Mass wasting processes along the Owen Ridge (Northwest Indian Ocean)

International audienceThe Owen Ridge is a prominent relief that runs parallel to the coast of Oman in the NW Indian Ocean and is closely linked to the Owen Fracture Zone, an 800-km- long active fault system that accommodates today the Arabia-India strike-slip motion. Several types of mass failures mobilizing the pelagic cover have been mapped in details along the ridge using multibeam bathymetry and sediment echosounder. Here we present a synthetic map of the different types of mass wasting features observed along the ridge and we further establish a morphometric analysis of submarine landslides. The spatial variation of failure morphology is strongly related to the topography of the basement. The highest volumes of multi-events generated slides are mobilized along the southern portion of the ridge. There, the estimated volume of evacuated material during a slide is up to 45 km3. Combining these new observations with re-interpreted ODP seismic lines (Leg 117) documents sporadic mass wasting events through time along the southern segment of the ridge since its uplift in the Early Miocene, with a typical recurrence rate of the order of 105-106 years. Although seismicity may still be the final triggering process, mass wasting frequency is mainly controlled by the slow pelagic sedimentation rates and hence, time needed to build up the 40-80 m thick pelagic cover required to return to a mechanically unstable pelagic cover

Application of Automated Throw Backstripping Method to Characterize Recent Faulting Activity Migration in the Al Hoceima Bay (Northeast Morocco): Geodynamic Implications

This study was supported by projects CGL2016-80687-R AEI/FEDER, P18-RT-3275, B-RNM-301-UGR18 and RNM148 (Junta de Andalucia/FEDER); ALBAMAR JCJC ANR-17-CE030004; the EUROFLEETS program (FP7/2007-2013; no 228344); project FICTS-2011-03-01; and the FPU PhD grant (16/04038), and also by the Spanish Government through the 'Severo Ochoa Centre of Excellence' accreditation (CEX2019-000928-S).The IHS KINGDOM software package was utilized in the present study. We also to the marine surveys, MARLBORO2 and SARAS (https://campagnes.flotteoceanographique.fr/ campagnes/12450090/; https://campagnes.flotteoceanographique. fr/campagnes/12000010/).Automation of the throw backstripping method has proven to be an effective tool for the determination of the evolution of tectonic activity in wide fault zones. This method has been applied to the Al Hoceima Bay (southwesternmost Mediterranean, Alboran Sea) for a time period covering the last 280 kyr on 672 faults imaged on 265 high-resolution seismic reflection profiles. This area was affected by major earthquakes and corresponds to a transtensional basin deformed by growth faults. The automated application of throw backstripping allowed for a faster deciphering of the migration of tectonic activity. Results show a westward migration of the deformation with quickly increasing deformation rates in the most recent time frames near Al Hoceima, one of the most populated cities. This migration is in agreement with the current seismicity, the GPS data, and recent brittle deformation data. Vertical throw rates of up to 0.47 mm/year have been calculated, for the most recent time periods, in segments of the Bokkoya fault zone. The westward migration of the deformation fits with the reconstruction suggested by the westernmost Mediterranean geodynamic models during the Pleistocene epoch, and it might be the consequence of the interaction between the northwest (NW) movement of the South Alboran indenter and the back Rif south-westward displacement. The highly accurate constraints of the evolution of the tectonic activity offered by this automation will substantially improve the seismic hazard assessment.Junta de Andalucia European Commission CGL2016-80687-R AEI/FEDER P18-RT-3275 B-RNM-301-UGR18 RNM148ALBAMAR JCJC ANR-17-CE030004EUROFLEETS program (FP7/2007-2013) 228344German Research Foundation (DFG) 16/04038Spanish Government through the 'Severo Ochoa Centre of Excellence' accreditation CEX2019-000928-SFICTS-2011-03-0

The ALBACORE oceanographic cruise: tectonic and sedimentary processes at distinct temporal and spatial scales in the Alboran Sea

