Strike-slip Faults Research Articles

Dynamic simulation of differential accumulation history of deep marine oil and gas in superimposed basin: A case study of Lower Paleozoic petroleum system of Tahe Oilfield, Tarim Basin, NW China

According to the complex differential accumulation history of deep marine oil and gas in superposition basins, the Lower Paleozoic petroleum system in Tahe Oilfield of Tarim Basin is selected as a typical case, and the process of hydrocarbon generation and expulsion, migration and accumulation, adjustment and transformation of deep oil and gas is restored by means of reservoine-forming dynamics simulation. The thermal evolution history of the Lower Cambrian source rocks in Tahe Oilfield reflects the obvious differences in hydrocarbon generation and expulsion process and intensity in different tectonic zones, which is the main reason controlling the differences in deep oil and gas phases. The complex transport system composed of strike-slip fault and unconformity, etc. controlled early migration and accumulation and late adjustment of deep oil and gas, while the Middle Cambrian gypsum-salt rock in inner carbonate platform prevented vertical migration and accumulation of deep oil and gas, resulting in an obvious “fault-controlled” feature of deep oil and gas, in which the low potential area superimposed by the NE-strike-slip fault zone and deep oil and gas migration was conducive to accumulation, and it is mainly beaded along the strike-slip fault zone in the northeast direction. The dynamic simulation of reservoir formation reveals that the spatio-temporal configuration of “source-fault-fracture-gypsum-preservation” controls the differential accumulation of deep oil and gas in Tahe Oilfield. The Ordovician has experienced the accumulation history of multiple periods of charging, vertical migration and accumulation, and lateral adjustment and transformation, and deep oil and gas have always been in the dynamic equilibrium of migration, accumulation and escape. The statistics of residual oil and gas show that the deep stratum of Tahe Oilfield still has exploration and development potential in the Ordovician Yingshan Formation and Penglaiba Formation, and the Middle and Upper Cambrian ultra-deep stratum has a certain oil and gas resource prospect. This study provides a reference for the dynamic quantitative evaluation of deep oil and gas in the Tarim Basin, and also provides a reference for the study of reservoir formation and evolution in carbonate reservoir of paleo-craton basin.

Subsurface basement structures of Usangu basin, East African rift system, with implications for basin structural configuration and hydrocarbon potential

The Usangu basin is a rift basin developed along the Eastern arm of the East African rift system trending in the NE-SW direction. Although the general structures of the basin have been well studied, the structural configuration of the basin and the spatial and depth variations of sediment thickness are still not well known. This study investigates the structures in relation to basement configuration and the variation of sediment thickness within the basin using the Shuttle Radar Topography Mission (SRTM) Digital Elevation Model (DEM), aeromagnetic and gravity data. Results from DEM data indicate a few lineaments on the basin flanks representing the Usangu and Chimala border faults with no structures in the central part of the basin. The aeromagnetic and gravity data highlight three sets of normal and strike-slip faults, most of which trend NE-SW and others NNE-SSW, while a few trend WNW-ESE or NW-SE. Structures on the southwest of the basin reveal complex patterns attributed to the concentration of important tectonic and seismic activities in the study area. The Euler deconvolution and gravity models used to calculate the depth to the basement show that the basement is shallow in the north and south to southwest, and the basin deepens in the northeastern, northwestern and western parts. The findings also reveal that the basin has two grabens, troughs, depression and intrabasinal basement trending in the same direction as the basin configuration. The general thickness of sediments filling the basin ranges from 3 to 4.5 km, with the maximum accumulation of sediments reaching up to 4.8 km in the two depocenters at the south and southwest of the basin. The depth range of the sediments obtained implies that the basin has potential for hydrocarbon exploration with the possibility of natural gas occurrence.

