSPAN and POLCRUST-01 deep reflection profiles in SE Poland. The WNW-ESE structural trend in the Variscan foreland is parallel to a set of major strike-slip fault zones in the area that are considered to convey a significant dextral displacement between Laurussia and Gondwana. The revised position of the Variscan deformation front shows a similar, uninterrupted, generally WNW-ESE trend, up to the SE border of Poland, which indicates an initial continuation of the more internal Variscan zones into the area of the present-day Carpathians. The geometry of the Variscan deformation front along with the pattern of the Variscan structural grain are inconsistent with the idea of an oroclinal loop affecting the external, non-metamorphic Variscan belt.</p>

Relevance of the work. The paper considers challenging problems related with outlining of intervals with oil and gas presence in the mature Khylly field by use of latest 3D seismic survey techniques in order to gain larger crude resources base. The purpose of this research is to discover the most promising intervals of target horizons with relatively high reservoir properties outlined by 3D seismic data. The subjects of research are 3D seismic survey data, downhole seismic survey – Vertical Seismic Profiling (VSP) and well logging diagrams. The object of research is the Khylly deposit. The paper describes in brief geological and geophysical characteristics, stratigraphic and lithological features of rocks making the section. It is noted that despite repeated surveys by use of various geological and geophysical techniques, the field setting is not thoroughly studied and it has been covered by 3D seismic survey in 2012. Research results. 3D seismic survey applied across Khylly area is resulted in drawing of 4 structural maps for III and I horizons of Productive Series (PS), Akchagyl and Lower Absheron suites. Taking into account the relevance of structural planes of various stratigraphic levels and III horizon of PS being one of the major reference horizons the paper gives description of structural map drawn for this horizon. The detailed velocity model is designed based on VSP data with wide use of velocity analysis data. It has been made clear that Khylly area has block structure and each block has been described in detail. Based on acquired data it has been recommended to drill exploratory well R-1. Conclusion. Processing and interpretation of seismic data are aimed at solving some geological problems; the main task was to obtain results that ensure the study of the geological structure in the seismic survey area, including tracing of seismic horizons, faults and outlining the areas and section intervals which may be of interest due to possible oil and gas presence. VSP data acquired in well 2012 and velocity analysis made it possible to design velocity model of the section under the study, with the use of which the temporary 3D cube was transformed into a depth cube. The quality of seismic data is good and made it possible to solve the tasks set for this research.

This study actively investigates stress ratios, principal stress orientations, and stress regimes in the West Java Province, Indonesia, by simultaneously inverting both the stress tensor and fault orientations from 232 moment tensors. It identifies diverse stress regimes, including normal and reverse faulting in the subduction zone, as well as mixed reverse and strike-slip faults across the island. Stress ratios range from 0.08 to 0.97. Sedimentary basins in the northeast produce lower values, while tectonic forces near the southern subduction zones generate higher values. In the subduction zone, plate bending generates normal faulting, while compressional forces lead to reverse faulting. The fore-arc region exhibits a variety of regimes: normal, reverse, and strike-slip, indicating transitions in the dynamics of subduction. Across the island, a combination of reverse and strike-slip faulting suggests crustal compression, with Mount Anak Krakatau exhibiting evidence of normal faulting. The study uncovers a complex interplay of subduction processes, crustal deformation, and geological heterogeneities. It outlines stress regimes ranging from normal and reverse faulting in the subduction zone to mixed reverse and strike-slip faulting on the island. These findings offer crucial insights into the tectonic processes shaping West Java, and lay the groundwork for more informed seismic hazard assessments and risk mitigation strategies.

The Eastern Depression in the Bayanhaote Basin in western Inner Mongolia has experienced multi-stage Meso-Cenozoic tectonic events and possesses considerable exploration potential. However, structural deformation patterns, sequences and the genesis of oil-bearing structures in the basin are still poorly understood. In this study, based on high-quality 2D seismic data and drilling and well-logging data, we elucidate the activities and structural styles of faults, the tectonic evolution and the distribution characteristics of styles, as well as assessing potential petroleum traps in the Eastern Depression. Five types of faults that were active at different stages of the Meso-Cenozoic faults have been recognized: long-lived normal faults active since the late Middle Jurassic; reverse faults and strike-slip faults active in the late Late Jurassic; normal faults active in the Early Cretaceous; normal faults active in the Oligocene; and negative inverted faults active in the Early Cretaceous and Oligocene. These faults constituted 12 geometric styles in NE-trending belts at various stratigraphic levels, and were formed by compression, strike-slip, extension and inversion. The temporal development of structural styles promoted the formation and reconstruction and finalization of structural traps, while regional unconformities and open reverse and strike-slip faults provided migration pathways for petroleum to fill the traps. In general, potential traps that formed by compressional movement and strike-slip movement in the late Late Jurassic are primarily faulted anticlines. Those traps developed in Carboniferous rocks and are located in the southwestern region of the Eastern Depression, being controlled by NNE-NE-striking reverse and transpressive faults.

