Seismic Reflection Profiles Research Articles

Constrained 3D gravity modelling of a multilayered aquifer system in an arid region: Case of Sebkhat El Bhira basin (Central Tunisia)

In arid regions, the significant and increasing demand for water has caused intensive exploitation of groundwater resources. The Sebkhat El Bhira basin, shared between Kairouan and Sidi Bouzid governorates in Central Tunisia, presents a multi-layer aquifer system composed of four main reservoirs: the sandy Mio-Plio-Quaternary (MPQ), the Paleogene, the Upper Cretaceous limestone and the Lower Cretaceous limestone, sand and dolomite reservoirs. The intensive exploitation of the shallower aquifer has led to a drawdown of the water table and a deterioration of water quality. The purpose of this work is to characterize the geometry of these potential reservoirs for sustainable water management, by applying geophysical methods.We used land gravity data covering 1387 Km2, twelve seismic reflection profiles with a total length of approximately 308 Km, two petroleum wells and 39 water wells.The processing of the gravity data shows the subdivision of Sebkhat El Bhira basin into four sub-basins and the identification of principal and minor lineaments oriented N-S, NE-SW, NNW-SSE, and E-W. The interpretation of reflection seismic lines allowed the identification of five main horizons: the bottom of MPQ, the bottom of Paleogene, the bottom of Upper Cretaceous, the bottom of Lower Cretaceous and the bottom of Jurassic (Top Triassic). For a better understanding of the subsurface structuring, we built twelve two-dimensional (2D) forward models of density. These latter are constrained in the area inside the plain by the converted time-to-depth seismic reflection data and wells. The interpolation of the 2D models allowed us to visualize the lateral and vertical thickness variations of each of the chrono-stratigraphic units and to produce a three-dimensional (3D) density model. The geophysical modelling allowed us to highlight the post-Jurassic tectonic and the Triassic halokinesis activities responsible for the actual subsurface geometry.The Triassic evaporites, in the study area, flow and rise through the fault's subvertical branches. It outcrops locally at the North-South Axis mountains range (NOSA). Inside the plain, the evaporitic uprising shows different schemes like diapir, wall and pillow. This Triassic halokinesis, with the tectonics, has shaped the deep morphology of the basin and managed the available space for the deposition of the overlying stratigraphic formations.The general structure of the potential aquifers is characterized by a depth which increases from the East to the West and towards the central part of the plain. Inside the basin, the structure of these aquifers is complex.

Detailed Imaging of a Seismogenic Fault That Potentially Induced the Two 2019 Weiyuan Moderate Earthquakes in the Sichuan Basin, China

Abstract Induced earthquakes are becoming a significant issue. Several destructive induced earthquakes (Ms ≥5.0) have occurred in shale gas fields located at the southwestern Sichuan basin, China, in the recent years. Specifically, two moderate earthquakes with magnitudes of Ms 5.4 (occurred on 8 September 2019) and 5.2 (occurred on 18 December 2019) exceeded the largest earthquake ever recorded in the Weiyuan. It remains unclear which seismogenic faults were responsible for the two moderate events due to insufficient knowledge of the subsurface structure and contradictory hypocenter depths obtained from different seismological methods. In this study, mainshock locations, focal mechanisms, and precise relocations of microseismicity were used to map the 3D geometry of the seismogenic fault. The result shows that the two moderate earthquakes occurred on the same fault. High-resolution seismic reflection profiles indicate several preexisting faults at various depths and a potential seismogenic fault. No large-scale faults are identified in the sedimentary cover above the Cambrian at the shallow centroid depth of these earthquakes. However, the seismic reflectors show phase discontinuous feature, indicating the existence of preexisting faults in the basement. A preexisting fault in the basement is consistent with a seismogenic fault that may have induced the two moderate earthquakes. Our study suggests that poroelastic stress propagation is likely responsible for the basement fault reactivation. The rupture on a stressed basement fault was triggered and produced two moderate earthquakes in a short period during hydraulic fracturing. The previous strategy of avoiding direct injection of fluids into preexisting faults to reduce seismic risk in operation region is not enough to avoid the possibility of the coupled poroelastic stress triggering deep fault rupture. We need to reevaluate the potential seismic risk of shale gas development in Weiyuan, the southern Sichuan basin shale gas field considering the preexisting faults in sedimentary and in basement and the effect of the fully coupled poroelastic stress field.

