Éditeur(s) : Université des Antilles AREBio Groupe de recherche BIOSPHERES : BIOlogie, Sciences Physiques & Humaines pour les énergies Renouvelables, l
Extrait de : 1er colloque international BIOSPHERES, du 18 au 20 juin 2019. Université des Antilles
Description : Volcano tourism plays an important role in the economies of volcanic islands in the Lesser Antilles. On islands like St. Lucia and Dominica these volcanoes have been utilized as geoparks and the areas even being designated as World Heritage Sites. In many of these islands, farming communities also live on the slopes to these volcanoes and with the increased pursuit of geothermal energy the siting of geothermal operations are also located in close proximity. Volcanic activity, therefore, has a significant impact on these islands at a local and national level. Many volcanomonitoring institutions face the financial and human resources challenge of providing ongoing monitoring services to economically burdened small island states. This has often led to the exploration of alternative low-cost monitoring options and strategies to be adopted by monitoring agencies. One such strategy is the adoption of a volcanic risk reduction approach to research and monitoring activities, which integrates the social and physical sciences through the engagement of local communities as partners with scientists in disaster risk reduction. We present a recent approach adopted using this type of strategy in St. Lucia and lessons learnt from this approach with implications for volcano tourism on island. The potential use of this strategy in Dominica is also presented, given the economic challenges the island currently faces during its ongoing recovery efforts from Hurricane Maria in 2017.

Droits : CC-BY-NC-ND - Attribution - Pas d'utilisation commerciale - Pas de modification
Permalien : http://www.manioc.org/fichiers/V19086
V19086

Éditeur(s) : HAL CCSD Springer Verlag
Résumé : The activity of the Damavand volcano (Central Alborz, northern Iran) began 1.8 Ma ago and continued up to 7 ka BP. Although the volcanic suite is clearly of shoshonitic affinity, only two petrographic types can be distinguished in the studied lavas: (1) weakly differentiated absarokites (49 < %SiO2 < 51), scattered around the volcano but with a regional extension, (2) highly differentiated banakites (59 < %SiO2 < 63), which form the bulk of the 4,000 m thick volcanic pile. All lavas are alkalic (3.7 < %K2O < 5), REE and LILE-rich (e.g., 85 < La < 148 ppm; 9 < Th < 32 ppm) and show highly fractionated REE patterns (69 < La/Yb < 115) and pronounced Nb-Ta negative anomalies. The absarokites are characterised by Sr (0.7045-0.7046) and Nd (0.51266-0.51269) isotope compositions close to the Bulk Earth values, and distinct from those of the banakites (0.7047 < Sr-87/Sr-86 < 0.7049, 0.51258 < Nd-143/Nd-144 < 0.51262). The Pb isotope ratios are also slightly lower in the absarokites than in the banakites (18.71 < Pb-206/Pb-204 < 18.77, 15.62 < Pb-207/Pb-204 < 15.63, 38.85 < Pb-208/Pb-204 < 38.91, and 18.77 < Pb-206/Pb-204 < 18.84, 15.62 < Pb-207/Pb-204 < 15.64, 38.94 < Pb-208/Pb-204 < 39.06, respectively). Overall, there is a clear tendency towards higher Sr, Pb and lower Nd isotope ratios with increasing degree of differentiation. This study suggests that the absarokites result from a low degree of partial melting (similar to 5%) of a highly metasomatized mantle source, which inherited its characteristics from an old subduction setting. The initiation of volcanic activity 1.8 Ma ago results from variations in the lithospheric thermal regime, probably related to lithospheric delamination as proposed for Anatolia (Pearce et al. 1990). The banakites are mainly generated by extensive fractional crystallisation (similar to 70%) of the absarokitic magma, with a limited amount (a few percents) of assimilation of an old crustal component, in the form of bulk assimilation or AFC processes, which both can explain the Sr, Nd and Pb isotope data.
ISSN: 1437-3254

hal-00411553
https://hal.archives-ouvertes.fr/hal-00411553
DOI : 10.1007/s00531-006-0159-6

