Marta Neres

The largest and longest ocean bottom seismometer (OBS) experiment so far in the Atlantic Ocean occurred as part of the UPFLOW project to better constrain upward mantle flow, which is crucial to understanding global mantle flow. UPFLOW deployed 50 and recovered 49 OBSs in a ∼ 1,000 × 2,000 km2 area in the Azores-Madeira-Canary islands region with a station spacing of ∼110-160 km between June 2021 and August 2022. Most instruments had three-component broadband seismic sensors and hydrophones, and three different designs of OBS frames were used. Our analysis shows ∼91 % data completeness. Vertical-component long-period noise (T>∼30s) is reduced compared to previous experiments. The orientations of horizontal components were estimated from the polarisation of long-period body and surface waves from teleseismic events. Earth’s free oscillations with frequencies as low as ∼1.8 mHz are observed following two Mw > 8 earthquakes, and the signal-to-noise ratio of these observations is enhanced after applying tilt and compliance corrections. We show illustrative recordings and spectrograms of teleseismic and local events as well as non-seismic signals (whales, instrument resonances), demonstrating the wide variety and richness of UPFLOW data and their potential to address many outstanding questions in solid Earth sciences, oceanography, and marine biology.

Southwest Portugal is the most seismically active region in Portugal mainland. Historical and instrumental seismicity, transpressive deformation accommodated by brittle structures (from which NNE-trending reverse left-lateral faults are the prominent ones), and uplifted marine landforms attest for the ongoing Quaternary crustal deformation. Geophysics highlights a positive gravimetric anomaly, consistent with the uplifted area. Simultaneously, geodesy suggests this region to be limited northward by a likely continuous right-lateral NW-trending structure, inferred to be 90 km long. However, this inferred structure is poorly understood, and southward partially overlaps a known active fault (São Marcos Quarteira) for ~50 km. The northward remaining length of 40 km lacks recognition of Quaternary deformation, despite a noticeable 50-100 m height scarp in the landscape along a ~10 km segment. This geomorphic feature has not been interpreted as an active fault, but as an inherent Variscan structure, possibly reactivated during the Miocene and since, evolved as a scarp retreated due to differential erosion promoted by the presence of Paleozoic quartzites, which are more resistant to erosion.We present a preliminary analysis based on recently available 50 cm high-resolution lidar and revisited Plio-Quaternary data, together indicating evidence of likely subtle geomorphic deformation, which is expressed by small linear features NW-trending, some associated with changes of topography across a ~2km wide area. We propose these features to possibly correspond to subtle evidence of a cryptic fault system, likely to correspond to an inherited fabric, that has been reactivated. The newly discovered features will be investigated through combining geology, geophysics, and geochronology methods. Fault reactivation will be investigated through a detailed analysis of the damage zone and fault gouge, applying trapped-charges dating methods, namely OSL (Optically Stimulated Luminescence) and ESR (Electron Spin Resonance).This work is supported by FCT, I.P./MCTES through national funds (PIDDAC): LA/P/0068/2020-https://doi.org/10.54499/LA/P/0068/2020, UID/50019/2025, https://doi.org/10.54499/UID/PRR/50019/2025 ,UID/PRR2/50019/2025 and by Marie Skłodowska-Curie Actions, European Union (project SEISMO-REACT, GA101211167). Keywords: Quaternary activity, seismogenic sources, low strain deformation, cryptic structures, SW Iberia

