Manel Prada

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.

In subduction zones, seismic imaging reveals increasing permanent active deformation toward the trench, particularly within accretionary systems. Yet, how these rock bodies deform coseismically and influence megathrust rupture behavior is elusive. Here we combine geophysical observations from seismic imaging with visco-plastic dynamic rupture simulations to investigate how realistic upper-plate rock bodies influence megathrust earthquake dynamics and off-fault deformation. Our models reproduce the elastic structure of three subduction systems that differ primarily in the width of the accretionary prism, a key parameter for comparison. These configurations, referred to as Models I, II, and III, include a narrow compliant prism of approximately 20 km, an intermediate prism of about 60 km, and a wide prism exceeding 100 km, respectively. Elastic rock properties for each upper-plate model are derived from 2D P-wave velocity models obtained from controlled-source seismic data. Upper-plate bulk cohesion and bulk friction define visco-plastic strength and are set to depend on rigidity distribution and empirical observations. Based on laboratory measurements from JFAST drilling samples, we use rate-and-state friction law with strong velocity weakening in the shallow portion of the fault.Results show that coseismic upper-plate plastic deformation in Model I is confined to the ~20-km-wide wedge, whereas in Models II and III it extends 40–60 km landward from the trench. This is consistent with seismic reflection profiles that reveal increasing active internal deformation of the prism at similar distances from the trench in regions such as the Japan Trench, Chile, and Sumatra. Such contrasting upper-plate deformation patterns lead to distinct uplift scenarios, particularly in their high-frequency response. In particular, Model I produces shorter-wavelength uplift near the trench, likely generating a tsunami with higher-frequency content than Model II and III, where uplift exhibits a longer wavelength. Although we do not explicitly simulate independent faults within the prism, the bulk plastic strain can be considered a proxy for the amount of deformation that is accommodated by these structures. Our results suggest that permanent deformation within accretionary prisms is active during trench-breaching megathrust earthquakes, indicating that substantial prism deformation occurs coseismically. Plastic deformation leads to a reduction in slip toward the trench, implying that coseismic energy is absorbed by the overlying rock body. This effect explains the low-radiated-energy of near-trench earthquakes, including tsunami earthquakes. Depending on the plastic strength of upper-plate material and the available energy along the fault, this effect may even prevent the rupture from reaching the trench, while still producing substantial coseismic uplift and horizontal seafloor displacement. Overall, this study indicates that identifying permanently deformed, low-rigidity regions near the trench can serve as a proxy for locating areas where coseismic deformation is strongly accommodated and tsunamigenic uplift is likely amplified.

The Tyrrhenian Sea is a young back-arc basin that began to open in the Langhian/Serravallian (15.97-13.82 Ma). Its formation was driven by the eastward roll-back of the Apennine-Maghrebide subduction system, leading to the exhumation of the mantle in the Vavilov Basin. The spatio-temporal evolution of this exhumation occurred just after the Messinian Salinity Crisis (MSC). Consequently, the distribution and thickness of Messinian evaporites (5.97–5.33 Ma) provide a chronostratigraphic marker to constrain the transition from continental rifting to mantle exhumation. Within this framework, the present study aims to reconstruct a refined 3D Moho topography to reveal the relationship between crustal thinning and mantle exhumation.In the Tyrrhenian Sea, we analysed a comprehensive suite of legacy seismic lines, including the SITHERE (1985), CS (1989), CROP (1995), and MEDOC and CHIANTI (2010 and 2015) surveys. We then converted Two-Way Travel time (TWT) into depth, integrating a robust velocity-depth model generated from five 2D seismic reflection profiles with coincident refraction data collected during the Spanish Survey MEDOC/CHIANTI. The resulting Moho geometry and the boundaries of mantle exhumation are validated and constrained by a synthesis of borehole data from DSDP, ODP (Sites 651 and 655), and the recent IODP Expedition 402 (Sites U1612, U1615, and U1616).Our mapping reveals that a prominent, high-amplitude reflector is consistently observed across the region, typically occurring around 7s TWT. Once converted into depth, this interface deepens toward the continental margins and shallows toward the basin centres. In the Vavilov Basin, where mantle exhumation has been confirmed by drilling (U1614, U1616, and 651), we have identified reflectors within the exhumed basement. Notably, as imaged by the MEDOC-9 seismic profile crossing the heterogeneous exhumed domain at IODP Site U1612, one of these reflectors is sub-horizontal and truncates a set of rotated reflectors, suggesting a possible complex fault-like feature within the mantle.The identified reflectors occurring within the mantle may be either a tectonic or hydrothermal boundary, such as a serpentinization front or a major detachment fault within the exhumed domains. Spatial correlations between Moho shallowing and the thinning of Messinian units indicate that the most intense phase of crustal thinning and mantle exhumation in the Vavilov Basin occurred shortly after the Messinian. Our new 3D Moho contour map provides a refined geodynamic framework for constraining the timing and magnitude of lithospheric extension in this back-arc region and for guiding future geodynamic modelling.

