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Currently, Ocean Bottom Seismometers (OBS) have sensors comparable to those used on land stations. However, they are exposed to very different conditions that degrade the recordings. One major issue is being directly exposed to global and tidal oceanic currents that, depending on the water velocity flowing around the instrument, can excite parts of the frame or produce drag and lift effects due to vortex shedding. Any of these conditions is detrimental for signal integrity, either from variations of the instrument-to-ground coupling or by introducing unwanted energy that is unrelated with the seismic events the experiment is aimed at.The UPFLOW project is aimed at understanding mid-plate, deep upward flow that cannot be explained by plate tectonics, but is critical for continental growth, for returning volatiles to the atmosphere and for producing Earth’s largest melting events. For this reason, 50 OBS of different types were deployed for a year in the North Atlantic Ocean, including several prototypes aimed at reducing the tidal-induced noise generated by water flowing around the instrument's frame.In this work, we show the seasonal variation of the tidal-induced noise on different instrument types across the Madeira and Seine abyssal plains of the North Atlantic Ocean during neap and spring tides between July 2021 and July 2022. In some instances, where harmonics are detected, individual frame components of the OBS can be identified as a major contributor, paving way to finding mitigation solutions on future deployments.This work was funded by the Portuguese Fundação para a Ciência e a Tecnologia (FCT) I.P./MCTES through national funds (PIDDAC) – UIDB/50019/2020.

Ocean-bottom seismometers (OBSs) are usually deployed for seismological investigations, but these objectives are impaired by noise resulting from the ocean environment. We split the OBS-recorded seismic noise into three bands: short periods, microseisms and long periods, also known as tilt noise. We show that bottom currents control the first and third bands, but these are not always a function of the tidal forcing. Instead, we suggest that the ocean bottom has a flow regime resulting from two possible contributions: the permanent low-frequency bottom current and the tidal current. The recorded noise displays the balance between these currents along the entire tidal cycle, between neap and spring tides. In the short-period noise band, the ocean current generates harmonic tremors corrupting seismic dataset records. We show that, in the investigated cases, the harmonic tremors result from the interaction between the ocean current and mechanical elements of the OBS that are not essential during the sea bottom recording and thus have no geological origin. The data from a new broadband OBS type, designed and built at Instituto Dom Luiz (IDL – University of Lisbon)/Centre of Engineering and Product Development (CEIIA), hiding non-essential components from the current flow, show how utmost harmonic noise can be eliminated.

Portugal, located in the southwest region of the Eurasian plate, has been affected by several destructive earthquakes throughout its history, the most well-known being the 1755 Great Lisbon earthquake. The seismicity of the territory, both in the mainland and in the Azores and Madeira islands, has prompted the continuous development of seismic monitoring, from the first known macroseismic inquiry, following the 1755 Great Lisbon earthquake, to the current state-of-the-art seismic network. Once scattered in separate efforts, at present, most seismic stations in Portugal relay its data to a common data center, at Instituto Português do Mar e da Atmosfera, where data are automatically processed for the downstream generation of both manually revised and automatically generated products and services. In this article, we summarize the evolution of the permanent seismic network, its current status, the products and services that are publicly available, a recent effort of rapid deployment of a dense network following a mainshock, and state-of-the-art ocean-bottom seismometer developments.

Ocean bottom seismometers (OBS) are usually deployed for seismological investigations but these objectives are impaired by noise resulting from ocean environment. We split the OBS recorded seismic noise into three domains, short-period, microseisms and long-period, also known as tilt-noise. We show that the first and third domains are controlled by bottom currents but these are not always a function of the tidal forcing. Instead we suggest that the ocean bottom has a flow regime resulting from two possible contributions, the permanent low frequency bottom current and the tidal current. The recorded noise displays the balance between these two currents along the full tidal cycle, between neap and spring tides. In the short-period noise band the ocean current generates harmonic tremors that corrupt the dataset records. We show that, in the analyzed cases, the harmonic tremors result from the interaction between the ocean current and mechanical elements of the OBS that are not essential for sea bottom recording and thus have no geological origin. The data from a new Broadband OBS type, designed and built at Instituto Dom Luiz (University of Lisbon)/CEIIA, hiding no essential components from current flow, shows how utmost of the harmonic noise can be eliminated.