We investigate the magnetic structure of the M-series and J-anomaly oceanic crust in the Central Atlantic with the integration of seismic data in magnetic anomaly modelling. We find that traditional magnetic models of oceanic crust, which assume uniform layers with constant magnetization and geomagnetic polarity reversals, fail to explain the observed anomalies, especially the lack of high-frequency reversals. This suggests that the complex 3D crustal structure created at slow to intermediate spreading rates plays a significant role in the anomaly patterns, because faulting and magmatic processes act as geological filters. Our new modelling approach includes defining the magnetic structure using the crustal seismic structure to adjust the magnetic layer thickness, and laterally varying the magnetization intensity. We explain the high amplitude of the J-anomaly due to a Fe-Ti enrichment in the magma and not to increases in layer thickness as previously proposed. We also discover a previously unrecognized K-anomaly, younger than the J-anomaly. We provide a new kinematic reconstruction of the central Atlantic showing asymmetry in the magnetic and crustal structure between the African and American plates. These findings emphasize the importance of combining seismic data to realistically model magnetic data and better understand crustal formation at slow-spreading ridges.This work has been funded by the Spanish Ministry of Science and Innovation MCIN/AEI under project ATLANTIS (ref. PID2019-109559RB-I00), and by the Portuguese Fundação para a Ciência e Tecnologia FCT, I.P. / MCTES under project LISA (https://doi.org/10.54499/PTDC/CTA-GEF/1666/2020) and through national funds (PIDDAC): LA/P/0068/2020 (https://doi.org/10.54499/LA/P/0068/2020), UID/50019/2025 (https://doi.org /10.54499/UID/PRR/50019/2025), UID/PRR2/50019/2025.

Within the framework of Portuguese policy for the energy transition and economy decarbonisation, the Portuguese Institute for the Sea and the Atmosphere (IPMA) is carrying out project RP-C21-i07.01 – Technical studies for offshore energy potential. This project, funded with 42 M€ by the European Recovery and Resilience Plan, through the component C21-REPOWEREU of the Climate Transition dimension, aims to support Portugal’s ambitions regarding energy independence and ecological transition, in the context of new geopolitical and energy market challenges.Led by the Marine Geology and Geophysics Laboratory (SEISLAB) team at IPMA, the projects is developing studies to provide detailed data on the geological, geophysical and geotechnical properties of the seafloor, as well to define an environmental baseline. The main objective is to support offshore wind farm developers regarding engineering and financial planning, thereby providing the basis for launching auctions in offshore areas designated for windfarm development in the Portuguese Allocation Plan for Offshore Renewable Energy (PAER).This project started in early 2024, has a duration of 2.5 years and focuses on surveys in the PAER areas of Leixões and Figueira da Foz, totalling approximately 2000 km2, located offshore the western Portuguese mainland coast, at water depths ranging from 120 m to 530 m.Hydrographic and geophysical survey methodologies included multibeam echosounder (MBES), side scan sonar (SSS), magnetometer (MAG), two sub-bottom profilers (SBP) and multichannel ultra high-resolution seismic (UHRS) reflection data. Geotechnical methodologies included cone penetrating tests (CPT) and sedimentological and physical properties of sediments recollected with grabs and Vibrocoring (VC).Preliminary works conducted in 2024 included desktop studies and exploratory surveys with the acquisition of approximately 2000 km of geophysical data (MBES, SBP, UHRS). Survey activities carried out in 2025 involved the acquisition of circa 15000 km of geophysical data (MBES, SSS, MAG, SBP, UHRS), 122 grabs samples, 71 VCs and 43 CPTs.Seafloor surface characterisation relied on cartographic products derived from the MBES and SSS mosaic datasets, as well as on the identification of outcropping units from the seismo stratigraphic model calibrated with the geotechnical data. Seafloor features, including landforms and contacts were interpreted from the MBES and SSS data and validated against magnetic anomalies. These included anthropogenic features like shipwrecks, trawl marks and lost objects (e.g. fishing gear) and geological features like sorted bedforms, boulders, sinkholes and outcrops.Sub-seafloor seismic data reveal a complex geological framework associated with the rifted margin and orogenic units. The upper units are dominated by unconsolidated sediments and polyphase channel complex events associated with sea level variations, while the lower units frequently display mass-transport deposits, extending for tens of kilometres, tectonic deformation and faulting.Environmental analysis are based on water and sediment analytical work and on the characterisation of species communities, aiming to establish the biodiversity baseline and assess the environmental condition. Surveys were conducted in compliance with the Joint Nature Conservation Committee guidelines.The thematic cartography resulting from these pioneering and unprecedented studies in Portugal constitutes a key asset for the development of the floating offshore wind industry, supporting the ongoing Portuguese energy transition

