Seismic Reflection Profiles Research Articles

Structural configuration and tectonics of the Flemish Cap, offshore Newfoundland, from newly acquired seismic reflection data

Although the Flemish Cap played a pivotal role in the opening of the North Atlantic, the tectonic history of this continental ribbon has been poorly constrained owing to insufficient seismic coverage. In this study, we present 13 newly acquired seismic reflection profiles over the Flemish Cap, on which seismic reflectors show highly variable seismic facies both on and beneath the top acoustic basement, with exceptional imaging of layered crustal structure. The upper crust is primarily characterized by transparent, chaotic amplitude reflectivity. The lower crust, particularly on the flanks of the cap, exhibits relatively bright and coherent reflection packages interpreted as Appalachian orogenic fabrics based on onshore–offshore correlations from pre-rift plate reconstructions. Extensional systems within the continental crust of the Flemish Cap record a transitional stage between Paleozoic orogenic collapse and pre-Jurassic rifting. The crustal architecture associated with Mesozoic rifting of the Flemish Cap is also mapped and the interpreted distinct rift domains display along-strike variations. Overall, the complex tectonic history of the Flemish Cap involved dominantly ductile deformation during the Paleozoic orogenic stage, multiple deformation styles (primarily ductile and brittle–ductile) during the orogen-to-rift transitional stage and brittle deformation during the major Jurassic–Cretaceous rifting stage.

A Late Triassic depositional age for the Xujiahe formation, Sichuan basin: Implications for the closure of the Paleo-Tethys Ocean

The Late Triassic transition from marine carbonate rock to clastic in the Sichuan Basin, east of the Tibetan Plateau, not only records the evolutional process of peripheral foreland basin, but also preserves the evidence of closure of the Paleo-Tethys Ocean. The depositional age of the Xujiahe Formation, Late Triassic clastic, is debated. A new radiometric date based on sensitive high-resolution ion microprobe U–Pb ages for zircons grains from a tuff sample is presented here, which is used to reinterpret existing magnetostratigraphic data from the Xujiahe Formation. From these data, we infer a 224-210 Ma depositional age range for the formation. In addition, a comprehensive data set of seismic-reflection profiles and wire-line logs indicates there are four basinal scale unconformities (including U/C-1, U/C-2, U/C-3 and U/C-4) in the Late Triassic in the Sichuan basin. Together, the age constraints and hiatus relationships not only imply that the initiation of the Sichuan foreland basin is represented by the unconformity in the Late Carnian. This unconformity (U/C-2) is interpreted here to be the result of the closure of the Paleo-Tethys Ocean, and also indicate that the Sichuan foreland tectonics probably ceased by 211 Ma following the extensive lithosphere delamination from the Qiangtang to Songpan-Ganzi terranes. The new understanding of the tectonic and depositional evolution of the Sichuan foreland basin provides insight into the quasi-simultaneous collisional geodynamic processes of the Paleo-Tethys Ocean.

Formation evaluation utilizing a new petrophysical automation tool and subsurface mapping of the Upper Cretaceous carbonate reservoirs, the southern periphery of the Abu-Gharadig basin, Western Desert, Egypt

The southern periphery of the Abu-Gharadig basin in the Northern Egyptian Western Desert is characterized by some subsurface geological challenges related to the carbonate reservoir's quality, which requires precise petrophysical evaluation and seismic structural interpretation. Therefore, we conducted a subsurface mapping and formation evaluation for the Upper Cretaceous carbonate reservoirs in the Southwest Abu Sennan (SWS) area utilizing seismic reflection profiles and borehole geophysical data. Seismic mapping of the Upper Cretaceous carbonate reservoirs (Abu Roash (AR)/B,/D, and/F) revealed 3-way folds with NE-SW trends divided by NW-SE normal fault trends presenting significant chances for exploration. These closures were filled by hydrocarbons generated from the Jurassic source rocks. Formation evaluation was performed using the new petrophysical tool “Gaialog” which was coded using Python. Petrophysical parameters for the recognized net pay intervals of AR/B, AR/D, and AR/F carbonate reservoirs showed that the effective porosity (φeff: Phie) and the hydrocarbon saturation (Sh) increases towards the East to Southeast direction while the water saturation (Sw) increases to the Northwest of the study area. The highest net pay and the effective porosity were found in the Eastern part of the study area. The study procedures can be applied in neighboring areas to evaluate and understand similar reservoirs.