Deep CO2 emissions facilitated by localized shear deformation: A case study of the Karakoram fault system, western Tibet

Strike-slip faults play a significant role in creating deeply penetrating fractures with high permeability, thus promoting rapid migration of CO2-rich fluids to the surface. However, there are rare observations regarding how strike-slip movement could affect deep CO2 emissions. Here, we focus on the Karakoram fault system (KKFS), western Tibet, to estimate diffuse soil CO2 fluxes and to unravel potential controlling factors for CO2 emissions. Average CO2 fluxes of geothermal fields range in 22–2475 g m−2 d−1, significantly higher than the across-fault profiles (6–116 g m−2 d−1). A mass balance model based on δ13C-CO2 and CO2 concentration of soil gases reveals that deep carbon constitutes 49.1–91.5 % (average = 73.9 %) and 0.2–40.5 % (average = 25.5 %) of soil-gas carbon released from geothermal fields and across-fault profiles, respectively. Deep carbon could be produced by thermal decomposition of crustal rocks considering CO2-rich fluids with radiogenic helium isotopes. Strikingly, higher CO2 fluxes preferentially occur in geothermal fields along a bending segment of the KKFS, where localized shear deformation is prominent as documented by high slip rates over geological timescales, dense splay faults, clustering of earthquake events, and elevated strain rates. We suggest that high stress acting on the KKFS bend could enhance the deformation and fracturing of fault zone rocks, leading to production of metamorphic CO2 and efficient release of CO2-rich fluids through the highly permeable fault system. Our results could shed new light on CO2 origins and fluxes of strike-slip faults that are characterized by spatially heterogeneous strain partitioning and thus localized enhanced shear deformation.

Microseismicity and fault structure in the Daliangshan block within the Southeastern Tibetan Plateau

The Daliangshan block is located between the Tibetan Plateau and the South China block and has accommodated several M > 6.5 damaging earthquakes in the past ∼600 years, as well as intense tectonic deformation and complex fault structures. In this study, we analyze more than two years of continuous seismic data recorded by a recently deployed dense seismic array. We used a recently developed machine learning-based earthquake location workflow (ESPRH) to construct a high-precision earthquake catalog for the region and obtained 3539 earthquakes, which is approximately three times as many as the National Earthquake Data Center (NEDC) catalog contains. The seismicity distribution not only confirms the nature of the faults marked on the map but also delineates the detailed geometry of the unmapped faults, including the en échelon faults at the northern end of the Zemuhe Fault and the “V”-shaped conjugate fault within the Mabian Fault Zone. The Zemuhe Fault and Lianfeng Fault are prone to hosting large earthquakes according to the derived low b-value. The western side of the Daliangshan block is dominated by strike-slip faults. Combining the fault geometry presented in this paper, we observed that the fault properties on the eastern side are complex. This tectonic phenomenon is attributed to the fact that during the lateral extrusion of the southeastern edge of the Chuandian fragments, the northeastern part of the Daliangshan block was squeezed by the South China block more strongly than its southwestern part. We provide the first precise earthquake catalog for Daliangshan block, which can be used as important seismological data for regional hazard assessment and research on the southeastern (SE) margin of the Tibetan Plateau.

Coupled Effects of Paleofluid Evolution on Ultra-deep Microbialite Reservoir Modification: A case study of the upper Ediacaran Deng-2 Member within the Penglai area of central Sichuan Basin, SW China