Ignition of the southern Atlantic seafloor spreading machine without hot-mantle booster

The source of massive magma production at volcanic rifted margins remains strongly disputed since the first observations of thick lava piles in the 1980s. However, volumes of extruded and intruded melt products within rifted continental crust are still not accurately resolved using geophysical methods. Here we investigate the magma budget alongside the South Atlantic margins, at the onset of seafloor spreading, using high-quality seismic reflection profiles to accurately estimate the oceanic crustal thickness. We show that, along ~ 75% of the length of the Early-Cretaceous initial spreading centre, the crustal thickness is similar to regular oceanic thickness with an age > 100 Ma away from hot spots. Thus, most of the southernmost Atlantic Ocean opened without anomalously hot mantle, high magma supply being restricted to the Walvis Ridge area. We suggest that alternative explanations other than a hotter mantle should be favoured to explain the thick magmatic layer of seaward dipping reflectors landward of the initial mid-oceanic ridge.

Effect of Dam Emplacement and Water Level Changes on Sublacustrine Geomorphology and Recent Sedimentation in Jackson Lake, Grand Teton National Park (Wyoming, United States)

Dam installation on a deep hydrologically open lake provides the experimental framework necessary to study the influence of outlet engineering and changing base levels on limnogeological processes. Here, high-resolution seismic reflection profiles, sediment cores, and historical water level elevation datasets were employed to assess the recent depositional history of Jackson Lake, a dammed glacial lake located adjacent to the Teton fault in western Wyoming (USA). Prograding clinoforms imaged in the shallow stratigraphy indicate a recent lake-wide episode of delta abandonment. Submerged ∼11–12 m below the lake surface, these Gilbert-type paleo-deltas represent extensive submerged coarse-grained deposits along the axial and lateral margins of Jackson Lake that resulted from shoreline transgression following dam construction in the early 20th century. Other paleo-lake margin environments, including delta plain, shoreline, and glacial (drumlins, moraines) landforms were likewise inundated following dam installation, and now form prominent features on the lake floor. In deepwater, a detailed chronology was established using137Cs,210Pb, and reservoir-corrected14C for a sediment core that spans ∼1654–2019 Common Era (CE). Dam emplacement (1908–1916 CE) correlates with a nearly five-fold acceleration in accumulation rates and a depositional shift towards carbonaceous sediments. Interbedded organic-rich black diatomaceous oozes and tan silts track changes in reservoir water level elevation, which oscillated in response to regional climate and downstream water needs between 1908 and 2019 CE. Chemostratigraphic patterns of carbon, phosphorus, and sulfur are consistent with a change in nutrient status and productivity, controlled initially by transgression-driven flooding of supralittoral soils and vegetation, and subsequently with water level changes. A thin gravity flow deposit punctuates the deepwater strata and provides a benchmark for turbidite characterization driven by hydroclimate change. Because the Teton fault is a major seismic hazard, end-member characterization of turbidites is a critical first step for accurate discrimination of mass transport deposits controlled by earthquakes in more ancient Jackson Lake strata. Results from this study illustrate the influence of dam installation on sublacustrine geomorphology and sedimentation, which has implications for lake management and ecosystem services. Further, this study demonstrates that Jackson Lake contains an expanded, untapped sedimentary archive recording environmental changes in the American West.

Seismic Multiple Attenuation in the Continent–Ocean Transition Zone of the Northern South China Sea

In this study, we process four new multichannel reflection seismic profiles acquired in 2015 and 2016 in the continent–ocean transition zone (COT) of the northern South China Sea (SCS). We apply a multi-domain, progressive, and seabed-controlled denoising technique and obtain a good denoising effect. Combining velocity analysis in the multi-round time domain and forward modeling, we analyze the types and characteristics of multiples in the study area and formulate an effective demultiple technique to attenuate strong seabed multiples, diffracted multiples from rough seafloor, and other multiples from deep reflectors. The processing results show that the sea surface-related multiple elimination technique predicts the sea surface-related multiples accurately by data convolution, and has a good effect in attenuating seabed multiples. Diffracted multiple attenuation method extracts high-frequency and high-energy diffracted multiples, and suppresses multiples by the energy ratios of multiples to primary events. To attenuate deep multiples, we select predictive deconvolution to attenuate periodic deep multiples after many trials and detailed analysis. The combination of these different techniques in sequence proves to be quite effective in attenuating different seismic multiples in the COT. The imaged crustal structures near the COT often show strong magmatism and/or basement uplifting. The faulted and thinned continental crust adjacent to the COT corresponds to the lowest free-air gravity anomalies. Gravity anomalies often increase from the COT to the oceanic crust. An exception is to the northeast of the SCS, where the relatively wide COT shows very high gravity anomalies, likely induced by mantle upwelling and serpentinization.

