Ocean Drilling Program Site 1256 was drilled in the Guatemala Basin, eastern Pacific Ocean, sampling superfast-spreading crust. It is one of the deepest drill holes sampling intact oceanic crust and the only site that has penetrated gabbroic rocks away from a tectonic window. Two gabbroic units were sampled at 1157 m and 1283 m below the basement. We collected seismic refraction and wide-angle reflection data across the drill site, and the resulting tomography models show that the first encountered gabbro does not mark the top of the seismic boundary between the upper (layer 2) and the lower (layer 3) crust, which we observe 500-600 m deeper. We propose that the drilled gabbroic rocks may represent either shallow intrusions or depth variations of the magma lens, marking the upper limit of a layer 2-layer 3 transition zone. Seismic tomography and wide-angle migration of mantle reflections reveal rather thin crust of 5 +/- 0.2 km (i.e., similar to 1.5 s two-way traveltime), being 1 km thinner than normal oceanic crust. The crustal deficit occurs solely within the lower crust. The observed thin crust distinctly differs from typical fast-spreading crust and may indicate the occurrence of a depleted mantle source. Yet, our preferred interpretation is that at superfast spreading rates of >200 mm/yr, the melt transport through the mantle is too slow to provide enough melts to form 6 km of oceanic crust.

Oceanic crust represents the largest formation of Earth’s surface, yet its structural variability and accretion mechanism remain enigmatic. Here, we compare crustal thickness and structure at intermediate/fast- and superfast-spreading systems using worldwide seismic observations and new constraints from seismic wide-angle data from the equatorial North Pacific. Seismic tomography reveals abnormally thin oceanic crust (<5 km-thick) formed at superfast center with half-spreading rates of >70 mm/yr in the Guatemala Basin, in contrast to ~6.1 km-thick crust in the intermediate-spreading central Pacific. The global seismic data also show a systematic trend toward thinner crust that deviates from the global average thickness (6.17±0.64 km), suggesting a deficit in melt supply at superfast spreading centers. By coupling numerical modeling with observational results, we demonstrate that superfast spreading ridges produce more melt but focus it less efficiently to the ridge axis to form oceanic crust, which explains the formation of anomalously thin crust at superfast spreading rates. Our findings highlight a previously unrecognized change in the dynamics of the partially molten region from intermediate/fast to superfast spreading rates, controlling the variability of oceanic crustal thickness.

AbstractThe Chilean margin is one of the Earth's tectonically most active plate boundaries, and yet, some of its segments are still underexplored. Here, we present amphibious data from the Copiapó region at ∼27°S located within the mature Atacama seismic gap. Combined 2D seismic refraction, multibeam bathymetry, and local seismicity data show a typical oceanic crust thickness of 6–7 km and seismic P‐wave velocities between 3.0 and 7.3 km/s with slightly lower velocities and increased thicknesses underneath the Copiapó Ridge seamounts. The latter is most likely due to predominantly extrusive formation. Elevated velocities underneath one of the seamounts indicate a local region of magmatic underplating, while bending‐related faults visible in the bathymetry and reduced mantle velocities near the trench suggest mantle hydration. The subduction angle of the down‐going Nazca plate smoothly increases from 12° below the marine forearc to 22° at greater depths (40–60 km) with no abrupt change in the dip angle as observed at ∼22°S. The local seismicity off‐ and onshore Copiapó shows three separated bands of earthquakes sub‐parallel to the down‐going plate, and are most likely related to the plate interface, the oceanic Moho and the Double Benioff Zone. The largest event (MW 5.9) during our observation period (December 2022–June 2023) and its aftershocks occurred in the deepest band ∼20 km below the subduction interface. Along the interface, seismicity is most pronounced in areas of high locking offshore, whereas areas of low locking are characterized by previously observed slow slip events and sparse seismicity.

