Laura Gómez de la Peña

The south-central Chilean seismogenic zone has produced some of the largest megathrust earthquakes ever recorded, including the 2010 Mw 8.8 Maule event. To understand the rupture behaviour of this earthquake in the region of maximum coseismic slip at 34.5°S, we analyse the tectonic and elastic structure of the margin using 2D wide-angle seismic (WAS) data, and spatially coincident 2D multichannel (MCS) data acquired with a 15-km-long streamer.To improve the seismic velocity model relative to previous results along the same WAS line, we jointly invert travel times from WAS and MCS data using a combined refraction–reflection tomographic approach and statistical uncertainty analysis. In addition, we apply downward continuation to the MCS shot gathers to increase the number of usable MCS travel times and to improve ray coverage with refracted arrivals from the shallow part of the velocity model. This approach enhances coverage and reduces tomographic velocity uncertainties, and improves constraints on the position of the interplate reflector from the megathrust.The resulting 2D P-wave velocity (Vp) model includes the velocity structure of a 50-60 km-wide accretionary prism, and a sharp velocity transition into crystalline basement landward. We convert the velocity structure of the upper plate into density and S-wave seismic velocity to then calculate rigidity (Shear modulus), and infer dynamic rupture parameters such as slip and rupture velocity. Comparison of the expected slip distribution from our results with existing kinematic slip models shows significant discrepancies, particularly beneath the accretionary prism, where the time-migrated 127-km-long seismic profile reveals intense internal deformation and increasing thrust faulting and folding towards the trench. We discuss potential upper-plate coseismic deformation processes to explain such discrepancy.

The structure of the Newfoundland–West Iberian conjugate margins has been extensively studied during the past 50 years in hundreds of papers. The crustal structure has been evaluated through seismic surveys and drilling expeditions, but those are not equally distributed in Iberia and Newfoundland. More work, and in particular recent studies on the West Iberian margin, have identified a complex crustal architecture characterised by continental, oceanic, and exhumed mantle domains that vary along the margin. This structural complexity has only been recently documented with modern data that allow to image the basement domains in detail.In contrast, the Newfoundland basement remains comparatively less well understood due to a relative scarcity of seismic and drilling data. The main wide-angle and streamer data for this area, the SCREECH survey, were acquired in 2000 and modelled under the computational limitations of that time. The resulting models and images have been subject to debate and failed to unequivocally define the nature of the basement domains of the margins. This uncertainty has left open key questions regarding the evolution of deformation during rifting and, thus, also the degree of symmetry of this conjugate pair of margins.The SCREECH acquisition parameters were similar to modern marine acquisition standards. We leveraged their inherent data quality with the current computational facilities and up-to-date methodologies to re-process the data, imaging the structure and modelling seismic phases. Recent advancements in parallel computing and novel geophysical techniques now allow for enhanced-resolution seismic models and a mathematically robust uncertainty analysis—tasks that were previously very computationally demanding.Our study utilises the original SCREECH field data, consisting of three transects with coincident multichannel seismic (MCS) reflection data (6-km streamer) and wide-angle data recorded by short-period OBS and OBH stations at ~15 km spacing. By performing a joint inversion of the streamer and wide-angle data (utilising both reflection and refraction arrivals), we significantly improved the definition of geological units and the spatial resolution of the velocity models. A statistical uncertainty analysis was conducted to validate the reliability of these observed features.Our findings reveal previously unrecognised crustal heterogeneity at the Newfoundland margin, including significant variations in thickness and composition along the margin. Notably, we challenge prior classifications of the crustal domains and the location and dimensions of the Continent-Ocean Transition (COT). Previous models identified an intra-basement deep reflector as the Moho, defining a 4–5 km thick layer interpreted as continental crust. However, our results suggest this reflector may not represent the Moho, as the observed crustal properties are inconsistent with typical continental or oceanic crust, and rather support a COT formed by >250 km of exhumed mantle. By integrating MCS imagery with these new velocity models, we provide a re-interpretation of the margin’s crustal structure and propose a refined evolutionary model for the West Iberian–Newfoundland conjugate system.

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.

Oceanic transform faults and their fracture zones are among the most striking features of ocean basins. Plate tectonics describes them as strike‐slip zones connecting mid‐ocean ridge segments. Still, no generally accepted theory exists for the lateral strain partitioning resulting in the deep and wide transform valleys and extensively tectonized inside corners. Here, we present results from multibeam bathymetry and a micro‐seismicity survey from the slow‐slipping Oceanographer transform on the Mid‐Atlantic Ridge near 35°N. Swath‐mapping echosounder data reveal a segmented transform fault. Away from the ridge‐transform intersections (RTI) and in the eastern half of the transform valley, micro‐earthquakes recorded on ocean‐bottom‐seismometers focus along the observed fault strands. Approaching the RTI, however, many micro‐earthquakes cut across the inside corner, while the active faults step toward the inside corner, paralleling the trend of the transform valley. Focal mechanisms point to extension in the inside corner region, while strike‐slip deformation is only recorded at distances larger than 15 km and away from the RTIs. These observations support a scenario in which deformation beneath a right‐angular ridge‐transform boundary at the seafloor develops into an oblique shear zone at depth, causing crustal thinning and consequently forming transform valleys. Away from RTIs, seismicity is focused on a narrow and segmented strike‐slip fault as predicted by plate tectonics. Oceanic transform faults are consequently not only strike‐slip but are also shaped by extensional processes, arguing for a revision of the concept of conservative plate boundaries to account for their morphology, segmentation, and significant lateral differences in seismic behavior.