Structural Observations of the Northern North Sea: Insights into Rift Failure Dynamics

Lithospheric extension leads to rift formation and may continue to the point of breakup, with oceanic ridge initiation and the formation of two conjugate rifted margins. In some settings, extension can cease, and the rift may be abandoned. These so-called failed rifts archive snapshots of early phases of deformation, with geometries that may help better constrain the parameters that can prevent a rift from reaching breakup, such as lithospheric rheology, thermal state, rift opening direction and rate, inheritance. This contribution summarizes a study of the Norwegian Continental Shelf which includes the North Sea Rift and the Møre and Vøring rifted margins. We proceeded to the interpretation of a new dataset of deep penetrating seismic reflection profiles and worked at the regional scale, deliberately ignoring local particularities, to focus on the large-scale structural picture. The aim is to list architectural similarities and differences between the failed rift and the successful rifted margins. Our mapping shows that the North Sea structural geometries and basement seismic facies are very similar to the observations listed for the adjacent Møre and Vøring rifted margins. Various types of tectonic structures are observed, from thick anastomosing shear zones possibly evolving into core-complex geometries, to composite large-scale detachment faults and standard high-angle normal faults. These are categorized into five classes and interpreted as exemplifying the rift tectonic evolution through distinct generations of deformation structures that can activate, de-activate and re-activate. Based on these observations, rift failure dynamics are discussed, and it is proposed that the North Sea rift abandonment may not be related to pre-rift local conditions but rather to the ability to initiate specific tectonic structures such distal breakaway complexes.

Seismic mapping of shallow bedrock shelves in the hanging wall of the Wasatch fault

The Wasatch fault (WF) has been the subject of intensive study. Adjacent to a large and growing urban corridor, it poses a distinct seismic hazard for ∼2.5 million residents who live on its hanging wall, and has numerous Quaternary scarps and produced a M5.7 quake in March of 2020. Thus, the shallow architecture of the fault is important for understanding its earthquake hazards.Prior work has revealed shallow bedrock shelves in the hanging wall near the fault. To detect and image these shelves, we have employed the HVSR method (horizontal-to-vertical spectral ratio) at three locations along and across the WF. This method is powerful in that data can be collected rapidly in an urban setting. However, this method requires knowledge of the Vs of sediment overlying bedrock in order to estimate bedrock depth. We employed the MASW (multichannel-analysis of surface waves) method to obtain the characteristic Vs of sediment overlying bedrock.At Corner Canyon in Draper, Utah, Lake Bonneville sands and gravels overlie intrusive rocks of the Little Cottonwood Stock. Fault offsets inferred from HVSR correlate to mapped scarps. At Traverse Ridge, an HVSR profile co-located to a prior seismic reflection profile also detected shallow bedrock beneath alluvial fan sediment, including a graben system. However, at this site the geology is more complex. Fan sediment is underlain by altered volcanic rocks with subjacent quartzite. The HVSR method detected and characterized these boundaries.A majority of data were collected across the WF in the vicinity of Rock Canyon, Utah in order to create a 3D surface of the bedrock shelf. This area is heavily developed, but with numerous mapped scarps. A 3D model of the bedrock shelf indicates that it is broad, >1 km from the main trace of the WF. This width was not previously known. The HVSR results conform to mapped fault offsets, but also reveal a large, buried (and previously unknown) graben.One main finding of this study is that HVSR is a useful tool for mapping the shallow architecture of bedrock shelves in the hanging wall of normal faults, as long as a reasonable estimate of the Vs of sediment overlying bedrock can be made. Mapping can be accomplished rapidly in uneven topography or in urban settings as the instrumental footprint is very small. A second main finding is that large normal faults may commonly have concealed bedrock shelves. These shelves may affect engineering inputs like Vs30. However, they may also have other unanticipated effects on the nature of ground shaking, perhaps due to the trapping of energy or reverberation between the ground surface, bedrock shelf, and bedrock in the foot wall.

