Footwall Of Fault Research Articles

Tectonic implications of raised Quaternary relative sea‐level indicators along the NE border of the Campania Plain (southern Italy)

AbstractTectonically raised paleoshorelines have been recently identified along the southern fault scarps of the Mt. Fellino and Roccarainola horst blocks, which are part of the northeastern border of the Campania Plain coastal basin (southern Apennines, Italy). Such horst blocks are bounded to the south by the Polvica Fault, a roughly E‐W trending normal fault. The sequence of uplifted paleoshorelines has been studied in detail by integrating geomorphological, structural and stratigraphical analyses to assess the Quaternary uplift of the Mt. Fellino and Roccarainola horst blocks. Yet, the staircase of paleoshorelines is still not chronologically well constrained.Aimed at constraining the uplift history of Mt. Fellino and Roccarainola horst blocks and the rate of activity of the Polvica fault, in this study, we integrate former knowledge on paleoshorelines with a geomorphological analysis to map erosional terraces, that we interpret as remnants of shore platforms. We apply the synchronous correlation method, driven by new and a former 230Th/234U dating of calcite veins cutting marine sands, to infer the age of the paleoshorelines and terraces. Based on the synchronous correlation, the mapped paleoshorelines and terraces are correlated with sea‐level peaks of the late Early to Late Pleistocene. In particular, the paleoshorelines along the Mt. Fellino ridge are correlated with the Marine Isotope Stage (MIS) 7e and 9c or 11, while the oldest terrace is correlated with the sea‐level peak of 980 ka. Using inferred paleoshorelines ages, we estimate the uplift rate of the Polvica Fault footwall. The uplift rate varies from c. 0.2 mm/yr close to the western fault tip up to c. 0.5–0.6 mm/yr in the East, in the Roccarainola block. We combine surface evidence with subsurface data from a shallow well to constrain the vertical throw of the Polvica Fault. A mean fault throw rate of c. 0.4 mm/yr in the last c. 1 Ma is estimated for the central part of the PF. Assuming that the Polvica Fault is still active, we estimate the maximum expected earthquake by means of empirical relationship and obtain a Mw ~ 6.2 value and recurrence interval value of c. 1,200 yr. Historical seismicity activity of the PF has not been acknowledged to date. However, our results raise the crucial question of an in‐depth assessment of the seismic hazard for the densely populated Campania Plain.

International Continental Scientific Drilling Program (ICDP) workshop on the Fucino paleolake project: the longest continuous terrestrial archive in the MEditerranean recording the last 5 Million years of Earth system history (MEME)

Abstract. During the last 5 million years (Pliocene–Holocene), the Earth climate system has undergone a series of marked changes, including (i) the shift from the Pliocene warm state to the Pleistocene cold state with the intensification of Northern Hemisphere glaciation; (ii) the evolution of the frequency, magnitude, and shape of glacial–interglacial cycles at the Early Middle Pleistocene Transition (∼ 1.25–0.65 Ma); and (iii) the appearance of millennial-scale climate variability. While much of this paleoclimate narrative has been reconstructed from marine records, relatively little is known about the impact of these major changes on terrestrial environments and biodiversity, resulting in a significant gap in the knowledge of a fundamental component of the Earth system. Long, continuous, highly resolved, and chronologically well-constrained terrestrial records are needed to fill this gap, but they are extremely rare. To evaluate the potential of the Fucino Basin, central Italy, for a deep-drilling project in the framework of the International Continental Scientific Drilling Program (ICDP), 42 scientists from 14 countries and 32 institutions met in Gioia dei Marsi, central Italy, on 24–27 October 2023 for the ICDP-supported MEME (the longest continuous terrestrial archive in the MEditerranean recording the last 5 Million years of Earth system history) workshop. The existing information and unpublished data presented and reviewed during the workshop confirmed that the Fucino Basin fulfils all the main requisites for improving our understanding of the mode and tempo of the Plio-Quaternary climatic–environmental evolution in a terrestrial setting at different spatial and temporal scales. Specifically, the combination of the seismic line evidence with geochronological and multi-proxy data for multiple sediment cores consolidated the notion that the Fucino Basin infill (i) is constituted by a sedimentary lacustrine succession continuously spanning at least 3.5 Myr; (ii) has a high sensitivity as a paleo-environmental–paleoclimatic proxy; and (iii) contains a rich tephra record that allows us to obtain an independent, high-resolution timescale based on tephrochronology. Considering the typical half-graben, wedge-shaped geometry of the basin, four different potential drilling targets were identified: MEME-1, located in the middle of the basin, should reach the base of the Quaternary infill at ∼ 500 m depth; MEME-2, located west of MEME-1, has sedimentation rates that are lower, with the base of the Pliocene–Quaternary at ∼ 600 m depth; MEME-3b has the same target as MEME-2 but is located further west, where the base of the Pliocene–Quaternary should be reached at ∼ 300 m; and MEME-3a (∼ 200–300 m depth) is located, for tectonic purposes, on the footwall of the basin master fault. Overall, the MEME workshop sets the basis for widening the research team and defining the scientific perspectives and methodological approaches of the project, from geophysical exploration to the development of an independent chronology and to the acquisition of multi-proxy records, which will contribute to the preparation of the full MEME proposal.

