Seismic Profiles Research Articles

Feasibility Study of Anisotropic Full-Waveform Inversion with DAS Data in a Vertical Seismic Profile Configuration at the Newell County Facility, Alberta, Canada

Feasibility Study of Anisotropic Full-Waveform Inversion with DAS Data in a Vertical Seismic Profile Configuration at the Newell County Facility, Alberta, Canada

Characteristics and Environmental Indications of Grain Size and Magnetic Susceptibility of the Late Quaternary Sediments from the Xiyang Tidal Channel, Western South Yellow Sea

To reveal the characteristics and environmental indications for the combination of the grain size and magnetic susceptibility of coastal sediments, we provided a necessary basis for further study on their genetic mechanisms. Based on the data of grain size and magnetic susceptibility of the 36.10 m long core 07SR01 sediments in the Xiyang tidal channel of western South Yellow Sea, we analyzed their variations and correlations and further revealed their environmental indications and corresponding regional sedimentary evolution via the combination of the aforementioned analysis results, the reinterpretation results of the sedimentary sequence and the age of core 07SR01 and shallow seismic profiles, and the findings of climate and glacial–eustatic cycles during Late Quaternary. The three stages of the sedimentary evolution of the Xiyang tidal channel between marine isotope stage (MIS) 7 and MIS 5 were summarized as follows: First is the stage of marginal bank and riverbed developments in the tidal estuary under a relatively high sea level and strong hydrodynamic conditions during MIS 7 (core section: 36.10–26.65 m). The sediments deposited in this stage were mainly affected by the paleo-Changjiang River and characterized by a coarse grain size (mean: 4.02 Φ) and relatively high magnetic susceptibilities (mean: 27.06 × 10−8 m3·kg−1), with small fluctuations which were strongly and positively correlated with the sand component. Second is the stage dominated by fluviolacustrine and littoral environments with the weak hydrodynamics during MIS 6–5, in which the climate changed from cold and dry to warm and humid as the sea level rose after a drop (core section: 26.65–15.77 m). The sediments deposited in this stage were characterized by a fine grain size (mean: 5.27 Φ) and low magnetic susceptibilities with minor variations (mean: 10.83 × 10−8 m3·kg−1) which were weakly and positively correlated with the coarse silt component. Third is the stage of delta front in the tidal estuary with a relatively high sea level and strong hydrodynamics during MIS 5 (core section: 15.77–0 m). The sediments deposited in this stage were strongly influenced by the paleo-Yellow River and characterized by a relatively coarse grain size (mean: 4.86 Φ), and high magnetic susceptibilities (mean: 37.15 × 10−8 m3·kg−1) with large fluctuations which were weakly and positively correlated with the sand and coarse silt components.

3D pre-stack inversion constrained by spatial reflection features using the Sylvester's equation

Reflection feature-constrained inversion (RCI) is a multichannel strategy that can effectively improve the stability and continuity of seismic inversion in complex geology, especially for pre-stack inversion with higher uncertainty. To address the limitations of conventional RCI to 2D profiles and high computational costs, a 3D pre-stack seismic inversion constrained by spatial reflection features was developed. First, a new approach to characterize seismic reflection features by decomposing seismic events along the vertical and lateral directions was proposed, which significantly reduces the size of the reflection feature operators. Second, we constructed reflection feature regularization terms and designed a fast reflection feature-constrained inversion (FRCI) for 2D seismic profiles. Finally, the proposed FRCI was extended to 3D by considering the spatial reflection features in two mutually perpendicular directions. Fast spatial reflection feature-constrained inversion (FSRCI) was proposed by constructing spatial reflection feature operators in a 3D coordinate system. The key to this method is that the parameter estimation is transformed into solving the 3D Sylvester equation such that the model parameters can be estimated directly from 3D seismic data. The inversion results of the overthrust model and field data showed that the proposed method can improve efficiency while ensuring spatial continuity. In summary, this study developed a fast pre-stack seismic inversion constrained by spatial reflection features based on the characterization of stratum spatial features, which is effective in complex geology, such as high-dipping and faults.