Three tectonic plates meet at the Rodriguez Triple Junction in the Central Indian Ocean. The plates are separated by the Central Indian Ridge (CIR), the South-East Indian Ridge (SEIR) and the South-West Indian ridge (SWIR), which all show highly different spreading behaviours. While the northernmost segment of the SEIR is magmatically robust, the eastern tip of the SWIR is highly amagmatic. The CIR appears to oscillate between opening mechanisms, associated either with magmatic or magma-starved spreading processes, which can be observed over a very confined stretch of crust. Even though the area has been studied thoroughly, using a variation of geophysical and geological methods in the past decades, seismic images of the region were missing. From November 2023 to January 2024, RV Sonne (SO301 - SCIROCCO) set out for a seismic reflection and refraction survey to fill this gap and to provide a database for a better understanding of the tectonic setting and evolution of the area. A special focus was put on studying the structure and extent of the Oceanic Core Complex (OCC) at 25 °S.Here we present preliminary results of an east-west trending 150 km long profile crossing the OCC and the CIR. Along the profile, 33 ocean bottom seismometers were deployed with a spacing of 4-5 km that grew denser over the OCC. The shot spacing was between 50-110 m. Clear crustal refracted P- and S-phases were observed to offsets of up to 40 km in the shot sections and mantle reflections, as well as Pn-phases could be identified sporadically. First results of travel time tomographies, which were executed separately for P- and S-waves, and used for the calculation of a Vp/Vs-ratio section indicate a strongly variable crustal construction. Highly fractured areas seem to interchange with highly hydrated areas within short distances. Correlations of the new bathymetric data to the seismic images and the integration of the new gravimetric and magnetic data will sharpen the geophysical image and its tectonic interpretation along the profile.

Wide-angle refraction seismic experiments are generally executed along 2D profiles. In this study, we investigate the potential and limitations of using adjacent 2D wide-angle seismic profiles for 3D tomography. From this, we provide suggestions on best practices when designing new offshore experiments so that the data can be used for both 2D and 3D tomography. We use two example experiments from the Ligurian Sea, the 2006 SARDINIA Experiment and the 2017/8 AlpArray—LOBSTER Experiment, to highlight the benefits and pitfalls of two common station-shot geometries: parallel 2D seismic profiles and crossing seismic profiles through a network of Ocean Bottom Seismometers (OBS). We interpolate the lateral resolution of these experiments, and compare this with the potential resolution that could be achieved by the strategic addition of shots or stations. The synthetic results show that when two parallel 2D seismic profiles are shot (Sardinia Experiment), the resolution can be equally improved by the addition of a line of shots between profiles as by a line of stations between profiles. For an OBS network (AlpArray—LOBSTER Experiment), the synthetic results show that additional shot lines throughout the network are necessary to resolve the network area. One major difficulty with this specific area, is the complex geological structure of the Liguro-Provençal Basin, especially the presence of a Messinian evaporite layer that interferes with and scatters the seismic signal. The resolution achieved by these different network geometries shows that while these experiments alone were not sufficient for 3D tomography, they could both have been made suitable for 3D tomography by the addition of shot profiles, which are cost-effective and easier to add than stations. This workflow for estimating the lateral resolution of a 3D seismic refraction experiment can be applied to any tectonic setting, and should be considered when planning offshore experiments to enable 2D and 3D tomography and increase the output of this valuable data.

Interactions between melting ice and a warming ocean drive the present-day retreat of tidewater glaciers of Greenland 1–3 , with consequences for both sea level rise 4 and the global climate system 5 . Controlling glacier frontal ablation, these ice–ocean interactions involve chains of small-scale processes that link glacier calving—the detachment of icebergs 6 —and submarine melt to the broader fjord dynamics 7,8 . However, understanding these processes remains limited, in large part due to the challenge of making targeted observations in hazardous environments near calving fronts with sufficient temporal and spatial resolution 9 . Here we show that iceberg calving can act as a submarine melt amplifier through excitation of transient internal waves. Our observations are based on front-proximal submarine fibre sensing of the iceberg calving process chain. In this chain, calving initiates with persistent ice fracturing that coalesces into iceberg detachment, which in turn excites local tsunamis, internal gravity waves and transient currents at the ice front before the icebergs eventually decay into fragments. Our observations show previously unknown pathways in which tidewater glaciers interact with a warming ocean and help close the ice front ablation budget, which current models struggle to do 10 . These insights provide new process-scale understanding pertinent to retreating tidewater glaciers around the globe.