Evaluating karst features and geological fault leakage risks based on geophysical method in Dongzhuang reservoir area, Shaanxi

Leakage along faults, particularly in karst area faults, is a critical concern that can prevent impounding a reservoir. The Laolong Mountain fault in the Dongzhuang Reservoir Project Area in Shaanxi Province, China, is a large fault that may impede the project. To assess whether concentrated leakage can occur along this fault, we used a comprehensive approach involving footrill exploration, an electromagnetic method, optical imaging techniques, water pressure testing, and large-scale groundwater tracer tests. Footrill exploration results revealed that the karst features predominantly comprise karst cavities with some fissures and karst caves. These formations are typically clustered along fractures with a linear joint density of 0.4–1.5 joints/m. The linear karst rate was 0.39 %, and the karst cavities have small diameters of only a few centimeters and depths not exceeding 15 cm. A geophysical exploration indicated that low resistivity values (approximately 200 Ω·m) on the north side of the fault zone's hanging wall, with the lowest values being approximately 100 Ω·m. The fault's footwall was noted to have higher resistivity (approximately 2000 Ω·m). The rock properties on either side of the fault zone differ considerably. The upper plate of the fault (downstream of the river) has high-resistance carbonate rock formations with a well-preserved structure, whereas the lower plate (upstream of the river) comprises low-resistance sandstone and mudstone formations with notable fragmentation at the fault's surface compression zone. Tracer tests indicated an eastward groundwater flow from Zuantian Ridge toward the Jing River in the west. The results suggest that eastward leakage along the Laolong Mountain fault and its influence zone is unlikely upon reservoir impoundment. The geophysical exploration method in this study integrated and cross-validated the footrill exploration, hydrological test, groundwater tracing, optical imaging, and other methods; it can thus serve as a reference for future research.

Far-field response to the closure of the Meso-Tethys Ocean: New geochronological evidence from the Chem Co graben in the westernmost part of Central Tibet

The Chem Co graben is located in the westernmost part of the Qiangtang block, central Tibet. It is adjacent to the Longmu Co Fault to the north and approximately 50 km away from the Karakoram Fault to the west. The formation of the graben resulted in the exposure of basement rocks in the footwalls of the graben bounding normal fault, which hold crucial information on the Mesozoic closure of the Meso-Tethys Ocean. Garnet-biotite schist crops out sporadically in the footwall of the graben-boundary normal fault, and is intruded by leucogranite dikes. Pseudosection modeling indicates peak metamorphic conditions for the schist of 590–670 °C and 4.5–7.5 kbar, similar to the conditions of mid-crustal rocks at the western end of the Qiangtang block. Field investigations and microstructural analysis suggest syn-kinematical left-lateral strike-slip in both the biotite schist and granitoid veins. Zircon U − Pb, monazite U − Th − Pb, and 40Ar/39Ar ages show that intense regional intensive tectonic deformation and contemporaneous magmatism began at ∼120.6 Ma and ended with the peak metamorphism conditions at 105.3 ± 6.0 Ma. These results indicate that the closure of the Meso-Tethys Ocean in the westernmost part of central Tibet occurred over this period (i.e., 121–105 Ma) with final closure during the late Early Cretaceous. The closure of the Meso-Tethys Ocean likely triggered widespread far-field responses, extending from the Altyn Tagh Fault to the Longmu Co Fault, and reaching the Pangong and Hunza regions around the Western Himalayan Syntaxes. Episodic crustal thickening and surface uplift since the closure of the Meso-Tethys Ocean caused the upper crust to be extruded along the westernmost part of central Tibet, leading to the formation of the Chem Co graben.