European Geosciences Union (EGU) General Assembly, 23-27 May 2022, Vienna, AustriaThe Alboran Sea (Western Mediterranean) is a relatively small ocean basin connected with the Atlantic that provides a rich archive of tectonic and sedimentary processes at distinct temporal and spatial scales during the Quaternary. Since the collisional boundary of the Eurasia-Nubia plates crosses the Alboran Sea, this basin is also the locus of active geohazards: the constant seismic activity, concentrated mostly along the Al Idrissi strike-slip fault system and submarine landslides, that can cause tsunami hazards affecting the entire Alboran coasts and damages to submarine cables and infrastructures. Previous understanding of the Alboran Sea has been based on seafloor and subsurface geophysical data of differing resolution and scale, combined with very short sediment coring and IODP and industrial boreholes. In order to obtain new constrains on the geology of the Alboran Sea, the ALBACORE cruise was held in October and November 2021 onboard the R/V Pourquoi Pas? In addition to sites in the northern Alboran Sea targeting contourites, several sites in the southern Alboran Sea were selected as key study areas: the Al-Idrissi active fault zone, the Al-Hoceima shelf, the Xauen/Tofiño and the Francesc Pages banks. The scientific work of the ALBACORE campaign included the acquisition of Calypso cores (up to 28m long), sampling of consolidated strata with Cnexoville, in situ geotechnical measurements (Penfeld) with a seabed cone penetration test device (up to 50m long), heat flow measurements (up to 6m long), swath bathymetric imaging of the seafloor and water column, and sub-bottom profiling. The total length of sediments recovered reached 734m. Results from the ALBACORE cruise address the following scientific objectives: - To understand better the causal relationships between the present-day morpho-structural pattern and date Quaternary tectonic pulse and associated sedimentary systems - To determine the Late Pleistocene-Holocene stratigraphic pattern and the paleo-oceanographic implications of contourites. - To explore the chronological evolution of cold-water coral mounds and their paleoceanographic and palaeoclimatic signature since the Middle Pleistocene. - To investigate the causal factors of slope instability processes and evaluate the geological hazard associated with tectonic pulses and fluid seepage. - To determine the recent high-resolution sequence stratigraphy of the Al-Hoceima shelf in order to decode the late Pleistocene and Holocene sea-level changes at millennial scalePeer reviewe

Obtenir une représentation en continu de la lithologie et de la minéralogie. Exemples d'application du traitement statistique de données de diagraphie aux structures sédimentaires en régime de convergence de plaques (Leg ODP 134, 156 et 160)

Well-logging techniques provide a preferential way of investigating deep geological formations, not directly observable. They measure on a continuous basis and in situ numerous petrophysical parameters, as well as oxide contents in 7 major (Si, Ca, Fe, Al, S, K, Ti) and 3 (U, Th, Gd) trace chemical elements. A thorough knowledge of the physics underlying tool operation and the calibration steps is needed to estimate the uncertainty on the measurement. This uncertainty is mainly due to tool operating conditions (borehole diameter and irregularities,, operating speed). When good quality data are available, multivariate clustering techniques, such as k-means, are used as a first approach to visualize the variables provided by well-logging tools. One can also choose linear and non linear inversion methods to infer an accurate enough mineralogical log so it may be used in geological and petrophysical modeling. Wireline logging techniques are typically carried out during oceanic and continental scientific drilling programs, but are almost useless in such unstable geological environments as sedimentary structures associated with tectonic plates convergence zones. The improved state-of-the-art method of Logging-While-Drilling gives a best quality measurement before the borehole conditions worsen. Geological, petrophysical and textural interpretation of well-logging data gives valuable information on sedimentation type, as well as hints on possible mineralogical transformations. The in situ criterion pertaining to the well-logging measurement allows fluids dynamics modeling as well as variation and orientation of tectonic stress, often characterizing these geological environments.Les techniques de diagraphies sont un moyen privilégié pour étudier les formations géologiques profondes, inaccessibles à l'observation directe. Elles mesurent en continu et in situ de nombreux paramètres pétrophysiques, ainsi que les concentrations en 7 éléments majeurs (Si, Ca, Fe, Al, S, K, Ti) et 3 éléments traces (U, Th et Gd). Une connaissance préalable des différents modes de fonctionnement des outils et de leur calibration permet d'évaluer la précision de la mesure. Celle-ci est surtout fonction des conditions de mesure (diamètre et rugosité du puits, vitesse de mesure). Lorsque les données sont de bonne qualité, les méthodes de classification multivariée, comme la méthode des nuées dynamiques ou le k-means, sont employées comme premier outil de visualisation des grandeurs mesurées par diagraphie. En parallèle ou en complément, à l'aide de méthodes d'inversion linéaire ou non-linéaire, il est possible de calculer une minéralogie en continu avec une précision suffisante pour être utilisée dans des modèles pétrophysiques et géologiques. Les zones de convergence de plaques lithosphériques sont des environnements géologiques instables, dans lesquels les techniques de diagraphie par cable, classiquement utilisée dans les forages scientifiques océaniques ou continentaux, ne permettent pas d'obtenir des données de bonne qualité. La nouvelle méthode de Logging-While-Drilling, ne laisse pas à l'environnement de mesure le temps de se déteriorer et donne une mesure utilisable. L'interprétation géologique, minéralogique et faciologique des données de diagraphies apportent des indications précieuses sur la dynamique sédimentaire, ainsi que sur les éventuelles transformations minéralogiques. Le caractère in situ de la mesure rend possible la modélisation de la dynamique des fluides ou de la variation et de l'orientation des champs de contrainte, dont les environnements étudiés sont souvent le siège