Quaternary Lowstand Prograding Wedges of the Salento Continental Shelf (Southern Adriatic Sea, Italy): Architectural Stacking Patterns and the Control of Glacio-Eustatic Sea Level Fluctuations and Foreland Tectonic Uplift

The performance of both the tectonic uplift and of the 4th-order glacial eustatic sea level fluctuations in controlling the stratigraphic architecture of Quaternary lowstand prograding wedges of the Salento continental shelf (Southern Adriatic sea, Italy) during a time interval spanning from the Middle Pleistocene to the Holocene has been pointed out through the interpretation of high-resolution seismic reflection profiles and their correlation to the curves of the isotopic stratigraphy. Three main transgressive surfaces of erosion (RS1, RS2 and RS3) punctuate the stratigraphic architecture of the Salento continental shelf, separating Quaternary lowstand prograding wedges between them. All along the Middle Pleistocene, increasing the tectonic uplift of the Puglia offshore, combining with 4th-order glacio-eustatic variations, have dealt with the pattern of a broad forced regression prograding wedge, favoring a platform progradation of approximately 15 km. The architectural stacking patterns of the overlying Late Pleistocene and Holocene prograding wedges are controlled by 4th-order glacio-eustatic sea level changes, allowing for the formation of incomplete depositional sequences. In this period, the eustatic signature overcomes the tectonic mark, implying a decline in the uplift of the Apulian foreland in the course of the final 250 ky.

Fault characteristics and their control on oil and gas accumulation in the southwestern Ordos Basin

3D seismic data recently acquired from the Ordos Basin shows three sets of regularly distributed fault systems, which overrides previous understanding that no faults were developed in this basin. Seismic interpretation suggests that the faults in the southwestern Ordos Basin have three basic characteristics, namely extreme micro-scale, distinct vertical stratification, and regularity of planar distribution. These NS-, NW-, and NE-trending fault systems developed in the Meso-Neoproterozoic – Lower Ordovician strata. Of these, the NS-trending fault system mainly consists of consequent and antithetic faults which show clear syndepositional deformation. The fault systems in the Carboniferous – Middle-Lower Triassic strata are not clear on seismic reflection profiles. The NW- and NE-trending fault systems are developed in the Upper Triassic – Middle Jurassic strata. Of these, the NW-trending fault system appears as a negative flower structure in sectional view and in an en echelon pattern in plan-view; they show transtensional deformation. A NE-trending fault system that developed in the Lower Cretaceous – Cenozoic strata shows a Y-shaped structural style and tension-shear properties. A comprehensive analysis of the regional stress fields at different geologic times is essential to determine the development, distribution direction, and intensity of the activity of fault systems in the Ordos Basin. Current exploration suggests three aspects in which the faults within the Ordos Basin are crucial to oil and gas accumulation. Firstly, these faults serve as vertical barriers that cause the formation of two sets of relatively independent petroleum systems in the Paleozoic and Mesozoic strata respectively; this is the basis for the ‘upper oil and lower gas’ distribution pattern. Secondly, the vertical communication of these faults is favorable for oil and gas migration, thus contributing to the typical characteristics of multiple oil and gas fields within the basin, i.e. oil and gas reservoirs with multiple superimposed strata. Finally, these faults and their associated fractures improve the permeability of Mesozoic tight reservoirs, providing favorable conditions for oil enrichment in areas around the fault systems.

