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In situ mineral carbonation in porous and permeable mafic and ultramafic volcanic rocks is proposed to be a promising process that can contribute toward safe and permanent CO2 sequestration. Here, we investigated a partially buried Late Cretaceous composite volcano located offshore the central West Iberian margin as a proxy for potential in situ mineral carbonation in volcanic edifices on continental margins worldwide. Based on seismic data, geochemistry, and petrophysical properties, deterministic scenarios for permanent carbon storage were estimated. Overall analysis of the nature of the volcano and its internal architecture revealed that this single edifice has the potential to store 1.2–8.6 Gt CO2 in newly formed carbonate mineral assemblages. Results suggest that ancient, buried volcanoes on continental margins constitute auspicious sites for safe carbon storage, with a total storage capacity of hundreds of gigatonnes of CO2.

In-situ mineral carbonation is a process that occurs naturally, through the interaction of CO2 rich fluids and minerals of mafic and ultramafic rocks, towards the formation of new stable carbonate materials. Formed spontaneously in peridotites and serpentinites (e.g., the Samail Ophiolite of Oman), the concept has been successfully replicated through industrial applications with mineral trapping demonstrated to occur on Icelandic basaltic lava flows within a period of 2 years. A Late Cretaceous volcanic edifice located on central West Iberian Margin, offshore Portugal, is investigated as a conceptual site for in-situ mineral carbonation, and a study case for the application of this model on similar volcanic edifices on continental margins worldwide. Using seismic reflection surveys, the volcano is revealed as a 2800 m high edifice, with an estimated total rock volume of 327 km3. Dredges collected from an exposed crest of the volcano revealed vesicular olivine-rich sub-alkaline basalts, infilled with naturally formed carbonate minerals. Analysis of the internal architecture of the edifice reveals outward dipping reflectors, with its magmatic features assigned to alternating successions of lava flows and explosive debris, that have grown progressively to form a composite volcano. Lava flows directly associated with the final stages of volcanic build-up, comprise dendritic and lobate lava flows (pahoehoe or submarine flows) blanketing the flank of the edifice. Accounting for the auspicious architecture, nature, and rock properties of the edifice, a deterministic volumetric model is used to estimate different scenarios of the amount of CO2 that can be safely and permanently stored in the volcano. Combining comprehensive inputs from bulk rock volume, effective porosity, and sequestration ratios, our estimations indicates that on a base case, the volcanic edifice has the potential to capture nearly 1.2 Gt CO2 into new stable mineral phases. On a high case scenario, this single edifice could permanently capture up to 8.6 Gt of CO2. Considering that during the 2015-2018 period, the Portuguese energy sector emitted an average volume of about 48 Mt CO2 eq per year, our estimates suggest that the volcanic reservoir is capable of storing an equivalent of 24 years of the country’s industrial emissions. Compared with oceanic magmatic sequences worldwide, buried volcanic edifices on continental margins materialise as notable locations for in-situ mineral carbonation. This assessment provides timely insights on the overall process of in-situ mineral carbonation, on ancient buried volcanoes, to reveal critical geological controls that can lead this technique to be applied on a pilot phase and envisage further concepts at economic scale. Moreover, geohazards associated with the proximity to populated areas are significantly minimised. Ultimately, results suggest that volcanoes on passive continental margins can be considered for safe and permanent carbon storage, by accommodating 100’s of Gt of CO2 from energy intensive industry sources and contribute to mitigate the impacts of anthropogenic carbon emissions. This work was funded by the Portuguese Fundação para a Ciência e a Tecnologia (FCT) I.P./MCTES through national funds (PIDDAC) UIDB/04035/2020-GeoBioTec and UIDB/50019/2020-IDL. D. Gamboa thanks FCT funding for project MAGICLAND (PTDC/CTA-GEO/30381/2017).

The Euro-Mediterranean Submarine landSlide (EMSS) database is a catalogue of submarine landslides of the Mediterranean Sea and the European continental margins of the Atlantic and Arctic Oceans. The catalogue is compiled from data available in the literature as well as information collected from geophysical data and so far not published in the scientific literature. A first version has been recently made available online (https://ls3gp.icm.csic.es/?page_id=553) and OGC services are being developed to be available soon through the EPOS data portal (https://www.ics-c.epos-eu.org/) in the frame of the EU funded project Geo-INQUIRE. Within Geo-INQUIRE we are currently working on a second version of the catalogue improving both areal coverage in the Atlantic Ocean and information relative to the source areas (as opposed to the previous version where only deposits and scars was considered). The aim of the latter improvement is to better characterize the failure and post-failure stages of submarine landslides. The new catalogue stores polygon and polyline geospatial features related to landslide deposits, landslide source areas and landslide scars as well as information relative to age, volume, area, runout, thickness, typology, scar elevation, relevant slopes and depths as well as related metadata. The catalogue includes submarine landslides that span from Miocene to Present day, although a clear bias exists towards submarine landslides of younger age, particularly for the smaller events. The reason for this is that the older and smaller events are difficult to identify on lower resolution geophysical data sets in deep-water and large sub-surface depths. The catalogue aims to offer improved understanding of mass-wasting processes, the potentially resulting tsunamis and derived geohazard. Recent case studies using a data subset (Gulf of Cadiz, SW Iberian Margin) portray the application of such type of databases in (probabilistic) analysis of submarine slope instability and tsunami-genesis from submarine landslides. We believe the current EMSS is the seed for the world ocean submarine landslide database. In this regard, we encourage the offshore geohazards community to contribute to enlarge the database. Shapefile templates will be made available to ease the task. This work is supported by the European Union’s Horizon Europe Research and Innovation Program under grant agreement No 101058518 (Geo-INQUIRE).