At subduction zones, the bending of incoming plates and associated extensional stresses resulted in strong fault activity in the crust and upper mantle. The severe fracturing of the subducting slab in the trench outer rise facilitates the entrain of seawater into the lithosphere, leading to the serpentinization of peridotite in the upper mantle. Therefore, subduction zones are an important setting, nurturing material exchange between the hydrosphere and the solid earth, affecting the water cycle.To investigate the behavior of the subducting plate, during the experiment conducted aboard RRS JAMES COOK in the Guatemala Basin where the Cocos plate enters the Middle America Trench, we collected a wide-angle seismic refraction profile and coincident multi-channel seismic profile. Here, we present a seismic velocity model derived from a joint refraction and reflection seismic tomography using 10,508 crustal refraction arrivals, 6,533 Moho reflection arrivals, and 7,769 upper mantle refraction arrivals recorded by 37 ocean-bottom-seismometers. The spacing of instruments is ~7.5 km on the unaltered incoming plate and decreases to half of that from the outer rise into the trench. The results show that the unaltered oceanic crust is ~5-6 km thick and features a typical two-layer oceanic structure, ranging from ~4-5 km/s at the basement top to ~7 km/s at the bottom of the crust. Closer to the trench, at ~70 km away, we observe a prominent velocity reduction with lower-crustal velocities dropping to

The subduction of the oceanic Nazca plate beneath the continental South American plate shapes the Chilean margin and is known to generate large megathrust earthquakes. Our study focuses on the region defined by the pre-collision and subduction of the Copiapó Ridge with the Chilean margin at ~27°S. This area has been a seismic gap since 1922, and little is known about the geometry and deep structures of the incoming plate, the overriding plate, and the processes related to the subduction of the Copiapó Ridge. We model the seismic structure in the region by using wide angle seismic data from a recent amphibious seismic refraction experiment. Thereby, we utilize seismic signals from both offshore airgun-shots and onshore mining blasts. Overall, we use 36 Ocean-Bottom-Seismometers and 10 temporal seismic land stations along an approximately 420 km long profile ranging from more than 300 km offshore up to more than 100 km landwards.Our P-wave velocity model images the geometry and velocity structure of the incoming oceanic plate, including three seamounts belonging to the Copiapó Ridge, the marine and continental forearc, and the upper part of the downgoing slab. The model shows an oceanic crust with hardly any sediment cover (generally less than 10 m) and an average oceanic Moho depth of about 6.2 – 6.9 km below the seafloor, which increases to over 10 km below the seamounts of the Copiapó Ridge. The velocities beneath the seamounts are similar or slightly slower compared to the adjacent upper oceanic crust (Vp ranging from 3.5 to 6 km/s). This suggests that the Copiapó Ridge was predominantly formed by extrusive processes. In addition, the velocity model reveals a significant thinning (to less than 4 km) of the oceanic crust landwards of the trench axis.Together with recently acquired bathymetry data, we will compare our findings to other studies north and south of the Copiapó region and discuss the structural and geometric along-strike variations of the northern Chilean subduction zone.