Paleofluid-rock interaction results in the modification of the ultra-deep reservoir quality, but the coupling effects of the paleofluid evolution on reservoir quality modification are still underestimated. Here, the multi-stage dolomite cements have been studied by means of core observations, thin section identification, fluid inclusions, and in situ elements and isotopic analyses in order to reaveal the paleofluid evolution processes and their effects on the reservoir quality. The fibrous dolomite cement (FDC) and bladed dolomite cement (BDC) both have similar geochemical properties and homogenization temperature (Th) to the matrix dolostone. Subsequent early silicification occurs (QZ1). However, silt- to fine-sized crystalline dolomite cement (CD2) has higher concentration of Fe and medium rare earth element, more negative δ18O than for FDC and BDC, and 103.4 to 150.2 °C in Th. The first petroleum charge episode solid bitumen 1 (SB1) followed the CD2. The medium to coarse sized crystalline dolomite cement (CD3) is characterized by the higher Mn and lower Sr concentration than CD2, positive δEu anomaly, negative δ13C and δ18O, high 87Sr/86Sr ratio and 138.9 °C to 184.3 °C in Th. The solid bitumen 2 (SB2) occurs after CD3. Subsequently, the saddle dolomite (SD) has higher Fe and Mn concentration and lower Na and Sr than others cement, δEu positive anomaly, negative δ13C and δ18O, high 87Sr/86Sr ratio and 177.5 °C to 243.6 °C in Th. Eventually massive silicification (QZ2) took place. The FDC, BDC, QZ1 and SB1 formed in the early diagenetic stage and have little negative effect on the reservoir quality. But the CD2 and CD3 dramatically decreased the reservoir quality related to a quantity of hydrothermal fluids entrance in the mesodiagenetic stage along the strike-slip faults and the unconformity surface at top of the Deng-2 Member during the late stage of the Caledonian orogeny. The reservoir spaces were retained and enlarged during the late diagenetic stage when the peak petroleum charge occurred, massive silicification and thermochemical sulphate reduction took place with SB2, SD and QZ2 being formed. The research outcome may update our understanding on the retention mechanism and the insights for further hydrocarbon exploration of Precambrian ultra-deep microbial reservoirs.

Structure and Evolution of Multi-Trend Faults in BZ19-6 Buried Hill of the Bohai Bay Basin, Eastern China

Defining the structure and evolution of multi-trend faults is critical for analyzing the accumulation of hydrocarbons in buried hills. Based on high-resolution seismic and drilling data, the structural characteristics and evolutionary mechanism of multi-trend faults were investigated in detail through the structural analysis theory and quantitative calculations of fault activity, allowing us to determine the implication that fault evolution exerts on hydrocarbon accumulation in the BZ19-6 buried hill. There are four kinds of strike faults developed on the buried hill: SN-, NNE-, NE–ENE-, and nearly EW-trending, which experienced the Mesozoic Indosinian, Yanshan, and Cenozoic Himalayan tectonic movements. During the Indosinian, the BZ19-6 was in a SN-oriented compressional setting, with active faults composed of SN-trending strike-slip faults (west branch of the Tanlu fault zone) and near EW-trending thrust faults (Zhang-peng fault zone). During the Yanshanian, the NNE-trending normal faults were formed under the WNW–ESE tensile stress field. Since the Himalayan period, the BZ19-6 buried hill has evolved into the rifting stage. In rifting stage Ⅰ, all of the multi-trend pre-existing faults were reactivated, and the EW-trending thrust faults became normal faults due to negative inversion. In rifting stage II, a large number of NE–ENE-trending normal faults were newly formed in the NW–SE-oriented extensional setting, which made the structure pattern more complicated. In rifting stage III, the buried hill entered the post-rift stage, with only part of the NNE- and NE–ENE-trending faults continuously active. Multi-trend faults are the result of the combination of various multi-phase stress fields and pre-existing structures, which have great influence on the formation of tectonic fractures and then control the distribution of high-quality reservoirs in buried hills. The fractures controlled by the NNE- and EW-trending faults have higher density and scale, and fractures controlled by NE–ENE trending faults have stronger connectivity and effectiveness. The superposition of multi-trend faults is the favorable distribution of high-quality reservoirs and the favorable accumulation area of hydrocarbon.