Data and Methods and Table S1.

Submarine landslides are a ubiquitous geohazard in the marine environment and occur at multiple scales. Increasing efforts have been made during the last decade to catalogue and categorise submarine landslides in comprehensive databases, aiming to better understand their preconditioning and trigger factors. Using the recently compiled, open-access MAGICLAND dataset, we investigate the distribution and morphometric trends of submarine landslides observed in seven distinct geomorphologic domains offshore west and southwest Iberia. Higher densities of submarine landslides occur on the proximal regions of the south and southwestern margins of the study area. These regions are located adjacent to or coincident with higher density areas and clusters of earthquake epicentres. Submarine canyons are another major location for collapses which are particularly abundant at canyon mouths. However, significant numbers occur within all domains with pronounced relief, including distal regions hundreds of kilometres away from the foot of the continental slope. Landslide size range is inversely proportional to their spacing and frequency, a tendency observed within each domain on the whole study area. Positive correlations were obtained between the parameters analysed, but relationships between unidimensional parameters such as length and width exhibit lower correlation coefficients. Correlations between 2D and 3D parameters such as area and volume are stronger, supporting similar findings by other studies. The relationships obtained are, however, variable across domains, and the correlation values are influenced by the seafloor geomorphology. This work brings new insights on submarine landslide distribution in the understudied west and southwest Iberian continental margin, complements previous inventories made for nearby regions, and provides valuable data with wider applications for submarine landslide databases.

Submarine landslides are major geohazards occurring on distinct seabed domains ranging from shallow coastal areas to the deeper points of the ocean. The nature and relief of the seabed are key factors influencing the location and size of submarine landslides. Efforts have recently been made to compile databases of submarine landslide distribution and morphometry, a crucial task to assess submarine geohazards. The MAGICLAND (Marine Geo-hazards Induced by underwater Landslides in the SW Iberian Margin) database here presented contributed to that assessment offshore Portugal. Based on EMODnet bathymetric DEMs and GIS analysis, the morphometric properties of 1552 submarine landslides were analysed and wealth of 40 parameters was obtained. This dataset is now made available for the free use and benefit of the international marine community. Further contributions or analysis based on, and complementing the MAGICLAND database will be welcome., Measurement(s) Morphometry of submarine landslides Technology Type(s) Geographic Information System Sample Characteristic - Environment continental margin • seamount Sample Characteristic - Location Northeast Atlantic Ocean coastal waters of the Iberian Peninsula Machine-accessible metadata file describing the reported data: 10.6084/m9.figshare.14484342

Submarine mass-movements are a major hazard on continental margins, particularly on collisional tectonic settings where recurrent earthquakes may trigger catastrophic collapses. Associated mass-transport deposits (MTDs) are typically heterogeneous, often characterised by a mixture of allochthonous slope lithologies transported to the abyssal depths, being further mixed with autochthonous basin sediments. Examples of such complex MTDs on thrust-controlled slopes are the North Gorringe Avalanche on the flank of the Gorringe Ridge, located on the Southwest Iberian Margin (NE Atlantic), and the Ruatoria MTD on the Hikurangi Subduction Margin, offshore New Zealand. Both MTDs present morphological similarities, such as a large evacuation area with significant height differences (between 2500 m to 3000 m for both cases), numerous blocky debris still observable on the seafloor despite the post-collapse burial and marked deformation of basin sediments over large areas. With a volume of circa 4500 Km3 and covering 9850 km2, the Ruatoria is particularly impressive and comprises one of the largest MTDs in the world. A geomorphological analysis is complemented by models to assess the tsunamigenesis of such impressive collapses and the hazards for margins across the oceans where they occur.This work is supported by FCT project MAGICLAND (ref: PTDC/CTA-GEO/30381/2017)

Calcareous rocks are commonly found in subduction zones, but few studies have investigated the consolidation and compactive deformation of these rocks prior to subduction, and their potential effects on subduction and accretionary processes are thus poorly understood. Using drilling data obtained during International Ocean Discovery Program (IODP) Expeditions 372 and 375 combined with 2D and 3D seismic reflection data, the structure, growth history, and slip rates of normal faults identified in the incoming pelagic sedimentary sequences of the Hikurangi Margin were investigated. A seismic coherence depth slice and vertical profiles show that these faults exhibit polygonal structure that has rarely been documented at subduction margins. The polygonal faults are closely spaced and layer-bound within sequences dominated by pelagic carbonate and calcareous mudstone of Paleocene-Pliocene age. Kinematic modeling and 2D displacement analysis reveal that fault throws decrease toward the upper and lower tipline. In detail, two groups of throw profiles are defined by locations of displacement maxima, possibly reflecting lateral variations in physical properties. The polygonal fault system (PFS) likely formed by syneresis processes that involve diagenetically induced shear failure and volumetric contraction of the pelagic unit associated with fluid escape. Fault growth sequences reveal multiple, weakly correlated intervals of contemporaneous seafloor deformation and sedimentation and allow estimates of fault slip rates. We find evidence for a significant increase in typical slip rates from 0.5-3 m/Ma during pelagic sedimentation to >20 m/Ma following the onset of terrigenous sedimentation. These observations suggest that rapid loading of the pelagic sediments by the trench-wedge facies was associated with renewed and faster growth of the PFS. The PFS will eventually be transported into the base of the accretionary wedge, enhancing geometric roughness and heterogeneity of materials along the megathrust, and providing inherited zones of weakness. Selective fault reactivation may facilitate deformation and episodic vertical fluid migration in the lower wedge associated with microearthquakes, tremor, and slow slip events.

