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The Source Physics Experiment (SPE) aims at improving explosion monitoring techniques by investigating source characteristics of chemical explosions in geologic formations. One of the critical tasks in Rock Valley Direct Comparison (RV/DC), SPE phase III, is to prepare for the main experiment by characterizing the subsurface structures at the test site. Based on the seismic data acquired during an accelerated-weight-drop (AWD) seismic survey at Rock Valley, we first pick the P-wave first-arrival travel times and derive a P-wave velocity model using the adjoint-state first-arrival travel-time tomography. We then apply reverse-time migration to the processed seismic data and obtain high-resolution images of the subsurface structures along the two main survey lines. Our migration results show several reflectors corresponding to major geologic formation boundaries. We employ a multitask machine learning model to enhance the reverse-time migration images and identify faults from these images. We find that our automatically picked faults correlate well with the locations of known faults in the region in addition to many geologically undetected faults. Our subsurface characterization results refine our understanding of the geology in this region and provide valuable velocity and structural information for RV/DC geologic model building and fault identification. [ABSTRACT FROM AUTHOR]

The Neogene and Quaternary hinterland basins of the Northern Apennine have been the subject of different tectonic interpretations. Several studies considered these basins as the result of polyphase normal faulting framed in a continuous crustal extensional regime since the middle Miocene. On the contrary, geophysical and geological studies provided evidence of the important role played by out‐of‐sequence thrusts and backthrusts in the evolution of these basins during a prolongated and intense period of shortening. Here we present an integrated analysis of 2D stacked seismic reflection profiles, stratigraphic and geophysical data from deep exploration wells, gravity data, and published geological and biostratigraphic data for the Valdera‐Volterra basin (central Tuscany, Italy). The results support a polyphase and composite evolution of the basin, subdivided into three main phases. During the late Tortonian–Zanclean, the growth of major thrust‐related anticlines controlled the evolution of the sedimentary basin. The growth of a syncline determined the creation of accommodation space for the sediments. This main compressional deformation occurred during the Messinian and ended during the Late Zanclean. NE migration of the depocentre during the Early Zanclean was identified, likely possibly due to a differential activity growth between the bordering anticlines. During the Piacenzian, an extensional phase has been recognised, superposed to the previous compressive phase. During the Latest Piacenzian–Early Pleistocene (?), a final compressional phase took place resulting in the positive inversion of the Piacenzian WSW dipping main border fault. [ABSTRACT FROM AUTHOR]

Introduction: The Holocene mud deposits that extend from the Yangtze River mouth to the Taiwan Strait along the Zhejiang-Fujian coast, East China Sea (ECS), have attracted considerable research attention. However, there is a lack of consensus regarding the redistribution flux of Yangtze River sediment after it enters the sea. There are many bays along the Zhejiang and Fujian coasts, but their role in the source-sink process of Yangtze River sediment is not well-documented owing to limited data. Methods: In this study, data from shallow seismic profiles, core samples, and surface sediment samples were analysed to assess the role of Sanmen Bay, the second largest bay in Zhejiang Province, in the source-sink process of Yangtze River sediments. Results: The results showed that Sanmen Bay is an important sink for Yangtze River sediments. The characteristics of the clay minerals indicate that the finegrained sediments in Sanmen Bay are mainly derived from Yangtze River sediments. The thickness of Holocene deposits in Sanmen Bay ranges from 8.2 to 32.0 m, with an average of 23.4 m and a total sediment volume of 5.06 x 10[sup 4] Mt, accounting for 1% of Yangtze River sediment in this time period. The Bayesian age-depth model based on borehole accelerator mass spectrometry (AMS) [sup 14]C dating shows that a high sedimentation rate occurred in the early and late Holocene but decreased significantly in the mid-Holocene, which is similar to that of the inner shelf of the East China Sea (ECS). Conclusion: The variation in the Holocene sedimentation rate in Sanmen Bay is related to the southward transport process and mechanism of Yangtze River sediments. The results of this study provide a basis for understanding the source-sink process of sediment in large rivers. [ABSTRACT FROM AUTHOR]

Introduction: The Holocene mud deposits that extend from the Yangtze River mouth to the Taiwan Strait along the Zhejiang–Fujian coast, East China Sea (ECS), have attracted considerable research attention. However, there is a lack of consensus regarding the redistribution flux of Yangtze River sediment after it enters the sea. There are many bays along the Zhejiang and Fujian coasts, but their role in the source–sink process of Yangtze River sediment is not well-documented owing to limited data.Methods: In this study, data from shallow seismic profiles, core samples, and surface sediment samples were analysed to assess the role of Sanmen Bay, the second largest bay in Zhejiang Province, in the source–sink process of Yangtze River sediments.Results: The results showed that Sanmen Bay is an important sink for Yangtze River sediments. The characteristics of the clay minerals indicate that the fine-grained sediments in Sanmen Bay are mainly derived from Yangtze River sediments. The thickness of Holocene deposits in Sanmen Bay ranges from 8.2 to 32.0 m, with an average of 23.4 m and a total sediment volume of 5.06 × 104 Mt, accounting for 1% of Yangtze River sediment in this time period. The Bayesian age-depth model based on borehole accelerator mass spectrometry (AMS) 14C dating shows that a high sedimentation rate occurred in the early and late Holocene but decreased significantly in the mid-Holocene, which is similar to that of the inner shelf of the East China Sea (ECS).Conclusion: The variation in the Holocene sedimentation rate in Sanmen Bay is related to the southward transport process and mechanism of Yangtze River sediments. The results of this study provide a basis for understanding the source–sink process of sediment in large rivers.

Ice scours are formed when the keels of floating icebergs or sea ice hummocks penetrate unlithified seabed sediments. Until now, ice scours have been divided into "relict" and "modern" according to the water depth that corresponds with the possible maximum vertical dimensions of the keels of modern floating icebergs. However, this approach does not consider climatic changes at the present sea level, which affect the maximum depth of ice keels. We present an application of 210Pb dating of the largest ice scour in the Baydaratskaya Bay area (Kara Sea), located at depths of about 28–32 m. Two sediment cores were studied; these were taken on 2 November 2021 from the R/V Akademik Nikolay Strakhov directly in the ice scour and on the "background" seabed surface, not processed via ice scouring. According to the results of 210Pb dating, the studied ice scour was formed no later than the end of the Little Ice Age. Based on the extrapolation of possible sedimentation rates prior to 1917 (0.22–0.38 cm/year), the age of the ice scour is estimated to be 1810 ± 30 AD. The mean rate of ice scour filling with 70 cm thick sediments from the moment of its formation is around 0.33 cm/year. [ABSTRACT FROM AUTHOR]

Abstract—For the Middle and North Urals segments and adjacent territories of the East European Platform and West Siberian Plate (within the graticular trapezoid with geographic coordinates 53°–65° N, 48°–72° E), ten deep seismic sounding (DSS) profiles were reprocessed using two-dimensional (2D) seismic tomography method, and gradient sections of crustal velocities were constructed in the form of grid functions. In the same format, density sections were constructed. The coefficients of density–velocity empirical correlation were calculated using the solution algorithm of 2D inverse problem of gravimetry. The method and calculation technology of a three-dimensional (3D) density distribution with tying to 2D data from reference seismic sections are embedded in the procedure of quantitative interpretation of potential fields with construction of 3D geophysical models. A stable solution of the 3D inverse problem of gravimetry is sought on the correctness set of the family of horizontal layers with 2D density distribution. [ABSTRACT FROM AUTHOR]