Stretching–buoyancy interplay in the magma-poor rifting process

Abstract The Cauvery Basin in East India represents a failed rift zone in the west and transform-related termination in the east. The deformation associated with a westward-propagating rift zone involves stretching and necking-related deformation from west to east. The rift axis and the flanks exhibit maximum and minimum deformation. In this study, we document the increasing role of buoyancy-driven processes and the development of the rift asymmetry during the advanced stages of rifting in a magma-poor setting. We use a series of reflection seismic profiles intersecting the failed rift zone maturing eastward. The onset of buoyancy-controlled extension correlates with the localized extension. It creates a relatively symmetrical axial dome, and exhibits rift flank rotations and central up-warping. This permanent uplift is associated with lower crustal ductile flow. Notably, the deep-seated syn-rift buoyancy forces progressively operate eastward. We deduce the associated transient dome uplift and its subsequent dissipation using a seismic flattening technique. The axial dome formation is associated with an upwelling asthenosphere and lower lithospheric mantle. This correlates with localized contraction within flat-lying fault blocks at its flanks, concurrently forming the typical hanging-wall and footwall geometry. The multiple shallow- to deep-seated mechanisms promote strain acceleration in the uplifted regions along the rift zone.

Joint passive seismic imaging based on surface wave inversion and reflection wavefield retrieval: A case study in the sedimentary basin areas adjacent to Well Songke-2

Owing to their cost-effectiveness, environmental friendliness, and high-efficiency, passive seismic methods are widely used in geophysical exploration. However, field passive seismic data suffer from low signal-to-noise ratio, as well as the fact that different types of seismic waves are naturally mixed together, which can affect the accuracy of subsurface imaging results and the subsequent geological interpretation. In this paper, we demonstrate that these problems can be addressed and present a case study on passive seismic detection in sedimentary basin areas adjacent to Well Songke-2 in Songliao Basin. To obtain accurate and reliable imaging results of the sedimentary strata, a detailed practical scheme is proposed, where fundamental and higher mode surface wave dispersion curves are inverted for obtaining the near-surface S-wave velocity profile, and the body wave component of ambient noise is utilized to retrieve the reflection wavefield information. The obtained profiles from surface wave inversion and reflection wavefield retrieval illustrate similar underground structures. The marker boundaries T2 (1.5 s) and T4 (2.1 s) are well demonstrated, and a low velocity stratum (0.4 s) is detected at a shallow depth of around 400–600 m. Further, the results are highly consistent with the data obtained from borehole logging of Well Songke-2 and the deep reflection seismic profile adjacent to this area, which indicates that the surface wave and body wave in passive seismic data can be utilized together to contribute to a detailed and accurate subsurface imaging and interpretation. Overall, this study investigated and validated the reliability and accuracy of the combination use of passive seismic methods for geological structure exploration, which can further boost their applications for geological interpretation in sedimentary basin areas.

Seismic imaging of the gold deposit and geological structures through reprocessing of legacy seismic profiles near Kloof–Driefontein Complex East Mine, South Africa

AbstractTwo legacy reflection seismic profiles were acquired in 1988, north of the Kloof–Driefontein Complex East Mine in the West Rand goldfield (South Africa), for the purpose of gold exploration and mine planning. These legacy 2D seismic data have been reprocessed using the latest processing tools to improve imaging. Special interest is given to the Black Reef Formation, which hosts a known gold orebody. The original legacy data are of poor quality, especially in areas that are dominated by dolomitic outcrops. To improve the quality of the data, special attention was given to the refraction static correction to enhance the continuity of the reflections below dolomitic rocks. Refraction seismic tomograms from both profiles exhibit three‐layer P‐wave velocity models: (1) topsoil (1000–2000 m/s), (2) a weathered layer ranging from ca. 100 to 300 m in thickness (2000–5000 m/s) and (3) bedrock (> 5000 m/s). Seismic profile OK‐212 shows poor imaging of the Black Reef Formation because of the scattering of seismic energy in the near‐surface due to dolomites from the Transvaal Supergroup, while seismic profile OK‐213 exhibits south‐dipping reflections that are associated with the Black Reef Formation. To improve the structural imaging resolution, we tried pre‐stack time migration, pre‐stack depth migration and post‐stack time migration using the Kirchhoff algorithm. PreSDM most improved the imaging of deeper reflections due to its ability to honour complex lateral variations in the velocity field. Both pre‐stack time migration and post‐stack time migration enhanced the continuity of the near‐surface reflections below the dolomitic rocks.

