Abstract
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.
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.
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 Espírito 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.
Key Points
Permeability enhancement through blocks in MTD units
Genesis of MTD blocks due to halokinesis
Distribution of MTD blocks on top and flanks of salt structures
Slow slip events (SSEs) accommodate a significant proportion of tectonic plate motion at subduction zones, yet little is known about the faults that actually host them. The shallow depth (<2 km) of ...well-documented SSEs at the Hikurangi subduction zone offshore New Zealand offers a unique opportunity to link geophysical imaging of the subduction zone with direct access to incoming material that represents the megathrust fault rocks hosting slow slip. Two recent International Ocean Discovery Program Expeditions sampled this incoming material before it is entrained immediately down-dip along the shallow plate interface. Drilling results, tied to regional seismic reflection images, reveal heterogeneous lithologies with highly variable physical properties entering the SSE source region. These observations suggest that SSEs and associated slow earthquake phenomena are promoted by lithological, mechanical, and frictional heterogeneity within the fault zone, enhanced by geometric complexity associated with subduction of rough crust.
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 outcrop information ...from SE Crete to investigate multi-scale deformation patterns within mass-transport blocks. Block morphology in the two study areas relates to the orientation of internal faults and fractures, with wide chasms separating block fragments that opened along these planar features. Two families of sub-perpendicular faults associated with intra-block extension are observed at multiple scales. On seismic data, we show new evidence of intra-block horizontal shearing and thrusting. At outcrop, downslope verging folds, load casts and injectites are observed along poorly consolidated sandy intervals that are less than 1m thick. Documented 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 mass-transport blocks, which are characterised by the intersection of faults and fractures with bed-parallel shear planes. These meshes greatly increase the 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.
•Shear structures are identified in seismic-scale mass-transport blocks.•Shear structures are developed along ductile beds.•Deformation meshes are formed by intersecting fractures and shear structures.•Multi-scale deformation meshes increase the permeability of mass-transport blocks.
•CCS seen to be able to improve the image of Port Talbot and bring inward investment.•Focus group participants seek genuine, open engagement between stakeholders (industry and government) to help ...build trust.•A collective distrust for Port Talbot steel firm and Government to implement CCS.•Scientific/research bodies’ perceived as most trusted amongst three CCS stakeholders.•Main negative view of CCS was that it may pose a threat to industry competitiveness.
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.
The occurrence of soft-sediment deformation structures (SSDS) have long been recognized in several types of sedimentary environments and deposits. However, their presence in contourite drift deposits ...is still unreported in the literature. In this work, we present the first detailed description of SSDS found within the Pliocene sedimentary record of the Faro Drift, recovered during the Integrated Ocean Drilling Program (IODP) Expedition 339. The Faro Drift is the largest contourite drift of the Contourite Drift Depositional System developed in the Gulf of Cadiz since the Late Miocene by the circulation of the Mediterranean Outflow Water. The SSDS were identified in archive-halves of core sections located between ∼458 and ∼ 510 m below seafloor (mbsf) (hole U1386C), and between ∼599 and ∼ 670 mbsf (hole U1387C). Their identification and characterization was made by visual core description, structural geometrical analysis in core-scan high-resolution images, and scanning electron microcopy (SEM) analysis in selected intervals. The SSDS were classified based on the exhibited geometry, structural configuration and respective kinematics. The main deformation process and potential trigger were inferred from the geometrical and kinematics analysis. We identified five categories of SSDS: i) microfaults (normal and thrust faults), ii) slump sheet (formed by several types of folds, such as eye-folds, fish-hook folds, spiral folds), iii) convolute bedding, iv) folds within debrite mudclasts', and v) sigmoidal-like structures. Although the first three are well known types of SSDS, the folds within debrite mudclasts' and sigmoid-like structures have been scarcely recognized and described at core-scale. The inferred deformation processes responsible for the formation of these SSDS were i) brittle deformation by hydrofracturing and compaction faulting (microfaults), ii) hydroplastic (ductile) deformation (slump folds, folds within debrite mudclasts'), iii) liquefaction (convolute bedding), iv) shearing by flow movement (sigmoid-like structures). The most probable triggering agents seem to have been overloading, downslope movement of slump sheet and debris flow, and shearing by currents.
•Soft-sediment deformation structures identified for the first time in contourites.•Structures formed by hydrofracturing, hydroplastic deformation, liquefaction, shear.•Overloading and shear by flow movement have been as the main potential triggers.
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.
•Two distinct types of mass-transport deposits (MTDs) are presented for a salt minibasin.•Type 1 MTDs have higher, less complex internal deformation.•Type 2 MTDs are characterised by low deformation translational slabs.•Headwall length/distance-to-toe ratios distinguish the MTD types.•MTDs are used to locate discrete halokinetic pulses along salt ridges.
•First detailed study of Mass Transport Deposits (MTDs) on the Gorringe Bank's flank.•MTD magnitude is relatable to tectonic cycles of the GB.•MTDs mark the shift of tectonic activity locus through ...time.•Multiple cycles of morphological rejuvenation occur on tectonic seamounts.•Morphological rejuvenation hinders evidence of large magnitude collapses.
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.
PDF