The SE continental shelf of the Korean Peninsula was deformed by back-arc rifting associated with the separation of the SW Japan Arc in the Cenozoic. However, the deformation character of the inner continental shelf of the peninsula is not well known. High-resolution seismic profiles reveal a structure representative of a strike-slip duplex on the inner shelf that consists of bounding master faults joined by an array of splay faults. Structural interpretation of this duplex enables us to explain the deformation of the inner shelf with three tectonic stages: (1) generation of normal rift faults in the early stage of back-arc rifting in the late oligocene, (2) sinistral slip on the rift faults under northward compression induced by back-arc closing since the Middle Miocene, and (3) dextral slip on the rift faults induced by ENE–WSW compression since the early pliocene. In the first stage, back-arc rifting generated NNE–SSW oriented rift faults. In the second stage, the interior region between a pair of outer rift faults was subjected to NE–SW extension, creating a duplex with the generation of second-order splay faults oriented NW–SE. In the third stage, the interior region was deformed by ENE–WSW compression, causing convex upward stratigraphic reflectors in individual fault blocks. Our study suggests that the geologic deformation of the continental shelf of the SE Korean Peninsula, up to the inner part, is tied closely to the tectonic evolution in the back-arc region in the Pacific subduction zone. [ABSTRACT FROM AUTHOR]

Following the Mw4.9 Le Teil surface rupture earthquake that occurred on the north-eastern Cévennes fault system (NCFS) in France, several investigations were carried out to understand the origin of the earthquake rupture. A few studies performed local modeling of the NCFS structures in three dimensions integrating the rheology of the sedimentary layers within the hypocenter zone. However, the geometry of the NCFS at the scale of the Southeast French Basin is poorly constrained and it remains difficult to locate its trace beneath the Quaternary sediments of the Rhône river valley. To address this issue, Électricité de France (EDF) carried out a deep reflection seismic survey along the NCFS. This new set of seismic profiles was interpreted using a geological data base including surface data, well data, and previous seismic data that were reprocessed. The resulting 3D structural model allows us to reconstruct a polyphase geological history during the past 320 Ma, which we divide into three major tectonic phases. We show that all structures in the basin in the study area were initiated as normal faults during the Lower Jurassic and the Lower Cretaceous. During the Upper Cretaceous, these structures were reactivated, acting as a major transfer fault zone during the Pyrenean shortening phase, then as normal faults during the Oligocene extension. The morphology and faults at the top-Carboniferous basin initiated during the Lower Jurassic strongly shaped the final structure of the NCFS during the subsequent tectonic phases. Our new results allow updating the historical geology of the Vivaro-Cévenol region and our knowledge about the structures that have affected the Southeast Basin since the Mesozoic. In the context of the Le Teil earthquake, our new structural model provides important constraints for continuing paleoseismological works that will better assess the seismic hazard in this region.

Twelve available two-way time high-resolution seismic reflection profiles located in the central part of the middle Rhône valley are interpreted. In addition, one of the profiles was reprocessed to determine the P-wave velocities of the main geological units and to convert this profile into a depth cross section. The Lower and Upper Cretaceous units are clearly identifiable on all the profiles, along with the Messinian Erosion Surface (MES) carved out during the Messinian Salinity Crisis (MSC) by the paleo-Rhône and its western tributaries, the Ardèche and Cèze paleo-canyons. The Plio-Quaternary fill of these paleo-canyons shows at least 4 main units with an overall transgression. The combination of geological data from geological maps, geological field surveys and borehole data made it possible to model the MES in 3D at the scale of the region, and to produce depth/elevation model. From a geological point of view, the interpretation of the seismic profiles enabled us to reconstruct the stages in the sub-aquatic filling of the Messinian-Pliocene aggradation of the paleo-river. Several Mass Transport Deposits (MTDs) were identified both during the drop and during the rise in the Mediterranean Sea level. From a geomorphological point of view, this study provides new insights in the route and longitudinal profile of paleo-rivers and, in particular, it deepens the profile of the Paleo-Rhône at the latitude of the Tricastin region (up to −700 m b.s.l.) and significantly modifies the course and depth of the Ardèche proposed in previous studies. The N-Ardèche river, known to develop a karstic system during the MSC, is connected to a deep canyon, most likely through a karstic pocket valley, as suggested by the very steep longitudinal profile of the MES. Finally, from a structural point of view, our interpretation of the seismic profiles shows a broad ENE-trending anticline structure associated with a normal fault which apparently did not affect the Mio-Pliocene fill. In the southern part of the area, near the Uchaux anticline, the imaged structures suggest the presence of a recent (syn- to post-Pliocene) fault propagation fold. In addition to all the new information on the geology, morphology and methods of excavation and filling of the Messinian paleo-canyon, the proposed topographic model of the paleo-canyon is crucial for modelling seismic movement in the context of a basin with a complex geometry and, in particular, for the numerical assessment of site effects in a context of low seismicity.

The geological evolution of the SE continental margin of the Korean Peninsula resulted from crustal extension with back-arc rifting to spreading (from the Late Oligocene to the Middle Miocene) and crustal shortening with back-arc closing (from the Middle Miocene to the present), associated with the separation of the SW Japan Arc. Earthquakes occur more frequently in this region compared to other offshore regions of the Korean Peninsula; among them, the Mw 5.0 earthquake that occurred in 2016 is the largest event ever recorded instrumentally. We investigate the geological structure of the epicentral area of the Mw 5.0 earthquake and address neotectonic activity at the margin. Seismic reflection profiles reveal abundant faults in the epicentral area that make up strike-slip fault systems. A fault system encompassing the epicenter of the Mw 5.0 earthquake is suggested as the source structure, with its attitude consistent with the focal mechanism solution. We propose that the Mw 5.0 earthquake occurred due to the reactivation of an extensional fault created during back-arc rifting which currently induces dextral slip under the ENE–WSW-oriented compressional stress field in and around the Korean Peninsula. The maximum magnitude of earthquakes expected at the margin is estimated as no higher than Mw 6.0. Restoration of seismic profiles indicates that the current stress field was established after 5.5 Ma. The S-wave velocity structure of the uppermost mantle shows asthenospheric upwelling elongated along the continental margin, which may be considered an important regional source of the current stress field by inducing convection in the uppermost mantle toward the Korean Peninsula lithosphere. [ABSTRACT FROM AUTHOR]

Ice scours are formed when the keels of floating icebergs or sea ice hummocks penetrate unlithified seabed sediments. Until now, ice scours have been divided into “relict” and “modern” according to the water depth that corresponds with the possible maximum vertical dimensions of the keels of modern floating icebergs. However, this approach does not consider climatic changes at the present sea level, which affect the maximum depth of ice keels. We present an application of 210Pb dating of the largest ice scour in the Baydaratskaya Bay area (Kara Sea), located at depths of about 28–32 m. Two sediment cores were studied; these were taken on 2 November 2021 from the R/V Akademik Nikolay Strakhov directly in the ice scour and on the “background” seabed surface, not processed via ice scouring. According to the results of 210Pb dating, the studied ice scour was formed no later than the end of the Little Ice Age. Based on the extrapolation of possible sedimentation rates prior to 1917 (0.22–0.38 cm/year), the age of the ice scour is estimated to be 1810 ± 30 AD. The mean rate of ice scour filling with 70 cm thick sediments from the moment of its formation is around 0.33 cm/year.