Identification of log units in clay rock formations based on local and spatial statistics of well-log properties: application to the Opalinus claystone in the Benken borehole

International audienceDue to their particularly good mechanical and self-healing properties combined with exceptionally efficient cation adsorbents and exchanger capacities, clay minerals and clay rock formations are considered as suitable geological barrier for radioactive waste disposal. The Middle Jurassic Opalinus clay formation has been identified as a potential host rock”. Logging Data were measured at the Benken borehole drilled through this formation in Northern Switzerland. The paper presents a statistical methodology to improve the description of the physical properties of the clay rock based on the well-log data. The methodology involves the classification of a set of local statistics, calculated from a reduced number of principal components computed from well-log properties. The use of kernel-based method to calculate local statistics allows the analysis of spatial variability at different scales, and scale effects. The first-order layering is found to be robust and independent of kernel size, i.e. observation scale, while preserving small scale heterogeneities useful for further interpretation. The log-units can be more clearly interpreted in terms of stationary or transitional log-units, depending on the behaviour of local statistics. Finally, the derived spatial variability of the log-units property is compared with earlier lithological descriptions and stratigraphic data

Subsurface geophysics of the Phlegrean Fields: New insights from downhole measurements

International audienceThe volcanic complex of Phlegrean Fields, located northwest of Naples (Italy), has been the site of deep geothermal exploration in the 1980s. Several wells were drilled by an Agip-Enel joint venture, with downhole continuous physical properties acquired in each well. The main purpose of this study is to map and describe the spatial variations of the volcanic deposits, in terms of their nature, thickness and in situ physical properties. We apply fuzzy k means classification of the well-logging data available in the wells cored in the San Vito area. Fuzzy set theory provides an approach that quantitatively assigns individuals to physically continuous classes. The optimal number of classes is found by minimization of three mathematical functions, thus reducing subjectivity. The resulting classifications are found (1) to reflect the main lithologies in the San Vito plain, (2) to provide more detail on the geological stratigraphy, allowing a more precise volcanic history, and (3) to differentiate between transition zones and interbedded well-defined deposits. In addition to discriminating between lithologies that have different physical properties, this study gives information on the degree of homogeneity of each lithologic unit, and the range of variation for the measured properties. Finally, using the physical classification of the deposits, we are able to propose a detailed two-dimensional compressional acoustic velocity structure of the studied area

Evolution néogène supérieur de la marge marocaine du bassin d’Alboran : Etude intégrée Terre-Mer du bassin de Boudinar