Geophysical appraisal and hydrocarbon potential of the Pre-Cenomanian and Miocene reservoirs in the onshore and offshore Gulf of Suez Basin

The purpose of this study is to geophysically assess the petroleum potential of the Pre-Cenomanian (Nubia sandstones) as well as the Miocene oil reservoirs in the Rabeh field and Edfu-Saqqara field, located in the Gulf of Suez Basin. This will serve as a supplementary source for future exploration in the onshore and offshore Gulf of Suez Basin. This research utilizes the wireline logs of twelve drilled wells, eight of them drilled in Rabeh field, onshore southern Gulf of Suez Basin (RE-8, RE-22, RE-25, RE-2, RE-4, Nageh-1, South Malak-1 & Tawoos-1) and the rest four wells (Edfu A-3, Edfu A-5A, GS323-1 A & GS323-4 A) drilled in Edfu-Saqqara field, offshore central Gulf of Suez Basin. Moreover, twenty seismic profiles covering the Rabeh field were structurally interpreted. This interpretation exposed that the basement rocks are severely intersected by numerous NW–SE normal faults, along with minor E–W faults. The presence of these faults has a great role in forming suitable structural traps for holding hydrocarbon. Based on the qualitative and quantitative appraisal of the well logging data, Nubia, Nukhul and Rudies formations display positive petrophysical signs for being a potential reservoir in the studied fields. These reservoirs display respectable net pay thickness varying between 21 and 550 ft (i.e. 6.5–166.5 m), good net-to-gross ratio (0.01–0.90), excellent effective porosity (0.12–0.20), little shale content (0.03–0.20), minor water saturation (0.05–0.40) and high hydrocarbon saturation (0.60–0.95). The created lateral distribution maps for the considered petrophysical parameters in the Rabeh Field suggest that the drilling efforts should be essentially directed in the southeastern side of the Rabeh field to access the high-quality Nubia sandstone reservoirs.

Identification of the subaerial unconformity, genesis, and distribution in Lower Triassic Baikouquan Formation, Mahu Sag, Junggar Basin, Western China

The genesis of unconformities involves multiple influences on basin formation and evolution, which affects the favorable reservoir and hydrocarbon distribution. Within the Early Triassic Baikouquan Formation in the Mahu Sag of the Junggar Basin, we identified subaerial unconformities (SU), namely SU1 and SU2. SU1 is characterized by regional, irregular valleys, whereas SU2 displays extensive lateral extent with comparatively lower relief. These distinctions stem from detailed analyses involving cores, well data, seismic profiles, and spatial distributions, enriching our understanding of SUs in the Junggar Basin. Key findings from our study include: (1) SU occurrences within the Baikouquan Formation span the falling-stage systems tract (FSST) and expanding system tract (EST), corresponding to relative lake level changes. SU1 emerges during descending lake levels, whereas SU2 develops during rising levels. (2) The extensive uplift of the Junggar Basin's perimeter, driven by the late Hercynian movement, heightened topographic gradient shapes a steeper lake shoreline profile, fostering SU development. Arid paleoclimatic conditions during the Permian-Triassic interval accelerate SU formation in the FSST. (3) SU typically comprises regional compound scour surfaces (RCS) and river intermittent exposure surfaces (IES). Continuous winnowing at RCS led to relatively high primary porosities, IES can develop better secondary porosity with superposed freshwater leaching. The investigation into the subaerial unconformity in the study area holds broader implications for comprehending depositional processes, reservoir distribution, and petroleum prospects, both locally and within a global lake basin context.

Toward Tectonic-Type and Global 1D Seismic Models of the Upper Mantle Constrained by Broadband Surface Waves

ABSTRACT The unprecedentedly dense current sampling of the upper mantle with seismic data offers an opportunity for determining representative seismic velocity models for the Earth’s main tectonic environments. Here, we use over 1.17 million Rayleigh- and 300,000 Love-wave, fundamental-mode, phase-velocity curves measured with multimode waveform inversion of data available since the 1990s, and compute phase-velocity maps in a 17–310 s period range. We then compute phase-velocity curves averaged over the globe and eight tectonic environments, and invert them for 1D seismic velocity profiles of the upper mantle. The averaged curves are smooth and fit by VS models with very small misfits, under 0.1%, at most periods. For phase-velocity curves extending up to 310 s, Rayleigh waves resolve VSV structure down to the shallow lower mantle. Love-wave sampling is shallower, and VSH and, thus, radial anisotropy profiles are resolved down to 375–400 km depth. The uncertainty of the VS models is dominated by the trade-offs of VS at neighboring depths. Using the model-space-projection approach, we quantify the uncertainty of VS in layers of different thickness and at different depths, and show how it decreases with the increasing thickness of the layers. Example 1D VS models that fit the data display the expected increase of the lithospheric seismic velocity with the age of the oceanic lithosphere and with the average age of the continental tectonic type. Radial anisotropy in the global and most tectonic-type models show a flip of the sign from positive (VSH>VSV) to negative at 200–300 km depth. Negative anisotropy is also observed in the shallow mantle lithosphere beneath oceans down to 45–55 km depth. We also compute a global model with the minimal structural complexity, which fits the data worse than the best-fitting one but does not include a sublithospheric low-velocity zone, providing a simple reference for seismic studies.