Late-Permian subduction-to-collision transition and closure of Paleo-Asian Ocean in eastern Central Asian Orogenic Belt: Evidence from borehole cores in the Songliao Basin, Northeast China

The process and timing of the closure of the Paleo-Asian Ocean remain uncertain. The upper Permian Linxi Formation in the Songliao–Xilinhot block provides a key sedimentary record of the closure of the eastern Paleo-Asian Ocean and the associated orogenesis. Here we present a seismic reflection profile and geochronological, paleontological, and geochemical data from 600 m of borehole cores (2022–1394 m depth) from the Songliao Basin to constrain the timing, provenance, and tectonic background of the Linxi Formation. Detrital zircons from the Linxi Formation yield a maximum depositional age of 257.4 ± 4.1 Ma. The formation was intruded by a syenite porphyry dike that crystallized at 245.6 ± 2.7 Ma. Furthermore, the paleontological assemblage indicates an upper Permian stratigraphic age. Borehole samples yield fingerprints of major oxides that are similar to clastic rocks in continental arc basins. Their Rb contents are relatively high (92 ppm on average), Rb/Sr (0.02–2.86) and Th/U (1.12–6.30) ratios are low, and (La/Yb)N and Eu/Eu* ratios are 3.85–8.13 and 0.54–0.98, respectively. These geochemical characteristics indicate a source of continental magma arc. Aided by discrimination diagrams, we propose that the Linxi Formation was deposited within a continental arc or on a continental margin during the closure of the Paleo-Asian Ocean. The Linxi Formation was deposited in a water body that experienced a gradual reduction in salinity, transitioning from a marine environment at the bottom to a transitional marine-terrestrial environment at the top. The water body also became gradually shallower and deposited sediment in the tectonic setting of continental arc. These changes indicate that there was a transition from subduction to collision during the Late Permian.

Fluid venting submarine structures in the middle slope of the Spanish continental margin of the Gulf of Cádiz: Geomorphology, internal structure, benthic features and control factors

This paper explains the current seafloor morphology and processes that affect the formation and evolution of three mud volcanoes and one mud volcano/mud diapir complex in the deepest sector of the Spanish margin of the Gulf of Cádiz. The present study provides novel results and interpretations based on an extensive multidisciplinary data set. New high resolution bathymetric and backscatter data from multibeam echosounders enabled a detailed geomorphological analysis aimed at identifying diverse seafloor features in the different edifices studied and their adjacent bottoms. These features are mainly related to fluid escape (e.g., mud volcanoes, mud flows and depressions), gravitational (e.g., slide deposits and scars), and tectonic (e.g., faults and uplifted antiforms) processes. Very high-resolution parametric profiles and single channel seismic reflection profiles were interpreted for further analysis of the internal structures, demonstrating their important interplay with diapiric processes. Box-corer and gravity-corer have been used to identify different sediment types that have been correlated with backscatter values. The dominant benthic species associated with fluid venting and also with different types of substrates (hard and soft) were characterized using submarine images obtained with an underwater camera deep-towed sled. The benthic species observed were contrasted, and added to those collected with beam trawl and box-corer for characterisation of the benthic and demersal communities. Different geological and biological indicators have been used as proxies of the interaction of these features with the geological processes (such as fluid-escape-related, gravitational, or structural) to characterise the environmental conditions that determine the geomorphology, substrates, habitats and their associated biota. Multivariate analyses combining faunistic and environmental data resulted in the presence of 3 main faunistic assemblages linked to different levels of fluid venting and the importance of depth and variables linked to fluid venting processes (e.g. mud breccia, Methane-derived authigenic carbonates) in the distribution of these assemblages. A conceptual model has been proposed to explain the actual seafloor morphology and the different processes that affect the formation and evolution of the fluid venting submarine structures studied.