Lafosse, Manfred ... et. al.-- 24e Réunion des Sciences de la Terre (RST Pau 2014), 27 au 31 Octobre 2014, Pau.- 1 pageLe bassinde Boudinar est undes principaux bassins néogènes de lamarge marocaine qui a enregistré l'évolution post-rift des marges du basin d'Alboran. La sédimentation dans cebassin a démarré au Miocène supérieur et s'est poursuivie jusqu'à l'actuel. L'objectif de ce travail est de décrire la dynamique sédimentaire de cette portion de la marge par une étude intégrée Terre-Mer à l'aide de l'interprétation de lignes sismique industrielle et académique et de nouvelles études de terrain. L'étude des séries à terre a mis en évidence que la sédimentation démarre au Tortonien inferieur-Serravalien? et s'est poursuivie sans hiatus majeur jusqu'au Messinien supérieur. La surface d'érosion messinienne a pu être cartée sur l'ensemble du bassin et révèle une morphologie relativement plane avec des incisions locales de faible profondeur. Elle est surmontée localement par des dépôts de marnes (d'âge Pliocène basal) à blocs de récifs messiniens. La sédimentation marine pliocène est dominée par des dépôts silto-sableux d'âge Pliocène inférieur et organisés en séquence faiblement progradante. Enfin cet ensemble est tronqué par une Surface d'érosion majeure au dessus de laquelle une sédimentation principalement continentale se met en place. En mer le socle acoustique est recouvert par environ 1500m de sédiments interprétés Miocène à plio-quaternaire. Deux surfaces d'érosions majeures limitent la base et le sommet d'une unité qui presente localement des facies sismiques chaotiques. La base de cette unité sismique correspond à la Surface d'érosion messinienne enregistrée sur l'ensemble du Bassin d'Alboran. La géométrie des dépôts Pliocène est une séquence montrant des clinoformes faiblement pentés en biseau de progradation/agradation sur la Surface d'érosion sous-jacente. Au sommet, des unites plio-quaternaires progradantes sont clairement organisées en clinoformes plus fortement pentés. La limite entre ces deux séquences est marquée par une Surface d'érosion Pliocène.Peer Reviewe

Characterisation of oceanic sediments and basalts from Hole 833B, New Hebrides Island Arc (Vanuatu) from downhole measurements.

International audienceDuring Ocean Drilling Program Leg 134, a mixed sequence of volcaniclastic and carbonate sediments was cored together with basaltic breccias and a single basalt sill in Hole 833B. In this study, data from Schlumberger's Geochemical Logging Tool, together with physical property logs, characterise part of the section and establish a complete log-derived lithostratigraphy. The major transition between the sedimentary rocks and a basaltic sill at 830 mbsf (metres below sea floor) is clearly seen as well as the distinction between the silicate-rich sediments and the carbonate-rich part of the section. The transition between the volcanic sandstone interbedded with basaltic and sed-lithic breccia of Unit III, and the volcanic sandstone of Unit IV is clearly marked by the physical property logs. The accuracy of the logging data was evaluated and discussed with an improved log versus core correlation. The cluster analysis of the complete data set shows a correlation with the data provided by the mechanical caliper device, which in turn indicates the quality of the borehole

Deep Learning Strategies for Seismic Demultiple

An important step in seismic data processing to improve inversion and interpretation is multiples attenuation. Radon-based algorithms are often used for discriminating primaries and multiples. Recently, deep learning (DL), based on convolutional neural networks (CNNs) has shown promising results in demultiple that could mitigate the challenges of Radon-based methods. In this work, we investigate new different strategies to train a CNN for multiples removal based on different loss functions. We propose combined primaries and multiples labels in the loss for training a CNN to predict primaries, multiples, or both simultaneously. We evaluate the performance of the CNNs trained with the different strategies on 400 clean and noisy synthetic data, considering 3 metrics. We found that training a CNN to predict the multiples and then subtracting them from the input image is the most effective strategy for demultiple. Furthermore, including the primaries labels as a constraint during the training of multiples prediction improves the results. Finally, we test the strategies on a field dataset. The CNNs trained with different strategies report competitive results on real data compared with Radon demultiple. As a result, effectively trained CNN models can potentially replace Radon-based demultiple in existing workflows