Mineralogy and Geochemistry of Upper Miocene Igneous Rocks, Kos Island, Greece: Extension during Strike-Slip Faulting and Subduction Rollback

Upper Miocene volcanic and plutonic rocks on Kos island preserve a record of magmatic and tectonic events in the transition zone between the Aegean and Anatolian microplates. Their field setting, syn-intrusion deformation, mineralogy, and geochemistry were investigated. Volcanic rocks, including trachyandesite flows and trachyandesite to rhyolite domes, were extruded on a central E–W horst and directly overlie Alpine basement. Thick successions of trachytic flow tuffs are interbedded with fluvial and lacustrine basinal sediments to the south of this horst. Volcanism was synchronous with the emplacement of the Dikeos monzonite pluton, which is geochemically similar to some lithic clasts in the thick flow tuffs and is cut by mafic dykes including lamprophyres. Two main types of mafic magma were present: a K-rich lamprophyric magma that evolved to trachyandesite and more calc-alkaline magma similar to mafic enclaves in the monzonite. Syn-intrusion structures in the monzonite indicate emplacement during E–W sinistral strike-slip faulting that created local transtensional deformation, providing accommodation for a Dikeos magma reservoir. A change in the style of deformation in the Late Miocene led to NW-striking extension in the footwall, occupied by mafic dykes and mineralized veins, and extensional detachment of the hanging wall, resulting in unroofing of the monzonite.

The landform Deformation at the Iraq-Iran Border due to Earthquakes in the Period (2017-2018)

The study targets to assess the potential of Interferometric Synthetic Aperture Radar (InSAR) in detecting ground distortion caused by earthquakes. The inSAR technique integrates Synthetic Aperture Radar (SAR) and interferometry to reveal the slightest changes on the earth's surface through a specified period, impregnable to climate or time of day. The research analyses some scholarly articles to demonstrate the interest of InSAR in examining earthquakes and their outcome. These articles demonstrate the practical application of InSAR in enhancing fault slip analysis, ground deformation assessment, and early post-seismic changes in earthquakes. InSAR is beneficial with measurements from other tools, such as GPS and time series analysis, but it still offers valuable insights into earthquake characteristics and associated effects. The insights from these methodologies can help devise solutions to mitigate the impacts of earthquakes. In addition, the paper presents information about three earthquake swarm events and their corresponding fault types. The first event occurred on November 12th, 2017, while the second happened on November 25th, 2018. Despite their differences in magnitude and location, the second event was associated with a strike-slip fault. InSAR provides extensive practical applications, from natural hazard monitoring to infrastructure projects and topographic mapping.

Fault characterization and its significance on hydrocarbon migration and accumulation of western Tazhong Uplift, Tarim Basin: Insight from seismic, geochemistry, fluid inclusion and in situ U-Pb dating

Understanding the mechanisms of deep hydrocarbon accumulation is of paramount importance in the field of petroleum geology. Studying deep hydrocarbon accumulation mechanisms contributes to the development of effective reservoir management strategies and efficient extraction techniques. In this study, fluid inclusion observation, homogenization temperatures, in situ calcite U-Pb dating, geochemical analyses and seismic data were applied to investigate the hydrocarbon charging history of the western Tazhong Uplift, and the migration pathways were further analyzed to establish the history of oil and gas accumulation in the study area. The results reveal three distinct episodes of oil and gas charging processes in the western Tazhong Uplift. The first episode, determined by in situ calcite U-Pb dating bearing primary oil inclusions, occurred during the late Caledonian to early Hercynian orogeny. This episode is characterized by yellowish fluoresce color oil inclusions. The second episode involved a complex variation of the thermal maturity of oil. Mature oil, with oil inclusions preferentially fluorescing yellow-green color, was charged into the reservoirs near the Tazhong No.1 fault. Subsequently, the high mature oil characterized by blue-fluorescing oil inclusions was charged. At the same time, the mature oil migrated vertically into the reservoir away from the Tazhong No.1 fault along the strike slip faults. The third charging process is dominant by high mature oil in the Southwest of the western Tazhong Uplift, whereas the gas intrusion occurred in the area near the Shuntuoguole Low Uplift. Furthermore, the strike slip faults and reverse faults were distinguished based on the seismic profiles and coherence diagram. The intersections of strike slip faults and Tazhong No.1 fault developing more fractures served as oil and gas charging points. The oil production revealed that the strike slip faults acted as important hydrocarbon migration pathways. This study provides valuable insights into the processes of hydrocarbon accumulation and offers further evidence for deep oil exploration in the region.