On June 18, 2018, an MJMA6.1 inland crustal earthquake occurred on the northeast edge of the Osaka basin, Japan. This event impacted the region by the maximum PGA larger than 0.9 g, and it was followed by a series of weaker aftershocks. The earthquakes were located near the Arima-Takatsuki Tectonic Line (ENE–WSW dextral strike-slip faults) and the Uemachi fault system (N–S reverse faults), hence the seismotectonic interpretations we assumed to be rather complex. Here we propose a seismotectonic model of this sequence based on seismological data and stress field considerations. In particular, we infer to a centroid moment tensor for the mainshock using Bayesian full-waveform inversion from strong motion records. The solution of Mw5.6 involved a significant CLVD component, which we interpreted as being due to rupture process on a complex fault geometry. Decomposition of the non-DC moment tensor into major and minor pure-shear moment tensors suggests a combination of strike-slip and reverse faulting mechanisms. We also analyzed the 108 strongest aftershocks with MJMA between 2.0 and 4.1 using records from broadband and short-period stations. Aftershocks’ moment tensors inverted from P-wave amplitudes exhibit mainly strike-slip and reverse faulting mechanisms, having significant spatial variations. The local stress field inverted from these mechanisms had a dominant maximum (compressional) principal stress σ1 in ESE–WNW direction, while σ2 ≅ σ3. Both ENE–WSW dextral strike-slip and N–S reverse faults can be active in such stress field as observed in the mainshock (without any need for stress spatial inhomogeneity). To conclude, the activated strike-slip fault is parallel to the Arima-Takatsuki Tectonic Line. The activated N–S reverse fault is dipping to east by 50° similarly as the Uemachi fault system. Joint shear movements on both of these faults contributed significantly to the total seismic moment of the mainshock.

Strike-slip faults are closely related to the enrichment of hydrocarbon resources, with a series of large oil and gas fields associated with strike-slip faults discovered in regions such as the Ordos Basin in China and the West Siberian Basin. The Ediacaran hydrocarbon resources in the Sichuan Basin are abundant. Identifying strike-slip faults and understanding their control over hydrocarbon systems is crucial for expanding exploration efforts. Based on lithology, seismic interpretation, and absolute age data, the strike-slip faults in the Ediacaran system and the overlying strata have been identified and classified. The patterns and evolutionary processes of strike-slip faults have been revealed. The results indicate that the planar patterns of strike-slip faults can be classified into linear, en echelon, and oblique structures. Strike-slip faults are typically seen as vertical (or steep) linear faults or flower-shaped structures in seismic profiles. Vertical (or steep) linear faults can further be categorized into transtensional high-steep structures and transpressional high-steep structures. The evolution of strike-slip faulting in the Central Sichuan Basin can be divided into four distinct stages: (1) a rifting stage during the Cryogenian, (2) a dextral transtensional strike-slip stage from the late Ediacaran to early Cambrian, (3) a dextral, weak transpressional strike-slip stage from the early Ordovician to early Permian, and (4) a sinistral transtensional strike-slip stage during the late Permian to early Triassic. The aulacogen, formed during the Cryogenian, controlled the distribution of the mound-shoal complex of the Dengying Formation and the thickness zones of the Cambrian hydrocarbon source rocks. The strike-slip faults in the first stage facilitated direct lateral and vertical contact between the overlying hydrocarbon source rocks and reservoirs, significantly enhancing the migration and accumulation efficiency of hydrocarbons. The strike-slip faults in the second stage controlled the distribution of ancient sedimentary paleogeomorphology and favorable karst locations. The strike-slip faults in the third stage governed the distribution of gas and water.