[Display omitted] • We explained the tectonic evolution of the Eastern Subbasin since the Late Cretaceous that marks the eastern margin of the Northern South Yellow Sea Basin. • The evolution of the subbasin includes not only subsidence (rapid, slow, accelerated, and gradual) but short-term uplift. • The subbasin evolved with sequential development of nested duplex structures created by dextral extension. • The NW subduction of the Pacific Plate oblique to the NE Asian margin played an important role by inducing SE extension at the margin and NE-SW transtensional dextral slip parallel to the margin. The South Yellow Sea Basin is the largest sedimentary basin in the Yellow Sea. The Gunsan Basin in the central eastern part of the Northern South Yellow Sea Basin comprises the Western, Central, and Eastern Subbasins. The Eastern Subbasin marks the eastern margin of the South Yellow Sea Basin. Interpretation of multi-channel seismic profiles and balanced cross-section restoration of depth-converted seismic profiles reveal the structural characteristics and evolution of the Eastern Subbasin. The subbasin comprises three groups of faults: NW-SE, NE-SW, and NNE-SSW trending faults. The subsidence pattern of the subbasin, derived from the cross-section restoration analysis, indicates five distinguished evolution phases: (i) rapid subsidence in the Late Cretaceous, (ii) slow subsidence from the Paleocene to the Eocene, (iii) accelerated subsidence in the Oligocene, (iv) alternation of the uplift and subsidence in the Early Miocene, and (v) gradual subsidence since the Middle Miocene. The main and moderate subsidence can be explained by the combination of extension in the SE and NE-SW directions that formed double duplex structures. We suggest that the NW oblique subduction of the Pacific Plate under the NE Asia margin induced both extension toward the trench and dextral strike-slip parallel to the margin. The extension toward the trench caused SE transtension in a local pull-apart setting, whereas the dextral strike-slip parallel to the margin caused NE-SW extension, inducing more significant subsidence. The combined processes resulted in the progressive development of nested duplex structures. The evolution of the Eastern Subbasin is not compatible with previously suggested models for the western part of the South Yellow Sea Basin including foreland basin formation and transtension induced by branch faults of the Tan-Lu Fault. [ABSTRACT FROM AUTHOR]

The design of important structures for earthquake resistance requires an assessment of the local seismic hazard. One of its essential components is a site response that evaluates the amplification and attenuation of ground motion on a local scale. The shaking on the ground surface (in which it is generally measured) differs from the one at a depth; therefore, there is a need to characterize the ground motion at depth for important underground structures and buildings with deep foundations. In this study, we introduce a method to characterize the high-frequency (>1 Hz) ground motion at depth. The method makes use of a novel stochastic model (SM) that relates the ground motion at depth and on the surface in the Fourier domain. The SM is physics-based, its spectral amplification resembles an empirical 1D site response, and it allows reliable full-waveform ground-motion predictions. The method is validated through the comparison with empirical surface-to-borehole amplification curves observed in 144 selected KiK-net vertical arrays in Japan. Using a frequency range of 0.1-50 Hz, we identified 36 and 83 sites with a good and partially good mutual fit of theoretical and empirical amplification curves, respectively. Finally, we demonstrate the performance of the method in two diverse applications. First, we design a Bayesian inversion of the empirical surface-to-borehole amplification to retrieve the S-wave velocity model and an effective value of t* (the path-integrated effect of the quality factor). This inversion is applied to all selected KiK-net sites. Second, we perform a full-waveform prediction of the ground motion at depth from surface recordings of the 2018 northern Osaka MW 5.6 earthquake. Both of these applications demonstrate a good performance of our SM in a broad frequency range. [ABSTRACT FROM AUTHOR]

The moment magnitude (MW)~7 earthquake that struck Charleston, South Carolina, on 31 August 1886 is the largest historical earthquake in the United States east of the Appalachian Mountains. The fault(s) that ruptured during this earthquake has never been conclusively identified, and conflicting fault models have been proposed. Here we interpret reprocessed seismic reflection profiles, reprocessed legacy aeromagnetic data, and newly collected ground penetrating radar (GPR) profiles to delineate faults deforming the Cretaceous and younger Atlantic Coastal Plain (ACP) strata in the epicentral area of the 1886 earthquake. The data show evidence for faults folding or vertically displacing ACP strata, including apparent displacements of near-surface strata (upper ~20 m). Aeromagnetic data show several northeast (NE)-trending lineaments, two of which correlate with faults and folds with vertical displacements as great as 55 m on the seismic reflection and radar profiles. ACP strata show only minor thickness changes across these structures, indicating that much of the displacement postdates the shallowest well-imaged ACP strata of Eocene age. Faults imaged on the seismic reflection profiles appear on GPR profiles to displace the erosional surface at the top of the upper Eocene to Oligocene Cooper Group, including where railroad tracks were bent during the 1886 earthquake. Some faults coincide with changes in river trends, bifurcations of river channels, and unusual river meanders that could be related to recent fault motion. In contrast to our interpreted NE fault trends, earthquake locations and some focal mechanisms in the modern seismic zone have been interpreted as defining a nearly north-striking, west-dipping zone of aftershocks from the 1886 earthquake. The relationship between the modern seismicity and the faults we image is therefore enigmatic. However, multiple faults in the area clearly have been active since the Eocene and deform strata in the upper 20 m, providing potential targets for field-based geologic investigations. [ABSTRACT FROM AUTHOR]

Abstract—The seismic data acquired by the Bazhenov Geophysical Expedition on the regional DSS profiles are revised to study the structure of the Earth's crust in the northern part of the Ural region. Seismic material is reprocessed by two-dimensional (2D) seismic tomography inversion, and sections of crustal velocity gradient constructed in the format of grid functions for five profiles located within the studied trapezoidal area with geographical coordinates 58° N, 64° N, 54° E, 72° E. In the same format, density sections are constructed. The coefficients of empirical correlation "density–velocity" are calculated using the solution algorithm of 2D inverse gravimetric problem. [ABSTRACT FROM AUTHOR]

Back-arc rifting at the middle eastern continental margin of the Korean Peninsula took place in the early stage of separation of the SW Japan Arc from mainland Asia in the Cenozoic. As a result, the margin preserves structural elements of rifting seawards that include a narrow rift (Hupo Basin), a major syn-rift border fault (Hupo Fault), and an uplifted rift flank (Hupo Bank). We correlated current seismicity at the margin with the rifting structures and estimated the potential seismic hazards. The Hupo Basin, in its overall shape, is a half-graben created by back-tilting of the hanging wall toward the Hupo Fault. The trace of the Hupo Fault is composed of multiple segments arcuate seawards, suggesting nucleation of rift faults at multiple places. The Hupo Fault is vertical at a shallow depth, but hypocentral locations of earthquakes indicate that the Hupo Fault is listric down to the upper and lower crustal boundary. Stochastic estimations of the maximum possible magnitude of earthquakes at the margin encompassing the Hupo Basin and the Hupo Bank average to ML 5.86. The estimated b-value of 0.63 is lower than that in the Korean Peninsula, which may suggest the dominance of thrust faulting with a strike-slip (or oblique) component on the listric and lower dipping portions of the faults at the margin. [ABSTRACT FROM AUTHOR]