This interdisciplinary study describes the integration of gravity field analysis, curvature techniques and various spatial applications. The data are based on land-based Free Air and Bouguer gravity data from the AlpArray Gravity Research Group, complemented by recent satellite missions. New seismic and seismological data from the AlpArray initiative and the German MB-4D Priority Program were used as independent boundary conditions for the 3D modeling and inversion of the gravity data. Prior to this modeling, Euler deconvolution, terracing/clustering techniques, and advanced filtering methods were employed to reveal intricate details of the region's gravitational signatures. For example, a distinct zoning of gravity is observed in the central part of the Ligurian Sea, pointing to traces of past rifting processes. Analysis of various curvature parameters (e.g., dip-, min-, max- and shape-curvature) of the processed gravity fields, in particular gradients and residual fields support the identified zonation of the gravity fields, which reflect the geological structures in the crust. The final 3D modeling of the Ligurian Sea area is based on a previous density model of the entire Alpine region and includes density distribution of the upper mantle. These densities were derived from tomographic velocity models, accounting for petrology, temperature, and pressure. Additional information of the upper crust was obtained from the refraction seismic results of the LOBSTER project, offering a comprehensive understanding of spatial phenomena. Calculations of the gravitational potential energy (GPE) provide additional information on local stresses, facilitating a deeper understanding of the flexural rigidity in the area. By elucidating the relationship between processing techniques and 3D modeling, this work advances interdisciplinary interpretation crucial for geological studies in the Ligurian offshore area.

The subduction of seamounts greatly affects arc volcanism, earthquakes, and tectonic deformation of the overriding plate, but the role of seamounts during bending and hydration of the incoming plate at subduction zones is poorly understood. We present seismic tomographic results along three profiles from the Middle America Trench offshore northern Costa Rica. The crustal and upper mantle P-wave velocities decrease toward the trench, with the onset of velocity reduction at similar to 70 km from the trench axis, indicating bend-faulting, alteration, and hydration of the incoming plate. The most prominent low-velocity anomaly of 7.6-7.8 km/s in the upper mantle occurs beneath a seamount at the outer rise, indicating enhanced hydration with similar to 2.4 wt% water content, compared to similar to 1.1-1.2 wt% in the subducting plate away from the seamount. Near the seamount, extremely low heat flow (<10 mW/m(2)) supports vigorous hydrothermal recharge of seawater. Our results reveal that subducting seamounts efficiently increase the permeability of the oceanic crust prior to subduction, facilitate the transport of seawater into the mantle, exert control on widespread serpentinization, and potentially promote water recycling back into Earth's interior.

On 27 March 2021 a 3‐months lasting seismic sequence struck the Central Adriatic Basin that is part of the Adria plate, a relatively undeformed plate since recent times. Analyzing the waveform data acquired by the Italian and Croatian seismic networks, we computed the location parameters of 160 earthquakes and the focal mechanisms of the Mw 5.2 mainshock and the larger aftershocks. Most events align along a WNW‐ESE trending, 30 km long, narrow belt. The depth distribution of events indicates that the mainshock and a few aftershocks occurred within the upper 4 km, while most aftershocks were located below 5 km within the carbonate platform. We propose that the evolution of the 2021 earthquake distribution is primarily ruled by the top ductile salt layer. Moreover, the presence of a salt layer explains the relatively high VP/VS ratio of 1.83 in the sediment rocks surrounding the salt bodies, as also observed in similar tectonic settings. We suggest that the seismogenic fault likely responsible for the 2021 events is an inherited SW‐dipping normal fault, reactivated by reverse kinematics in response to the regional compressive stress. These results, and the understanding that salt deposits play a key role in focusing deformation and seismogenesis, represent a novel contribution to the long‐standing challenge of seismic hazard assessment of the Central Adriatic Basin, where moderate to large events could have devastating impacts along the densely populated coasts.