The North Natal Valley (NNV) and the Mozambique Coastal Plain (MCP) are key areas for the understanding of the SW Indian Ocean history since the Gondwana break‐up. Nevertheless, the deep structures and the nature of the NNV and MCP remain discussed in the absence of deep geophysical data. In 2016, the NNV, MCP and Limpopo margin (LM) have been investigated along 7 wide‐angle and MCS profiles. The combined wide‐angle and reflection seismic interpretation along the N‐S MZ7 profile reveals an upper sedimentary sequence characterized by low velocities generally not exceeding 3 km/s, with thicknesses varying from 0.150 km in the central part to ∼2.8 km in the south. The underlying sequence is formed of a 2.5‐3.0 km thick volcano‐sedimentary sequence which presents important lateral and with depth changes and presence of high velocity lenses, indicating inter‐bedded volcanic sills and recurrent magmatic episodes. The south of the NNV including the Naude Ridge (NR) presents a disturbed sedimentary cover with structural highs and southward‐dipping reflectors and sub‐basins. The crust, reaching 35‐40 km onshore below the MCP, gently thins below the continental shelf to a regular thickness of ∼29 km below the NNV. Crustal velocities reveal low velocity gradients, with atypical high velocities. South the ND, the crust thins to 15 km. We interpret the velocity architecture combined with the evidences of volcanism at shallower depths as indicating an intensively intruded continental crust. Contrary to what is proposed in most geodynamic models, the Mozambique Coastal plain and the Natal Valley are both of continental nature, with an abrupt necking zone located south of NR. The Antarctica plate was therefore situated at the eastern limit of these two domains before the Gondwana breakup. Plain Language Summary About 200Ma ago, the mega‐continent Pangaea broke up. The dispersion of the pieces of this mega‐continent, linked to the closure and disappearance of the Thetys paleo‐ocean, gave the birth of the Atlantic and Indian Oceans. In detail, the initial position of each piece of this jigsaw is of great importance as it has an impact on the palaeotopography and palaeogeography, and our understanding of the genesis of the continental passive margins, the role of tectonic inheritance, the pre‐rift and post‐rift evolution of the topography dynamic (vertical movement) and of the geodynamic of the plates (horizontal movement). Nevertheless, in the Western Indian Ocean, the initial pre‐beak‐up position of Antarctica plate respect to Africa plate is still under debate, mainly due to the lack of deep geophysical data. In 2016, an academic‐industrial collaboration succeeded in acquiring deep information along 7 seismic profiles crossing the North Natal Valley off the coast of Mozambique. The results falsify the presence of an oceanic crust in that area and thus most of the plate reconstruction models. They also argue in favour a new paradigm for the genesis of continental passive margin.