Confluences are geomorphologic features fed by distinct channel tributaries that record the contribution of multiple sediment sources. They are key features of both fluvial and submarine channels in geomorphologic and sedimentologic terms. Here, we use high-quality three-dimensional seismic data from SE Brazil to document the response of a submarine channel confluence to turbidity currents originating from a tributary. The studied channel system consists of a west tributary, an east tributary, and a postconfluence channel, with the last two comprising the main channel at present. Downstream from the confluence, changes in planform morphology and architecture were found due to the effect of turbidity currents sourced from the west tributary channel. A channel bend in the main channel curved toward the west when it was first formed but later curved toward the east, and so remains until the present day. This process led to the migration of the confluence point ∼500 m to the east, and changed the bed morphology from discordant (where the beds of tributaries and main channels meet at an unequal depth) to concordant (where the beds of tributaries and main channels meet at approximately the same depth). In addition to the channel bend near the confluence, two other bends further downstream recorded significant changes with time, increasing channel sinuosity from 1.11 to 1.72. These three channel bends near the confluence accumulated a large volume of sediment at their inner banks, generating depositional bars. Multiple channel forms within the depositional bars indicate the occurrence of large-scale lateral migration near the confluence. Hence, turbidity currents from the west tributary are shown to influence the submarine channel by promoting lateral channel migration, confluence migration, increases in channel sinuosity, and the formation of large depositional bars. These variations near the confluence reveal a change in tributary activity and a shift in sediment sources from east to west on the continental shelf. Such a shift suggests variations in sedimentary processes on the continental shelf probably due to avulsions on Doce River Delta.

Submarine landslides are major geohazards occurring on distinct seabed domains ranging from shallow coastal areas to the deeper points of the ocean. The nature and relief of the seabed are key factors influencing the location and size of submarine landslides. Mass-failures on the continental slopes are frequent, but collapses on and along chains of oceanic seamounts and ridges can account also for a high frequency of events. Regardless of their area of occurrence, submarine landslides are a major hazard that needs to be recognised and categorised. For this purpose, numerous efforts have been made to compile databases of submarine landslides with the aim to better understand their distribution and characteristics on marine settings around the world.This work presents the initial efforts of the MAGICLAND (Marine Geo-hazards Induced by underwater Landslides in the SW Iberian Margin) database which, based on bathymetric DEMs available through EmodNET, compiled geomorphological properties of 1552 morphological scars and submarine landslides offshore West and Southwest Portugal. These are distributed through seven morphological domains: 1) canyons incising the continental slope (232 landslide episodes); 2) continental slope (233 landslide episodes); 3) large seamounts (437 landslide episodes); 4) submarine ridges and small seamounts (263 landslide episodes); 5) Gulf of Cadiz (226 landslide episodes); 6) Gulf of Cadiz banks and channels (123 landslide episodes); and 7) Estremadura Spur (38 landslide episodes). A wealth of 43 parameters were measured or calculated, which include a subset of morphological quantifications for the evacuation and deposit sections for 347 occurrences where the latter was observed. We present the morphological data and any derived computations as measured on the 3D surface in order to increase their accuracy and mitigate the effect of slope gradient on map-based 2D analysis. The larger events were recorded on the large seamounts and the ridges domains, which also correspond to the larger recorded landslide heights (measured as the difference between minimum and maximum depths). Good correlations (coefficient of determination R2>0.8) where obtained for Area-Volume, Width-Area, and Length-Area relationships. Where evacuation and deposit sections were discernible, their area relationships present a better correlation compared to their lengths.Further stages of the database development will involve the addition of still unmapped scars, as well as further statistical analysis and integration with available geophysical and geotechnical datasets for the areas of study. This dataset will be made available for the free use and benefit of the international marine community. Further contributions or analysis based on, and complementing the MAGICLAND database will be welcome.This work is supported by the FCT funded project MAGICLAND - MArine Geo-hazards InduCed by underwater LANDslides in the SW Iberian Margin (Ref: PTDC/CTA-GEO/30381/2017).

Slope instability is probably the most effective process shaping the seafloor of continental margins. This process often leads to the occurrence of submarine mass failures that, if large enough, can cause potential tsunamis. Yet, the dynamics of the landslide evacuated material and their induced tsunamigenic potential remain largely uncharacterized in most continental margins. This applies to the SW Iberia Margin, where large underwater landslide episodes have been evidenced.In this work, we investigate the sensitivity of landslide-generated tsunami to the physical properties of marine sediments involved in the slope failures in the SW Iberia Margin. This includes the landslide dynamics, the tsunamigenic potential and the tsunami hazard extent. Based upon the MAGICLAND (Marine Geo-hazards Induced by Underwater Landslides in the SW Iberian Margin) project database, we select promising sizable submarine landslide scenarios. We then use an in-house developed two-layer numerical code (based on a Bingham visco-plastic model for the landslide and a non-linear shallow water model for the tsunami) to simulate both the landslide dynamics and the induced tsunami generation and propagation.In a first stage, the numerical simulations are done considering uncertain sediments properties deduced from the literature. Next, we perform numerical simulations of the selected landslide scenarios using accurate geotechnical properties (mainly the in-situ shear strength obtained from undisturbed samples) determined by laboratory tests conducted on from the analysis of available marine gravity cores in the SW Iberian Margin. Results show that the geotechnical parameters significatively influence the simulation results of both the landslide dynamics and induced tsunami. Particularly, we noticed major effects on the landslide downslope deformation, failure speed, deposited thickness and run-out, which considerably control the momentum transferred to the generated tsunami wave. This demonstrates that the use of inappropriate material properties leads to a misquantification of landslide tsunamigenesis and hazard extent.This work was financed by national funds through FCT—Portuguese Foundation for Science and Technology, I.P., under the framework of the project MAGICLAND – Marine Geo-hazards Induced by Underwater Landslides in the SW Iberian Margin (PTDC/ CTA-GEO/30381/2017).