Interrogating an along-strike variation in the evolution and rheology of a large continental strike-slip fault zone

Along-strike variations in lithology, temperature, fluid activity, etc. can induce rheological changes in strike-slip faults that may be recorded by different fault rocks and fabrics. This article interrogates localized formation of granite-derived mylonite in a large strike-slip fault zone in which ultramylonite is the principle granite-derived fault rock to better understand this rock record of faulting. Microtextures show that rate-limiting deformation mechanisms in mylonite were dislocation creep in quartz and diffusion creep in very-fine-grained feldspar aggregates. Microtextures also show that mylonite formation is fully compatible with continuous viscous deformation whereas coeval ultramylonite along strike formed after whole-rock cataclasis at the brittle-viscous transition. Differential stresses determined from quartz aggregates in ultramylonites are 40–150% greater than stresses in mylonites. Hence, mylonites represent a local weak sector within this otherwise relatively strong fault zone. Mylonite formation is correlated with syndeformational chemical alteration as well as quartz microstructures and mineral assemblages indicating elevated deformation temperatures. Not all mylonite samples record significant chemical alteration. Therefore, mylonite formation likely records locally elevated temperatures. These results illustrate how a local shift in deformation conditions can affect the evolution and rheology of a large strike-slip fault zone, and how fault rocks record these processes.

Fault geometry and kinematics at the intersection of the Zemuhe, Daliangshan and Xiaojiang Faults

The complexity of strike-slip fault segmentation affects the initiation, propagation, and termination of earthquake ruptures and the earthquake magnitude. Studying the fault geometry, kinematics, and segmentation provides fundamental knowledge for mitigating earthquake hazards along faults. The Zemuhe, Daliangshan, and Xiaojiang Faults intersect along the eastern boundary of the Tibetan Plateau in the area from Ningnan in Sichuan Province to Qiaojia in Yunnan Province. Although few large earthquakes have occurred on these faults, the relationships between the intersections of these three faults and earthquake rupture behavior in this region are poorly constrained. The interpretation of aerial photographs and detailed field surveys revealed the geometric pattern and fault kinematics in the area of intersection. The distribution patterns and focal depths near the faults were obtained via analysis of seismic data in the area of intersection. The northern segment of the Xiaojiang Fault deviates approximately 25° northwest of Qiaojia, forming a conspicuous bend. The Xiaojiang Fault continues to extend southeast of the Ningnan Basin, where it intersects with the southern segment of the Zemuhe Fault, forming a pull-apart basin approximately 4.5 km wide. The bend and Ningnan pull-apart basin mark the segmented boundary between the Zemuhe Fault and the Xiaojiang Fault, which may prevent the propagation of large earthquake ruptures along the eastern boundary fault. Moreover, the lack of obvious geometric complexity between the Daliangshan Fault and Xiaojiang Fault might hinder the prevention of earthquake rupture propagation. Additionally, our results suggest that different earthquake prevention and disaster reduction measures should be taken for different cities in the region.