Pliocene–Quaternary faults are relevant structures with which to constrain the seismotectonic context and contribute to the evaluation of the seismic hazard of a region. Many of these faults, however, do not show clear surface evidence even when releasing earthquakes. For these reasons they can be extremely dangerous as they receive relatively little attention and can be difficult to identify. From among the various surface geology studies and/or palaeoseismological investigations, we focus our attention on the integration of different datasets such as seismic reflection profiles, surface kinematic data and the relocation of seismological data, which make it possible to identify and characterize active faults whose dimension and earthquake potential would otherwise not be large enough to make them identifiable. We take as an example the Montespertoli NE-trending fault in southern Tuscany (central Italy) with which we associate the 2016 M=3.9 Castelfiorentino earthquake. This structure is part of a wider (in the order of 15–20 km) crustal-scale shear zone, which may be responsible for strong historical earthquakes in the area. [ABSTRACT FROM AUTHOR]

Detecting imaging artifacts is a precondition for interpreting seismic profiles, as well as one of the fidelity (accuracy) measures for all seismic images. Based on field seismic reflection profiles, this paper analyzes some common and often miss-interpreted seismic imaging artifacts, and proposes to detect the artifacts through analyzing their origins. From the perspective of seismic imaging process, the origins of seismic imaging artifacts include three main factors: mistaking the signals, imaging distortions and errors in the reference velocity model. Many deceiving artifacts are originated by mistaking the signals in the processing and imaging processes. The imaging distortions are due to insufficiencies in seismic illumination, data frequency bandwidth and assumptions of the imaging methods, leading to smearing and other imaging distortion artifacts; With an erroneous reference velocity model, seismic images may show not only position errors, but also diffraction artifacts at discontinuous positions of seismic impedance. Hence, the measurable elements of the fidelity of seismic images should include resolution, position accuracy and artifact detection. These elements are connected with each other, thus should be evaluated jointly in detecting artifacts, according to the given study objectives and resources available.

Kinematic constraints on the Cenozoic deformation along the northwestern edge of the Tibetan Plateau remain limited. Combining surface geological data and seismic profiles, we document the structural geometry and kinematics of the large‐scale east‐west striking Hotan anticline, along the foothills of the Western Kunlun Range. Four new balanced cross sections are constructed, and the temporal evolution of deformation is deciphered from the exceptionally well‐imaged growth strata at the front of the fold. This anticline results from a broad fault‐bend fold, subsequently deformed by a footwall duplex. The total shortening across the whole structure is relatively constant along strike, from ∼40 to ∼35 km. However, the shortening accommodated by the duplex varies laterally from ∼50–40% to 0% of the total shortening. Two distinct successive patterns of growth strata are recognized and are interpreted to be representative of deformation on the ramp anticline, followed by deformation on the duplex. The onset of deformation initiated by ∼16 Ma. Deformation of the underlying duplex began at ∼12 Ma to the west and subsequently propagated eastward. From these results, we determine a shortening rate of ∼5 mm/yr from ∼16 to ∼8–9 Ma across the Hotan thrust system, followed by a significant decrease in shortening rate, possibly down to <0.5 mm/yr. We explore the significance of this deceleration of deformation at the scale of the Western Kunlun foothills and at a broader regional scale as it may point to a regional kinematic reorganization by the late Miocene. Key Points: Four new balanced cross sections across the Hotan anticline (foothills of the Western Kunlun, China)Measured amount of shortening ranges from ∼40 to ∼34.5 km, and deformation probably initiated by ∼16 MaGrowth strata analysis points to a decrease in shortening rates since ∼8–9 Ma, probably related to a regional kinematic reorganization [ABSTRACT FROM AUTHOR]

New data on the crust structure of the Black Sea‒Caspian region, including the Scythian and Anatolian plate margins, the Caucasus, Black Sea and Southern Caspian structures are reported. Generalization and analysis of the data of deep seismic studies with an estimate of their reliability were performed and the velocity sections of the crust were constructed. Based on the data of deep drilling data and studies of the crust composition in xenoliths in these sections, three major layers were identified in the crust: granite-gneiss (6.0‒6.4 km/s), granulite-gneiss (6.5‒6.7 km/s), and basic (6.8‒7.2 km/s). According to the thickness of these layers, the major types of the crust were distinguished. Three continental types with all three layers, but different in the total thickness of the crust types were distinguished in the area of the Scythian and Anatolian plates. The oceanic type with thin basic crust and two transitional types, subcontinental and suboceanic, with the different total thickness of the crust and the thickness of the basic layer were distinguished within the deep sea basins. There are anomalous types of the crust in the Caucasus region: the thick crust of the Lesser Caucasus with anomalously low velocities and the thick high-velocity crust of the Reon‒Kura Trough. According to the seismological data, the crust of the Black Sea–Caspian region is separated from the platform plates bounding it by the deep faults and crossed by two transform faults; the upper mantle of the Caucasus differs from neighboring regions by reduced velocities. Based on the analysis of the material obtained and CDP data on the basement structure, the new structural and geodynamic schemes of the crust of the entire region were compiled, and it was shown that the formation of depressions with oceanic and suboceanic crust types corresponds to the platform regime characteristic of the depressions of Eastern Europe. A new collisional model with the overthrust of the Anatolian Plate crust onto the crust of the Lesser Caucasus without change of the structure of the upper mantle was proposed to explain the structure of the Caucasus region. [ABSTRACT FROM AUTHOR]

The South Korea Plateau (SKP) is a structural high at the eastern continental margin of the Korean Peninsula. Earthquakes occur frequently in the SKP although they are not larger than ML 5.0 in magnitude. The SKP is a region of highly rifted continental crust engraved with rifts created during back-arc rifting in the NW Pacific subduction zone that led to the separation of the SW Japan Arc in the Cenozoic. The Bandal, Onnuri, and Okgye Rifts are well-defined rifts in the SKP. Multichannel seismic profiles show that the rifts in the SKP are bounded by large-offset normal faults and their subsided basement is deformed by domino-style faulting. A close spatial correlation is recognized between the epicentral locations of earthquakes with relatively large magnitude and the rift-bounding fault of the Onnuri Rift. The faults in the SKP is interpreted to be reactivated with strike-slip since the middle Miocene. The maximum expected magnitude of earthquakes (Mmax) computed statistically using the catalog including instrumentally recorded seismicity is ML 5.42. However, Mmax estimated from the catalog including instrumentally recorded seismicity and historical records increases to ML 6.67.