The need for submarine observatories to monitor offshore tectonic sources that can generate destructive earthquakes and tsunamis is widely recognized but the requirements of real-time communications and cost has hindered its Implementation. Only very few dedicated cables with sensors are in operation today. If the dozens of commercial telecommunication submarine cables that are deployed every year were instrumented, they could revolutionize the offshore earthquake monitoring. These cables, named as SMART (Science Monitoring And Reliable) have been advocated by the JTF of United Nations (Joint Task Force) for nearly a decade but none has been deployed today. However, there are several identified projects that should become the first pilots worldwide.Fiber optic research have shown that the cable itself can be used as strain meters and useful for seismic monitoring.One technology is DAS, Distributed Acoustic Sensing. DAS uses a single dedicated portion of (dark) fiber on a submarine cable, with a length about ~100 km. It can be modelled as a distributed strain sensor, with localization ability of a few meters. The DAS signal using OTDR (optical time domain reflectometry) and signal phase detection measures the fiber strain and record earthquakes with a resolution like broadband seismic sensors.Another technology is LI (Laser Interferometry). LI may use a dark fiber or a single telecom wavelength channel in an optical fiber pair with commercial traffic, thousands km long. It relies on frequency stable laser sources and coherent detection. LI detects the changes of fiber optical transmission parameters over the whole cable. Using recording instruments on both ends, the arrival point of the first seismic waves is determined, and the azimuth to the epicenter estimated.This work proposes and applies one methodology to assess the gain in earthquake source information using any of the three cable sensor technologies mentioned, against a background scenario that includes only land stations. We use a Monte-Carlo simulation to allow for picking uncertainties, local and regional variations of propagation velocity models. We parametrize the gain in information by measuring the epicenter uncertainty ellipse and the focal depth variability.The proposed methodology is applied to the NE Atlantic domain, SW Iberia and the Azores archipelago, an area where the relative motion of the Nubia, Eurasia and North America plates can generate large and destructive earthquakes and tsunamis.While the inclusion in the monitoring network of SMART observatories, placed inside cable repeaters, spaced every ±70 km, is straightforward, the use of DAS and LI is not. For DAS and LI we consider that observations can be decimated to virtual seismic stations every 5 km and 1 km respectively. To avoid using a set of very close stations, we implement different station selection algorithms.The investigation presented in this work was conducted by LEA, Listening to the Earth under the Atlantic, a partnership between IT, IPMA and IDL. One of the main objectives of LEA is to promote research, development, training and outreach on geophysical and oceanographic phenomena using submarine cables, fostering its applications to Science and Civil Protection.

One of the aims of project SIGHT (SeIsmic and Geochemical constraints on the Madeira HoTspot system) is to obtain a 3D model of SV-wave velocities of the crust and upper mantle of the Northeast Atlantic area encompassing Madeira and Canary Islands to the Atlas-Gibraltar zone, using seismic noise cross-correlations in the period range 2-100 s. Ambient noise cross-correlation has been successfully applied in a variety of tectonic environments to image the structure of the Earth subsurface. This technique overcomes some limitations ascribed to source–receiver geometry and sparse and irregular earthquake distribution, allowing to image Earth structure with a resolution that mainly depends on the network design. However, the effect of the water layer in the short period Empirical Green Functions, which are obtained by seismic noise cross-correlation, for interstation paths crossing the ocean is still poorly understood.In several studies, it has been observed that the presence of water and sediments is responsible for later wave-train arrivals. Those later arrivals are frequently disregarded when measuring group velocity, either by considering only longer periods or by specifying a given velocity range.In this work, we present a systematic study of the influence of the water layer on both vertical and radial synthetic Rayleigh waves, as well as on higher-mode conversion and on the group velocities dispersion measurements.We show that although the fundamental mode dominates, the presence of the first overtones at short periods (typically below 8 seconds) cannot be neglected. We also show that specifying a given velocity range when retrieving group velocity can result in a mixture of modes. Our tests reveal that, at short periods, the water has a dominant effect on ocean-continent laterally varying media.This is a contribution to projects SIGHT (Ref. PTDC/CTA-GEF/30264/2017) and STORM (Ref. UTAP-EXPL/EAC/0056/2017). The authors would like to acknowledge the financial support FCT through project UIDB/50019/2020 – IDL.