Seamounts are spectacular bathymetric features common within volcanic and tectonically active continental margins. During their lifecycles, they evolve through stages of construction and destruction. Seamount chains on the Southwest Iberian Margin are prone to instability and collapse due to regionally complex tectonism with moderate to high seismicity. In this work we investigate collapse episodes during the lifecycle of the tectonic Gorringe Bank (GB), the largest submarine seamount offshore European margins, based on recurrence patterns of MTDs on the active thrust flank. Eight MTDs with relevant expression on the seismic data were analysed, four of estimated Miocene age and four on a Pliocene-Quarternary interval. Miocene MTDs are overall larger and correlate with the main uplift stages of the GB structure. Their distribution and relative timing suggest that failure-triggering earthquakes were common along the whole length of the GB. Pliocene to Quarternary MTDs tend to cluster along the northern half of the GB flank and are generally smaller. Based on our observations, we propose that the lifecycle of tectonic seamounts is marked by morphological rejuvenation episodes driven by tectonic activity between major collapse events or cycles. Tectonic-driven rejuvenation is thus key to hinder or obliterate evidence of past high-magnitude destructive events on tectonic seamount morphology.

The consequences of subaqueous landslides have been at the forefront of societal conscience more than ever in the last few years, with devastating and fatal events in the Indonesian Archipelago making global news. The new research presented in this volume demonstrates the breadth of ongoing investigation into subaqueous landslides, and shows that while events like the recent ones can be devastating, they are smaller in scale than those Earth has experienced in the past. Understanding the spectrum of subaqueous landslide processes, and therefore the potential societal impact, requires research across all spatial and temporal scales. This volume delivers a compilation of state-of-the-art papers covering regional landslide databases, advanced techniques for in situ measurements, numerical modelling of processes and hazards

Submarine landslides are common features occurring on the flanks of seamounts. Often triggered by earthquakes or volcanic activity, such landslides are potential generators of tsunamis that constitute a dire geohazard for coastal communities. Understanding the recurrence history and geomorphology of seamount-flanking landslides and their link to seismic triggers is crucial for tsunami hazard assessment. This work aims at revealing the recurrence history of the landslides on the Gorringe Bank and their role on regional geohazards. Morphologically, the Gorringe Bank is the largest submarine seamount in Europe, with a length of circa 180 km and a height of 5000 m. It is linked to NW-directed thrusting which led to the exhumation of upper mantle lithologies in this major bathymetric structure. Numerous landslide scars are identified on both its northern and southern flanks, yet there is limited evidence of their presence and morphology on modern bathymetric data. A wealth of 2D seismic reflection profiles from offshore Southwest Portugal is here used to analyse the occurrence, timing and morphology of landslides complexes on the northwestern flank of the Gorringe Bank. A widespread frontal landslide complex of approximate Upper Miocene age is present along the whole flank, likely associated with the main phase of uplift. However, the recurrence of expressive submarine landslides in the Plio-Quarternary sequence is generally focused towards the northern segment of the Gorringe Bank. The geographical correlation between the areas of higher landslide number and clusters of seismicity epicentres suggest a close link between the two. This has direct implications for the assessment of landslide-prone locations on the seamount and to regional tsunami hazard models applicable to the Iberian and Northern African margins.This work is supported by the FCT funded project MAGICLAND - MArine Geo-hazards InduCed by underwater LANDslides in the SW Iberian Margin (Ref: PTDC/CTA-GEO/30381/2017)

Despite having been affected by several stages of exhumation during the Cretaceous and Cenozoic, the contemporary stress state of the East Irish Sea Basin (EISB) is poorly characterised. As the basin is mature in terms of exploitation of hydrocarbons, future exploration beyond the conventional Sherwood Sandstone Group reservoir (Triassic) necessitates a greater understanding of the in situ stress field, while proposed natural gas storage and carbon sequestration schemes also require detailed stress field information. Using petroleum well data, the in situ stress field of the EISB has been characterised to assess the mechanical seal integrity. A strike-slip stress regime most-likely prevails in the basin, meaning the Maximum Horizontal Stress (SHmax) is the greatest of the principal stresses. Interpretation of stress orientation data suggests that SHmax is oriented 152° ± 12°, consistent with mean stress orientations across the wider region associated with plate boundary forces. Some degree of structural control appears to influence the orientation of SHmax, with orientations locally aligned sub-parallel to major Permo-Triassic basin-bounding faults. Fault reactivation risk is evaluated through modelling the pore pressure increase required to induce failure on pre-existing faults. Vertical faults striking 30° from SHmax are optimally-oriented to become reactivated under elevated pore pressure conditions. For any project relying on an element of fault seal for the containment of buoyant fluids at the average reservoir depth of 800 m, pore pressure increase should be less than 3.3 MPa to avoid reactivating pre-existing optimally-oriented faults. Higher pressure increases would be required to initiate reactivation of faults with other orientations. Vertical faults striking perpendicular to SHmax are least likely to become reactivated, and in the absence of halite, seal integrity would instead be limited by caprock strength and capillary-entry pressure. Major faults affecting the basin have been analysed for their slip tendency (ratio of shear to normal stress), which provides an indication of their susceptibility to become reactivated. Although the analysis is limited due to lack of an accurate 3D representation of the fault network, the results suggest that many of the fault orientations observed in the EISB exhibit high slip tendencies, including N–S striking faults to the north and west of the East Deemster Fault, where the SHmax orientation is NW–SE. Faults striking perpendicular to SHmax, such as the Lagman Fault, are least likely to become reactivated due to higher normal stresses that inhibit frictional sliding, while faults striking parallel or very close to SHmax also exhibit low slip tendency as they are not subjected to significant shear stresses.