3D DAS VSP for Coal Seam Exploration: A Case Study from Queensland, Australia.

Seismic methods are extensively used in coal mining for expanding resource discoveries and definition as well as for mine monitoring. However, the use of borehole seismic methods is relatively uncommon due to the high cost of borehole seismic acquisition using conventional downhole tools. The introduction of distributed acoustic sensing (DAS), which uses optical fibres to record seismic data, has dramatically increased the cost-effectiveness of borehole seismic methods. Fibre-optic cables are inexpensive and, once deployed in a borehole, can be abandoned or used later for further monitoring of the subsurface. The case study presented here concerns the use of DAS to record a 3D VSP (vertical seismic profiling) for coal seam exploration in Queensland, Australia. This study trialled effective strategies for deploying cables into boreholes and demonstrated how this technology could be incorporated into the standard coal exploration process. The final processing results produced a high-resolution 3D seismic cube where the coal seams below the basalt cover are clearly identifiable around the boreholes. Permanent installation of the fibre-optic cables into a set of boreholes provides immediate benefits of 3D seismic imaging and can create additional value in utilising these sensors for further discrete or continuous subsurface measurements, including stability monitoring of underground workings and detection of methane accumulations.

DAS-VSP coupled noise suppression based on U-Net network

Abstract The emerging distributed fiber-optic acoustic sensing (DAS) technology has broad prospects for application in vertical seismic profiles (VSP). However, the acquired DAS-VSP data often suffers from coupled noise that seriously affects data quality. Traditional methods for suppressing coupled noise are usually time-consuming and not suitable for the large-scale denoising of DAS-VSP data. To address this, a coupled noise suppression method based on the U-Net network is proposed, and a self-attention (SA) block is introduced to enhance the denoising ability of the network. Transfer learning is employed to achieve coupled noise suppression from synthetic data to field data. Denoising results demonstrate that the network can effectively suppress coupled noise in DAS-VSP data while preserving signal energy to a certain extent, exhibiting strong generalization capability. Upon completion of network training, denoising results can be obtained within seconds, making it more convenient and efficient compared to traditional methods.

Crustal structure of the central and southern Kyushu-Palau Ridge: Implications for intra-oceanic arc evolution

As an intra-oceanic arc, the Kyushu–Palau Ridge (KPR) is an exceptional place for studying intra-oceanic arc evolution and related magmatism using its interior velocity structure. Two wide-angle seismic profiles along the KPR provide an opportunity to unveil the crustal structure of its central and southern parts. Strong along-ridge variations are found either in P-wave velocity or crustal thickness of the central and southern KPR. The crustal thickness is between 6 and 12 km, with the velocity increasing from 4.0 km/s to 7.0 km/s from top to bottom. The upper crust has a large velocity gradient of ∼1 s−1 and a thickness between 2 and 4 km, while the lower crust has a lower velocity gradient of <0.2 s−1 and is characterized by inhomogeneous velocity anomalies and a substantial lateral variation in thickness. By comparing with the mature arc in the Izu-Bonin-Mariana arc in the east, we suggest the central and southern KPR is a thickened oceanic crust rather than a mature arc crust. Partly thick crust, velocity anomalies in the lower crust and upper mantle imply the crust is in a transition stage from oceanic crust to mature arc one. Compared with the quantitatively calculated seamount volumes, the lower crustal thickness is generally correlated well with the distribution of the seamount volumes along the central and southern KPR. These observations imply that the central and southern parts of the KPR are at the juvenile stage of arc evolution, with crustal growth primarily attributed to the lower crust thickening.