Constraining the slip history of the Katschberg normal fault (Eastern Tauern Window) by thermo-kinematic modeling: Implications for the tectonic evolution of the Eastern European Alps in the late Cenozoic

The Katschberg normal fault borders the Tauern Window to the east and played a crucial role during Miocene lateral tectonic extrusion in the Eastern European Alps. In this study, we present new cooling ages from low-temperature thermochronology as well as thermo-kinematic models, which constrain the exhumation history of the Penninic units in the footwall of the Katschberg normal fault and its slip history. Zircon and apatite fission track and apatite (U–Th)/He ages from footwall units range from 16.0 ± 1.9 Ma to 12.8 ± 1.4 Ma, 10.4 ± 1.8 Ma to 7.9 ± 1.3 Ma and 8.2 ± 0.8 Ma to 3.9 ± 0.4 Ma, respectively. Thermo-kinematic modeling indicates that the Katschberg normal fault was active between 21.1 ± 1.8 Ma and 12.2 ± 1.3 Ma and accommodated 27 ± 6 km of crustal extension at a total rate of 3.5 ± 0.3 km/Myr. After the end of normal faulting, exhumation continued with a rate of 0.21 ± 0.06 km/Myr until 2.0 ± 0.5 Ma and with a rate of 0.84 ± 0.08 km/Myr until present. A comparison with another Miocene low-angle normal fault in the Eastern Alps – the Brenner fault – reveals that the amount of extension accommodated by these faults decreases from west to east, which is consistent with an eastward decrease in N-S shortening. Therefore, Miocene deformation is greatest in the western Tauern Window near the Brenner normal fault where shortening in front of the Adriatic Indenter is at its maximum.

Geothermal distribution and evolution of fault-controlled Linyi geothermal system: Constrained from hydrogeochemical composition and numerical simulation

This study explores the Linyi geothermal field, located in Shandong Province, China, characterized by its non-magmatic, active fault-controlled geothermal system. Utilizing a combination of geochemical analyses, temperature measurements, and numerical simulations, a detailed genetic model of the geothermal system has been developed. The analysis included extensive water geochemical and isotopic characterization to determine reservoir temperature, depth, and origin of the geothermal waters. The thermal-hydro coupling model was integrated with these data to refine the thermal distribution and assess the evolutionary dynamics of the geothermal system. Our findings indicate that the geothermal anomalies in the Linyi field are predominantly controlled by hydrothermal convection within the Ordovician and Cambrian carbonate layers, facilitated by the high permeability of the Yishu Fault. The fault acts as a crucial conduit for meteoric water recharge, which undergoes significant heating due to the geothermal gradient in deeper rock formations. Isotopic analyses of hydrogen and oxygen revealed the meteoric origin of the geothermal waters, with recharge likely originating from the nearby Yimeng Mountains. Furthermore, the study established a conceptual evolutionary model to understand the mechanisms driving the geothermal resource development in the area. It was determined that the geothermal resources are typically fault-controlled, with significant potential for further exploration due to the identified hydrothermal anomalies at the fault's footwall. The model predicts the preservation of heated meteoric water in the reservoir rock for periods ranging from 10 to 50 thousand years, providing a sustainable source of geothermal energy. This comprehensive approach not only enhances the understanding of the heat accumulation mechanism but also highlights the potential for optimizing geothermal exploration strategies within fault-controlled geothermal systems.

Geomorphological traits of landscapes in continental rifts—From fault‐elastic rebound to sedimentary sinks

AbstractWe analyse 498 faults identified in satellite imagery and interpret the height and width of associated footwall ranges with respect to co‐seismic elastic rebound from tectonic and erosional unloading. The dynamics of footwall uplift link uplands to catchment patterns and interrelated hanging wall sedimentary fans. Height–length relations of some catchments and associated alluvial fans scale linearly whereas others, such as fault‐slope catchments and related down‐fault fans (building out from faults) show a significant scatter without an obvious trend. Perched basins abandoned in the footwalls of younger faults offer catchment‐fan height–length relations like watergap and dipslope‐related fans and, besides, hint at reduction of dip angle due to rollback of larger faults before abandonment. Analysis of the width‐to‐height ratio (W/h) of footwall ranges offer a robust linear statistical trend, h = 0.06 W and is identical between datasets. This trend is valid for both arid and tropical rifts, the latter offering smaller rebounds. Contributions of elastic rebound on fault throw in our data are simplistically considered through comparison to global trends on fault length versus throw. This allows consideration around maximum throw (Tmax) linked to the maximum height of footwall ranges (h) and to their width (W) above the reference level. Basic calculations indicate that co‐seismic rebound contributes from <1% to 17% of extensional fault throw. Width‐to‐height ratios for large faults (L > c. 50 km) show less spread than smaller faults. Such large faults expectedly dissect the brittle crust, indicating that these large faults which root in the ductile–brittle transition approach a balanced, steady‐state kinematic pattern. We speculate that significant crustal thinning associated with these large faults triggers the onset of isostatic adjustments that drive fault rotation, instigating fault abandonment and disconnected perched basins.