Carbon Capture and Storage (CCS) is a key technology for a low-carbon energy future and will have an important role on the economic future of the UK Continental Shelf (UKCS). The East Irish Sea Basin (EISB) is a prospective area for CCS in the western UKCS. 3D seismic from the EISB were used in this study to characterise the fault network and potential fault reactivation risks associated with CO2 injection. Two main structural domains are present: a Northern domain with NW-SE faults, and a Southern domain with faults following a N-S orientation. The main storage sites consist of structural closures in Triassic strata of the Sherwood Sandstone Formation (SSF), overlain by alternations of mudstones and evaporites of the Triassic Mercia Mudstone Group (MMG). The closures occur predominantly at fault-bounded horsts, with adjacent grabens filled by thick sequences of the Triassic Mercia Mudstone Group (MMG). The fault framework was used to test, in 3D, the stress model published for the EISB and assess the fault reactivation risk associated with CO2 storage. Slip tendency values were predominantly below 0.6, suggesting the presence of stable structures in the EISB. Under the tested conditions, faults are capable of withstanding pressure increases between 3 MPa and 10 MPa before the onset of slip. The limited fault reactivation risk suggests CCS operations are suitable prospects for the EISB. This work demonstrates the additional value gained from integration of accurately constrained fault geometries in 3D stress models.

Slow slip events (SSEs) at the northern Hikurangi subduction margin, New Zealand, are among the best-documented shallow SSEs on Earth. International Ocean Discovery Program Expeditions 372 and 375 were undertaken to investigate the processes and in situ conditions that underlie subduction zone SSEs at the northern Hikurangi Trough. We accomplished this goal by (1) coring and geophysical logging at four sites, including penetration of an active thrust fault (the Pāpaku fault) near the deformation front, the upper plate above the SSE source region, and the incoming sedimentary succession in the Hikurangi Trough and atop the Tūranganui Knoll seamount; and (2) installing borehole observatories in the Pāpaku fault and in the upper plate overlying the slow slip source region. Logging-while-drilling (LWD) data for this project were acquired as part of Expedition 372, and coring, wireline logging, and observatory installations were conducted during Expedition 375. Northern Hikurangi subduction margin SSEs recur every 1–2 y and thus provide an ideal opportunity to monitor deformation and associated changes in chemical and physical properties throughout the slow slip cycle. In situ measurements and sampling of material from the sedimentary section and oceanic basement of the subducting plate reveal the rock properties, composition, lithology, and structural character of material that is transported downdip into the SSE source region. A recent seafloor geodetic experiment raises the possibility that SSEs at northern Hikurangi may propagate to the trench, indicating that the shallow thrust fault (the Pāpaku fault) targeted during Expeditions 372 and 375 may also lie in the SSE rupture area and host a portion of the slip in these events. Hence, sampling and logging at this location provides insights into the composition, physical properties, and architecture of a shallow fault that may host slow slip. Expeditions 372 and 375 were designed to address three fundamental scientific objectives: Characterize the state and composition of the incoming plate and shallow fault near the trench, which comprise the protolith and initial conditions for fault zone rock at greater depth and which may itself host shallow slow slip; Characterize material properties, thermal regime, and stress conditions in the upper plate directly above the SSE source region; and Install observatories in the Pāpaku fault near the deformation front and in the upper plate above the SSE source to measure temporal variations in deformation, temperature, and fluid flow. The observatories will monitor volumetric strain (via pore pressure as a proxy) and the evolution of physical, hydrological, and chemical properties throughout the SSE cycle. Together, the coring, logging, and observatory data will test a suite of hypotheses about the fundamental mechanics and behavior of SSEs and their relationship to great earthquakes along the subduction interface.

Seamounts are spectacular bathymetric features common within volcanic and tectonically active continental margins. During their lifecycles, they evolve through stages of construction and destruction. The latter are marked by variable magnitude flank collapses that often interrupt the evolution of seamounts and constitute a major source of hazard. The Southwest Iberian Margin is a tectonically complex region with moderate to high seismicity where numerous seamounts occur. On such a setting, earthquake-triggered collapses on seamount flanks are common, leading to the deposition of Mass-Transport Deposits (MTDs) on the surrounding abyssal plains. Using a wealth of 2D seismic reflection profiles, we investigate the lifecycle of the tectonic Gorringe Bank (GB), the largest submarine seamount offshore European margins, based on the magnitude and recurrence patterns of MTDs along the active thrust flank. Eight MTDs with relevant expression on the seismic data were analysed, four of estimated Miocene age and four on a Pliocene-Quaternary interval. Miocene MTDs are overall larger and correlate with the main uplift stages of the GB structure. Their distribution and relative timing suggest that failure-triggering earthquakes were common along the whole length of the GB. Pliocene to Quaternary MTDs tend to cluster along the northern half of the GB flank and are generally smaller. Overall, the size and magnitude of the mass-waste events is directly relatable to the magnitude of the uplift stages. Given the lack of indicators of large MTDs on the modern GB morphology, we propose that the lifecycle of tectonic seamounts is marked by morphological rejuvenation driven by thrust fault activity in between major collapse events or cycles. Tectonic-driven rejuvenation is thus key to hinder or obliterate evidence of past high-magnitude destructive events on tectonic seamount morphology.