Stress heterogeneity in the eastern Tibetan Plateau and implications for the present-day plateau expansion

The eastward expansion of the Tibetan Plateau has resulted in different earthquake types in the eastern Tibetan Plateau, but the mechanism remains unclear. Here, we construct a three-dimensional visco-elastoplastic finite element model considering the topography to investigate the influence of fault geometry and rheological heterogeneity on stress fields. In our best-fitting model, the minimum principal stress is nearly vertical around the southern Huya fault zone, which is adjacent to the Longmen Shan fault zone, due to the significant mid-lower crust lateral rheological heterogeneity, and the thrust stress regime accounts for the reverse fault and thrust-dominated earthquakes. In this scenario, the eastward horizontal motion of the mid-lower crust is obstructed and facilitates thrust faulting, suggesting the limited eastward expansion of the Tibetan Plateau. In contrast, the northern Huya fault zone, one of the terminal branches of the East Kunlun fault, accommodates the continuous eastward extrusion of the East Kunlun fault, where the stress regime under a more homogenized crust favors the strike-slip faulting process, along with the dominant strike-slip earthquakes. Moreover, the best-fitting of stress regime explains the thrust-dominated 2008 Ms. 8.0 Wenchuan and 2013 Ms. 7.0 Lushan earthquakes on the Longmen Shan fault zone. Combining geophysical and geodetic observations and model analyses, we propose that the hybrid deformation mode in the eastern Tibetan Plateau is accommodated by upper crustal shear and thrusting deformation and mid-lower crustal thickening driven by the gravitational potential energy gradient. Our results elucidate the mechanism for differences in strong historical earthquakes and, more importantly, isolate the effect of fault geometry from those of heterogeneous viscosity on crustal deformation and stress heterogeneity in the eastern Tibetan Plateau.

Segmentation characteristics of strike-slip fault zone and its reservoir control mechanisms in the southwestern Tarim Basin

Understanding how fault-related structures influence oil and gas accumulation is crucial for geological investigations and exploration planning. This study, based on 3D seismic data, analyzes the northeast-trending strike-slip fault zone in the eastern part of the Bachu Uplift. Automatic fault extraction techniques were employed to delineate the strike-slip fault zone, and the parallel bedding indicator was used to identify reservoirs and investigate the fault’s segmented features and reservoir-controlling characteristics. The results show that the northeast-trending strike-slip fault is primarily governed by simple shear stress and conforms to the Riedel shear model. Three distinct structural styles were developed: vertical, pull-apart, and push-up segments, each exhibiting varying profile characteristics and planar patterns. The segmentation of the strike-slip fault controls the distribution of Ordovician fault-karst reservoirs. An oil and gas enrichment model for the strike-slip fault zone has been established, characterized by external hydrocarbon supply, fault-mediated migration, segmented reservoir control, and high-elevation accumulation. This study offers valuable insights for the exploration of fault-karst reservoirs controlled by strike-slip faults.

A new example of polyphase basin formation in western Anatolia: Plio-Quaternary Tavşanlı Graben, Kütahya

ABSTRACT The southwestern part of Turkey is called the ‘western Anatolia Extensional Province‘. Today, there is an approximately N-S-oriented extension in this area. The seismically active region is characterized by E-W and N-S-trending grabens. The tectonism and evolution of Tavşanlı Graben, one of these grabens, during the Plio-Quaternary period are the main subjects of this study. The Tavşanlı Graben, about which there is no information in the literature, has been defined for the first time in this study, and the geometrical and kinematic properties, relative ages, and interrelationships of some Neogene-aged faults, especially Quaternary-aged faults, have been presented in the manuscript. The data obtained indicate strike-slip faulting in the late Pliocene in the region. These E-W striking faults and the basin they formed are the first in western Anatolia with these features. In the Quaternary, E-W-oriented normal faults were formed in the region. The asymmetric topography of the graben area is consistent with the other E-W-oriented grabens in western Anatolia. Late Cretaceous basement rocks and Miocene-aged units are observed at the margins of the graben, which are fragmented by faults. The fill of the graben is Quaternary-aged fan deposits and alluvium. In this study, it was determined that the Tavşanlı Basin, which started to form with a transtensional mechanism at the end of the Pliocene, was transformed into the Tavşanlı Graben in the Pleistocene. The basin formation, which started with directional faulting in the late Pliocene, evolved into a graben in the Quaternary, and reached its present form by completing its development in two phases, supports the views that adopt the multi-stage deformation of western Anatolia in the late Cenozoic. In addition to contributing to the literature on this subject, the article will also serve as a basis for future paleoseismological studies.