Extensional fault geometry and evolution within rifted margin hyper-extended continental crust leading to mantle exhumation and allochthon formation

Abstract. Seismic reflection interpretation at magma-poor rifted margins shows that crustal thinning within the hyper-extended domain occurs by in-sequence oceanward extensional faulting which terminates in a sub-horizontal reflector in the topmost mantle immediately beneath tilted crustal fault blocks. This sub-horizontal reflector is interpreted to be a detachment surface that develops sequentially with oceanward in-sequence crustal faulting. We investigate the geometry and evolution of active and inactive extensional faulting due to flexural isostatic rotation during magma-poor margin hyper-extension using a recursive adaptation of the rolling-hinge model of Buck (1988) and compare modelling results with published seismic interpretation. In the case of progressive in-sequence faulting, we show that sub-horizontal reflectors imaged on published seismic reflection profiles can be generated by the flexural isostatic rotation of faults with initially high-angle geometry. Our modelling supports the hypothesis of Lymer et al. (2019) that the S reflector on the Galician margin is a sub-horizontal detachment generated by the in-sequence incremental addition of the isostatically rotated soles of block-bounding extensional faults. Flexural isostatic rotation produces shallowing of emergent fault angles, fault locking, and the development of new high-angle shortcut fault segments within the hanging wall. This results in the transfer and isostatic rotation of triangular pieces of hanging wall onto exhumed fault footwall, forming extensional allochthons which our modelling predicts are typically limited to a few kilometres in lateral extent and thickness. The initial geometry of basement extensional faults is a long-standing question. Our modelling results show that a sequence of extensional listric or planar faults with otherwise identical tectonic parameters produce very similar seabed bathymetric relief but distinct Moho and allochthon shapes. Our preferred interpretation of our modelling results and seismic observations is that faults are initially planar in geometry but are isostatically rotated and coalesce at depth to form the seismically observed sub-horizontal detachment in the topmost mantle. In-sequence extensional faulting of hyper-extended continental crust results in a smooth bathymetric transition from thinned continental crust to exhumed mantle. In contrast, out-of-sequence faulting results in a transition to exhumed mantle with bathymetric relief.

Segmentation of the Tashkurgan normal fault in the eastern Pamir: Insights from geomorphology and thermochronology and implications for fault-slip transfer

At the northwestern end of the India–Asia collision zone, in the eastern Pamir interior, the Kongur Shan extensional system extends for ∼250 km as a composite system of normal faults. As the southernmost segment of the extensional system, the Tashkurgan fault can be divided into a northern and southern segment by the intersection of the Tahman and Tashkurgan faults. To evaluate the tectonic activity along the Tashkurgan fault and explore the extensional characteristics of the southern Kongur Shan extensional system, we integrate geomorphologic analysis with thermochronologic data and modeling. Geomorphic indices, including local relief, normalized channel steepness index (ksn), and river χ-plots, show that the southern Tashkurgan fault is more active than the northern Tashkurgan fault. On the footwall of the northern Tashkurgan fault, most thermochronologic data, which include biotite 40Ar/39Ar (Arbt), zircon (U-Th)/He (ZHe), apatite fission track (AFT), and apatite (U-Th-Sm)/He (AHe) dates, record emplacement-related cooling, and only a few AHe dates possibly record exhumation of <2 km since ∼7 Ma ago. On the footwall of the southern Tashkurgan fault, almost all of the ZHe, AFT, and AHe dates record significant late Miocene to present exhumation; thus, we perform three-dimensional thermokinematic modeling for the normal slip along this fault segment. Modeling results indicate a probably constant slip rate on the southern Tashkurgan fault at a value of 1.4–1.5 mm/a, which corresponds to 6–7 km of both horizontal extension and footwall uplift since 6.5 Ma ago. All together, the geomorphic and thermochronologic evidences imply that the southern Tashkurgan fault is responsible for the ∼E–W extension along the southernmost portion of the Kongur Shan extensional system, while the northern fault segment plays a minor role in the extension. This result, combined with the previously published magnitude of extension along the southern Kongur Shan fault, indicates that the extension at any site along the southern Kongur Shan extensional system can be primarily attributed to normal faulting along a single border fault, which is a typical characteristic of an interbasin transfer zone with a transfer fault.

Stratigraphic and geochronologic investigation of the Muddy Creek Basin: Implications for the Eocene tectonic evolution of southwest Montana, USA