The J magnetic anomaly in the Central Atlantic has 10 times larger amplitude than surrounding seafloor‐spreading magnetic lineations and is often associated with thick oceanic crust formed by excess magma. The anomaly has also been identified in the southern North Atlantic, where it has been linked to the onset of seafloor spreading, challenging traditional 2D models of lithospheric break‐up offshore Iberia. These findings underscore the importance of constraining the crustal structure along the J anomaly to fully understand its genetic processes and geodynamic significance. Yet, the crustal structure in the Central Atlantic, where the anomaly is strongest, remains poorly defined by low‐resolution legacy seismic data. We present wide‐angle and multichannel seismic data from the 2022 ATLANTIS survey across the J anomaly at ∼31°N in the Central Atlantic. We use 2D seismic tomography to invert for P‐wave ( Vp ) and S‐wave ( Vs ) velocities. Results reveal significant lateral variations in igneous basement thickness and seismic velocities, contradicting the idea of uniformly thick crust. The peak of the anomaly is not aligned with the thickest segment (10 km) but with a region where oceanic layer 3 exhibits the fastest Vp and Vs . Variations in basement thickness are accompanied by lateral differences in Vp / Vs , reflecting changes in composition and/or basement fracturing. These findings suggest diverse crustal accretion processes, influenced by a fertile mantle source and short‐term mantle temperature differences during the formation of the J anomaly.

The high amplitude J magnetic anomaly is usually described as corresponding to the M3-M0 anomalies of the M-series and marks the boundary with the Cretaceous Normal Superchron in the Central Atlantic. A seafloor spreading nature of J is undisputed, but remains debated a potential extension into the southern North Atlantic west of Iberia, with its implications for the kinematic reconstructions of the rift-to-drift transition of Iberia-Newfoundland margins. To image the structure of the J anomaly, coincident wide angle seismic, multichannel seismic and magnetic data were collected across the Mesozoic oceanic crust at ~31°N during the ATLANTIS cruise in 2022. A seismic tomography model reveals a complex velocity structure with significant lateral crustal thickness variation that is at odds with the classical view of a uniformly thick J anomaly crust. Instead of the invoked excess magma production, the structure supports complex variation of the seafloor spreading processes.We present new magnetic modeling for the ATLANTIS profile that constrains the geometry of the magnetic layers with the seismic velocity model, the basement and Moho topography, and the crustal thickness. We first show the canonical approach of modeling the oceanic crust as a constant thickness layer with alternating polarity blocks, which is not able to match neither the amplitude nor the wavelength of anomalies, either considering constant depth or integrating top of basement topography for the magnetic layer. This may be related to the slow spreading processes that tend to cancel short wavelength anomalies and decrease the anomaly amplitude, which strongly suggests that the crustal structure should be integrated in magnetic modeling, especially of non-fast spreading crust.We used the seismic velocity structure to constrain the thickness of the magnetic layer, either from 6.0 or 6.5km/s isovelocity contour, or varying proportionally to total crustal thickness. Our results show that the M-series domain (up to M3n) can be modeled by defining the magnetic layer thickness as ~20% of total crustal thickness and with a simplified alternating polarity sequence. For the J-anomaly domain, however, a simple relation doesn’t apply, and adjustments in the layer thickness and magnetization are required. A progressive increase in magnetization is needed from the time of M3n onwards, reaching maximum values between M1r and M0r anomalies and decreasing towards the CNS. The magnetic layer thickness follows the same tendency. However, the crustal thickness varies in a much distinct way: maximum magnetization values are modeled at the thinner crust, and intermediate magnetization is kept for the region where the crust is thicker, already located at the CNS and offset of the highest anomaly amplitude.These results challenge the use of classical methods to model oceanic magnetic anomalies generated at slow spreading centers, and more particularly, the classical view of the J-anomaly structure. A temporal lag is suggested between the source mantle processes that originated the alteration of magma composition to higher magnetization (mantle fertility / chemical composition) and the increase in crustal thickness (likely more related to mantle temperature).Work supported by the Portuguese FCT, I.P./MCTES through national funds (PIDDAC): UID/50019/2025, UIDB/50019/2020 (https://doi.org/10.54499/UIDB/50019/2020) and LA/P/0068/2020 (https://doi.org/10.54499/LA/P/0068/2020).