The Relationship Between Inverted Normal Faults and Pure Thrusting During the Tectonic Inversion of the Domeyko Cordillera, Northern Chile: Structural and Seismic Interpretation and Analog Modeling Experiments

AbstractThe orogenic growth of the Domeyko Cordillera was induced by a positive tectonic inversion. In this work, we have validated this interpretation from new field data, which were combined with 2‐D reflection seismic profile interpretations obtained along the Central Andes forearc of northern Chile. To compare with this information, we performed a new series of Analog Models dealing with positive tectonic inversion. On the basis of this, we propose an integrated kinematic model that describes the relationships between extensional structures, inversion structures, and pure thrust faulting. The proposed model is developed with an initial syn‐rift phase related to the filling of half‐graben basins, followed by a positive tectonic inversion phase. Our models show two main structural styles: partially inverted normal faults and newly formed pure thrust faulting. The partial inversion of previous normal faults represents the initial stage of exhumation of the syn‐rift deposits. The pure thrusting consists of east‐verging faults, which decapitate early or partially inverted normal faults. The first type of structures are compared with west‐verging inverted, or partially inverted, normal faults, inversion anticlines, and buttressing structures, exposed on the western flank of the Domeyko Cordillera. The second type of structures are compared with the east‐verging thrust faults exposed on the eastern flank of the Domeyko Cordillera. Finally, we consider that the architecture of the Domeyko Fault System is associated with inversion structures and pure thrust faulting; being these faults first‐order structures that led to the orogenic growth of the Domeyko Cordillera from the Upper Cretaceous.

Gas Hydrate Resource Potential Of Deepwater Sabah, Malaysia: A Preliminary Assessment

Offshore NW Sabah is one of the localities identified in the United States Geological Survey (USGS) global hydrates database but not much work has been done on this potential source of energy for Malaysia and the surrounding region. The presence of gas hydrates in this area is mainly inferred from bottom-simulating reflectors (BSR) identified in seismic reflection profiles across the margin. BSRs have been mapped across almost the entire length of the deepwater fold-thrust belt in the Sabah Trough where they are commonly observed within the crests of fold-thrust anticlines. Based on an average geothermal gradient of 62.5 °C/km, the thickness of the gas hydrate stability zone is predicted to vary with water depth from zero at 640 m water depth to 300 m at 2900 m water depth. The total in-place methane resource from the Sabah gas hydrates is estimated to range from 72 to 852 trillion cu. ft. (TCF) (2.06 – 24.1 x 1012 m3) with a mean of 364 TCF (10.3 x 1012 m3 ) and a most likely (P50) value of 252 TCF (7.1 x 1012 m3). These preliminary estimates may seem large but they are comparable with those from other gas hydrate deposits in the region. More work is required to refine them in order to determine how much of the in situ volume is technically and economically recoverable.

Basin-scale estimates of thermal stress and expelled petroleum from Mesozoic-Cenozoic potential source rocks, southern Gulf of Mexico

The Campeche and Yucatan salt basins remain two of the least explored areas of the Gulf of Mexico basin. This study uses a grid of 23,600 line-km pre-stack depth migrated (PSDM) 2D seismic reflection profiles, shipborne gravity data, and open-source geologic information to model the thermal stress of four potential source intervals (Oxfordian, Tithonian-centered, Cenomanian-Turonian, lower Miocene). We performed map-based, and 1D thermal modeling along two margin-perpendicular transects, each consisting of five pseudo-wells tied to the regional grid of seismic reflection data. Our modeling takes into account thermal stress variations related to the depth of base lithosphere, crustal type and thickness, paleo-water depth, Jurassic salt thickness, and the transient heat flow effects related to recent clastic sedimentation. We predict that deeply-buried, salt-related minibasins along the outer marginal trough are mature for petroleum expulsion with deeply-buried Mesozoic source rocks within the oil window from late Paleogene to early Neogene time. The ‘lag time’ required for vertical oil migration explains why oil maturation occurred during the late Paleogene to early Neogene but active oil seeps are observed today at the sea surface. We predict that oil is present in subsurface traps in the deepest part of the outer marginal trough and we calculate that the Oxfordian source interval has expelled a cumulative 20 million bbl of oil equivalent [BOE]/km2 and that the Tithonian-centered source interval has expelled 67 million bbl of oil equivalent [BOE]/km2.