Carbon dioxide Capture and Storage (CCS) is considered a key strategy for decarbonising industries which have limited options for tackling CO2 process emissions. Previous efforts to develop CCS projects have been thwarted by adverse public perceptions amongst other issues. Understanding and tracking public perceptions prior to project development is therefore highly advisable. This study explores public perceptions of applying CCS technology at the Port Talbot Steelworks in South Wales. Opinions of local residents were gathered by means of two focus groups. Participants were concerned about the impact of implementing CCS on the competitiveness of the plant and, as a consequence, the possibility of closure. Perceived positive impacts were that a CCS facility would improve local air quality as well as the town’s public image, bringing inward investment. Acceptance or otherwise of CCS was found to be influenced by trust. Participants expressed particular distrust towards the local steel firm and various levels of Government, citing poor engagement, whilst showing tentative trust towards scientific/research organisations. Most participants saw emission reducing technologies as an inevitability, with most considering CCS to be of benefit to the Port Talbot Steelworks. If an effective engagement strategy and equal-voice procedures are applied, the residents of Port Talbot could be amenable to CCS.

International Ocean Discovery Program (IODP) Expedition 372 combined two research topics, slow slip events (SSEs) on subduction faults (IODP Proposal 781A-Full) and actively deforming gas hydrate-bearing landslides (IODP Proposal 841-APL). Our study area on the Hikurangi margin, east of the coast of New Zealand, provided unique locations for addressing both research topics.SSEs at subduction zones are an enigmatic form of creeping fault behavior. They typically occur on subduction zones at depths beyond the capabilities of ocean floor drilling. However, at the northern Hikurangi subduction margin they are among the best-documented and shallowest on Earth. Here, SSEs may extend close to the trench, where clastic and pelagic sediments about 1.0-1.5 km thick overlie the subducting, seamount-studded Hikurangi Plateau. Geodetic data show that these SSEs recur about every 2 years and are associated with measurable seafloor displacement. The northern Hikurangi subduction margin thus provides an excellent setting to use IODP capabilities to discern the mechanisms behind slow slip fault behaviour.

Landslides are common in aquatic settings worldwide, from lakes and coastal environments to the deep sea. Fast-moving, large-volume landslides can potentially trigger destructive tsunamis. Landslides damage and disrupt global communication links and other critical marine infrastructure. Landslide deposits act as foci for localized, but important, deep-seafloor biological communities. Under burial, landslide deposits play an important role in a successful petroleum system. While the broad importance of understanding subaqueous landslide processes is evident, a number of important scientific questions have yet to receive the needed attention. Collecting quantitative data is a critical step to addressing questions surrounding subaqueous landslides. Quantitative metrics of subaqueous landslides are routinely recorded, but which ones, and how they are defined, depends on the end-user focus. Differences in focus can inhibit communication of knowledge between communities, and complicate comparative analysis. This study outlines an approach specifically for consistent measurement of subaqueous landslide morphometrics to be used in the design of a broader, global open-source, peer-curated database. Examples from different settings illustrate how the approach can be applied, as well as the difficulties encountered when analysing different landslides and data types. Standardizing data collection for subaqueous landslides should result in more accurate geohazard predictions and resource estimation., peer-reviewed

Confluences points are important features of deepwater submarine canyons, but still poorly characterised. High-quality 3D seismic data is used to investigate a Miocene buried canyon and a modern, active one on the Rio Doce Turbidite System in the Espirito Santo Basin (SE Brazil). Detailed mapping of canyon thalwegs reveal two distinct confluence morphologies. Tributaries of the buried canyon merge at an equal junction of identical thalweg depth. Tributaries of the modern canyon merge at an unequal junction with a vertical offset of 100m between them. Submarine confluence scours are also observed, which occur either at central confluence region or preferentially adjacent to a tributary. The analysis of seismic amplitude attributes is used to highlight the preferential flow/depositional paths of sand-prone strata. In our examples both systems show a predominance of high amplitudes along the eastern tributaries and extending into the post-confluence path. We propose a classification for submarine confluences based on a combined analysis of canyon geometry and the use of seismic attributes. Confluences may be symmetric or asymmetric based on the similarity of the angles the tributaries bear to the post-confluence channel. Asymmetric confluences are primary or secondary depending on whether the dominant pre-confluence sediment flow (or deposition) takes place along the main or secondary tributary, respectively. This classification can be used to characterise the full sedimentary fill of buried canyons and channels and also of specific channel-fill events. The detailed assessment of the lateral continuity (or lack of it) of sand-prone strata shows that these can extend into the tributaries or be limited to the post-confluence segments. Furthermore, the strata geometry suggests episodic flow shifts and/or diachronous sediment deposition between tributaries. This has implications for the estimation of fluid flow paths at confluence regions, and to assess which tributaries constitute favourable fluid accumulation compartments.

Detailed morphological analyses of a Pleistocene-Holocene submarine channel system in terms of its hierarchical framework, were carried out using a 3D seismic volume from offshore Espirito Santo, SE Brazil. The channel morphology shows marked variations, with five segments (Segments a to e) being identified along its full length. For example, the cross-sectional area of the channel decreases by a factor of 70 from Segment a to Segment c, and is then followed by a nearly four-fold increase from Segment c to Segment d. The significant changes in channel morphology relate to temporal and spatial variations in flow volume within the channel. In the same channel system, the valley reveals three distinct segments (Segments A to C), with similar aspect ratios but marked variations in morphology along the valley distance. Valley morphological changes are chiefly affected by erosional processes. Segment B is characterised by the largest valley-base width, valley width, and cross-sectional area compared to the other two segments. Valley enlargement in Segment B results from relatively high degrees of lateral channel migration and associated cut bank erosion, leading to the widening of the valley, especially the valley base. In Segment C, the valley is characterised by inner bank erosion in the form of shallow-seated mass failures, which only enlarged the upper part of the valley wall. The spatial variations in both channel and valley morphology documented here suggest an important role of local factors (e.g. salt diapirs, tributaries, overbank collapse) in the development of channel systems. Hence, the morphological analyses developed in this work provide an effective tool for studying channels and valleys on continental slopes around the world.