Strike–Slip Fault Reactivation Triggered by Hydraulic-Natural Fracture Propagation during Fracturing Stimulations near Clark Lake, Alberta

Strike–Slip Fault Reactivation Triggered by Hydraulic-Natural Fracture Propagation during Fracturing Stimulations near Clark Lake, Alberta

Unveiling a major strike-slip fault system associated with the Somún Curá Large Igneous Province in central Patagonia, Argentina

This study presents new evidence of a major, regional strike-slip fault system linked to the emplacement of the Somún Curá Large Igneous Province in central Patagonia, Argentina. Employing a combination of remote sensing techniques and fieldwork, we provide additional insights into the structural complexities underlying this magmatic province, shedding light on its geological evolution. Our findings indicate a compelling correlation between the magmatic products of the Somún Curá Large Igneous Province and the left-lateral strike-slip fault system, resembling similar relationships observed in other magmatic large igneous provinces. Moreover, the strike-slip tectonics delineated in this study likely represent the culmination of the fault system's evolution, possibly originating from a longstanding basement fault and extending beyond the limits of the Somún Curá basaltic plateau.

Spatially-varied crustal deformation indicating seismicity at faults intersection in the SE margin of the Tibetan Plateau: Evidence of S-wave splitting from microseismic identification

The Sanjiang Lateral Collision Zone (SLCZ) in the SE margin of the Tibetan Plateau is a special area where several strike-slip faults intersect, resulting in strong deformation and frequent earthquakes. We employ seismic waveforms recorded by a dense temporary broadband array (SJ array) and regional permanent stations to construct more complete microseismic catalogs by the microseismic identification in the SLCZ. New microseismic catalogs effectively increase the number of small earthquakes, revealing the details of the fault structures and providing many more records for S-wave splitting (SWS) analysis. It provides with an uncommon opportunity to detect the detailed upper crustal anisotropy in the fault intersection zone of SLCZ and to dissect the influence of faults, such as the Lijiang-Xiaojinhe fault and Red river fault, on crustal deformation. The spatial distribution of SWS parameters suggests multiple disturbance mechanisms to the upper crustal anisotropy in the study zone. Spatial distribution of dual dominant polarization directions of fast S waves near the block boundary faults uncovers the stress-focus range. Strong deformation from SWS data indicates frequent local seismicity. It reveals the spatial upper crustal deformation indicated by SWS parameters is closely related to not only stress, fault and local structure, but also local seismicity.

Internal deformation of the North Andean Sliver in Ecuador-southern Colombia observed by InSAR

Summary In the Northern Andes, partitioning of oblique subduction of the Nazca plate beneath the South American continent induces a northeastward motion of the North Andean Sliver. The strain resulting from this motion is absorbed by crustal faults, which have produced magnitude 7 + earthquakes historically in the Andean Cordillera of Ecuador and southern Colombia. In order to quantify the strain in that area, we derive a high-resolution surface velocity map using InSAR time-series processing. We analyzed 6 to 8 years of Sentinel-1 data and combined different satellite line-of-sight directions to produce a reliable velocity map in the East direction. We use interpolated GNSS data to express the velocity map with respect to Stable South America and remove the long-wavelength pattern due to the post-seismic deformation following the 2016 Mw 7.8 Pedernales earthquake. The InSAR velocity map finds high E-W shortening strain rates along N-S trending structures within the Western Cordillera and the Interandean valley, with little deformation taking place east of them. This result strengthens the previous proposition of a ∼350 km long Quito-Latacunga tectonic block, forming a restraining bend in the overall right-lateral strike-slip fault system accommodating the northeastward escape motion of the North Andean Sliver. However, the high spatial resolution provided by InSAR indicates that previously proposed boundaries for this block need to be revised. In particular, InSAR results highlight high strain rate (>300 nstrain/yr) along undescribed active structures, south and west of the proposed limits for the Quito-Latacunga block, respectively in Peltetec and Ibarra regions. Interestingly, the two areas with the largest strain rates spatially correlate with the proposed areas of large historical earthquakes. Modeling of the InSAR and GNSS velocities in these areas suggests shallow coupling and high slip rates on structures which, previously, were not identified as active. We also demonstrate a slow-down of the shallow aseismic slip on the Quito fault after the Pedernales earthquake, suggesting that stress changes following large megathrust events might trigger transient slip behaviors on crustal faults. The high-resolution strain map provided by this work provides a new basis for future tectonic models in the Ecuadorian and southern Colombian Andes, and will contribute to the seismic hazard assessment in this highly populated area of the Andes.