The geometry of the Sefid-Zakhur anticline, a gas reservoir in the Fars province, and the main controlling factors of the structural style in this anticline are studied in this research. The integration of the 2D seismic profiles, well data, and the fieldwork was used to study the geometry variations of the Sefid-Zakhur anticline. The geometry of this anticline is different vertically and horizontally. It is a chevron fault in the western part and a box fold in the eastern part. Observed growth strata in the Mishan Formations show that the folding started in the Middle Miocene time in this area. The Sefid-Zakhur anticline indicates a significant over-thickening of the middle décollement horizon (Dashtak evaporites) in their crestal domain. In this region, the Triassic Dashtak evaporites and the Cambrian Hormuz salt are the main décollement horizons. The upper Cretaceous Gurpi shales are also minor décollement horizon. Decoupling across the décollement horizons is obviously visible in the Sefid-Zakhur anticline, especially across the thick Dashtak evaporites. The decoupling across the thick Dashtak evaporites causes the shift of the anticline crest in the underlying Permo-Triassic carbonates of the Dehram Group, which form the major gas reservoir. Therefore, the investigation of the décollement horizons is of utmost importance in the management of these reservoirs. The results of this research suggest that the presence of multiple décollement horizons is the main controlling factor of the structural style in this anticline. [ABSTRACT FROM AUTHOR]

The internal architecture and evolution of isolated carbonate buildups rely on multiple forcing factors, including tectonics and eustatic fluctuations. These parameters control the developmental phases of carbonate buildups such as initiation, growth, and termination stages, and give insights into other morphologic patterns such as backstepping and exposure events. The current study shows the evolution of a Middle Miocene isolated carbonate buildup of Central Luconia in the southern South China Sea, and describes it from large‐scale to very fine detail (km to mm) utilizing newly acquired (2016) 3D seismic data along with core lithofacies and thin sections. The buildup morphology and seismic facies are linked to core facies that can help to uncover the complex development of the carbonate platform. Core‐seismic calibration was used to create maps illustrating carbonate depositional settings for each stratigraphic unit. Here, we identified five seismic units that constitute the main stratigraphic stages of buildup development: (a) initiation as several isolated buildups, (b) coalescence, progradation, and aggradation, (c) aggradation and retrogradation associated with minor backstepping events and major karstification events, (d) retrogradation associated with major backstepping events, and (e) drowning stage. Our results demonstrate that Miocene reefal evolution and buildup architecture in Central Luconia were distinctly affected by diverse endogenic and exogenic processes. The initiation of localized carbonate growth appears to be strongly controlled by the morphology of the pre‐carbonate basement of Central Luconia where the SSW–NNE horst and graben structures were inherited from the poly‐stage opening of the South China Sea during the Early Miocene. Furthermore, sea‐level fluctuations, local and regional tectonic events during the Middle Miocene controlled the rates of accommodation changes, which directly impacted the stratigraphic architecture of the platform. The detailed seismic and sedimentological study documented in this work will benefit the understanding of the paleogeographic and stratigraphic evolution of carbonate buildups in the Luconia region of SE Asia, and in the current and future exploration for substantial conventional resources. [ABSTRACT FROM AUTHOR]

Acoustic sources based on electrical discharge, commonly called sparker sources, are employed in surveys for high-resolution marine stratigraphy. In this work, a new seismic sparker-type transducer has been designed, built and tested to obtain specific characteristics: low cost, small size (50x50x15 cm3), high resolving power, perfect symmetry of the acoustic beam emitted, and high directivity. This source can, thus, also be used in shallow water, to delineate the first sedimentary layers. First, an analysis of the determined experimental radiation pattern, signal to noise, and wavelet shape is presented. The radiation pattern is subsequently compared to the theoretical one. Lastly, comparative tests with traditional sparker sources and with the boomer source showed the validity of the performance of the new source. [ABSTRACT FROM AUTHOR]

Kwanza basin, located on the west coast of Africa and the east side of the South Atlantic Ocean, has the potential for deep-water oil and gas exploration. Previous studies have shown that the pre-salt system within the area has high potential for oil and gas storage. However, due to the shielding effect of the evaporating salt rock during the Aptian period, the quality of seismic reflection profiles of the pre-salt layers is poor. This means that the pre-salt sequences, the main fault, the scale and distribution pattern of the rift are not clear. To clarify the pre-salt regional structure pattern and further guide pre-salt exploration, we carried out a series of analyses and target processing of seismic and gravity data. Further, combining other available geological and lithology data as well as a tectonic model, we put forward a new understanding of the pre-salt structure of Kwanza basin. The research shows that the Kwanza basin can be divided into three uplift belts below the salt layer, which are distributed in the NW–SE trending direction. The three key profiles illustrate the distribution of uplift and depression in detail. The explained structural highs distributed in the outer Kwanza basin may be related to oil and gas reservoir. This study could provide the geophysical basis for the re-interpretation of the pre-salt seismic sequence, the strategic selection of pre-salt oil and gas and the next exploration deployment. [ABSTRACT FROM AUTHOR]

In the last decade, a great effort was made to determine relative sea level changes along the Mediterranean coastlines through the integration of geophysical modelling and direct measuring of paleo-shoreline related to Late-Holocene and the Last Interglacial events. In this paper, we show the potential use and limitations of additional marine geomorphic markers of past and deeper sea levels. These markers are submarine depositional terraces (SDTs), i.e., deposits formed by a set of small prograding sedimentary wedges, having a terraced shape and found at variable shallow-water depths (mainly the first −150 m) on continental and insular shelves in the Tyrrhenian Sea. The shallowest terraces (near-shore) have their edges at depths of −10/−30 m, compatible with the present-day, local storm-wave base level. Their formation has been associated to present-day/highstand environmental conditions, and as such they can be used to interpret the genesis of deeper terraces formed during earlier sea levels on the middle and outer shelf. Mid-shelf terraces have their edges at variable depths between −40 and −90 m and likely formed during the last sea level rise. They show a patchy distribution and a large variability in their internal structure, so that they are not suitable for correlations at regional scale. Shelf-edge terraces have their edges at depths mainly comprised between −120 and −170 m, compatible or deeper than the sea-level depth reached during the Last Glacial Maximum (LGM). They show an overall similar prograding internal structure and have a remarkable lateral continuity, thus representing a good proxy of sea level position at ≈20 ka. However, the edge's depth of SDTs is not a direct measurement of paleo sea level at that time, since their depth depends on a complex interplay of different factors, such as storm-wave base level and its variation in response to coastal physiography, as well as the occurrence of later erosive-depositional processes. Depending on the geophysical and mapping methods used to determine their depth, the associated error range can also differ. Based on the analysis of these complexities and a wide range of settings from the Italian Seas, a rough estimate of these error ranges is discussed to determine the potential use and the limitations of the SDTs to assess the vertical mobility of an area. [ABSTRACT FROM AUTHOR]

Based on lithostratigraphic reinterpretation of five borehole sections and lithostratigraphic interpretation of two seismic profiles, new data on the Dvoynitsa Formation's lithology, subdivision and spatial distribution were obtained. The Armera and Gebesh Members were recognized in the area of the villages of Solnik and Bardarevo, as their spatial relationships and distribution are visualized by drawing up of four geological cross-sections. [ABSTRACT FROM AUTHOR]