The Instituto Português do Mar e da Atmosfera (IPMA) is undertaking extensive high-resolution geophysical and geotechnical studies over two areas proposed for the development of offshore windfarms in Portugal, surveying an area of circa 2000 km2. Leixões and Figueira da Foz study areas are located off the Portuguese mainland west coast, at depths between 120m and 530m, distant 21nm to 35nm to the coastline.The aim of this work, being conducted between February 2024 and June 2026, is to provide detailed data on the morphology, geology, geophysics and geotechnical properties of the seafloor to inform offshore wind farm developers towards engineering and financial strategies, therefore providing the basis for launching subsequent auctions for the offshore areas listed in the Portuguese National Maritime Spatial Planning Situation Plan.An initial exploratory campaign, commissioned to the Portuguese Hydrographic Institute, collected the initial MBES data (bathymetry and backscatter) and surface sediment sampling. Furthermore, in August-September 2024, a geophysical survey took place on board IPMA’s NI Mário Ruivo and retrieved over 2100 km of seismic data, from parametric sub bottom profiler (SBP) and multi-channel ultra-high resolution seismic reflection (UHRS). Preliminary results attest the scientific richness of the dataset already collected as well as the complexity and diversity of the seimostratigraphy present in the surveyed areas. Seabed morphology, sediment textural features, seismic horizons and geohazards have been identified which allow inference of a preliminary geomodel of the areas and the planning of subsequent surveys.Between May and November 2025 a survey will take place expanding the resolution of data collected (> 20 000 km lines planned) but also adding additional methodologies (magnetometer, side scan sonar, vibrocorer and CPT’s).The data to retrieve over these 2 years will allow to produce a detailed Terrain model supporting a holistic data interpretation, essential for succeeding actions in the pioneering development of floating wind farms offshore Portugal.This comprehensive geophysical and geotechnical characterization represents a pioneering effort in Portugal's energy transition, providing crucial data for the sustainable development of offshore wind energy and potentially serving as a model for similar initiatives.This research was funded by PRR funds - RP-C21-i07.01 - Technical studies for offshore energy potential. This work is also supported by the Portuguese Fundação para a Ciência e Tecnologia, FCT, I.P./MCTES through national funds (PIDDAC): UID/50019/2025, UIDB/50019/2020 (https://doi.org/10.54499/UIDB/50019/2020) and LA/P/0068/2020 https://doi.org/10.54499/LA/P/0068/2020).

The LISA and ATLANTIS geophysical cruises were conducted in 2021 onboard the Spanish R/V Sarmiento de Gamboa. We collected wide-angle seismic reflection and refraction (WAS) data (ATLANTIS) and coincident streamer data (FRAME) to constrain the seismic velocity structure on the region to the west of the Gorringe Bank (West Iberia Margin), where the nature and structure of the lithosphere are mostly unknown. The LISA profile runs across different geological domains: from the Ampère seamount at SE, the West Horseshoe Abyssal Plain, the region of the Josephine seamount (at the intersection of the Tore-Madeira Rise with the Gloria fault) and the undisputed North Atlantic oceanic domain to the NW.WAS data were acquired with 21 ocean bottom hydrophones (OBH) spaced at ~15 km, along a NNW-SSE oriented, ~400 km long profile, at 250 Hz sampling frequency. The seismic source was designed to provide high penetration and map the entire crust and the upper mantle structure and consisted of two sub-arrays of 16 airguns with total volume of 5200 c.i., towed at 15 m depth. Multichannel seismic reflection (MCS) streamer data were also acquired with a 6 km long streamer towed at 23 m and using the same seismic source.OBH sections were analyzed for picking of Ps, Pg, PmP and Pn phases, and show high variability along the profile. Joint inversion of refraction and reflection travel times of key boundaries observed in the WAS and MCS data were used to build a final P-wave velocity (Vp) model, following a layer stripping strategy, and Vp uncertainty was evaluated using Monte Carlo analysis.In this work we focus on the northern part of the profile, sampled by the 14 northernmost OBH, to present the velocity structure and a seismic image across the region of the contact of the plate boundary and the Tore-Madeira Rise, near the Josephine seamount. A vertically and laterally complex velocity distribution is observed. An apparently low velocity (