Evolution of an oblique volcanic passive margin: The case of Nuussuaq in West Greenland

Most rifted margins involve a certain degree of obliquity. Oblique extension has been well-studied in a magma-poor continental rift setting. However, few studies have addressed the structure and evolution of oblique rifting in a magma-rich continental rift setting. In this study, we used remote sensing and field measurements combined with geophysical data in order to study the tectono-magmatic evolution of seaward-dipping basalt sequences, known also as seaward dipping reflectors (SDRs), along the western Nuussuaq oblique volcanic passive margin. We calculated the directions and dips of lavas within onshore SDRs based on remote sensing and field data and analyzed the offshore SDRs through seismic reflection profiles to obtain a precise 3D structure of the inner SDRs along this margin. Our results show that the development of the inner SDRs can be divided into two stages. During the first stage (the late Paleocene), the oblique extension was partitioned into strike-slip and dip-slip components, and the basalt sequences were mainly bounded by N-S-trending continentward-dipping faults. During the second stage (the early Eocene), a local stress reorientation occurred in the western Nuussuaq and the basalt sequences were mainly bounded by NE-SW-trending continentward-dipping faults. The obliquity of the margin originated from both the reactivation of the inherited Itilli Fault and the magma intrusion into the crust, which weakened the crust and produced a pressure-induced extension orthogonal to the margin.

Delineating tidal channel feature using integrated post-stack seismic inversion and spectral decomposition applications of the Upper Cretaceous reservoir Abu Roash C: A case study from Abu-Sennan oil field, Western Desert, Egypt

Delineating tidal channels that bear hydrocarbons in fluvial systems is crucial to minimize drilling risks, and raise the hydrocarbon potential. Therefore, we performed an integrated workflow that combines/compares the outcomes of a pair of post-stack inversion techniques (model-based inversion and colored inversion) and the spectral decomposition attribute to delineate (vertically and horizontally) the hydrocarbon-bearing tidal channel contained in the Upper Cretaceous Abu Roash (AR)/C reservoir in the South West Abu-Sennan (SWS) area in Abu-Gharadig basin in the Northern Egyptian Western Desert (NEWD). We used a dataset consisting of twenty seismic reflection profiles and borehole geophysical data of four wells. Data conditioning was performed in detail for the whole dataset that was used in this study. The application of the absolute impedance (model-based inversion) produced better results relative to the band-limited acoustic impendence (colored inversion). The model-based inverted sections gave an improved subsurface image of seismic data and delineated the reservoir properly. The low-frequency range detected through the use of seismic inversion techniques and the spectral decomposition attribute analysis showed a good fit with the low impedance values corresponding to hydrocarbons. The study results showed a correlation of roughly 0.99 exists between the generated synthetic impedance, original seismic, and the borehole geophysical data characterizing the tidal channel confined within the AR/C reservoir. The match between the post-stack inversion techniques and the spectral decomposition analysis results is considered a visual validation of the delineated tidal channel. The performed workflow can be applied and impact the understanding of comparable reservoirs with similar settings in near areas.

Buried Alive: Imaging the 9 November 2022, Mw 5.5 Earthquake Source on the Offshore Adriatic Blind Thrust Front of the Northern Apennines (Italy)

AbstractThe prompt identification of faults responsible for moderate‐to‐large earthquakes is fundamental for understanding the likelihood of further, potentially damaging events. This is increasingly challenging when the activated fault is an offshore buried thrust, where neither coseismic surface ruptures nor GPS/InSAR deformation data are available after an earthquake. We show that on 9 November 2022, an Mw 5.5 earthquake offshore Pesaro ruptured a portion of the buried Northern Apennines thrust front (the Cornelia thrust system [CTS]). By post‐processing and interpreting the seismic reflection profiles crossing this thrust system, we determined that the activated fault (CTS) is an arcuate 30‐km‐long, NW‐SE striking, SW dipping thrust and that older structures at its footwall possibly influenced its position and geometry. The activation of adjacent segments of the thrust system is a plausible scenario that deserves to be further investigated to understand the full earthquake potential of this offshore seismogenic source.

Mapping crustal structure across southern Australia using seismic ambient noise tomography