The westernmost Mediterranean basins formed in a supra-subduction system during the Miocene. We have found that since the late Miocene, the previously extending region has been deformed by contractional and strike slip fault systems due to the Iberia – Africa tectonic plates convergence, producing the reorganization of the main tectonic structures. The westernmost Mediterranean realm is seismically active because it hosts the plate boundary between the European and African tectonic plates. This plate boundary has been traditionally considered a wide deformation zone, in which plate convergence is absorbed by minor to moderate-size tectonic structures, each absorbing a comparatively small part of the deformation. However, the understanding of the crustal configuration and the evolution of this basin was limited due to the limited penetration and resolution of the images of the subsurface.We collected and processed >3.000 km of a modern seismic dataset to characterized for the first time 1) the deep structure and the crustal domains of the Alboran Basin, 2) the sedimentary infill and as a consequence, the basin evolution, and 3) the main active faults of the basin. Based on these results, we were able to identify the main fault systems and quantify the total slip accommodated by those prominent tectonic structures of the area, late Miocene - early Pliocene in age. Our results show that the estimated total slip accommodated by the main fault systems is similar (with error bounds) to the estimated plate convergence value since the Messinian time (~24 km). Thus, slip on those faults may have accommodated most of the Iberian – African plate convergence during the Plio-Quaternary, revealing that the contractive reorganization of the Alboran basin is focused on a few first-order structures that act as lithospheric boundaries, rather than widespread and diffuse along the entire basin. These results have implications not only for kinematic and geodynamic models, but also for seismic and tsunami hazard assessments. We performed a first appraisal of the seismogenic and tsunamigenic potential of the main fault systems offshore. Our simulations show that the seismogenic and tsunamigenic potential of the offshore structures of the Alboran Basin may be underestimated, and a further characterization of their associated hazard is needed.

The crustal structure of the Newfoundland-West Iberian conjugate margins has been extensively studied with seismic data and drilling legs. Recent surveys in the West Iberian margin have revealed a complex crustal architecture with continental, oceanic and exhumed mantle domains that change along the margin. In contrast, the Newfoundland margin, with lower seismic and drilling information available, remains comparatively more poorly understood. The main wide-angle and streamer SCREECH survey was acquired in 2000 and was modelled with comparative computational limitations at the time. The resulting images and model have been debated and did not unequivocally characterize the nature of the basement domains along the margin. Thus, the evolution of the deformation during rifting and the symmetry or asymmetry of the conjugate pair of margins are still discussed. The SCREECH data acquisition parameters are similar to modern data, and we took advantage of their quality to re-process, image the structure and model the seismic phases with methodologies that have been refined during the last decade. Recent developments in parallel computing and novel geophysical approaches provide now the means to obtain a new look at the structure with enhanced resolution seismic models and a mathematically-robust analysis of the data uncertainty, that was formerly difficult, if not unfeasible, to achieve. We use the SCREECH original field data, formed by three transects with coincident multichannel seismic (MCS) reflection data acquired with a 6-km streamer and wide-angle data recorded by short-period OBS and OBH spaced at ~15 km. We reprocessed the streamer data and also performed the joint inversion of streamer and wide-angle OBS/OBH seismic data, using reflections and refraction arrivals, which improved the definition of the geological units and the spatial resolution of the velocity model for each unit. We performed a statistical uncertainty analysis of the resulting model, supporting the improved reliability of the observed features. Our results reveal previously unrecognized crustal heterogeneity, including variations in crustal thickness and composition along the margin. In particular, the crustal domain classification and the COT location were done considering the existence of a deep reflector, interpreted as the Moho and defining a 4-5 km crust that was interpreted as oceanic. Our results suggest that this reflector may not represent the Moho, as the observed crustal properties are not consistent with typical oceanic crust. The integration of the MCS images with the velocity models allowed us to re-interpret the crustal structure of this margin and integrate all the observations in a refined evolution model for the West Iberian – Newfoundland conjugate margins.

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 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).

Fracture zones were recognized to be an integral part of the seabed long before plate tectonics was established. Later, plate tectonics linked fracture zones to oceanic transform faults, suggesting that they are the inactive and hence fossil trace of transforms. Yet, scientist have spent little time surveying them in much detail over the last three decades. Recent evidence (Grevemeyer, I., Rüpke, L.H., Morgan, J.P., Iyer, K, and Devey, C.W., 2021, Extensional tectonics and two-stage crustal accretion at oceanic transform faults, Nature, 591, 402–407, doi:10.1038/s41586-021-03278-9) suggests that the traditional concept of transform faults as being conservative (non-accretionary) plate boundary faults might be wrong. Instead, transform faults are always deeper than the associated fracture zones and numerical modelling results suggest that transform faults seem to suffer from extensional tectonics below their strike-slip surface fault zone. In 2021, we tested this hypothesis by collecting, in a pilot study, micro-seismicity data from the Oceanographer transform fault which offsets the Mid-Atlantic Ridge by 120-km south of the Azores near 35°N. Analysis of 10-days of seismicity data recorded at 26 ocean-bottom-seismometers and hydrophones showed 10-15 local earthquakes per day. Furthermore, a sparse network recorded micro-earthquakes for three months. Joint interpretation of the data shows that earthquakes away from the ridge-transform intersections cluster along the fault trace imaged in bathymetric data and focal mechanisms support strike-slip motion. However, at the ridge-transform intersections seismicity does not mimic a right-angular plate boundary; instead, seismicity occurs below the inside corner and focal mechanism indicate extensional tectonics. In addition, we put published micro-earthquake data from surveys conducted in the 1970 to 1980s from the Oceanographer, Kane and Vema transform fault in a new context by plotting them onto modern swath-bathymetric data. In concert, micro-seismicity supports features found in numerical simulations, revealing that transform faults have an extensional as well as a strike-slip component.