The Mariana Trough is the youngest back-arc basin in a series of basins and arcs that developed behind the Izu-Bonin-Mariana subduction zone in the western Pacific. In addition to active seafloor spreading, the Mariana Trough also exhibits a pronounced asymmetry, with the spreading axis closer to the Mariana Arc. The formation and development of this back-arc basin and its predecessor is controlled by a complex interplay of temporal mantle heterogeneities, subduction dynamics of the Pacific Plate and large-scale tectonics since ~50 Ma. Here, we present new insights into the development of the central Mariana Trough at ~17°N from analyses of a 2-D P-wave traveltime tomography together with high-resolution bathymetric data. The refraction and wide-angle reflection data have been recorded by R/V KAIYO (JAMSTEC) on 41 ocean bottom seismometers (OBSs) along a 250 km profile in 2003. The results allow a subdivision of the Mariana Trough into different stages of back-arc basin opening and seem to imply a transition from symmetric rifting to asymmetric seafloor spreading. Fast-velocities in the lower crust in the rifting domain indicate that magma generation and crust formation was highly affected by hydrous melting from the subducting slab during this stage. This slab contribution decreases with the onset of active seafloor spreading due to a change in mantle flow and hence seems to be accompanied by a tectonic rearrangement of the eastern side of the basin.

The Mariana Trough is the youngest back-arc basin in a series of basins and arcs that developed behind the Izu-Bonin-Mariana subduction zone in the western Pacific. In addition to active seafloor spreading, the Mariana Trough also exhibits a pronounced asymmetry, with the spreading axis closer to the Mariana Arc. The formation and development of this back-arc basin and its predecessor is controlled by a complex interplay of temporal mantle heterogeneities, subduction dynamics of the Pacific Plate and large-scale tectonics since ~50 Ma. Here, we present new insights into the development of the central Mariana Trough at ~17°N from analyses of a 2-D P-wave traveltime tomography together with high-resolution bathymetric data. The refraction and wide-angle reflection data have been recorded by R/V KAIYO (JAMSTEC) on 41 ocean bottom seismometers (OBSs) along a 250 km profile in 2003. The results allow a subdivision of the Mariana Trough into different stages of back-arc basin opening and seem to imply a transition from symmetric rifting to asymmetric seafloor spreading. Fast-velocities in the lower crust in the rifting domain indicate that magma generation and crust formation was highly affected by hydrous melting from the subducting slab during this stage. This slab contribution decreases with the onset of active seafloor spreading due to a change in mantle flow and hence seems to be accompanied by a tectonic rearrangement of the eastern side of the basin.

Geophysical data from the Liguro-Provençal Basin show prominent margin asymmetry but the nature of the crust, especially in the northeastern part of the basin, remains unclear. The basin formed at the junction of the northern Apennines and the western Alps due to the rollback of the Calabrian-Apennines subduction zone in the Oligo-Miocene. The opening of the basin was accompanied by counter-clockwise rotation of the Corsica-Sardinia block relative to Europe with the basin widening southwestwards. Recent weak compressional earthquakes offshore within the basin suggest possible basin inversion due to the ongoing Africa-Eurasia convergence. An insight into the crustal structure of the basin is therefore the key to understanding these recent processes. To this end, we compiled existing geological and geophysical data, including new data from the German project “Mountain Building Processes in Four Dimensions” (4DMB), to constrain the crustal and sedimentary thicknesses throughout the basin. Moreover, we derived kinematic parameters of extension using regional tectonic reconstructions and used the coupled ASPECT and FastScape geodynamic code to model the opening of the basin in its northeastern (Corsica – Provence) and southwestern (Sardinia – Gulf of Lion) parts. The comparison of the geodynamic models and geophysical data suggests: 1) the extent of oceanic crust in the Liguro-Provençal Basin did not reach as far north as previously presumed; 2) rift-related structures are possibly being reactivated offshore to the northwest of Corsica. We also present new constraints on the lateral extent of rifted continental crust and exhumed mantle and evolution of the basin through time.