The rocks of southern Australia record over three billion years of Earth’s evolution, but the basement geology is veiled by sediment. Geophysical data are needed to unveil the geology. The 2018–2022 Lake Eyre Basin and 2020–2022 AusArray SA seismic arrays expand seismic coverage in South Australia. In conjunction with permanent and preceding temporary arrays, we extracted Rayleigh wave dispersion data from ambient noise recordings at a total of 501 seismic stations spanning the transition from Precambrian to Phanerozoic Australia. These data were used to develop Rayleigh wave phase velocity maps of southern Australia at periods 3–20s, and in turn, a shear wave velocity model to 20km depth. At upper-crustal depths, low velocity structure tracks Phanerozoic sedimentary accumulations. The Moyston Fault, regarded as the boundary between the Delamerian and Lachlan Orogens, has an intermittent expression in the shear velocity model: it has no obvious expression at depths shallower than ∼10km, but in the mid-crust is marked by a velocity contrast in southern Victoria and a velocity contrast tracing the southern edge of the Darling Basin in western New South Wales. An arcuate velocity contrast characterising the western edge of deep, sediment-filled troughs of the Darling Basin is a candidate for the transition from Precambrian to Phanerozoic crust. Fluid derived from neotectonic metamorphic devolatilization and/or remnant hydrated mantle is our preferred hypothesis for explaining seismicity and coincident seismic and conductivity anomalies in the mid-to-lower crust beneath the Ikara–Flinders Ranges. Our model suggests that the Olympic Dam and Carrapateena IOCG deposits reside above the margin of a mid-crustal low seismic velocity zone. We surmise that this might reflect past metalliferous fluid movement associated with the Olympic Cu-Au Province, akin to low reflectivity and low resistivity zones evident in 2D reflection seismic and magnetotelluric profiles, respectively.

Intracontinental convergence accommodated by underthrusting of Tarim Basin beneath central Tian Shan, Central Asia: Insights from Cenozoic upper crust deformation across the western Kepingtage fold-and-thrust belt in the northern Tarim Basin

The way in which intracontinental convergence caused by remote continent-continent collision has been accommodated remains debatable, but it is attributed to either pure shear thickening or continental subduction/underthrusting. Quantification of the deformation architecture of the upper crust and its shortening is vital for testing these competing models. For this purpose, we conducted quantitative analyses of four seismic reflection profiles along the western Kepingtage fold-and-thrust belt of the intracontinental convergence zone between the northern Tarim Basin and the central Tian Shan, a result of the remote India-Eurasia collision, which capture the structures of the upper crust and constrain the amount of shortening in the region. The structural analyses show a thin-skinned style of deformation of the western Kepingtage fold-and-thrust belt, with minimum north−south shortening estimates of ∼71.1 km (∼46.6% strain), ∼76.3 km (∼51.4% strain), ∼67.1 km (∼56.1% strain), and ∼53.0 km (∼49.9% strain), respectively, from east to west. Assuming that coupling shortening occurred across the entire crust and an initial crustal thickness of ∼41−46 km, these shortening ratios would produce a ∼83−95-km-thick crust along the northern Tarim Basin, which is significantly larger than the actual thickness previously reported. This inconsistency leads us to rule out the pure-shear thickening model, which predicts crustal-scale coupling deformation. Alternatively, our results imply that the crust of the northern Tarim Basin was deformed in a decoupling style. These results, combined with those of previous studies, lend support to the intracontinental underthrusting model. We suggest that both the upper crustal fold-and-thrust belts and the lower crustal underthrusting of the northern Tarim Basin accommodated intracontinental convergence.

Tracing the “missing shortening” in fold-and-thrust belts: Insights from structural analyses of the Hotan-Mazatagh transect in the West Kunlun foreland, NW China

Use of balanced cross-section methods, which assume length and area conservation in two dimensions, to quantitatively analyze fold-and-thrust belts is vital in structural analyses. However, layer-parallel shortening is beyond this assumption and thus indescribable by balanced cross-section methods. The contribution of layer-parallel shortening in accommodating shortening has rarely been quantitatively determined, especially in sections hundreds of kilometers in scale. In this study, we conducted structural analyses on the ∼230-km-long Hotan-Mazatagh transect along the West Kunlun foreland of the NW Tibetan Plateau, based on interpretations of seismic reflection profiles. The results reveal that the transect forms a long thrust sheet detaching along the basal Cenozoic detachment, with deformation localized in the Hotan, Manan, and Mazatagh belts. Out of the ∼23.82 km of cutoff displacement translating into the thrust sheet, only ∼1.4 km and ∼4.94 km are absorbed by the Hotan anticline and the Mazatagh detachment thrust, respectively. The remaining ∼17.48 km extent of shortening is absorbed by layer-parallel shortening in the ∼180-km-long section between the Hotan and Mazatagh belts. The layer-parallel shortening produces a strain rate of ∼2.43 × 10−8 yr−1 and absorbs ∼77.97% of the shortening of the segment. Our results argue for caution when using balanced cross-section methods to determine deformation magnitudes. We suggest that localized deformation and layer-parallel shortening function together to shape the ∼230-km-long Hotan-Mazatagh transect into a combined discrete-and-distributed deformation style.