Sedimentary basins record crustal-scale tectonic processes related to the construction and demise of orogenic belts, making them an invaluable archive for the reconstruction of the evolution of the North American Cordillera. In southwest Montana, USA, the Renova Formation, considered to locally represent the earliest accumulation following Mesozoic−Cenozoic compressional deformation, is widespread but remains poorly dated, and its origin is debated. Herein, we employed detrital zircon U-Pb and (U-Th)/He double dating and sanidine 40Ar/39Ar geochronology in the context of decimeter-scale measured stratigraphic sections in the Renova Formation of the Muddy Creek Basin to determine basin evolution and sediment provenance and place the basin-scale record within a regional context to illuminate the lithospheric processes driving extension and subsidence. The Muddy Creek Basin is an extensional half graben in southwest Montana that is ∼22 km long and ∼7 km wide, with a &amp;gt;800-m-thick sedimentary package. Basin deposition began ca. 49 Ma, as marked by multiple ignimbrites sourced from the Challis volcanic field, which are overlain by a tuffaceous fluvial section. Fluvial strata are capped by a 46.8 Ma Challis ignimbrite constrained by sanidine 40Ar/39Ar dating. An overlying fossiliferous limestone records the first instance of basinal ponding, which was coeval with the cessation of delivery of Challis volcanics−derived sediment into the Green River Basin. We attribute initial ponding to regional drainage reorganization and damning of the paleo−Idaho River due to uplift and doming of the southern Absaroka volcanic province, resulting in its diversion away from the Green River Basin and backfilling of the Lemhi Pass paleovalley. Detrital zircon maximum depositional ages and sanidine 40Ar/39Ar ages show alternating fluvial sandstone and lacustrine mudstone deposition from 46 Ma to 40 Ma in the Muddy Creek Basin. Sediment provenance was dominated by regionally sourced, Challis volcanics−aged and Idaho Batholith−aged grains, while detrital zircon (U-Th)/He (ZHe) data are dominated by Eocene cooling ages. Basin deposition became fully lacustrine by ca. 40 Ma, based on an increasing frequency of organic-rich mudstone with rare interbedded sandstone. Coarse-grained lithofacies became prominent again starting ca. 37 Ma, coeval with a major shift in sediment provenance due to extension and local footwall unroofing. Detrital zircon U-Pb and corresponding ZHe ages from the upper part of the section are predominantly Paleozoic in age, sourced from the Paleozoic sedimentary strata exposed in the eastern footwall of the Muddy Creek detachment fault. Paleocurrents shift from south- to west-directed trends, supporting the shift to local sources, consistent with initiation of the Muddy Creek detachment fault. Detrital zircon maximum depositional ages from the youngest strata in the basin suggest deposition continuing until at least 36 Ma. These data show that extension in the Muddy Creek Basin, which we attribute to continued lithospheric thermal weakening, initiated ∼10 m.y. later than in the Anaconda and Bitterroot metamorphic core complexes. This points to potentially different drivers of extension in western Montana and fits previously proposed models of a regional southward sweep of extension related to Farallon slab removal.

Analysis of Rock Burst Mechanism in Extra-Thick Coal Seam Controlled by Thrust Fault under Mining Disturbance

A fault is a common geological structure encountered in underground coal mining. Interactions between the discontinuous structure of a fault and mining activities are the key factors in controlling the rock bursts induced by the fault. It is of great importance to study the rock burst mechanism of an extra-thick coal seam under the combined influence of reverse faults and coal mining for the prediction and prevention of rock burst. In this study, we establish a sliding dynamics model of rock mass in a fault zone and analyze the mechanical distribution of fault-induced rock bursts under the combined action of mining disturbances. Additionally, we utilize theoretical calculation and a 3D numerical simulation method to clarify the rockburst mechanism in an extra-thick coal seam controlled by a thrust fault under mining disturbance and a fault. The results showed that the distribution range of the shear stress increment in the fault footwall was larger than that in the hanging wall, revealing a skewed distribution. The fault dip angle and mining thickness exhibit significant influence on the structure around the fault. With increases in the dip angle of the fault and mining thickness, the maximum vertical stress and peak stress first increase and then decrease. A position 80 m away from the fault is the dividing line between the fault-non-affected area and the fault-affected area. The 13,200 working face of the Gengcun coal mine is used as a case study to study the influence of mining disturbances on microseismic events. The results of this study are in good agreement with the theoretical calculations and numerical simulation results.

How Hydrothermal Cooling and Magmatic Sill Intrusions Control Flip‐Flop Faulting at Ultraslow‐Spreading Mid‐Ocean Ridges