Echo-characterization of the Sloggett Canyon and the interfluve with Valentín Canyon, Tierra del Fuego Continental Margin, Argentina

Our recent echo-character analysis of the Tierra del Fuego Continental Margin, focusing on Sloggett Canyon and the interfluve with Valentín Canyon, provides insights into contemporary sedimentary processes. Utilizing high-resolution seismic profiles obtained from the R/V Austral in 2017, we categorized sub-bottom echoes into 10 distinct types, shedding light on various processes such as hemipelagic deposition, mass wasting events, glacial influence, and the impact of bottom water masses. By integrating data from the GLORYS12V1 model (1993–2020), CTDs from the World Ocean Database, and sediment samples, we analyze the interaction between bottom currents, seafloor topography, and sediment characteristics. We conclude that the flow of the Subantarctic Water Mass acts as an active transport of coarser sediment from the continental shelf into the canyon, maintaining the Sloggett Canyon's activity, while the flows of the Upper and Lower Circumpolar Water Masses contribute to contourite formation along the eastern canyon flank and the erosion of the lower interfluve, leading to the generation of distinctive longitudinal scours. Additionally, in the continental rise, the interaction of water masses with the seafloor influences the redistribution of the deep-sea fans from the Sloggett and Valentín canyons towards the northeast. This study significantly enhances our understanding of the sedimentary dynamics in this area, establishing the basis of the sedimentary distribution for future interdisciplinary studies and for setting a new baseline in marine protected areas.

Use of resistivity and density borehole image logs to identify and distribute facies in the Pikka unit — A case study from the Nanushuk Formation, North Slope, Alaska

Over the past few decades, the North Slope of Alaska has yielded several major hydrocarbon discoveries in the deltaic topsets of the Brookian Nanushuk Formation. Together, the Nanushuk topsets and genetically related foreset and bottomset beds of the Torok Formation comprise part of a giant clinothem system that prograded across the Colville Foreland Basin during the lower Cretaceous (the Aptian through the Cenomanian). The Nanushuk Topset Play contains stratigraphically trapped hydrocarbons within multiple fairways trending roughly north to south along the basin’s extent. Inside the Pikka Unit, the Nanushuk Formation represents a shelf-edge delta and attached shoreface system, defined primarily from sedimentological interpretations of conventional cores integrated with 3D seismic reflection data and well-log motifs. In this study, we build a structural and stratigraphic framework for the Nanushuk reservoir across the Pikka Unit through integrated observations of the borehole image logs, seismic data, and core. In the described workflow, the boundaries delimiting dip zones interpreted in the wells are correlated to higher order stratigraphic cycles within the Nanushuk clinothem zone. These boundaries are observed in seismic profiles and provide the basis of the structural framework. In addition, core facies interpretations are calibrated to CT-scan data to establish each facies character and vertical distribution within the wells. In the absence of core data, core-calibrated borehole images are instrumental in guiding sedimentological and structural interpretations. This extrapolation is dependent on the image log quality and resolution. The calibrated facies interpretations are applied to wells without core data and guided by seismic amplitude interpretation to extrapolate reservoir presence and distribution across the area.

Application of seismic refraction and MASW methods for investigating the Spillway Fault trace along the western side of the Aswan High Dam, Egypt

AbstractAn earthquake of local magnitude ML = 4.6 occurred on November 7, 2010, 4.5 km northwest of the Aswan High Dam on the Spillway Fault. In the Aswan metropolitan region this earthquake was felt intensely. As no surface rupture was found, the focal mechanism and the distribution of seismic activity was one of the tools used for finding fault dimensions. The composite fault-plane solutions for the observed events on the Spillway Fault showed a left lateral strike-slip faulting with normal-fault component striking NNW-SSE. Also, remote sensing techniques were applied for the detection and identification of the geomorphology and geometry of the Spillway Fault. In this research, sub-surface layers and structures are delineated utilizing near-surface seismic techniques. Furthermore, the area’s supposed path and position of the Spillway Fault are also investigated. Two active seismic techniques, Seismic Refraction and Multi-Channel Analysis of Surface Waves (MASW), are utilized for recording near-surface seismic wave data at 9 sites. The seismic refraction profiles are conducted as a 2D cross-section on the trace of the detected Spillway Fault in the study area to evaluate the maximum depth of penetration of the P-wave for fault investigation. The constructed 2D seismic and structural sections from P-wave results show that the obtained average depth of about 30 m. In addition, the estimated P-wave velocities extend from 600 m/s to over 6500 m/s. Some lateral variation in the seismic wave velocities in all layers may represent fault zones. Moreover, the 1D MASW technique is conducted to estimate the velocities of the shear wave for the upper 30 m (Vs30) to provide the site classes and soil characteristics along both sides of the detected Spillway Fault trace in the study area. The calculated Vs30 values emphasized the idea of the existence of a normal dip-slip fault trace which divides the study area into two different lithological parts. The first part is located on the eastern side and characterized by almost class B (hard rock, according to NEHRP classification), while the other part is located to the west, and shows almost class type C (denoted as dense soil and soft rock soil).