Revitalizing vintage seismic reflection profiles by converting into SEG-Y format: case studies from publicly available data on the Italian territory

In recent decades, geological modeling has significantly evolved, relying on the growing potential of hardware and software to manage and integrate vast datasets of 2D-3D geophysical underground data. Therefore, digitization and integration with other forms of data can often improve understanding of geological systems, even when using so-called vintage or historical data. Seismic reflection data have been extensively acquired mainly for hydrocarbon exploration since the 60s generating large volumes of data. Typically, these data have been for private commercial use and are relatively unavailable for research. However, with time, large volumes of vintage seismic reflection data in many countries worldwide are now becoming publicly available through time-based de-classification schemes. Such data have a great potential for modern-day geo-research, unleashing opportunities to improve geological understanding through re-interpretation with modern methods. However, a downside of these vintage data is that they are often only available in analog (paper, raster) format. The vectorization of these data then constitutes an essential step for unlocking their research potential. In 2018 INGV established the SISMOLAB-3D infrastructure, which is mainly devoted to analyzing digital subsurface data, such as seismic reflection profiles and well-logs, to build 2D-3D geological models, principally for seismotectonics, seismic hazard assessment, and geo-resources applications. In this contribution, we discuss the robustness of the WIGGLE2SEGY code, firstly published by Sopher in 2018, focusing on examples from different tectonic and geodynamic contexts within Italian territory. We applied the SEG-Y conversion method to onshore and offshore raster seismic profiles related to ceased exploration permits, comparing the results with other published archives of SEG-Y data obtained from the conversion of vintage data. Such an approach results in digital SEG-Y files with unprecedented quality and detail. The system- atic application of this method will allow the construction of a comprehensive dataset of digital SEG-Y seismic profiles across Italy, thereby expanding and sharing the INGV SISMOLAB-3D port- folio with the scientific community to foster innovative and advanced scientific analysis.

New insights into the Rhône–Simplon fault system (Swiss Alps) from a consistent earthquake catalogue covering 35 yr

SUMMARYSeismotectonic interpretations in regions characterized by low to moderate seismicity require consistent earthquake catalogues covering periods of several decades. Inevitable changes in network configuration and analysing procedures, however, introduce significant bias to the hypocentre parameters and uncertainty estimates reported in such catalogues. To overcome these limitations, we developed a procedure using coupled hypocentre-velocity inversions to compute consistent hypocentre locations covering time periods of several decades while accounting for changes in network geometry. We apply these procedures to 35 yr of instrumentally recorded seismicity along the Rhône–Simplon fault system in southwest Switzerland, which is at the transition between the Central and Western Alps. The entire catalogue is relocated using a probabilistic location algorithm in combination with the derived minimum 1-D velocity models. A combination of location parameters is used to define consistent location-quality classes allowing for reliable interpretation of epicentres and focal depths. The relocated catalogue is interpreted together with a recent 3-D P-wave tomographic model and available 2-D reflection seismic profiles. The relocated hypocentres indicate that the major band of seismicity north of the Rhône valley is associated with a 30–40 km long, steeply north-dipping shear zone, which roots in the crystalline basement of the Aar Massif and extends to the shallowest levels of the sedimentary cover of the Helvetic nappes in the Rawil Depression. Seismicity towards the southwest indicates the existence of a similar shear zone within the Aiguille Rouge Massif. This zone possibly extends to the northeast and joins the Rawil fault zone. To the south of the Rhône valley, seismicity is scattered within the Penninic nappes, but limited to the hanging wall of the Pennine Basal Thrust (PBT). The Penninic nappes are characterized by a relatively higher VP of about 5 per cent compared to the Aar Massif, indicating differences in composition or metamorphic grade across the PBT.

Deformation structural style of the rioni foreland fold-and-thrust belt, western greater caucasus: Insight from the balanced cross-section