Active faulting in the Beagle Channel (Tierra del Fuego)

AbstractIn Tierra del Fuego, the Magallanes‐Fagnano Fault System (MFFS) accommodates a significant portion of the relative motion between the South America and Scotia plates. However, it remains unclear whether some of the deformation is partitioned southwards, along the Beagle Channel Fault System (BCFS). In this paper, high‐resolution seismic reflection profiles were used to identify fault‐related ruptures in the submerged Quaternary sediments of the Beagle Channel. Some faults reach the seafloor, affecting marine sediments, indicating they are Holocene in age. The correlation with outcrop data and lineaments mapped onshore suggests the post‐glacial reactivation of two structures: the E‐W striking BCFS and the NW‐SE‐trending Lapataia Fault Zone (LFZ). Whereas the BCFS displays along‐strike variation in throw, the LFZ shows significant normal displacements. These results imply that deformation occurs in a wider and more complex manner than previously thought and highlight the need for a thorough hazard assessment of the area.

Joint Inversion of Geodetic and Strong Motion Data for the 2012, Mw 6.1–6.0, May 20th and May 29th, Northern Italy Earthquakes: Source Models and Seismotectonic Interpretation

AbstractWe present the first rupture models of the two mainshocks of the 2012 northern Italy sequence, determined by jointly inverting seismic and geodetic data. We aim at providing new insights into the mainshocks for which contrasting seismotectonic interpretations are proposed in literature. Sources' geometric parameters were constrained by seismic reflection profiles, 3‐D relocations and focal mechanisms of mainshocks/aftershocks. Site‐specific velocity profiles were used to model accelerograms affected by strong propagation effects related to the Po basin. Our source models differ significantly from previous ones relying on either seismic or geodetic data. Their comparison against geological sections and aftershock distribution provides new insights about the ruptured thrust faults. The May 20th Mw6.1 mainshock activated the Middle Ferrara thrust‐ramp dipping ∼45° SSW‐wards, breaking a main eastern slip patch 4–15 km deep in Mesozoic carbonates (maximum slip 0.7–0.8 m) and Paleozoic‐Triassic basement rocks, and a small western patch in the basement. The May 29th Mw6.0 mainshock featured two separated asperities along the Mirandola thrust‐ramp dipping ∼42° S‐wards: an eastern asperity 4–15 km deep in Mesozoic carbonates and basement rocks (maximum slip 0.7 m) and a deeper western one (7–16 km depth) mainly in the basement (slip peak 0.8 m). On‐fault aftershocks were concentrated within the basement and Mesozoic carbonates, devoiding high‐slip zones. Slip and aftershock distribution was controlled by the rheological transition between Mesozoic carbonates and Cenozoic sediments. Unlike previous thin‐skinned tectonic interpretations, our results point to a complex rupture process along moderately dipping (40°–45°) thrust‐ramps deeply rooted into the Paleozoic crystalline basement.

MORPHOLOGY OF LAKES OF THE CENTRAL TUNGUSKA PLATEAU (SIBERIA, EVENKIA): NEW INFORMATION ON THE PROBLEM OF THE “TUNGUSKA EVENT 1908”

The bottom morphology and thickness of bottom sediments of lakes Zapovednoye and Peyungda were studied by echo-sounding and seismic reflection profiling. The lakes are located in 60 km and 50 km from inferred explosion epicenter of “Tunguska event 1908”, respectively. We showed that both lakes have circular shape and funnel-like morphology with 60 and 34 m maximum water-depth, respectively, close to their geometrical centers. The shape of the lake is similar to famous Lake Cheko which is believed to be a secondary impact crater for Tunguska event of 1908. The shape of Lake Cheko was suggested to be highly unusual that was one of arguments to support the hypothesis of impact origin of Lake Cheko. We have shown that lakes Zapovednoye and Peyungda are examples of funnel-like deep lakes, and the age of both lakes exceeds are two thousand years. Therefore, we assume that all three lakes are most likely of karst origin. The similarity of the shape of the three reservoirs and their location in the riverbeds indicate the similar origin and testify against the hypothesis of the impact origin of Lake Cheko in 1908.