CAM is the acronym of the submarine telecommunication fibre optic cables that interconnect in a ring Portugal mainland, Azores and Madeira archipelagos. The current cables will cease their operation by 2024 (due to the end of cable lifetime), and the process of their replacement by a new set of cables is now under consideration by the Portuguese authorities with the technical requirements to be defined until mid-2020.The CAM cables span along the plate boundary between Eurasia and Nubia, an offshore domain prone to generate destructive earthquakes and tsunamis. The impacts caused by these natural hazards can be mitigated by effective tsunami (TWS) and earthquake (EEWS) early warning systems that would benefit (but not only) Portugal, Spain and Morocco. In TWS, a confirmation that a tsunami was generated, and an evaluation of its amplitude, are only obtained after the recordings from the closest coastal tide-gauge are analysed. Hence, this information will not benefit large stretches of coastline. EEWS that rely on land station observations of strong motion will not profit the regions closest to the epicentre. Furthermore, the quality of the offshore earthquake parameters computed by the operational centres is less than optimal when land stations only are used.All these difficulties can be overcome by deploying sensors integrated in the commercial telecom submarine cables to be installed in the future, without reduction of the reliability, lifetime, operational and functional requirements demanded by operators. Being closer to the tectonic sources, such sensors (and the cable itself) will record the geophysical parameters and transmit them to land much faster than the speed of destructive waves, providing the processing centres with critical lead time. This is the approach that has been advocated by the Joint Task Force led by three U.N. agencies (ITU, WMO and UNESCO-IOC) (Howe et al., Front. Mar. Sci. 6:424, 2019). Such initiative was given the name of SMART, for Science Monitoring and Reliable Telecommunications.In this work we evaluate the contribution of a SMART CAM fibre optic ring of cables, with repeaters equipped with geophysical sensors, to three critical aspects of TWS and EEWS: 1) quality of fast earthquake parameters; 2) earthquake early warning lead time; 3) tsunami confirmation warning time. The performance parameters selected where: i) azimuthal gap between the minimum set of stations required for an earthquake location to be accepted; ii) size of the estimated location error ellipse; iii) error on the focal depth estimation; iv) gain in P-wave advance time for the minimum set of stations required by the EEWS; v) gain in tsunami travel time to the closest tide-gauge or pressure sensor.The methodology and results obtained are valuable to encourage national authorities to implement the SMART cable concept in the technical specifications for future telecommunication submarine cables. This has been recently suggested by the ANACOM President (the Portuguese regulator for telecommunications advising the national authorities) for the CAM cables that must be operational in early 2024. The first author would like to acknowledge the financial support from FCT through project UIDB/50019/2020-IDL.

©2019. American Geophysical Union. All Rights Reserved. Independent models of P wave and S wave velocity anomalies in the mantle derived from seismic tomography help to distinguish thermal signatures from those of partial melt, volatiles, and compositional variations. Here we use seismic data from SW Europe and NW Africa, spanning the region between the Pyrenees and the Canaries, in order to obtain a new S-SKS relative arrival-time tomographic model of the upper mantle below Iberia, Western Morocco, and the Canaries. Similar to previous P wave tomographic results, the S wave model provides evidence for (1) subvertical upper-mantle low-velocity structures below the Canaries, Atlas Ranges, and Gibraltar Arc, which are interpreted as mantle upwellings fed by a common lower-mantle source below the Canaries; and (2) two low-velocity anomalies below the eastern Rif and Betics that we interpret as the result of the interaction between quasi-toroidal mantle flow induced by the Gibraltar slab and the mantle upwelling behind it. The analysis of teleseismic P wave and S wave arrival-time residuals and the conversion of the low-velocity anomalies to temperature variations suggest that the upwellings in the upper mantle below the Canaries, Atlas Ranges, and Gibraltar Arc system may be solely thermal in nature, with temperature excesses in the range ~100–350 °C. Our results also indicate that local partial melting can be present at lithospheric depths, especially below the Atlas Ranges. The locations of thermal mantle upwellings are in good agreement with those of thinned lithosphere, moderate to high heat-flow measurements, and recent magmatic activity at the surface.