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.

A seismic transect across the Xisha Trough failed rift provides information on processes active during the opening of the South China Sea (SCS). The rift basement gradually thins at the conjugate flanks from ∼25 to 15 km toward the central sector, where it abruptly thins to ∼10–6 km in thickness. The seismic velocity model supports that 6.5 km/s velocity separates an upper from a lower crust layer, where Vp reaches 7.1 km/s above Moho. The upper crust extends across the entire rift, but the lower crust layer does not occur in the thin crust of the central sector, which is underlain by mantle with anomalously low Vp, indicating serpentinization. Changes in tectonic structure mimic the Vp distribution. The rift flanks have comparatively small faults associated to gradual thinning, whereas the central sector has larger faults that possibly reach the mantle. The faulting in the central sector thus indicates whole‐crust embrittlement, which possibly led to synrift mantle serpentinization. Despite the weaker rheology, serpentinized mantle did not result in the development of low‐angle faulting or continental break‐up. Furthermore, the rift overall thinning and faulting structure is asymmetric with respect to the rift center, supporting an initial widespread moderate extension creating the flanks. When extension thinned the crust to <15 km, the whole crust was brittle and deformation first focused and subsequently laterally migrated to create the central sector. The continental Xisha Trough rift evolution is similar to classical magma‐poor margins, but synrift magmatism described in adjacent regions indicate abrupt segmentation of the rift system.

SUMMARY: We investigate the lithospheric structure of the Southwest Iberian Margin along an active seismic profile southwest of São Vicente Cape, ranging from the southern Tagus Abyssal Plain to the westernmost part of the Gulf of Cadiz. This profile, approximately 320 km long, intersects almost perpendicularly three major thrust faults: the Tagus Abyssal Plain, Marquês de Pombal and Horseshoe faults. The crustal structure, derived from spatially coincident wide-angle seismic (WAS) and multichannel seismic (MCS) data, was validated and constrained using gravimetric data. Joint traveltime inversion of refracted phases identified in WAS and reflected seismic phases from both WAS and MCS records were used to build a detailed 2-D P-wave velocity (Vp) structure. The resulting model reveals a Vp distribution with abrupt lateral velocity and structural variations, characterized by a rugged basement top and sharp changes in crustal thickness. Three main lithospheric domains consisting of continental, oceanic and exhumed mantle affinity were identified from south to north. The traveltime inversion of the deepest reflected seismic phases reveals four major southeast-dipping reflectors, likely corresponding to major regional thrust faults with significant seismic and tsunamigenic potential. Integrating the modelled and interpreted seismic results with the locations of recent well-constrained earthquakes suggests that the Marquês de Pombal and Tagus Abyssal Plain extend deeper than previously thought, with fairly high seismic activity in the deep levels. This has significant implications for their seismogenic potential and should be taken into account for accurate assessment of seismic hazards in the region.

SUMMARY: Controlled-source marine seismic experiments are key in advancing our understanding of the Earth’s subsurface structure to study tectonic, magmatic, sedimentary and fluid flow processes. Joint acquisition of wide-angle seismic (WAS) and multi-channel seismic (MCS) streamer data stands as the most robust approach for marine exploration, however effectively mapping subsurface structure remains challenging. The lack of identifiable refractions as first arrivals at short offsets in WAS data creates shallow subsurface illumination gaps up to 6–8 km offsets around Ocean Bottom Seismometers or Hydrophones. This inadequate ray coverage, more pronounced in areas with deeper water column and lower seabed velocities, limits the performance of Travel Time Tomography (TTT) techniques. Velocity determination in the sedimentary layer and reflector location are affected, and errors propagate to deeper layers. This study integrates Downward Continuation (DC) to WAS data. Similarly to our former study where DC is applied to MCS data, redatuming WAS data involves solving the acoustic wave equation backward in time. This process virtually repositions the sources to the seafloor, revealing previously masked near-seafloor refractions as first arrivals. This transformation significantly enhances ray coverage in the shallow subsurface, leading to more accurate determinations of both seismic velocity and reflector geometry. By bridging theoretical concepts with a real data application, this study demonstrates the optimization of field seismic data for improved TTT results. This methodology is particularly beneficial for deep water exploration where spatially coincident WAS and MCS are jointly inverted. In such scenarios, DC-processed WAS data provides the refracted phases key for velocity determinations, and that are typically not present in MCS data due to insufficient streamer length relative to the water column depth. Additionally, we contribute to the community by releasing our open-source, High-Performance Computing software for WAS data redatuming.