We used previously obtained marine geophysical and geotechnical data for the proposed Galsi pipeline route from Algeria to Sardinia to analyze the buried salt distribution, rates of fault displacements, and frequency and lateral extent of submarine slope failures. Crossing the convergent African/Nubian-European plate boundary, the southern section of the pipeline route traverses continental shelves and slopes of Algeria and Sardinia as well as the Algerian abyssal plain of the western Mediterranean. Deeply buried Messinian-aged salt is present throughout this area. Being less dense and more buoyant than the overburden sediment, the salt tends to flow upward to form diapiric structures that, in turn, result in the formation of faults and landslides in the overlying sediment. Measured offsets from seismic profiles of different resolutions were compared with predicted sediment age at depth of each offset, yielding an average rate of fault displacement of 1.5 cm/kiloyear (ky). The highest rates of displacement are along the Cagliari slope near Sardinia (2.5-2.7 cm/ky) and near the convergent plate boundary (2.3 cm/ky). Utilizing the same geophysical data, the frequency and lateral extent of submarine slope failures in the study area can also be linked to the distribution of salt and the influence of salt tectonics. Turbidity currents and hyperpycnal flows are present within the Algerian basin, whereas local debris flows, landslide runouts, and channelized debris flows are present along the Sardinian slope. The low sedimentation rates, determined in this study, suggest that the most recent slope failures related to salt tectonics occurred more than 12,000 years ago. [ABSTRACT FROM AUTHOR]

In the Lesina Marina village area, the cropping out gypsum rocks, that rose up from the deep and thick Upper Trias Burano Fm anhydrite layer, have been analyzed to investigate the trigger mechanism for their ascent. In this regard, we focus on the anhydrite-to-gypsum transformation starting from the deep source layer. Indeed, petrographic observations of the widespread corroded anhydrite crystals embedded in these gypsum rocks revealed unequivocal evidences of the anhydrite-to-gypsum transformation. In addition, and referring to gypsum, microstructural features indicate that ductile deformation mechanisms initially operated under higher temperature conditions. This temperature should be close to 107 °C, namely the value of the upper temperature limit of stability of gypsum from Lesina Marina, above which it starts to transform and dehydrate, as revealed by microthermometry heating/dehydration experiments combined with micro-Raman analyses. All these evidences are in favor of the dramatic density decrease and volume increase due to anhydrite-to-gypsum transformation by hydration in the deep source layer; these variations of physical conditions, triggered by hydration, promoted diapirism of the gypsum mass, in other words "hydration diapirism". As revealed by seismic lines interpretation, the diapirism, which gave rise to the Lesina diapir, occurred during Plio-Pleistocene and was genetically related to the Lesina graben-type structure. Hydration at depth was favored by the downward circulation of water-rich fluids channeled in faults, and the gypsum mass used the weakened zone of the southern fault to pierce the overlying Mesozoic and Tertiary sediments. [ABSTRACT FROM AUTHOR]

The late Mesozoic-Cenozoic evolution of the Central Andes of northern Chile consists of a series of events related to changing conditions along the plate margin, leading to different episodes of compression and extension. A long-lasting basin which records these changes corresponds to the Salar de Atacama Basin. Its tectonic history has been blurred by several interpretations of seismic reflection lines and multiple chronostratigraphic correlations between subsurface-surface units. As such, many aspects of its tectonic evolution are still unclear. In this study, we performed an E-W gravimetric profile across the Barros Arana Syncline and the basin. We analyzed interval velocities obtained from seismic reflection studies and reviewed the profiles closest to the gravity survey. Four U-Pb samples for detrital zircon analysis were obtained from Late Cretaceous-Paleogene units. Geophysical data show a segmentation of physical properties within the basin, with denser units and faster interval velocities around the late Mesozoic-early Cenozoic units, and lighter, slower units in the actual salt pan. The main contrast in physical properties is observed in the evaporitic and fine-grained continental deposits of the San Pedro Formation. Geophysical and geological constraints show that its thickness varies between 800 and 1200 m, and that it was deformed during later events. The U-Pb data show that the rocks within the Barros Arana Syncline reach well into the Paleogene, and that they were mainly deformed during the late Eocene Incaic Event, where an east-verging thrust system also involving Permo-Triassic units was developed, establishing the actual structural configuration. The late Oligocene-early Miocene units were then deposited in a post-orogenic setting, with minor compression. A stronger phase around the late Miocene reactivated previous structures and folded these deposits. This continuous, compressive history of the basin, which is mostly a result of the Incaic Event, is in agreement with the regional evolution of the Central Andes. • New geophysical and geological data were obtained from the Salar de Atacama Basin. • A distinct geophysical contrast is found between the various geological units. • The area was mainly deformed during the Incaic Event. • New ages show a long-lasting sedimentation within Cretaceous-Paleogene successions. • Compression seems to have been dominant over the last 100 Ma. [ABSTRACT FROM AUTHOR]

Childers, D.P.; Madsen, J.A.; Krantz, D.E., and Deliberty, T.L., 2019. Constraining the geometry of subsurface paleochannels beneath Delaware Bay and the Mid-Atlantic inner continental shelf. Journal of Coastal Research, 35(3), 590–599. Coconut Creek (Florida), ISSN 0749-0208. This study improves the understanding of paleochannels underlying Delaware Bay and the Mid-Atlantic inner continental shelf. Major surfaces interpreted from analog seismic profiles were used in ArcGIS™ to create a three-dimensional (3D) model in ArcScene™ that constrains the geometry and relative age relationships of the paleochannels. Interpolation with kriging in the Geostatistical Analyst tool in ArcGIS was used to generate spatial models that were imported into ArcScene to create 3D perspective views of the primary subsurface features. The results better constrain the geometry of previously mapped paleochannels. These revisions enhance the understanding of the Quaternary geologic evolution of the region in response to sea-level fluctuations. A new nomenclature for previously named paleochannels is proposed based on their relative age relationships. The Central (renamed as Qc1) paleochannel in Delaware Bay is identified as the youngest and continues onto the inner shelf trending SE approximately 50 km across the shelf and then eastward toward Baltimore Canyon. The next oldest Delaware Bay paleochannel, the Southern (Qc2) paleochannel, correlates with the previously identified Orange (Qc2) paleochannel and also trends toward Baltimore Canyon. The oldest paleochannel in the Bay, the Northern (Qc3) paleochannel, is projected beneath the tip of Cape May, New Jersey, and continues on the inner shelf as the earlier defined Green (Qc3) paleochannel. [ABSTRACT FROM AUTHOR]