The geodynamic evolution of the Liguro-Provençal Basin and its crust and upper mantle structure remain debated, especially regarding the role of rifting in continental break-up and seafloor spreading. Our study incorporates updated datasets, including new gravity maps from the AlpArray Gravity Working Group (complete Bouguer, free air, and isostatic anomalies) for 3D modeling and gravity field analysis, seismic data from Lobster offshore campaigns for direct comparison, and geodynamic models, supplemented by seismic profiles from previous French and Italian campaigns to constrain the interpretation. We used GFZ’s IGMAS + software for interactive 3D modeling, creating a density model extending to 300 km depth that includes crustal and upper mantle inhomogeneities based on prior geodynamic models. This hybrid approach, with polygonal structures for the crust and voxels for the upper mantle, clarifies individual contributions to the gravity field. Extending initial gravity modeling from the SPP MB4D project INTEGRATE, our work provides a consistent 3D density model for the Alps and Ligurian Basin. The constrained 3D modeling and numerical analyses (terracing, clustering, filtering, curvature), along with vertical stress and gravitational potential energy calculations, suggest that rifting has significantly influenced the basin’s geological evolution.

Three tectonic plates meet at the Rodriguez Triple Junction in the Central Indian Ocean. The plates are separated by the Central Indian Ridge (CIR), the South-East Indian Ridge (SEIR) and the South-West Indian ridge (SWIR), which all show highly different spreading behaviours. While the northernmost segment of the SEIR is magmatically robust, the eastern tip of the SWIR is highly amagmatic. The CIR appears to oscillate between opening mechanisms, associated either with magmatic or magma-starved spreading processes, which can be observed over a very confined stretch of crust. Even though the area has been studied thoroughly, using a variation of geophysical and geological methods in the past decades, seismic images of the region were missing. From November 2023 to January 2024, RV Sonne (SO301 - SCIROCCO) set out for a seismic reflection and refraction survey to fill this gap and to provide a database for a better understanding of the tectonic setting and evolution of the area. A special focus was put on studying the structure and extent of the Oceanic Core Complex (OCC) at 25 °S.Here we present preliminary results of an east-west trending 150 km long profile crossing the OCC and the CIR. Along the profile, 33 ocean bottom seismometers were deployed with a spacing of 4-5 km that grew denser over the OCC. The shot spacing was between 50-110 m. Clear crustal refracted P- and S-phases were observed to offsets of up to 40 km in the shot sections and mantle reflections, as well as Pn-phases could be identified sporadically. First results of travel time tomographies, which were executed separately for P- and S-waves, and used for the calculation of a Vp/Vs-ratio section indicate a strongly variable crustal construction. Highly fractured areas seem to interchange with highly hydrated areas within short distances. Correlations of the new bathymetric data to the seismic images and the integration of the new gravimetric and magnetic data will sharpen the geophysical image and its tectonic interpretation along the profile.

We analyzed refraction and reflection seismic data covering the Central Lau Spreading Center (CLSC) and the Tonga volcanic arc at 18 degrees S in the Pacific Ocean to investigate tectonic inactivity in actively extending back-arc systems. Our P-wave travel time tomography shows a characteristic 6-8 km thick back-arc crust beneath and around the CLSC and a similar to 13 km thick arc-crust at the eastern end of our profile, which corresponds to the Tonga volcanic arc. Lower crustal velocities increase to 7.5 km/s toward the volcanic arc, marking the transition from back-arc to arc crust. These high P-wave velocities can be explained by a high pyroxene content in the lower crust originating from depleted melts. Our seismic reflection data show steep normal faults below the CLSC and volcanic structures closer to the volcanic arc, without a tectonically inactive zone (also knows as the "diffuse plate boundary") in between. Based on our results, we suggest that the Niuafo'ou and Tonga microplates should be treated as one tectonic plate with local zones of intra-plate deformation that are separated by zones that are tectonically quiet. In a subduction zone one tectonic plate sinks below another. A retreating downgoing plate causes tension in the overriding plate, which leads to thinning behind the volcanic arc: a back-arc basin is born. We investigate the crustal structure of a seismically inactive region within a back-arc basin in overall extension. Our aim is to understand why there is no seismic activity in this specific area. The Lau Basin is our case study, because it is a type-example for back-arc basin tectonics. We have acquired and interpreted seismic data to analyse the structure of the crust along a profile in the Lau Basin. We observe crustal thickness changes from typical back-arc crust (6 and 7 km) to arc-crust (13 km), and volcanic remnants in the crust with higher crustal velocities. Current tectonic activity only occurs at the Central Lau Spreading Center (CLSC), not in between the CLSC and the volcanic arc. We therefore reject the idea of a diffuse plate boundary, and propose that the Niuafo'ou and Tonga microplates should be treated as one tectonic plate that consists of localized zones that deform. In between those actively extending zones, there are areas that do not deform and that are tectonically quiet. The crustal structure of the central Lau Basin at 18 degrees S complies with typical back-arc/arc crustal velocities and thickness South of the FRSC no plate boundary is observed, suggesting one Niuafo'ou-Tonga plate with zones of intraplate deformation High crustal P-wave velocities result from the crystalisation of hydrous melts (upper crust) and pyroxene-rich material (lower crust)