Rift Basins and Intraplate Earthquakes: New High‐Resolution Aeromagnetic Data Provide Insights Into Buried Structures of the Charleston, South Carolina Seismic Zone

AbstractThe delineation of faults that pose seismic risk in intraplate seismic zones and the mapping of features associated with failed rift basins can help our understanding of links between the two. We use new high‐resolution aeromagnetic data, previous borehole sample information, and reprocessed seismic reflection profiles to image subsurface structures and evaluate recent fault activity within the Charleston seismic zone, the associated Mesozoic South Georgia rift basin, and surrounds. The new aeromagnetic data provide an unprecedented view of buried basement structures. NE‐ and NW‐trending lineaments of various lengths throughout the survey area are interpreted as Paleozoic orogenic structures and Mesozoic dikes, respectively. Within the rift basin, 15‐ to 20‐km long ESE‐trending lineaments are associated with faults in pre‐Cretaceous strata of the reflection data and are interpreted as Mesozoic rift structures. Various intersections and terminations of interpreted faults suggest rift‐related reactivation of Paleozoic faults and corresponding inheritance for Mesozoic structures. The reflection data show that several Paleozoic and Mesozoic faults are associated with deformation in Cretaceous and younger sediments, suggesting reactivation in the more recent passive margin setting. Two of these faults, one NE‐striking and one ESE‐striking, are coincident with surficial landforms, suggesting Quaternary slip; the ESE‐striking fault is also well‐aligned with a plan‐view offset in modern seismicity. A favorable orientation for reverse motion on ESE‐striking Mesozoic faults, a possible sub‐basin, and potentially weakened lithosphere are failed rift basin features that may influence intraplate seismicity within the Charleston seismic zone.

Cenozoic Shortening and Propagation in the Eastern Kuqa Fold‐And‐Thrust Belt, South Tian Shan, NW China

AbstractIn an orogen‐foreland basin system, syn‐orogenic sedimentation and deformation records within the foreland basin provide critical evidence for understanding uplift and erosion processes of adjacent orogenic belts. Foreland fold‐and‐thrust belts (FTBs) are widely developed around the Tian Shan range, Central Asia. Problem of how crustal shortening accumulates and propagates from the Tian Shan to adjacent foreland basins is essential for understanding the overall dynamics of Tian Shan. In this study, we interpreted three high‐resolution seismic reflection profiles to estimate the magnitude and distribution of Cenozoic shortening across the Eastern Kuqa FTB, South Tian Shan foreland. Combined with well‐dated syntectonic stratigraphy, we further evaluate the timing, rate, and migration of the deformation front of the Kuqa FTB. Our results suggest that the Kuqa FTB's total crustal shortening increases westward. The distribution of crustal shortening across secondary structural belts shows a gradual, basinward decrease, which can be explained by the telescoped mechanism. Propagation rates of the Kuqa FTB's deformation front indicate an episodic propagation of the foreland thrust wedge, with an acceleration after ∼12 Ma. Similar episodic propagation pattern has also been observed in other foreland FTBs around the Tian Shan, but they show significant spatio‐temporal variations in the propagation stages and related rates.

The 2021 Mw 5.2 Baicheng Earthquake: Implications for the Hazards of Extremely Shallow Earthquakes

Abstract On 23 March 2021, an Mw 5.2 earthquake struck Baicheng city at the southern foreland of the Tian Shan mountains and produced unexpected severe damages. Based on Interferometric Synthetic Aperture Radar observations, geological investigations, petroleum seismic-reflection profiles, and available seismological results, we found that (1) the earthquake rupture was sinistral-slip dominated and mostly concentrated at ≤2 km depth, suggesting an extremely shallow earthquake; (2) the earthquake produced a 4.1-km-long surface rupture zone, along which the lateral slip ranged from 0 to 135 cm and showed a significant short-wavelength variation; and (3) the causative fault is poorly developed (i.e., has low slip accumulation and slip rate) and cuts through a shallow-buried salt dome. These findings, along with those of previous studies, document some unique characteristics of moderate earthquakes at extremely shallow depths (≤3 km) relative to those at greater depths. First, shallow earthquakes occur on faults that are poorly developed and bracketed by rocks being able to behave as velocity weakening at shallow depth (including crystalline basement rocks, carbonites, volcanic rocks, or evaporites). Second, the surface rupture produced by shallow earthquakes has abnormally large length and slip, and possibly includes an abrupt slip variation. These characteristics highlight potential severe damages of the shallow moderate earthquake but enhance the challenge of identifying the earthquake causative fault (the earthquake source) prior to the event using traditional methods (e.g., geomorphic mapping, geophysical imaging surveys, and paleoseismic trenching).