Heterogeneous mantle effects on the behaviour of SmKS waves and outermost core imaging

SUMMARY Seismic traveltime anomalies of waves that traverse the uppermost 100–200 km of the outer core have been interpreted as evidence of reduced seismic velocities (relative to radial reference models) just below the core–mantle boundary (CMB). These studies typically investigate differential traveltimes of SmKS waves, which propagate as P waves through the shallowest outer core and reflect from the underside of the CMB m times. The use of SmKS and S(m-1)KS differential traveltimes for core imaging are often assumed to suppress contributions from earthquake location errors and unknown and unmodelled seismic velocity heterogeneity in the mantle. The goal of this study is to understand the extent to which differential SmKS traveltimes are, in fact, affected by anomalous mantle structure, potentially including both velocity heterogeneity and anisotropy. Velocity variations affect not only a wave's traveltime, but also the path of a wave, which can be observed in deviations of the wave's incoming direction. Since radial velocity variations in the outer core will only minimally affect the wave path, in contrast to other potential effects, measuring the incoming direction of SmKS waves provides an additional diagnostic as to the origin of traveltime anomalies. Here we use arrays of seismometers to measure traveltime and direction anomalies of SmKS waves that sample the uppermost outer core. We form subarrays of EarthScope's regional Transportable Array stations, thus measuring local variations in traveltime and direction. We observe systematic lateral variations in both traveltime and incoming wave direction, which cannot be explained by changes to the radial seismic velocity profile of the outer core. Moreover, we find a correlation between incoming wave direction and traveltime anomaly, suggesting that observed traveltime anomalies may be caused, at least in part, by changes to the wave path and not solely by perturbations in outer core velocity. Modelling of 1-D ray and 3-D wave propagation in global 3-D tomographic models of mantle velocity anomalies match the trend of the observed traveltime anomalies. Overall, we demonstrate that observed SmKS traveltime anomalies may have a significant contribution from 3-D mantle structure, and not solely from outer core structure.

Methane gas flares in the forearc basin of the Andaman-Nicobar subduction zone

Gas hydrates deposits in the Andaman forearc basin are inferred from seismic data and confirmed by drilling/coring during the NGHP-01 expedition. We present new evidence of gas flares in the Andaman forearc basin, detected through water column image (WCI), subbottom profiling, and high-resolution seismic data acquired onboard RV Sindhu Sadhana (SSD-085) in November-December 2021. The gas flares are located over an elongated sedimentary ridge, featuring two prominent mounds (M1 and M2) with distinct geological features. Compressional tectonics induced by the Diligent fault (DLF) formed the ridge with varying slopes and elevations. Gas flares observed above the mound M1 in WCI and sub-bottom profiler data. Seafloor samples reveal carbonate rocks with visible pores, indicating gas/fluid migration or burrows. The regional seismic profile delineates three sedimentary sequences: folded and faulted strata, mass transport deposits, and horizontal-to-sub-horizontal sedimentary layers. Additionally, we observed a bottom simulating reflector (BSR), indicating potential subsurface gas hydrate deposits. Detailed high-resolution seismic data revealed complex fault systems near bathymetry mounds (M1 and M2), which may serve as pathways for vertical fluid/gas migration.

The Late Cenozoic crustal deformation in the northeastern periphery of the Qaidam Basin, northwest China