Abstract“Flip‐flop” detachment mode represents an endmember type of lithosphere‐scale faulting observed at almost amagmatic sections of ultraslow‐spreading mid‐ocean ridges. Recent numerical experiments using an imposed steady temperature structure show that an axial temperature maximum is essential to trigger flip‐flop faults by focusing flexural strain in the footwall of the active fault. However, ridge segments without significant melt budget are more likely to be in a transient thermal state controlled, at least partly, by the faulting dynamics themselves. Therefore, we investigate which processes control the thermal structure of the lithosphere and how feedbacks with the deformation mechanisms can explain observed faulting patterns. We present results of 2‐D thermo‐mechanical numerical modeling including serpentinization reactions and dynamic grain size evolution. The model features a novel form of parametrized hydrothermal cooling along fault zones as well as the thermal and rheological effects of periodic sill intrusions. We find that the interplay of hydrothermal fault zone cooling and periodic sill intrusions in the footwall facilitates the flip‐flop detachment mode. Hydrothermal cooling of the fault zone pushes the temperature maximum into the footwall, while intrusions near the temperature maximum further weaken the rock and promote the formation of new faults with opposite polarity. Our model allows us to put constraints on the magnitude of two processes, and we obtain most reasonable melt budgets and hydrothermal heat fluxes if both are considered. Furthermore, we frequently observe two other faulting modes in our experiments complementing flip‐flop faulting to yield a potentially more robust alternative interpretation for existing observations.

The well log and seismic expression of faults in the Wisting field, Barents Sea

Seismic facies in large fault zones (dam to km throw) can rarely be constrained with well log data. High-resolution seismic data (ca. 3.1 × 3.1 m bins) from the highly faulted Wisting field in the Barents Sea, is compared with log data along a horizontal and a vertical well. The target of both wells is the Lower Jurassic, oil-bearing Stø Fm., which due to Cenozoic uplift and erosion is just ca. 250 m below sea floor. From SW to NE, the horizontal well crosses a horst structure before landing in the Stø Fm. The inner zones of the two normal faults bounding the horst show low acoustic impedance (Aimp) and high porosity. The horst is characterized by a chaotic seismic pattern, partly caused by several faults made visible by seismic attributes. The well logs show large variance within the horst which may be caused by small faults and fractures that were observed during drilling in addition to mud losses. Along the horizontal well path NE of the horst, the Stø Fm. is characterized by strongly varying porosity and Aimp logs, and the seismic horizons around the borehole are offset by several small faults. Farther NE from the horst in the last well interval, the Stø Fm. shows a clean sand with high porosity and a continuous seismic reflector along the well path. The vertical well is between two SW dipping normal faults, and it shows oil only. A gas cloud identified by a flat spot is observed SW of the well, on the footwall of the SW-most fault. The gas cloud has ca. 20% lower Aimp than the oil zone. The two faults exhibit inner fault zones which start at about the Stø Fm. in the hanging wall and are characterized by low Aimp values. The fault blocks do not show these low Aimp values, which means that gas rather than shale smears could be responsible for the low Aimp along the faults. The low Aimp fault zones can be followed up to the upper regional unconformity (URU). The Quaternary above the URU shows a weak fault pattern, which could explain how the gas from the reservoir is conducted through the faults up to the seabed. This emphasizes the importance of faults as fluid conduits in the area.

Research on the Surface Deformation, Fault Rupture, and Coseismic Geohazard of the 2022 Luding Mw 6.8 Earthquake.

An Mw 6.8 earthquake occurred in Luding County, Ganzi Tibetan Autonomous Prefecture, Sichuan Province, on 5 September 2022. This seismic event triggered numerous coseismic geohazards in the seismic zone. In this study, the ascending- and descending-track synthetic aperture radar (SAR) images observed by the Sentinel-1A satellite are utilized to extract the coseismic surface deformation of the Luding earthquake. Subsequently, a faulting model is estimated based on the elastic dislocation theory, under the constraint of the InSAR observation. Additionally, the POT technique was employed to detect coseismic geohazards. High-spatial-resolution optical remote sensing images served to validate the reliability of the detection results. The coseismic interferometric synthetic aperture radar (InSAR) deformation field indicated a maximum deformation of ~190 mm and ~140 mm along the ascending and descending tracks, respectively. The estimated best-fitting faulting model suggests that the optimal seismogenic fault strike and dip angles are 169.3° and 70°, respectively. The fault slip predominantly exhibits left-lateral strike-slip characteristics and is concentrated at depths of 3-12 km. The estimated maximum fault slip was 2.67 m, occurring at a depth of 7 km. The pixel offset tracking (POT) result derived from the pre- and post-earthquake SAR images found a total of 245 medium- to large-scale coseismic geohazards, with a verification rate from optical images exceeding 64%. The distribution of these geohazards is notably dense within the significant fault rupture segment. Geohazards on the fault hanging wall are densely packed, whereas landslides along the Dadu River's fault footwall are also notably frequent.