International audience; The structure and nature of the crust underlying the Camamu-Almada-Jequitinhonha-Sergipe-Alagoas basins System, in the NE Brazilian margin, were investigated based on the interpretation of 12 wide-angle seismic profiles acquired during the SALSA (Sergipe ALagoas Seismic Acquisition) experiment in 2014. In this work, we present two 220-km-long NW-SE combined wide-angle and reflection seismic profiles, SL 01 and SL 02, that have been acquired using 15 ocean-bottom-seismometers along each profile, offshore the southern part of the Sergipe Alagoas Basin (SAB), north of the Vaza-Barris Transfer zone. The SL 02 has a 150-km long inland continuation with 20 land-seismic-stations until the Sergipano Fold Belt (SFB). Wide-angle seismic forward modeling allows us to precisely divide the crust in three domains: beneath the continental shelf, a ∼100 km wide necking zone is imaged where the continental crust thins from ∼35 km on the Unthinned Continental Domain, which displays a three-layered crust structure, to less than 8 km on the Oceanic Crust Domain. In the necking zone, the upper and the middle layers thin dramatically and almost disappear, while the Moho discontinuity shows clear PmPs. The Continental-Oceanic Crust Boundary (COB) is located at ∼80 km from the coastline and is marked by intracrustal seismic reflectors and changes in the seismic velocity, showing a sharp transition. On profile SL02, the oceanic crust is perturbed by a volcanic edifice together with an anomalous velocity zone underneath the area.

Twelve combined wide-angle refraction and coincident multi-channel seismic profiles were acquired in the Jequitinhonha-Camamu-Almada, Jacuipe, and Sergipe-Alagoas basins, NE Brazil, during the SALSA experiment in 2014. Profiles SL11 and SL12 image the Jequitinhonha basin, perpendicularly to the coast, with 15 and 11 four-channel ocean-bottom seismometers, respectively. Profile SL10 runs parallel to the coast, crossing profiles SL11 and SL12, imaging the proximal Jequitinhonha and Almada basins with 17 ocean-bottom seismometers. Forward modelling, combined with pre-stack depth migration to increase the horizontal resolution of the velocity models, indicates that sediment thickness varies between 3.3 km and 6.2 km in the distal basin. Crustal thickness at the western edge of the profiles is of around 20 km, with velocity gradients indicating a continental origin. It decreases to less than 5 km in the distal basin, with high seismic velocities and gradients, not compatible with normal oceanic crust nor exhumed upper mantle. Typical oceanic crust is never imaged along these about 200 km-long profiles and we propose that the transitional crust in the Jequitinhonha basin is a made of exhumed lower continental crust.

The structure and nature of the crust underlying the Santos Basin-Sao Paulo Plateau System (SSPS), in the SE Brazilian margin, are discussed based on five wide-angle seismic profiles acquired during the Santos Basin (SanBa) experiment in 2011. Velocity models allow us to precisely divide the SSPS in six domains from unthinned continental crust (Domain CC) to normal oceanic crust (Domain OC). A seventh domain (Domain D), a triangular shape region in the SE of the SSPS, is discussed by Klingelhoefer et al. (2014). Beneath the continental shelf, a ~100 km wide necking zone (Domain N) is imaged where the continental crust thins abruptly from ~40 km to less than 15 km. Toward the ocean, most of the SSPS (Domains A and C) shows velocity ranges, velocity gradients, and a Moho interface characteristic of the thinned continental crust. The central domain (Domain B) has, however, a very heterogeneous structure. While its southwestern part still exhibits extremely thinned (7 km) continental crust, its northeastern part depicts a 2–4 km thick upper layer (6.0–6.5 km/s) overlying an anomalous velocity layer (7.0–7.8 km/s) and no evidence of a Moho interface. This structure is interpreted as atypical oceanic crust, exhumed lower crust, or upper continental crust intruded by mafic material, overlying either altered mantle in the first two cases or intruded lower continental crust in the last case. The deep structure and v-shaped segmentation of the SSPS confirm that an initial episode of rifting occurred there obliquely to the general opening direction of the South Atlantic Central Segment.