The FRAME geophysical cruise, conducted in 2018 onboard the Spanish R/V Sarmiento de Gamboa, acquired new multichannel seismic reflection (MCS) data on the SW Iberia and NW Moroccan margins. MCS data were acquired with a 6 km long solid-state digital streamer Sercel SENTINEL towed at 19 m water depth, and a 3920 c.i. source with two sub-arrays with 20 guns towed at 10 m depth. The system was designed to provide high penetration and map the entire crust and the upper mantle structure and retain enough resolution to image well the stratigraphy.In this work we present a 220 km long seismic line acquired on the NW Moroccan margin, from the shallow continental shelf across the continental slope and extending across the deep abyssal plain of the Gulf of Cadiz. The NW Africa margin was selected because the region was the focus of several geophysical campaigns, and several DSDP drill sites that drilled into the synrift strata. However, limited modern data has imaged the crustal-scale tectonic structure to unravel the late Triassic - early Jurassic rift history of the region.We applied a seismic processing flow tailored to the attenuation of the multiple energy, signal designature and for the creation of a detailed macro-velocity model to image the lateral changes of the synrift tectonic structure and stratigraphy. The high-quality image of the structure of this rifted margin reveals a complex tectonic structure from the shelf to the deep-water basin where a deep basement containing salt bodies across the entire profile extension. These new results are of high importance for the understanding of the rifting and continent-ocean transition (COT) processes on the northern Central Atlantic and Neothetys domains, as well as for the subsequent compressive deformation processes in the Gulf of Cadiz related to the Africa-Eurasia plate collision.This work was funded by the Portuguese Fundação para a Ciência e a Tecnologia (FCT) I.P./MCTES through national funds through the project LISA (https://doi.org/10.54499/PTDC/CTA-GEF/1666/2020).

The Josephine submarine seamount is located in the NE Atlantic Ocean around 470 km west of the coast of mainland Portugal and 500 km northeast of Madeira Island on the vicinity of the Africa-Eurasia plate boundary. With 47 km in length and 10 km in width, it rises 2500 meters above the adjacent abyssal plains, with its top standing at a depth of 170 m. It is a basaltic submarine seamount that yielded ages of 16.3 ± 0.9Ma to 11.7±0.7Ma (Geldmacher et al. 2006).Multibeam and backscatter data were acquired to increase our knowledge about the seamount. The backscatter data shows the presence of fine sediment on the eroded top of the seamount, not present in the northern part. The top of the seamount dips gently (~1º) to the northwest allowing the deposition of fine grained sediment down to ~500 m where the seafloor is irregular with slopes dipping between 10⁰ and 15⁰ and the igneous rocks crop out.Morphologic analysis suggests that the very flat and smooth surface of the southernmost portion of Josephine Seamount has been above sea level and subjected to near coastal erosive processes of areas lying at ~420 m depth. Since the sea level of the last 15 Ma has not been lower than 160 m of the present-day levels (Miller et al. 2020), tectonic and/or erosional processes must have lowered the seamount’s height by at least 260 meters.Sedimentary rocks were dredged from depths from 480 to 347 m, on the southeastern part of the Josephine seamount and were analyzed for their shape, composition and sedimentary facies. The dredged samples are calciclastic limestone blocks that have a half horn torus shape (donut). Most of the specimens are trespassed by a 3 to 5 cm long conical cavity that developed from the base to the top of each sample.The rocks consist of 96.6% of foraminifera tests (82.4% planktic and 17.6% benthic), with a very low mineral content. The grains are diagenetically cemented by a calcite matrix (confirmed by EDS analysis). The presence of the planktonic foraminifera species Globorotalia truncatulinoides, whose first occurrence dates of 1.93 Ma (Wade et al., 2011), provides a maximum age of formation, making these sedimentary rocks at least 10 Ma younger than the volcanic rocks that constitute the Josephine Seamount basement. The presence of the benthic foraminifera Lobatula lobatula and Discanomalina semipunctata indicate strong currents that could have contributed to the erosion of the seamount’s top.This work was funded by the Portuguese Fundação para a Ciência e a Tecnologia (FCT) I.P./MCTES through national funds through the project LISA (https://doi.org/10.54499/PTDC/CTA-GEF/1666/2020).