Timing of the initiation and duration of the Cretaceous extensional regime in South‐east China: Constraints from growth strata in terrigenous basins

AbstractThere has been no consensus yet regarding the precise initial timing and duration of the late Mesozoic extensional tectonics in the South‐eastern China Block. This work focusses on the growth strata of the Early Cretaceous red beds in the South‐eastern China Block to determine the late Mesozoic tectonics and the precise timing of the initiation and duration of extensional tectonics in this area. Field observation of several terrigenous basins shows that the dip angles of the Cretaceous red beds have varied from moderate to gentle from basin edges to interiors (or centres). The visible and estimated thickness within a single bed increases slightly downwards from the upper to the lower part. These characteristics indicate that the sedimentary area of these beds has undergone an extensional process with expansion and deepening of the sedimentary basins. Rotation of the border surfaces (limbs) and downward warping of the hanging walls or retreat of the footwalls of listric normal faults causes three types of extensional growth (or syntectonic) strata in the deposits of different basins. Dating of the volcanic rocks related to the growth beds reveals that the sedimentary basins were enlarged and deepened when the Early Cretaceous strata were deposited in the South‐eastern China Block from ca 140 to 137 Ma. Regionally, under the influence of Palaeo‐Pacific plate rollback since ca 140 Ma, the South‐eastern China Block stress field has led to lithospheric uplift and pull‐apart structures near the surface, causing the half‐graben basins to receive sedimentation. Although the extensional event was interrupted by a short compressional event during 120 to 105 Ma, with the oceanward retreat of the trench, the area of extension gradually enlarged and rejuvenated south‐eastwards until the end of the Cretaceous. This Cretaceous extension event of the South‐eastern China Block must belong to a worldwide geological event with global significance.

Research on dynamic response characteristics of normal fault footwall working face and rock burst prevention technology under the influence of the gob area

To study the effect of mining dynamic response characteristics on the footwall working face of the normal fault under the influence of the gob area, theoretical research, indoor experiment, and numerical simulation are adopted to analyze the stress manifestation characteristics, overburden movement, and energy evolution characteristics during the process of mining. The results show that: (1) In the process of mining toward the fault, the working face shows the change characteristics of “stable-activation mutation-final stability”. At 20 m from the fault, the arch structure of the working face was damaged, fissures appeared near the high fault fracture zone, and the displacement of the overburden rock increased significantly; (2) the maximum value was reached at 4–8 m from the coal wall, and the superposition of tectonic stress and mining stress led to the concentration of the stress and energy accumulating on the top plate near the fault, and the data close to the gob area were even larger; (3) If the plastic damage zone of the high-level rock layer on the hanging wall and footwall of the fault appears to have a wide range of penetration, and the area formed between the shear displacement curve of the fault plane and the X-axis appears to have a significant enhancement, it is considered that the fault has been activated; (4) The size of the coal pillar of the fault is determined to be 40 m, and combined with the pressure unloading technique of the variable-diameter drilling hole, the validation is carried out through the micro-vibration monitoring, and the results of which can be used as a reference for the safety of the working face under similar conditions.

Contrasting influence of salt structures and faults on the geothermal potential of regional structural highs: The Cleaver Bank High, Southern North Sea

High-quality 3D seismic reflection data, complemented by 448 bottom-hole temperatures (BHTs) from 48 boreholes, are used to investigate the influence of salt structures and faults on the geothermal potential of the Cleaver Bank High, Southern North Sea. Developed salt structures include multiple salt diapirs, salt pillows and a salt wall, with their presence influencing local geothermal potential. Strata deposited above the Zechstein Group record geothermal gradients that are enhanced proportionally to the thickness of this salt unit. Conversely, strata buried below the Zechstein Group reveal a moderate decreasing trend in geothermal gradients as salt thickens. Large supra-salt faults can act as fluid paths to deep and hot fluid into shallow strata, resulting in the presence of high geothermal gradients in shallow strata. Importantly, geothermal gradients on the footwall of these faults are much higher than that on the corresponding hanging-wall, decreasing as one moves away from them. For example, average geothermal gradients on the footwall of the largest supra-salt fault (Fault A) are, relative to its immediate hanging-wall, 105 % higher in the North Sea Group, 26 % higher in the Chalk Group, and 41 % higher in the Rijnland, Upper and Lower Germanic Trias Groups. Additionally, sub-salt faults influence the geothermal gradient of supra-salt strata in parts of the study area where there is very thin, or even absent, salt (<100 ms; or ∼230 m), forming distinct low-amplitude trails of fluid above these same faults. They also indirectly influence geothermal gradient by controlling the position, geometry and distribution pattern of salt structures. As a corollary, three potential geothermal exploration targets are suggested on the Cleaver Bank High, one located on the footwall of a large supra-salt fault, one above thick salt, and a third target above very thin Zechstein strata where low-amplitude fluid chimneys are found. The results in this work can be applied to similar salt-bearing structural highs in Northern Europe and worldwide.