We used ambient seismic noise recorded by 24 Broadband Ocean Bottom Seismometers (OBS) deployed in the Gulf of Cadiz during the EC funded NEAREST project and seven broadband land stations located in the South of Portugal to image the sedimentary and crustal structure beneath the Eastern Atlantic and SW Iberia. We computed ambient noise cross-correlations to obtain empirical Green's functions (EGFs) between all station pairs using land seismometers and both OBS sensors, seismometers and hydrophones. Despite the great difference in the recording conditions and local crustal structure between the OBSs and land stations, we could compute EGFs, by applying a linear cross-correlation with running absolute mean average time normalization, followed by a time-frequency phase weighted stack. Dispersion analysis was then applied to the EGFs, between 4 and 20s period. The obtained dispersion curves allowed mapping the lateral variation of Rayleigh-wave group velocities, as a function of period. Finally, dispersion curves extracted from each cell of the 2D group velocity maps were inverted, as a function of depth, to obtain the 3D distribution of the shear-wave velocities. The 3-D shear wave velocity model, computed from joint inversion of OBSs and land stations data allowed to estimate the thickness of sediments and crust and the Moho depth. Despite the gap that exists between the OBSs and land station locations, our model displays a good correlation with the known geological structure. The derived sedimentary layer and crustal thicknesses and the obtained Moho depth are locally in agreement with the models proposed by other studies using near vertical, refraction and wide-angle seismic profiling. We conclude that ambient noise tomography could be a valuable tool to image oceanic domains, and also that it is possible to integrate seafloor- and land-based stations to derive a structure model in the transition domain between continent and ocean. © 2017 Elsevier B.V., This article is a contribution of projects NEAREST FP6-2005-GLOBAL-4 (OJ 2005 C177/15), QuakeLoc-PT (PTDC/GEO-FIQ/3522/2012), AQUAREL (PTDC/CTE-GIX/116819/2010), WILAS (PTDC/CTE-GIX/097946/2008). The publication is supported by FCT through project UID/GEO/50019/2013 - Instituto Dom Luiz.

Ocean infragravity (IG) waves are low-frequency waves generated along shorelines by incident seas and swell and with heights of the order of 1 cm in the open ocean. Despite these small amplitudes, they can be of much importance for ice shelf break up and errors in measurements of sea level by future satellite altimeters. A combination of numerical model results and in situ data is used to show that bottom pressure signals in the infragravity frequency band can be dominated by bursts of energy that travel across ocean basins, and can last for several days. Two particularly strong events recorded in 2008 are studied, one in the North-Pacific and the other in the North-Atlantic. It is shown that infragravity waves can travel across whole oceans basins with the signal recorded on the western shores often dominated by IG waves coming from the opposite shore of that same ocean basin.

© 2014, Bulletin of the Seismological Society of America. All rights reserved. The West Iberia Lithosphere and Asthenosphere Structure (WILAS) project densely covered Portugal with broadband seismic stations for 2 yrs. Here we provide an overview of the deployment, and we characterize the network ambient noise and its sources. After explaining quality control, which includes the assessment of sensor orientation, we characterize the background noise in the short-period (SP), microseismic, and long-period (LP) bands. We observe daily variations of SP noise associated with anthropogenic activity. Temporary and permanent stations present very similar noise levels at all periods, except at horizontal LPs, where temporary stations record higher noise levels. We find that median noise levels are extremely homogeneous across the network in the microseismic band (3–20 s) but vary widely outside this range. The amplitudes of microseismic noise display a strong seasonal variation. The seasonality is dominated by very-long-period double-frequency microseisms (8 s), probably associated with winter storms. Stacks of ambient noise amplitudes show that some microseismic noise peaks are visible across the whole ground-motion spectrum, from 0.3 to 100 s. Periods of increased microseismic amplitudes generally correlate with ocean conditions offshore of Portugal. Some seismic records display an interesting 12 hr cycle of LP (100-s) noise, which might be related to atmospheric tides. Finally, we use plots of power spectral density versus time to monitor changes in LP instrumental response. The method allows the identification of the exact times at which LP response changes occur, which is required to improve the understanding of this instrumental artifact and to eventually correct data., This research was supported by Fundação para a Ciência e Tecnologia through projects WILAS (PTDC/CTE-GIX/097946/2008), QuakeLoc-PT (PTDC/GEO-FIQ/3522/2012), and SCENE (PTDC/CTE-GIX/103032/2008), and by the European Commission FP7 project NERA (Network of European Research Infrastructures for Earthquake Risk Assessment and Mitigation, GA-262330). This is a contribution to PEST-OE/CTE/LA0019/2011 (IDL). The first author acknowledges a Marie Curie International Reintegration Grant from the European Commission, FP7 (PIRG03-GA-2008-230922)