High-quality 3D seismic data reveal bi-modal deformation styles in mass-transport deposits filling a salt minibasin in SE Brazil (Espírito Santo Basin). We analyse three mass-transport deposits within the same Miocene stratigraphic interval, and four others in Holocene strata. Our interpretation reveals that deformation in the mass-transport deposits relates to their long-axis orientation. As a result, they are divided into two types: a) Type 1 have long axes parallel to the direction of movement and show significant internal deformation; b) Type 2 have long axes perpendicular to the direction of movement, are highly heterogeneous and include large undeformed slabs. The long axes of Type 2 mass-transport deposits are parallel to the strike of bounding faults and salt structures. The majority of mass-transport deposits show intense deformation at their headwalls, and relative short remobilisation distances are inferred for both Types 1 and 2. In the study area, the timing of emplacement of mass-transport deposits was controlled by the growth of adjacent salt ridges. Earlier halokinesis in the northern axial areas of the minibasin shifted southwards in a second stage. Holocene mass-transport deposits suggest alternating growth of the eastern and western salt ridges. Our results show that detailed seismic-stratigraphic analyses are a key to understanding the timings and magnitude of deformation of mass-transport deposits in salt minibasins. The classification proposed can be applied to MTDs on continental margins and in lacustrine settings.

Mass-wasting on the Brazilian margin during the Mid-Eocene/Oligocene resulted in the accumulation of recurrent Mass Transport Deposits (MTDs) offshore Espirito Santo, SE Brazil. In this paper, we use three-dimensional seismic data to characterize a succession with stacked MTDs (Abrolhos Formation), and to assess the distribution of undeformed stratigraphic packages (i.e. turbidites) with reservoir potential separating the interpreted MTDs. High-amplitude strata in less deformed areas of MTDs reflect their internal heterogeneity, as well as possible regions with a higher sand content. Separating MTDs, turbiditic intervals reach 100 ms Two-Way Travel Time (TWTT), with thicker areas coincident with the flanks of growing diapirs and areas of the basin where mass-wasting is less apparent. Turbiditic strata laterally grade into, or are eroded by MTDs, with transitional strata between MTDs and turbidites being also influenced by the presence of diapirs. MTDs show average thickness values ranging from 58 to 82 ms TWTT and constitute over 50% of Eocene-Oligocene strata along the basin slope. Low average accumulations of 58 ms TWTT in areas of high confinement imposed by diapirs suggest sediment accumulation upslope, and/or bypass into downslope areas. This character was induced by the high sediment input into the basin associated with coastal erosion and growth of the Abrolhos volcanic plateau. Our results suggest that significant amounts of sediment derive from the northwest, and were accumulated in the middle-slope region. Interpretations of (palaeo)-slope profiles led to the establishment of a model of margin progradation by deposition of MTDs, contrasting with the retrogressive erosional margins commonly associated with these settings.

High-quality 3D seismic data are used to interpret the styles and scale-relationships of architectural elements on the continental slope of Espírito Santo (SE Brazil). Sand-prone architectural elements identified in this work include: a) axial canyons incising a salt-withdrawal basin (Unit 1), b) turbidite lobes intercalated with heterogeneous mass-transport deposits (Unit 2), and c) channel complexes confined by salt-controlled topography (Unit 3). Analyses of width/height (W/H) ratios reveal two distinct dimensional groups: Mass-transport deposits and turbidite lobes with W/H ratios ≥ 100, and channels and blocks with W/H ratios between 1 and 30. Importantly, all buried submarine canyons and channels systems show average W/H ratios of 12-13 for different stratigraphic units. Length-width (L/W) ratios of structural and stratigraphic\ud compartments vary between 1 and 10. A significant result of this work is the confirmation that distributions and dimensions of architectural elements can be controlled by salt-related faults and topography, with higher dimensional variability and lower continuity of sand-prone elements occurring in the vicinity of salt ridges. Our data also shows a marked tendency for clustering, and scale overlaps, between distinct architectural elements. The approach in this paper is relevant for hydrocarbon exploration as it uses quantitative data to predict slope compartmentalisation as a function of basin geometry.

Submarine mass-transport deposits (MTDs) frequently include blocks of strata with variable deformation styles. In this paper, a 3D seismic volume from SE Brazil is compared with\ud outcrop information from SE Crete to investigate multi-scale deformation patterns within mass-transport blocks. Block morphology relates closely to the orientation of internal faults and fractures, with wide chasms separating block fragments that opened along these planar\ud features. Two families of sub-perpendicular faults associated with intra-block extension are observed on both scales. On seismic data, we show new evidence of intra-block horizontal shear and thrust faulting. At outcrop, downslope verging folds, load casts and injectites are observed along poorly consolidated sand-prone beds that are less than 1 m thick. Documented orientations and cross-cutting geometries suggest a syn-kinematic origin for these structures. By integrating the observations made at different scales we suggest the development of 3D meshes in MTD blocks, which are characterised by the intersection of faults and fractures with bed-parallel shear planes. These meshes greatly increase the relative permeability of individual blocks. The results in this work have implications for the analysis of fluid flow paths on continental margins, and show that mass-transport blocks can comprise important fluid bypass points when buried in low permeability strata.