Structural geometry and kinematic evolution of the central Canadian Rocky Mountain Foothills fold-and-thrust belt: Complex kinematic relationships controlled by detachment utilization

Abstract Balanced regional cross sections based on surface, seismic, and subsurface data show that the thin-skinned fold-and-thrust belt in the Rocky Mountain Foothills of the Kakwa area of the central Canadian Rockies consists of a lower buried thrust belt developed in Paleozoic and Triassic strata and an upper exposed faulted fold belt of Jurassic to Cretaceous strata. Changes in fold wavelength, amplitude, and geometry with stratigraphic level indicate that multiple detachments were utilized in the upper faulted fold belt. Exposed folds are chevron or box shaped. Most appear to be detachment or fault propagation folds formed by fault-to-fold displacement transfer. Geometric and kinematic relationships in the upper faulted fold belt vary from thrust faults congruently folded by underlying folds (early fault) to folds abruptly truncated by thrust faults (late fault). In contrast, folding of thrust sheets in the buried thrust belt is consistent with in-sequence deformation for all faults except one. A sequential restoration of the balanced regional cross section shows that the variable kinematic relationships observed in the upper faulted fold belt can be explained by changes in the detachment level utilized by successive faults as they climbed out of the buried thrust belt. Chevron-folded thrust faults indicate a younger fault with associated fault displacement transfer folds formed in the footwall of an older fault. These folded thrusts formed by in-sequence faulting and utilization of successively higher detachment levels. Late faults that truncate preexisting folds required out-of-sequence (hinterlandward) utilization of a higher detachment level, and they illustrate another mechanism by which critical taper is maintained in a fold-and-thrust belt.

Control of basin-scale accommodation zones on syn-rift Aptian lacustrine carbonate reservoirs. Implications for reservoir quality estimates of Brazilian pre-salt

This paper presents the tectono-sedimentary time and space evolution of the Sururu oil field (Brazilian Pre-Salt). The field is located at the well-known Santos External High (SEH), north of the Tupi oil field—the pioneer accumulation of the largest and most prolific hydrocarbon trend of the 21st century. In the central portion of the field, the regional NE-trending faults system that prevails in the Santos Basin bends to NNW and becomes diffused into several low-displacement normal faults. These faults control a series of segmented structural highs, with some holding significant amounts of oil within lower permeability mudstones. These are the reservoir rocks, controlled by an NW horst, segmented in three domains by 290° Az and 245° Az trending relay ramp systems. The structural domains control discontinuous depocenters that evolved during the late syn-rift phase (Mid Aptian, c. 117 Ma). In this work, the aim is to show how the evolution through time of these segmented domains influenced variations of sedimentary facies, affecting vertical connectivity of the oil within the production zones. The work was based on interpreting 3D multi-azimuthal high-resolution seismic data, eight wells, and cross-section restoration techniques. We interpret multi-stage fault growth along the NW structural trend as a mechanism for distributing reservoir rocks, promoting localized syn-rift footwall uplift of isolated normal faults. The intervening domains between interacting faults induce the nucleation of accommodation zones, which in turn, controls the distribution of sediment catchment areas. Facies quality degradation along syn-rift structural highs impacts the distribution of preferential fluid flow. Therefore, the association of structural elements described in this study demonstrates that shallow water facies were controlled by uplift at the footwall of low displacement normal faults, inducing local lake-level retraction. Such evolution is strongly influenced by displacement transfer along local transfer zones dissecting the structural highs, which in turn controls local structural highs and lows, hence the distribution of high- and low-quality reservoir rocks during later phases of rifting.

Grooving in the midcontinent: A tectonic origin for the mysterious striations of L’Anse Bay, Michigan, USA

Abstract A striated surface is present at an erosional unconformity between foliated Paleoproterozoic Michigamme Formation and fluvial conglomerate and sandstone of the Neoproterozoic Jacobsville Formation exposed at L’Anse Bay (Michigan, USA). These striations have been interpreted to be the result of ice flow in either the Proterozoic, the Pleistocene, or the modern. Recently, the glacial origin interpretation for this striated surface has been used to argue that it may be related to ca. 717–635 Ma Cryogenian snowball Earth glaciation. This interpretation would make the surface a rare example of a Neoproterozoic glacial pavement, with major chronostratigraphic implications that in turn impose constraints on the timing of intracratonic erosion related to the formation of the Great Unconformity. In this contribution, we present new observations showing that the surface is a tectonic slickenside caused by largely unconformity-parallel slip along the erosional unconformity. We document structural repetition of the Michigamme-Jacobsville contact with associated small-scale folding. The unconformity-parallel slip transitions into thrust faults that ramp up into the overlying Jacobsville Formation. We interpret that the surface records contractional deformation rather than ancient glaciation, recent ice movement, or recent mass wasting. The faulting likely occurred during the Rigolet phase of the Grenvillian orogeny, which also folded the Jacobsville Formation in the footwall of the Keweenaw fault.