The Rioni foreland fold-and-thrust belt is part of the Greater Caucasus pro-wedge and is one of the most important examples of the collision-driven far-field deformation of the Arabia-Eurasia convergence zone. Here we show the deformation structural style of the Rioni foreland fold-and-thrust belt based on seismic reflection profiles and regional balanced cross-section. The main style of deformation within the Rioni foreland fold-and-thrust belt is represented by a set of fault-propagation folds, duplexes, and triangle zone. The regional balanced cross-section shows that fault-propagation folds above the upper detachment level can develop by piggyback and break-back thrust sequences. Formation of fault-bend fold duplex structures above the lower detachment is related to piggyback thrust sequences. A balanced section restoration of compressional structures across the Rioni foreland fold-and-thrust belt provides a minimum estimate of shortening of −40%, equivalent −42.78 km. The synclines within the Rioni foreland fold-and-thrust belt are filled by the Middle Miocene-Pleistocene shallow marine and continental syn-tectonic sediments, forming a series of typical thrust-top basins. Fault-propagation folds and duplex structures formed the main structure of the thrust-top basin. The evolution of the thrust-top basins was mainly controlled by the kinematics of thrust sequences. Using end-member modes of thrust sequences, the thrust-top basins are divided into: 1) Type I-piggyback basin, 2) Type II-break-back basin, and 3) Type III—formation of thrust-top basin characterized by bi-vergent geometry and related to combined, piggyback and piggyback back thrust sequences.

Seismic Reflection and Potential Field Constraints on Imbrication and Exhumation of the Paleoarchean Narryer Terrane, Yilgarn Craton

AbstractThe Narryer Terrane, which is located on the northwest margin of the Yilgarn Craton, is one of the oldest preserved blocks of continental crust on Earth with rocks as old as 3.73 Ga and detrital zircons up to 4.4 Ga. In 2010‐11, three deep seismic reflection profiles were acquired over the terrane, and interpreted to show that during the Neoarchean the Narryer Terrane was thrust over the northwest edge of the Youanmi Terrane, which represents the core of the Yilgarn Craton, and in turn underthrust from the north by the Glenburgh Terrane during the Paleoproterozoic. We have reprocessed the seismic data to improve the imaging, extract 3D reflector orientations, and determine near‐surface velocity models. We locate the shear zone along which the Narryer Terrane was exhumed and correlate upper crustal faults interpreted in the seismic data with near‐surface faults and shear zones identified in a regional map of the first vertical derivative of the total magnetic field. One >150 km and two ∼50 km long shear zones divide the exposed Narryer Terrane into distinct structural domains that were probably juxtaposed relatively late in the thrusting of the Narryer Terrane over the Youanmi Terrane in the Paleoproterozoic. While most supracrustal rocks occur in the Northern and Southern domains, the Western Domain where magmatic ages are <3.0 Ga, high mass density, consistent with exhumation from the middle‐lower crust, and is made up of four blocks that exhibit differing patterns of seismic reflectivity, indicating they were likely combined prior to their exhumation.

Rift-enhanced foredeep and contractional tectonics interplay in the outer Albanides

The Albanides thrust belt is associated with the ENE-ward subduction of the Adriatic lithosphere facing the Peri-Adriatic Basin, a foredeep filled with a Neogene-Quaternary sedimentary sequence more than 6 km thick. This basin segment is anomalously deep, compared to the adjacent foredeeps, and dominated by Neogene strata deposited at a rate of circa 0.3–0.4 mm/yr. Moreover, the Upper Miocene deposits of the Peri-Adriatic Basin lie on deeply eroded anticlines composed of Meso-Cenozoic carbonate units. This observation is in contrast with the expected constant steady-state fold uplift trend generally observed in orogens related to E-NE directed subductions. These observations suggest that following a Late Oligocene to Early-Middle Miocene contractional tectonic phase associated with subaerial erosion, the northern portion of the frontal zone of the outer Albanides accretionary prism was affected by strong subsidence during the Late Miocene. Evidence from field mapping combined with the integration of exploration wells and seismic reflection profiles indicate that this unexpected subsidence may be related to a Miocene extensional/transtensional tectonic phase. The actual anomalously high heat flow (>80 mW/m2) in the offshore depocenter of the Peri-Adriatic Basin also supports this interpretation.This extensional tectonic phase was unrelated to the subduction process, suggested by the obliquely orientation of the new basin with respect to the strike of the Albanides thrust belt, also partially superimposed on it. This Miocene event and the associated thermal pulse could have played a crucial role for the generation of hydrocarbons in the Outer Albanides. The tectonic interplay between this rifting episode and the usual foredeep flexural evolution may explain the peculiar evolution of the Outer Albanides and the associated anomalous foredeep. This basin can be defined as a rift-enhanced foredeep generated by two spatially co-existing, but independent tectonic processes, i.e., by the flexural loading exerted by the orogenic fold-and-thrust system and the rifting in the foreland itself.