The northeastern periphery of the Qaidam Basin is a crucial region for comprehending the northeastward growth of the Tibetan Plateau, as it documents Late Cenozoic crustal deformation that elucidates the plateau's growth process. In this study, we reconstruct three stages of crustal deformation in the northeastern periphery of the Qaidam Basin during the Late Cenozoic based on interpretation of growth strata from five seismic profiles, structural mapping of the typical superimposed folds and detailed detrital zircon analysis within the study area. (1) During the Early Miocene to Late Miocene period (23–8.6 Ma), there was NW–SE extensional deformation in the northeast margin of the Qaidam Basin, which exerted control over the deposition of the Youshashan Formation. (2) The NW–SE shortening occurred during the Late Miocene period (8.6–8.1 Ma), subsequent to the deposition of the Youshashan Formation and preceding the deposition of the Shizigou Formation, resulting in a parallel unconformity between these two geological units. (3) The intense shortening of the NE–SW direction occurred during the Late Miocene and Pliocene epochs (8.1–2.5 Ma). The timing of this deformation aligns with the sedimentary age of the Shizigou Formation, suggesting that the initial deformation age may represent the onset of NE extrusion from the Tibetan Plateau towards the northeast margin of the Qaidam Basin. The present study not only delineates a Late Cenozoic structural dome resulting from two‐stage crustal shortening in the northeastern periphery of the Tibetan Plateau, but also provides a crucial evidence for reconstructing the Late Cenozoic intracontinental deformation process in this region.

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.

Exploring ophiolitic deposits offshore Scoglio d’Affrica islet (northern Tyrrhenian Sea): A comprehensive geophysical model of the shallow crustal dynamics

The islet of Scoglio d’Affrica (Tuscany Archipelago, northern Tyrrhenian Sea) is an emerging segment of the Elba-Pianosa Ridge. This ridge is a major tectonic-structural high formed by Eocene-Early Miocene clastic succession which separates the Tuscany shelf from the Corsica basin. The distinctive structural setting of the Scoglio d’Affrica region is a result of crustal fragmentation during the extensional tectonic regime of the northern Tyrrhenian Sea. Along the Elba Pianosa Ridge, a complex interplay between Miocene magmatism, active submarine gas emissions and mud volcanism has been observed. Currently, the Scoglio d’Affrica region experiences active mud volcanism, accompanied by diffuse seafloor gas leakages and sporadic violent mud-water mixed eruptions, as exemplified by the most recent event in 2017.In this study, we present a comprehensive analysis of shipborne magnetic data, swath bathymetry, single and multichannel seismic profiles of Scoglio d’Affrica region focalized to provide a comprehensive geophysical model of shallow crustal dynamics.Forward and inverse magnetic models reveal the presence of a continuous high magnetic susceptibility body running along a NNW-SSE direction, parallel to the main tectonic lineaments. This high magnetic source is interpreted as an ophiolite/high grade serpentinite deposit embedded in Eocene siliciclastic layers resulting from the disrupting of the Corsica Alpine basement. This deposits are related to sedimentary gravity processes originated from peripheral highs and accumulated in intra-wedge basins subsequently deformed during the Oligocene. Our reconstruction provides previously unknown details about geometry and distribution of shallow ophiolite-like deposits thereby improving the comprehension the intricate structural evolution of Elba-Pianosa Ridge featured by a multiphase tectonic deformation and shallow manifestations of fluid/gas circulation.

Crustal architecture and tectonic development of western Queensland, Australia, based on deep seismic reflection profiling: Implications for Proterozoic continental assembly and dispersal

Interpretation of 2014–2015 deep crustal seismic reflection and magnetotelluric data has revised the architecture and geodynamic framework of western Queensland, with implications for the assembly and dispersal of the supercontinents Nuna, Rodinia and Gondwana. In the Mount Isa Province, crustal-scale boundaries of the Leichhardt River Domain, Kalkadoon-Leichhardt Domain and Eastern Subprovince are mapped in the third dimension. The Leichhardt River and Kalkadoon-Leichhardt domains have similar Nd isotopic T2DM model ages to provinces to the west, indicating they were part of ancestral North Australian Craton (NAC); the Eastern Subprovince is a separate terrane, with the Pilgrim Fault a collisional suture. The Gidyea Suture Zone separates the Mount Isa Province from the subsurface Numil Seismic Province. To the east, the west-dipping Yappar Fault separates east-dipping structures in the west from west-dipping structures in the east, forming a classic doubly vergent orogen within the upper plate of a convergent margin. The northwestern boundary of the Bernfels Seismic Province, the Kynuna Fault, truncates the Gidyea Suture Zone, implying this seismic province was welded to the NAC prior to initial deposition of the Etheridge Province. The Cork Fault truncates the north-south grain of the Mount Isa Province; the easternmost part of the NAC has been excised, presumably during breakup of Nuna. The subsurface Brighton Downs Seismic Province, formerly part of the northern Thomson Orogen, is a discrete seismic province, located between the NAC and the Thomson Orogen, and welded to the NAC during the accretion of Rodinia. Basement to the Thomson Orogen is a collage of microplates, accreted to the Brighton Downs Seismic Province during the assembly of Gondwana. By 530 Ma, eastern Australia faced an open Pacific Ocean, with the Thomson Orogen in a backarc setting. Thus, northeastern Australia contains a record of repeated continental accretion and breakup over at least three supercontinent cycles.