Points of confluence are important morphological features of deep-water submarine canyons, but they are still poorly characterized and incompletely understood. Here, high-quality 3-D seismic data are used to investigate the confluence regions of the Miocene (C1) and Modern (C2) submarine canyons of the Rio Doce Turbidite System in the Espirito Santo Basin, on the southeastern Brazilian margin. Growing salt diapirs play a dominant role in the confinement of the studied canyons, because confluence points are located near slope regions with the highest degree of confinement. Continuous salt growth and interaction with evolving sedimentary systems has forced an up-slope migration of the submarine confluence areas during the late Cenozoic. Detailed mapping and measurements of canyon thalwegs reveal two distinct morphologies for both confluences. Tributaries of Canyon C1 merge at an equal junction, whereas in Canyon C2 tributaries merge at an unequal junction, with a vertical offset of 100 m between them. This study also documents the presence of submarine confluence scours. In C1, a confluence scour is located in the central confluence region, whereas in C2 the scour is adjacent to the hanging tributary. Seismic attribute-based analysis of the channel-fill deposits (namely maximum and RMS amplitude) highlight the predominance of sand-prone, high-amplitude deposits along the eastern tributary and postconfluence conduits in both canyons. We propose a classification scheme for submarine confluences based on a combined analysis of channel geometry and the use of seismic attributes to assess sedimentary paths. Confluences may be symmetric or asymmetric, based on the similarity of the angles that the tributaries bear to the postconfluence channel. Left- or right-symmetric confluences define whether the dominant flow path is along the left- or right-hand tributary. Pure or secondary asymmetric confluences depend on whether the dominant preconfluence flow takes place along the main or secondary tributary, respectively. Following these criteria, the studied canyons are classified as pure asymmetric with a predominance of high-amplitude strata in the eastern tributaries and postconfluence path. This classification can be used to characterize the full sedimentary fill of buried canyons and channels and also of specific channel-fill events. The latter allows a detailed assessment of the lateral continuity (or lack of it) of relevant sand bodies from the main canyon conduit into the tributary systems. This has important implications for the estimation of fluid flow paths at confluence regions, and for the assessment of which tributaries constitute the most favourable fluid accumulation compartments.

The Eocene-Oligocene stratigraphic succession of the Espirito Santo Basin, SE Brazil, comprises several Mass-Transport Deposits (MTDs), some of which contain individual blocks of strata. The blocks are classified as rafted blocks if transported over a glide plane, or remnant blocks if in situ, showing vertical stratigraphic continuity with underlying strata. A detailed 3D seismic analysis of a mass-transport deposit (MTD-A1) deposited at the base of an Eocene volcaniclastic complex (Abrolhos complex) reveals the presence of various blocks within the masses of failed strata. Blocks occur in the thickest areas of the MTD, along an alignment of salt diapirs and buried salt ridges. Block fragmentation is suggested to be associated to diapir-related faults, especially when these are closely aligned with in-situ blocks. The remnant blocks show low deformation, with sub-horizontal internal reflections, whereas rafted ones range from low to highly deformed blocks. Variations in the blocks’ geometries suggest a lateral remobilisation in the order of 1,000 m, for a maximum of 4,000 m, for MTD-A1. The low remobilisation led to an unusual location of the MTD over the salt structures, contrasting with the typical remobilisation towards peripheral basins. The relation between MTD and salt-related structures can provide indicators to constrain the timing of halokinesis.

Three-dimensional seismic data are used to assess the control of halokinetic structures on the distribution of blocks in a mass transport deposit in the Espirito Santo Basin, southeast Brazil. In contrast to what is commonly observed over growing salt structures, the thickness of the MTD-A1 is larger on top of a northwest trending salt ridge. Emphasis was given to the statistical analysis of 172 remnant and rafted blocks identified within Eocene mass transport deposits (MTD-A1). Three styles of block deformation are identified and scale relationships between the geometry of blocks and their relative position on the salt ridge are presented. Average block height reaches 130 m. Average block area reaches 0.43 km2, while 11.3% of the total area (A) investigated is covered by blocks (5% < A < 17%). On the basis of variations in block geometry (height, area, width/length ratio, orientation) and their relative distribution, we interpret that most failed strata have been remobilized by adjacent topography created during growth of the investigated salt ridge. We show that the origin of the blocks is linked to densely spaced sets of halokinetic-related faults that deformed the prefailure strata. The presence of underlying faults and blocks of remnant and rafted strata potentially induces sharp variations in the internal permeability of MTD-A1. Thus, the interpreted data shows that megablocks in MTDs can constitute viable fluid pathways on otherwise low-permeability units. This character can significantly decrease seal competence above and on the flanks of halokinetic structures.

The work presented characterises the distribution of continuous strata intercalated with Mass-Transport Deposits (MTDs) and their internal heterogeneities within a Late Palaeogene unit in the Espirito Santo Basin, Brazil. MTDs have low permeability and are considered as barriers to fluid flow, but sand-prone strata within the interpreted MTDs can constitute viable reservoirs as long as permeable pathways are present. Our work shows that the presence of continuous strata varies along the stratigraphic interval. They are of limited expression in the lower sections of the Palaeogene unit where thick MTDs occur. In contrast, the upper part of the latter unit shows continuous strata through a large portion of the interpreted survey, and relatively thinner MTD successions. Within the basal MTD numerous remnant blocks were identified, being related to pre-MTD faulting. Three block deformation types were established, namely low, moderate and high, reflecting the internal block tilting. We infer that the presence of pre-MTD faults and remnant blocks establishes permeable conduits across the studied MTD successions, eventually promoting fluid flow from pre-MTD successions to the Late Palaeogene reservoir-prone (continuous) strata. Proof of that is the distribution of basal remnant blocks, which partly follows pre-MTD faults.