Fault geometry invariance and dislocation potential in antiplane crustal deformation: physics-informed simultaneous solutions

Earthquake-induced crustal deformation provides valuable insights into the mechanisms of tectonic processes. Dislocation models offer a fundamental framework for comprehending such deformation, and two-dimensional antiplane dislocations are used to describe strike-slip faults. Previous earthquake deformation analyses observed that antiplane dislocations due to uniform fault slips are influenced predominantly by fault tips. Here, we state a general principle of fault geometry invariance in antiplane dislocations and exploit its theoretical consequence to define dislocation potentials that enable a streamlined crustal deformation analysis. To demonstrate the benefits of this theory, we present an analytical example and construct a rapid numerical solver for crustal deformation caused by variable fault slip scenarios using physics-informed neural networks, whose mesh-free property is suitable for modeling dislocation potentials. Fault geometry invariance and the dislocation potential may further the analysis of antiplane crustal deformation, particularly for uncertainty quantification and inversion analysis regarding unknown fault geometries in realistic crustal structures.

Structural controls on hydrothermal fluid flow in a carbonate geothermal reservoir: Insights from giant carbonate veins in western Germany

This study examines the impact of polyphase tectonics on the development of structurally controlled hydrothermal fluid pathways in carbonate geothermal reservoirs. Our case study focuses on hydrothermal carbonate veins and vein-filled faults in Devonian carbonates from the North Rhine-Westphalia region in western Germany, currently being explored as a potential low-enthalpy geothermal reservoir at depths of 4–5 km. These veins, which can be up to 20 m thick, are subvertical and strike NNW, N, or ESE. They exhibit pinch-and-swell undulating geometries, faulted vein-wall contacts, and occasional fillings of hydrothermal breccias. Vein-filled normal faults show hybrid shear-dilatant openings, with fault tips characterized by horsetail vein terminations. The textures, orientations, and age of the veins suggest their formation at low confining pressures and at depths < 2 km during the Post-Variscan East-West extension. Orthogonal North- and East-striking strike slip faults, inherited from the Variscan orogeny, were likely reactivated during post-Variscan extension, with a significant dilatant component that formed the observed veins. In the Ruhr Basin, the dilation tendency analysis indicates that NNW-striking veins or joints are optimally oriented for re-opening under the current strike-slip stress regime, characterized by NNW-trending maximum horizontal stress. The intersections of fractures may currently create moderately SSE-plunging linear zones of enhanced fluid flow. The main uncertainty regards the presence of similar structures at geothermal reservoir depths of ∼4–5 km in the Middle Devonian carbonates underneath the Ruhr Basin. As the study veins are likely to have formed at depths <2 km, the existence of analogous dilatant conduits at greater depths remains speculative. Eventually, we propose that zones characterized by open discontinuities and channelized fluid flow in carbonate geothermal reservoir in strike-slip tectonic settings can be: (a) dilational jogs between overlapping strike-slip faults, (b) bends along faults, and (c) strike-slip fault terminations with horsetail extensional structures. These zones can also be prone to enhanced karstification.