Cretaceous magmatic underplating and delamination beneath continental SE Brazil and their tectonic implications: Evidence from the PABBRISE wide-angle reflection and refraction seismic profile

Controlled-source seismology provides robust methods to obtain information on the velocity structure of the crust and uppermost mantle. We present the first systematic wide-angle reflection and refraction (WARR) seismic experiment for continental southeastern Brazil: the NW-SE-oriented and ca. 700 km-long PABBRISE (PAraná Basin, Brasília and RIbeira orogens Seismic Experiment) profile. Using ray tracing, we obtained a two-dimensional P-wave seismic velocity model of the crust and uppermost mantle. Our model shows that Moho depths vary between ca. 31 and 45 km, with crustal thinning towards the continental margin. The modeled velocity structure sheds new light on the present-day lithospheric morphology of the region, with the most striking features noted within the lower crust and uppermost mantle. We show that beneath the Paraná Basin, parts of the lower crust and uppermost mantle were pervasively intruded due to magmatic underplating. We modeled a ca. 200 km-long and 11 km-thick (maximum thickness), high-velocity (7.20–7.80 km/s) lower crustal (HVLC) body in this region. Outside the Paraná Basin, near the continental margin, comparatively thinner crust (∼31 km) with low mean P-wave velocity (6.20 km/s) and a low velocity (<7.90 km/s) uppermost mantle probably are the result of delamination. Magmatic underplating and delamination can be linked with the breakup of Pangea and the opening of the South Atlantic Ocean during the Cretaceous.

Silurian-Holocene tectonostratigraphy of Abu Dhabi, United Arab Emirates

The Emirate of Abu Dhabi is located south of the Arabian Gulf and is home to several prolific oil- and gas fields. The stratigraphic column is up to 15 km thick and reflects a complex history of extensional and compressional deformation since the Silurian. Here, we integrate sizable 2D seismic reflection profiles, 3D seismic volumes, and data from over 500 exploration wells to investigate the Silurian-Holocene tectonostratigraphic framework of Abu Dhabi and the adjacent areas. Seven seismic sequences were identified from well-log properties, seismic reflection configurations, reflector geometries, and reflection terminations: Silurian, Devonian-mid-Permian, Upper Permian-Jurassic, Lower Cretaceous-Turonian, Upper Cretaceous, Paleocene-Eocene, and Oligocene-Holocene. The sequences include regional-scale unconformities that can be linked to the tectonic evolution of the Arabian Plate. Four tectonostratigraphic units were defined by distinct seismic sequences, regional stratigraphic gaps, and plate-wide tectonic settings including intracratonic, back-arc to rift margin, passive margin, and compressional phases. In addition to basins with a tectonic origin, four intrashelf basins developed in the area at various times due to a combination of climatic and eustatic variations with differential intraplate subsidence. These basins encompass important hydrocarbon habitats in the basinal and organic-rich deposits of the Upper Jurassic Diyab, Lower Cretaceous Habshan and Shuaiba, and Upper Cretaceous Shilaif formations. An improved understanding of the tectonostratigraphic framework of Abu Dhabi facilitates hydrocarbon exploration endeavors by ascertaining the hydrocarbon prospectivity of deep plays in the region.

Cenozoic Fault Growth Mechanisms in the Outer Apulian Platform

This work focuses on a ca. 55 km-long extensional fault zone buried underneath the foredeep deposits of the southern Apennines, Italy, with the goal of deciphering the Cenozoic fault growth mechanisms in the Outer Apulian Platform. By considering public 2D seismic reflection profiles, well logs, and isochron maps data, the study normal fault zone is interpreted as made up of four individual fault segments crosscutting Top Cretaceous, Top Eocene, Top Miocene, and Top Pliocene chrono-stratigraphic surfaces. The computed cumulative throw profiles form either bell-shaped or flat-shaped geometries along portions of the single fault segments. The computed incremental throw profiles also show an initial fault segmentation not corresponding with the present-day structural configuration. Data are consistent with the initial, post-Cretaceous fault segments coalescing together during Miocene–Pliocene deformation and with fault linkage processes localizing at the stepover/relay zones. Pleistocene faulting determined the evolution of a coherent fault system. The computed n-values obtained for the single time intervals by considering the maximum fault throw–fault length relations indicate that the fault segments formed scale-dependent geometries. Variations of these computed values are interpreted as due to the higher degree of maturity reached by the entire fault system during Miocene to Pleistocene deformation.