This study presents an alternate site-response model to the existing ground-motion prediction equation (GMPE) from our previous study with some calibration to the magnitude term. We used a new site-response proxy TVH =4 × max(30, HB)/VS30 that combines VS30 (the travel-time-averaged shear-wave velocity to 30 m depth) with the engineering bedrock depth HB.VS30. is available for many strong-motion recording stations. However, GMPEs using VS30 do not directly account for the response of the soil layers between 30 m and bedrock depth. Site periodTS (four times the shear-wave travel time to the engineering bedrock depth) has also been used in recent GMPEs, with TS being considered a theoretically better parameter than a pseudosite period TVS30 (four times the shear-wave travel time to a depth of 30 m). Obtaining the shear-wave velocity profiles between 30 m and HB for a deep soil site can be expensive, whereas obtaining bedrock depth based on the geotechnical description of borehole data may be relatively easy. We used velocity profiles from the Kyoshin net and Kiban-Kyoshin net strong-motion networks and found that a pseudosite period TVH and TS have an excellent correlation with a small standard deviation at all spectral periods, suggesting that TVH is a suitable site-effect parameter. The poor correlations between TVS30 and TS and between TVS30 and TVH for sites with TS > 0.4 led to poor model performance at long spectral periods. We modified a GMPE by replacing with TVH, and we made a minor modification to the moment magnitude term of the GMPE that was necessary for the new site term. The response spectra predicted by models using TVH, TS and at short spectral periods up to 0.6 s are generally similar. At long spectral periods, the spectra predicted by the TVS30 are much smaller than those from the other two GMPEs. For all spectral periods, is an excellent substitute for TVS30. [ABSTRACT FROM AUTHOR]

The relevance of the research is in studying the upper part of the section of Southern Caspian deep part to distinguish gas hydrate zones by seismic data, to evaluate their thickness as well as calculation of gas hydrate gas volumes. The study of gas hydrates in the South Caspian is necessary for reliable assessment of energy potential of hydrocarbon gases in Azerbaijan. The results of the study of gas hydrates can also be applied to assess the role of gas hydrates in the near-surface layers of the geosphere, especially in connection with their possible impact on ecology of the Caspian Sea, the region and global climate change. The aim of the research is to identify and estimate the volumes of hydrocarbon gases of gas hydrates of the deep-water part of the South Caspian by seismic data. The object of the research - 17 regional seismic profiles and data on thermodynamics of the region. When interpreting seismic profiles the authors have emphasized the identification of horizons containing gas hydrates. Research methods are based on the presence of a direct relationship between the features of the geological structure of the gas hydrate zones and distribution of physical parameters in the medium. Anomalous changes in the seismic characteristics of waves can serve as indicators of gas hydrate at a time section: amplitude, frequency, phase, velocity of longitudinal and transverse waves. The presence of the reflecting seismic horizon BSR, as well as bright spots on the seismic records is widely used seismic attribute of gas hydrate. All the time sections are interpreted according to these criteria and the upper and lower boundaries of the zones with reflections characteristic of the gas hydrate zones are established. The data were interpreted using the licensed software package Kingdom Suite 2017. As a result of the research, the authors constructed the maps of the lower and upper boundaries of the gas hydrate zones, and calculated the thickness of the deposits containing gas hydrates. The rock volumes determined by seismic data enabled to calculate the volumes of hydrocarbon gases contained in gas hydrates. The maximum volume of gas in the investigated zone is 8,06 * 1012 of gas. The volume of gas hydrates contained in the rock within the structures was calculated as well. Ranking of the data by volume showed that the southern part of the Caspian contains the maximum amount of gas. Proceeding from the above, two perspective-gas hydrate zones can be distinguished in the deep-water part of the South Caspian: highly prospective zone in the southern part; prospecting zone in the northern deep-water part. These gas hydrate accumulation zones will ensure the energy security of Azerbaijan for many years.

The relevance of the research is determined by the growing demands to using volumetric geophysical methods of non/destroyed control for diagnostic of foundation bottom grounds fixed by special cementing works where the mandatory attribute is a geophysical control of the quality of strengthening in addition to the discrete measurements on samples taken in special pits and wells. The aim of the research: 1) analysis of physic/geological and technical situation on the research object with subsequent composing of physic/geological and physic/technical models for choosing the complex of modern geophysical non/destructive control technologies and methods of measurement results processing by using specialized processing complexes; 2) research of condition of technogenic fixed grounds of foundation bottom by GPR/radar and seismic methods in conditions of the long/term used object of the cultural heritage of the regional importance «Memorial building B. Dom Alfuzova», 1880, Taganrog. Methods of research: 1) GPR/radar survey inside and outside the building by parallel profiles laid along the walls on distance of 2,5 m from each other; 2) seismic survey by the methods: a) longitudinal profiling with many/point system of observations; b) seismo/translucency by the scheme of surface-basement with step between fluctuation receiving points 1 m and record of seismograms with the time of registration 256 ms, sampling frequency 4000 Gz and the evolvent 100 ms. Results. The authors have implemented the specific example of setting and resolving the tasks of the quality control of the grouting of foundation bottom using geophysical methods in conditions of long/term exploitation of buildings and structures, and namely: 1) the zone of grouting by Q/factor index on depth and as you move away from the faces of the foundation was determine by the GPR/radar survey; 2) the data on the: a) degree of grouting (K), right next to the foundation and as you move away from it at distance to 5 m; b) deformation module (Edef) of grounds near the side edges of foundation and away from them at distance to 5 m; v) distribution speed of the elastic waves into the grouting at horizontal section under foundation bottom, were obtained by seismic works. The results of research were analyzed on improvement of the complex of shallow depth geophysical methods. For this purpose the authors carried out the short review of domestic and foreign publications by shallow depth geophysics at building and archeological objects.

Analysis of available published geological-geophysical data by the new seismic data CDP and drilling allowed making a conclusion that there are two groups spatially separated salt dome structures within the Chu-Sarysu basin. Age of rocks in the cores of the Permian salt structures in the north-west and the Devonian in the southeast, and not only the Devonian as previously thought. The shear-thrust movements are the decisive role in the development history of the Permian salt domes in northwestern Chu-Sarysu basin.

Abstract Lake Izabal, located in eastern Guatemala, lies in an EW-trending basin located along the transform margin between the North American and Caribbean plates. This plate boundary consists of two main left-lateral, strike-slip faults known as the Polochic and Motagua Fault System (PMFS). The basin is a 100 × 20 km lens-shaped depression in which the lake occupies its eastern half. To the north, the basin is confined by a Principal Deformation Zone (PDZ) which is recognized in this area as the most important upper-crustal branch of the Polochic Fault. The eastern part of the basin has been uplifted and dissected, exposing the basin infill along the slopes of the Montaña del Mico. Analysis of a set of multichannel seismic reflection profiles, most of them acquired within the lake, combined with well and outcrop information, allowed to outline the structure and evolution of the basin and its stratigraphic architecture. The basin is strongly asymmetrical, both in cross and along-strike directions, and is filled up by Neogene to Quaternary sediments, with the deepest side of the basin being to the north, close and parallel to the PDZ. The base of the infill is a mid-Tertiary unconformity whose differential subsidence through time brought the basin to its present structural setting. Five main evolutionary stages are recognized based on seismo-stratigraphic and structural features, which are related to the development and activity of the bordering faults. Development of the basin began in its easternmost sector. A small half graben, tilted to the south, developed in response to the activity of an Oligocene (?) or Early-Middle Miocene growth fault. In the second stage (Late Miocene), the basin tilts to the north, causing the sedimentary sequences to thicken towards the northern PDZ. This stage is dominated by oblique extension, and by progressive migration of the basin depocenter towards the west. The third stage (Early Pliocene) records a strong acceleration of the strike-slip activity which causes a rapid westward migration of the depocenter. The fourth stage (Late Pliocene), although still dominated by regional transtension, is related to the development of a transpressional event along the eastern side of the basin, as evidenced by the occurrence of folds and reverse faults parallel to the northern bend of the Polochic Fault. During the fifth stage (Quaternary), the eastern part of the basin remains relatively quiescent while the western part undergoes subsidence with localized transtension, still related to the activity in this sector of the Polochic Fault. Left-lateral movement along the Polochic Fault caused the depocenter to migrate 75–80 km at different velocities, with slip rates ranging between 2.1 and 16.3 mm/yr. This study suggests that the Polochic Fault developed in the Early-Middle Miocene in connection to the deposition of the early sediments of the Izabal Basin, even though an older age (Oligocene?) could also be possible. To our knowledge, this is one of the best examples of sedimentary architecture documenting depocentre migration due to fault movement along a transform system. Highlights • Izabal Basin (E-Guatemala) lies along the N-American-Caribbean plate boundary. • The basin is strongly asymmetric in shape, both in cross and along-strike directions. • Five evolutionary stages of the basin (Early Miocene–Quaternary) are recognized. • The infill of the basin displays a ~75–80 km of westward migration. [ABSTRACT FROM AUTHOR]