Miocene-to-recent structure and basinal architecture along the Central Range strike-slip fault zone, eastern offshore Trinidad

The Lomfjorden Fault Zone in the eastern part of Spitsbergen is one of the prominent structures in Svalbard oriented parallel to the continental margin of the Barents Shelf. It consists of a network of three N–S-striking major faults (Veteranen, Lomfjorden, and Agardhbukta faults), two N–S-striking reverse faults (Lomfjella and Bjørnfjellet reverse faults), and a number of NE–SW- and NNW–SSE-striking normal, reverse, and strike-slip faults. Structural data collected during fieldwork in the northern and central segments of the fault zone, in combination with published data from the southernmost segment, indicate that N–S-striking reverse faults in the Lomfjorden Fault Zone were caused by convergence transferred from the West Spitsbergen Fold-and-Thrust Belt eastward along detachments during an initial phase of the Eurekan deformation in the early Eocene. The W–E contraction was followed by sinistral and dextral strike-slip tectonics along the Lomfjorden Fault Zone during a later phase of the Eurekan deformation in the late Eocene. The NNW–SSE-striking reverse and normal faults are oriented obliquely between the N–S-striking, en-échelon Lomfjorden and Agardhbukta faults. Shortening and extension across these, respectively, can be explained by left-stepping contractional overstep or left-stepping wrench faults in an overall dextral and left-stepping extensional overstep or left-stepping wrench faults in an overall sinistral, N–S-trending strike-slip system. It was not possible to determine if the sinistral phase pre-dated the dextral one or vice versa. The presence of a large granite massif, the Newtontoppen Granite, is suspected to influence or even control the course of the faults and their transfer systems. The involvement and reactivation of preexisting Carboniferous and even older structures and the superimposition of convergent and lateral movements along the Lomfjorden Fault Zone is similar to large fault zones in North Greenland and on Ellesmere Island, indicating that it represents an important element of the Eurekan Orogeny during the final break-up of Laurasia.

The geothermal potential in the deep subsurface of North Rhine-Westphalia (NRW) has been scarcely explored. Due to the increasing demand for zero-carbon heating applications, there has been a renewed phase of seismic exploration in the region to investigate potential geothermal aquifers. The prime exploration target is the Lower Carboniferous Ruhr Basin and the Devonian substratum of the Variscan foreland, as they host deep carbonate aquifers. Interpretation of the recently-acquired 70-km-long 2D seismic profiles, together with the 2D legacy seismic data in the northern part of the Ruhr basin, the Münsterland region, reveals two carbonate units; the Dinantian platform facies and the Givetian massive facies. These are located at depths that range from c. 4500 m to 6000 m. Considering their great burial depth, the permeability of the carbonate rocks is considered to be primarily facilitated by fault zones with dense fracture swarms. Therefore, understanding the complex deformation history of this fossil foreland basin is crucial to evaluate its geothermal potential. We here reveal the timing and geometric evolution of the fault zones. Using a multiattribute seismic analysis, we delineate three major types of faults; (1) SW–NE-⁠trending, syn-fold thrusts, (2) WNW–ESE-striking normal faults, and (3) E–W and N–S strike-slip faults. Interestingly, we do not observe in the available data flexure-induced faults that are typical for foreland basins and would be expected to strike parallel to the SW–NE-oriented Variscan Orogen. To constrain the relative timing of fault activity, we mapped seven well-constrained and age-calibrated stratigraphic horizons within the Carboniferous molasse sequence and the Cretaceous cover. The preliminary results confirm the observations of previous researchers that the thrust faults formed after the deposition of the Late Carboniferous strata, as evidenced by their concordant folding. Thrusts are crosscut by the normal faults, suggesting that the latter formed at a subsequent stage. Most of the strike-slip faults cut through the Carboniferous–Cretaceous unconformity, with some culminating in the Cretaceous cover as positive flower structures. Notably, one flower structure is co-linear with a thrust fault in the Carboniferous, suggesting that there is some degree of kinematic linkage between the two structural levels. Possibly, some of the optimally-oriented thrusts were reactivated and grew upward as strike-slip faults during Late Cretaceous transpression. Such multiphase evolution of fault zones may enhance permeability structure, since each reactivation event potentially contributes to the widening of the deformation zones, thereby increasing the density of interconnected fractures. In this study, we demonstrate how the integration of new seismic data provides valuable insights into the structural evolution of the Ruhr Basin and its geothermal potential. A 3D seismic acquisition campaign is planned in the investigated region. Using its results, we intend to conduct a high-resolution fault throw analysis to further constrain the kinematic development of the deformation structures.