Abstract The Mariana Trough is the youngest back‐arc basin in a series of basins and arcs that developed behind the Mariana subduction zone in the western Pacific. Active seafloor spreading is ongoing at a spreading axis close to the Mariana Arc, resulting in a pronounced asymmetric configuration (double rate to the west 2:1) at 17°N. The formation of back‐arc basins is controlled by the subducting slab, which regulates the temporal development of mantle flow, entrainment of fluids, and hydrous melts together with the magma generation. To better understand the formation process of back‐arc basin asymmetry in the central Mariana Trough, we combined 2‐D P‐wave traveltime tomography results with high‐resolution bathymetric data. Here, we show that the crust in the central Mariana Trough is 6.5–9.5 km thick, which is unusually thick for oceanic crust. While the lower crust exhibits average seismic velocities of 6.5–7.2 km/s, high‐velocity anomalies occur at the margins of the Mariana Trough, indicating that magmatic accretion was affected by hydrous melting during rifting. While the Mariana Trough developed from a rather symmetric rifting (0.89:1) to a strongly asymmetric seafloor spreading stage (5.33:1), the contribution of hydrous melts declined and the opening direction changed at ∼5 Ma. Asymmetric basin opening is potentially driven by the far‐field stress effect of the subduction zones on the western boundary of the Philippine Sea Plate.

In the last decades, the slow-spreading Red Sea rift has been the objective of several geophysical investigations to study the extension of the oceanic crust, the thickness of the sedimentary cover, and the formation of transform faults. However, local seismology datasets are still lacking despite their potential to contribute to the understanding of the tectonic evolution of the Red Sea. The Zabargad Fracture Zone is located in the Northern Red Sea and significantly offsets the rift axis to the East. Thus, it is considered a key tectonic element to understand better the formation of the Red Sea rift. To fill the gap in the dataset availability, we deployed the first passive seismic network in the Red Sea, within the Zabargad Fracture Zone. This network included 12 Lobster OBSs from the DEPAS pool, 2 OBS developed and deployed by Fugro, and 4 portable seismic land stations deployed on islands and onshore on the Saudi Arabian coast. Our data-quality analysis confirms that the head-buoy cable free to strum, as well as other additional elements of the DEPAS OBSs, generate seismic noise at frequencies $>$ 10 Hz. However, the Fugro OBSs show high-frequency disturbances even if they lack vibrating elements. Comparison between land and OBS stations reveals that noise between 1 and 10 Hz is due to ocean-generated seismic noise, and not due to resonance of the OBS elements. We also found that waveforms of teleseismic earthquakes recorded by the Fugro OBSs, islands, and onshore stations have comparable signal-to-noise ratios. Instead, differences in signal-to-noise ratio for local earthquakes are affected more by site and path effects than instrument settings.