The Eastern Siberian Arctic Shelf (ESAS) represents a geologically complex realm with a tectonic history that is related to the final stages of the formation of the Pangaea supercontinent during the Mesozoic and its subsequent disintegration during the Late Cretaceous and Cenozoic. It is a key region to constrain the origin of the deep-water basins and intervening ridges of the Amerasia Basin. We present results of gravity modeling of published seismic refraction and reflection profiles acquired between 1989 and 2012 over the ESAS and adjacent Arctic Ocean along five composite geotransects using Getech’s satellite altimeter-derived gravity data. Our main goal was to examine published crustal models and to present new models for the ESAS that are constrained by both seismic data and 2D gravity forward modeling. We consider several topics important for understanding Arctic geology: (i) hyperextension within the Laptev Rift System and the possible extent of the exhumed mantle, (ii) the relationship between the New Siberian Shelf and the Lomonosov Ridge, (iii) the nature of the collapsed upper Mesozoic fold belt in the southern part of the East Siberian Sea, (iv) the character of transition between the De Long Massif and the deep-water Podvodnikov Basin, (v) the lateral extent of the hyperextended North Chukchi Basin and the nature of its basement, and (vi) relationship between the Mendeleev Ridge and Chukchi Plateau crustal domains. Our results do not confirm the previously inferred extent of continental crust beneath the oceanic realm. The latter is dominated by High Arctic Large Igneous Province (HALIP) igneous crust. We discuss the existence of a dismembered continental Bennett-Barrovia block that is currently represented by three smaller fragments/massifs. When restored to its possible single state, this block can play a crucial role in reconstructing the pre-Canada Basin Arctic. [ABSTRACT FROM AUTHOR]

The northern shelf of the Strait of Gibraltar adjacent to Camarinal Sill, defined here as the Cape Paloma continental shelf, has been investigated by analyzing a set of geophysical data including multibeam bathymetric images, a side-scan sonar mosaic and high-resolution seismic profiles, and the simulation of water-mass circulation patterns along the northern coastal margin. The aim of the study was to establish the significance of factors determining the evolution of this shallow margin at different temporal scales and to assess the implications for bedform generation in strait settings, taking into account the complex tectonic evolution and the energetic hydrodynamic regime of the strait. Deformed basement rocks are part of the Betic-Rif thrust wedge, western Gibraltar Arc, mainly formed by the materials of the Flysch Complex units and covered by Pliocene to Quaternary post-orogenic deposits. A central high (Bajo de los Cabezos High) is delimited by lateral depressions, that nucleated two major depocentres with distinctive filling histories. The eastern depocentre is controlled by WNW-ESE faults cutting the Cretaceous-Miocene basement rocks; these faults generate horsts and grabens that could have contributed to the opening of the Strait of Gibraltar during the Pliocene. The largest and westernmost depocentre is related to the complete infilling of a shelf palaeovalley. The sediment cover is molded by different fields of submarine dunes and comet marks that indicate the influence of hydrodynamic processes on sediment transport at the coastal margin. The observations in the study area regarding bedform development must be placed into a wider context of strait sediment dynamics. The Cape Paloma continental shelf exhibits both erosional and depositional forms, due to its intermediate location between the strait, mostly dominated by erosional processes, and the Barbate Platform (northwest of the study area), mostly characterized by depositional forms. The long-term evolution of the sediment depocentres in the study area appears to be mainly influenced by the morpho-tectonic configuration of the margin, which in turn was established to a large extent by differential uplifting along the coast. In the shelf east of the central high, the basement horst and graben structure trapped sediments in the physiographic lows and fostered the formation of large-scale sediment banks. In the shelf west of the central high, the occurrence of a major infilled palaeovalley is in agreement with a gentle subsidence trend. The physiographic configuration is also thought to play a major role in defining short-term processes, particularly in confining a cyclonic eddy to the east of the Bajo de los Cabezos High during specific conditions of the tidal cycle. This eddy favors the recirculation of sediments in the coastal margin, as evidenced by small bedform fields that apparently show a wider distribution that the larger-scale, confined sediment banks, due to the instauration of the modern sediment dynamics after the complete shelf flooding. The sediment transport pattern established in the study area seems to be eventually captured by a submarine channel that provide an efficient mechanism for sediment export toward deep-water settings, where an extensive contourite depositional system has been documented. [ABSTRACT FROM AUTHOR]

In the last decade great effort was put in the study of relative sea-level changes on Mediterranean coastlines through the integration of geophysical modelling and proxy data of paleo-shorelines. In this paper, we show potential and limitations of using additional marine geomorphic/sedimentary markers for earlier and lower sea levels. These markers are submarine depositional terraces (SDTs), i.e., deposits formed by a set of small prograding sedimentary wedges, having a terraced shape and found at variable shallow-water depths (mainly the first −150 m) on continental and insular shelves in the Tyrrhenian Sea. The shallowest terraces (near-shore) have their edges at depths between −10 m and −30 m, approximating the modern, local storm-wave base level. Their formation is thought to be associated with the modern sea-level highstand and thus, can be used as the modern analogue for deeper terraces formed in the past when the sea level was on the middle and outer shelf. Mid-shelf terraces have their edges at variable depths between −40 m and −90 m and probably formed during the last sea-level rise. They show a patchy spatial distribution and a large variability in their internal structure, so that they are not suitable for correlation on a regional scale. Shelf-edge terraces have their edges at depths between −120 m and −170 m, which is close or deeper than the Last Glacial Maximum (LGM) sea-level stand. They show a remarkable lateral continuity and a prograding internal structure similar to those at shallower depth and, thus, represent a proxy for the sea-level position at around 20 ka. However, the position of SDTs' edges is not a direct measure of paleo sea level positions because their depth depends on a complex interplay of several factors, such as the base of the storm wave and its variation in response to coastal physiography, as well as the occurrence of subsequent erosional or depositional processes. Depending on the geophysical and mapping methods used to determine their depth, the associated error range can also differ. Based on the analysis of these complexities and a wide range of physiographic settings of the Tyrrhenian Sea, we discuss these error ranges in order to assess potential and limitation of the SDT for analyses of vertical mobility of an area. [ABSTRACT FROM AUTHOR]