The largest Precambrian gasfield in China has been found from the Ediacaran (Sinian) carbonates in the central Sichuan Basin. The deep ancient reservoirs were generally attributed to the high-energy mound-shoal body in the carbonate platform. However, there is still little understanding on the distribution of the mound-shoal bodies that hampers further gas exploitation from the deep subsurface. Based on the seismic data, a large strike-slip fault system was identified by new 3D seismic data in the central Sichuan Basin. Further, it was found that the strike-slip fault had some effects on the mound-shoal bodies of the Ediacaran Dengying Formation. First, the platform margin was divided by strike-slip faults into three distinct segments to show two weak-rimmed margins and one interbedded rimmed margin. Second, the platform margin could be offset or migrated with the strike-slip faults. Third, there is varied margin thickness across the strike-slip fault zone. In the inner platform, more carbonate mound-shoal bodies developed behind the weak-rimmed margin that was divided by the strike-slip fault zones. In addition, the mound-shoal bodies may be separated by faulted sag. Further, the mound-shoal bodies may have developed along the faulted higher position in one side of the strike-slip fault zone. These patterns of the mound-shoal bodies suggest that the strike-slip fault had an important role in the sedimentary microfacies’ diversity in the intracratonic carbonates. The low displacement of the strike-slip fault is chiefly responsible for a weaker controlling effect on the microfacies change in the intracratonic basin rather than other tectonic settings.

The Zahedan fault zone in Iran constitutes an active tectonic zone characterised by a complex network of strike-slip faults that dominate the local deformation pattern. This area is located within a large-scale transpressional shear zone accommodating relative motion between the Central East Iranian block and the Afghan Helmand block. The region provides a natural laboratory for investigating the relationship between strike-slip faulting and tectonic blocks rotated around vertical axes.We present herein, based on high-resolution 2025 Airbus satellite imagery and cartographic and geophysical data, a new strike-slip fault pattern that facilitated the development of the rotated tectonic blocks.Our observations show that the major strike-slip fault zones are accompanied by dense networks of second-order faults, including single sets of antithetic and synthetic strike-slip faults, conjugate strike-slip fault sets, restraining and releasing stepovers, and thrust faults. In several sectors along the major faults occur the zones of deformation consisting of the rotated tectonic blocks. The scale, orientation, and spatial organisation of the mapped structures indicate that block rotation is controlled by the interaction between major strike-slip faults and subsidiary fault networks.The individual second-order antithetic faults display that these faults commonly accommodate small displacements, but the faults play a critical role in allowing internal deformation within blocks and facilitate the progressive block rotation. The sense of movements along the major fault and the antithetic strike-slip faults bounding the tectonic blocks allows us to consider the structures as the blocks rotated around vertical axes in a domino-like orientation. Recognised examples of structures show that some rotating blocks are rigid, with no evidence of significant internal deformation, while other rotating blocks exhibit strong internal deformation.Understanding these spectra of behaviours and the determination of the relationships between them will improve our knowledge of fault interaction processes in eastern Iran and related patterns of seismicity, and it also has implications for seismic hazard assessment in active transpressional settings.

Structural characterization and hydrocarbon prediction for the SB5M strike-slip fault zone in the Shuntuo Low Uplift, Tarim Basin

Regional and local strike-slip systems in Chile are complex and pose interesting questions, such as the interaction between strike-slip and reverse faults, how they evolve, and the relationship between shortening, rotation and uplift. Within this context, we developed a new analytical method based on analogue and numerical modelling applied to 3D, pure and transtensional-transpressional strike-slip systems. Analogue modelling results indicate that in restraining stepovers of strike-slip fault systems, where antiformal pop-up structures are usually formed, pre-existent basement structures with a high angle to the main strike-slip fault will generate a higher rotation of blocks. However, when these structures are oriented at a high angle with respect to the main stress convergence vector, the rotation will be less and therefore a higher tendency to uplift will be produced. These results were applied to NW- and SE-striking basement faults oblique to N-S mega-thrust faults in central Chile (32o-35oS), for which we propose a simultaneous development based on the analogue model results. Moreover, we propose that strike-slip movement occurred on thrust faults in central Chile. Furthermore, we performed a numerical restoration of an analogue experiment which modeled a pure strike-slip system, and concluded that the restoration is very sensitive to shortening data as well as to rotational data. These results are extremely important for future numerical and regional analysis of strike-slip systems.

Late Tertiary tectonics of the Red River Fault Zone: Structural evolution of sedimentary rocks