Late Pleistocene-Holocene sea level and climate changes in the Gulf of Saros: Evidence from seismostratigraphic record and sediment core data

A detailed record of sea level changes and climate oscillations in the Gulf of Saros during the late Pleistocene to the Holocene is provided by high-resolution seismic reflection profiles and analysis of a sediment core. The seismic stratigraphy reveals the formation of four main depositional units bounded by prominent reflection surfaces, reflecting high sea level variations. The Last Glacial Maximum period in the gulf is associated with the lowstand sea level, forming the deepest marine terrace at −148 m. The increasing sea level due to post-glacial warming was accompanied by the deposition of transgressive units characterized by coastal onlaps together with local channel-fills. This transgressive phase was modulated by three brief still-stands sea levels at 17 cal ka BP, 14.6 cal ka BP and 13.6 cal ka BP, producing the younger marine terraces in the gulf at −135 m, −112 m and −90 m, respectively. A comparison of their depths with the global sea level curve reveals elevation differences with decreasing subsidence rates from the older to younger ages, implying tectonic subsidence along the gulf floor.The close correlation of multi-proxy data from core SAG-22 in the gulf with the northern Aegean and Anatolia data strongly indicates that the timings of the past climate events generally agree with the global and regional climate patterns. The warm climate around the gulf during the late phase of Bølling/Allerød (13.3–12.6 cal ka BP) is represented by high marine biological productivity and improved ventilation in the deeper water due to subsequent transgression. Permafrost formation in the catchment area during the following cold and dry Younger Dryas period (12.6–11.7 cal ka BP) resulted in reduced soil erosion and sediment input to the gulf. Noticeable warming during the Early Holocene between 11.2 cal ka BP and 9.4 cal ka BP is recorded by the multi-proxy data of the core when the enhanced marine biological productivity occurred above the poorly oxygenated deep water column. The climatic deterioration to a cooler and drier phase during the Early to Middle Holocene transition (9.4–7.8 cal ka BP) resulted in intense physical weathering and erosion, causing the highest sedimentation in the gulf. The later period of the Holocene is associated with the formation of two discrete sapropels at 7.8 cal ka BP and 5.4 cal ka BP that were accompanied by warm and wet climates around the gulf.

Characterizing shallow fault zones by integrating profile, borehole and array measurements of seismic data and distributed acoustic sensing

AbstractWithin the framework of the Intercontinental Scientific Drilling Programme (ICDP) ‘Drilling the Eger Rift’ project, five boreholes were drilled in the Vogtland (Germany) and West Bohemia (Czech Republic) regions. Three of them will be used to install high‐frequency three‐dimensional (3D) seismic arrays. The pilot 3D array is located 1.5 km south of Landwüst (Vogtland). The borehole, with a depth of 402 m, was equipped with eight geophones and a fibre optic cable behind the casing used for distributed acoustic sensing (DAS) measurements. The borehole is surrounded by a surface array consisting of 12 seismic stations with an aperture of 400 m. During drilling, a highly fractured zone was detected between 90 m and 165 m depth and interpreted as a possible fault zone. To characterize the fault zone, two vertical seismic profiling (VSP) experiments with drop weight sources at the surface were conducted. The aim of the VSP experiments was to estimate a local 3D seismic velocity tomography including the imaging of the steep fault zone. Our 3D tomography indicates P‐wave velocities between 1500 m/s and 3000 m/s at shallow depths (0–20 m) and higher P‐wave velocities of up to 5000 m/s at greater depths. In addition, the results suggest a NW–SE striking low‐velocity zone (LVZ; characterized by = 1500–3000 m/s), which crosses the borehole at a depth of about 90–165 m. This LVZ is inferred to be a shallow non‐tectonic, steep fault zone with a dip angle of about . The depth and width of the fault zone are supported by logging data as electrical conductivity, core recovery and changes in lithology. In this study, we present an example to test and verify 3D tomography and imaging approaches of shallow non‐tectonic fault zones based on active seismic experiments using simple surface drop weights as sources and borehole chains as well as borehole DAS behind casing as sensors, complemented by seismic stand‐alone surface arrays.