On November 1, 1755, the city of Lisbon was completely devastated by the combined effect of a tremendous earthquake, tsunami waves, and fire. The 1755 Lisbon earthquake was the most destructive cataclysm recorded in western Europe since the Roman Republic, with an estimated earthquake magnitude Mw ∼8.5 [Martins and Mendes Victor, 1990] and estimated tsunami magnitude of Mt= Mw= 8.5. The earthquake was felt as far away as Great Britain and Finland. The tsunami hit many coastal cities along southwest Iberia and North Africa, causing heavy destruction in Tanger and Casablanca.

The tsunami generated by the 1755.11.01 earthquake, as reported by coeval sources, was the major event of its kind in the North Atlantic, until nowadays. The coasts of the Iberian Peninsula and Northwest Morocco were deeply affected by that phenomenon, with tremendous impacts on the city of Lisbon. For the last 20 years, significant support was received from EU (Projects DETWS, IAM, GITEC, GITEC-TWO and BIGSETS), national projects (MATESPRO, RIFANO and RIMAR) and bi-lateral cooperation (HITS, TTR-10, SISMAR and VOLTAIRE). This allowed significant improvements on the knowledge of parameters sources and tsunami propagation. Tsunami propagation models were developed, being the simulations controlled by real data, deducted from historical reports or instrumental networks. In order to assess the considerable impacts along the Portuguese coasts, different run-up models have been used and tested. To evaluate the tsunami hazard, comprehensive studies were developed, recognizing the importance of the inter-disciplinary approach, including the study of induced continental sedimentary deposits. The location of the 1755.11.01 source has been a key question, motivating intensive marine research in the southern area of Portugal, looking for unquestionable morphological or geological evidence of fault rupture and the present-day seismic activity.

Upper-mantle upwellings are often invoked as the cause of Cenozoic volcanism in the Ibero-western Maghreb region. However, their nature, geometry and origin are unclear. This study takes advantage of dense seismic networks, which cover an area extending from the Pyrenees in the north to the Canaries in the south, to provide a new high-resolution P-wave velocity model of the upper-mantle and topmost lower-mantle structure. Our images show three subvertical upper-mantle upwellings below the Canaries, the Atlas Ranges and the Gibraltar Arc, which appear to be rooted beneath the upper-mantle transition zone (MTZ). Two other mantle upwellings beneath the eastern Rif and eastern Betics surround the Gibraltar subduction zone. We propose a new geodynamic model in which narrow upper-mantle upwellings below the Canaries, the Atlas Ranges and the Gibraltar Arc rise from a laterally-propagating layer of material below the MTZ, which in turn is fed by a common deep source below the Canaries. In the Gibraltar region, the deeply rooted upwelling interacts with the Gibraltar slab. Quasi-toroidal flow driven by slab rollback induces the hot mantle material to flow around the slab, creating the two low-velocity anomalies below the eastern Betics and eastern Rif. Our results suggest that the Central Atlantic plume is a likely source of hot mantle material for upper-mantle upwellings in the Ibero-western Maghreb region.

Tese de doutoramento, Ciências Geofísicas e da Geoinformação (Geofisíca), Universidade de Lisboa, Faculdade de Ciências, 2014 Submitted by Amelia Janeiro (ajaneiro@reitoria.ul.pt) on 2015-01-07T10:54:56Z No. of bitstreams: 1 tese_Carlos_Corela_2014.pdf: 244202861 bytes, checksum: 15aa69fd00906afc4c2a1747bf155175 (MD5) Made available in DSpace on 2015-01-26T18:05:44Z (GMT). No. of bitstreams: 1 tese_Carlos_Corela_2014.pdf: 244202861 bytes, checksum: 15aa69fd00906afc4c2a1747bf155175 (MD5) Previous issue date: 2014