Éditeur(s) : HAL CCSD AGU and the Geochemical Society
Résumé : International audience
Rainbow is a dome-shaped massif at the 36°14′N nontransform offset along the Mid-Atlantic Ridge. It hosts three ultramafic-hosted hydrothermal sites: Rainbow is active and high temperature; Clamstone and Ghost City are fossil and low temperature. The MoMARDREAM cruises (2007, 2008) presented here provided extensive rock sampling throughout the massif that constrains the geological setting of hydrothermal activity. The lithology is heterogeneous with abundant serpentinites surrounding gabbros, troctolites, chromitites, plagiogranites, and basalts. We propose that a W dipping detachment fault, now inactive, uplifted the massif and exhumed these deep-seated rocks. Present-day deformation is accommodated by SSW-NNE faults and fissures, consistent with oblique teleseismic focal mechanisms and stress rotation across the discontinuity. Faults localize fluid flow and control the location of fossil and active hydrothermal fields that appear to be ephemeral and lacking in spatiotemporal progression. Markers of high-temperature hydrothermal activity (∼350°C) are restricted to some samples from the active field while a more diffuse, lower temperature hydrothermal activity (<220°C) is inferred at various locations through anomalously high As, Sb, and Pb contents, attributed to element incorporation in serpentines or microscale-sulfide precipitation. Petrographic and geochemical analyses show that the dominant basement alteration is pervasive peridotite serpentinization at ∼160–260°C, attributed to fluids chemically similar to those venting at Rainbow, and controlled by concomitant alteration of mafic-ultramafic units at depth. Rainbow provides a model for fluid circulation, possibly applicable to hydrothermalism at oceanic detachments elsewhere, where both low-temperature serpentinization and magmatic-driven high-temperature outflow develop contemporaneously, channeled by faults in the footwall and not along the detachment fault.
ISSN: 1525-2027

hal-01115281
https://hal.archives-ouvertes.fr/hal-01115281
https://hal.archives-ouvertes.fr/hal-01115281/document
https://hal.archives-ouvertes.fr/hal-01115281/file/Andreani_et_al-2014-Geochemistry%2C_Geophysics%2C_Geosystems.pdf
DOI : 10.1002/2014GC005269

Éditeur(s) : HAL CCSD Universidad Complutense de Madrid
Résumé : Based on new seismological and recent faulting data, we analyze five main sectors in the western part of the Betic Cordillera from an active tectonic perspective: i. The northwestern frontal sector of the cordillera, including the Morón de la Frontera area, with shallow (< 15 km depth) seismogenic active NE-SW reverse and strike-slip faults that do not reach the surface. ii. The Teba area, in the External Zones, which is deformed by sparse N-S to NW-SE normal faults with associated wedges of Quaternary sediments and active strike-slip faults at intermediate crustal levels. iii. The Ronda Basin, representing the major Late Miocene intramontane basin of the western Betic Cordillera, is mainly deformed by NNE-SSW and WNW-ESE folds and locally by NW-SE normal faults. iv. The internal part of the orogen, which is characterized by shallow (<40 km) and intermediate (40 to 120 km depth) seismicity beneath Málaga and the Alborán Sea, ENE-WSW folding, relief uplift, river incision and scarce active faults with surface expression. v. The Spanish Atlantic coast, which coincides with the western end of the Betic orogen, where Pliocene to Quaternary shallowmarine sedimentary rocks are deformed by meso-scale NW-SE oriented normal faults and few ENE-WSW reverse faults. These data support the recent tectonic activity of the western Betic Cordillera determined by the NW-SE Eurasian-African convergence with variable features from the mountain front, characterized by shallow deformations, up to the Internal Zones that mainly undergo uplift and intermediate seismicity.
ISSN: 1698-6180

hal-00750359
https://hal.archives-ouvertes.fr/hal-00750359
DOI : 10.5209/rev_JIGE.2012.v38.n1.39211

Éditeur(s) : HAL CCSD Springer
Résumé : International audience
We present here a synthesis of the evolution of rifted continental margin systems in the Gulf of Aden. These margins are volcanic to the west of the Gulf of Aden, where they are influenced by the Afar hotspot, and non-volcanic east of longitude 46° E. The combined use of magnetics, gravity, seismic reflection, field observations (tectonic, stratigraphic and sedimentological) and oil well data allowed us to obtain better constraints on the timing of continental rifting and seafloor spreading. From the Permo-Triassic to the Oligocene, the Arabian-African plate was subject to distributed extension, probably due, at least from the Cretaceous, to tensile stresses related to the subduction of the Tethysian slab in the north. In Late Eocene-Early Oligocene, 34-33 Ma ago, rifting started to localise along the future area of continental breakup. Initially guided by the inherited basins, continental rifting then occurred synchronously over the entire gulf before becoming localised on the northern and southern borders of the inherited grabens, in the direction of the Afar hotspot. In the areas with non-volcanic margins (in the east), the faults marking the end of rifting trend parallel to the inherited grabens. Only the transfer faults cross-cut the inherited grabens, and some of these faults later developed into transform faults. The most important of these transform faults follow a Precambrian trend. Volcanic margins were formed in the west of the Gulf, up to the Guban graben in the southeast and as far as the southern boundary of the Bahlaf graben in the northeast. Seaward dipping reflectors can be observed on many oil industry seismic profiles. The influence of the hotspot during rifting was concentrated on the western part of the gulf. Therefore, it seems that the western domain was uplifted and eroded at the onset of rifting, while the eastern domain was characterised by more continuous sedimentation. The phase of distributed deformation was followed by a phase of strain localisation during the final rifting stage, just before formation of the Ocean-Continent Transition (OCT), in the most distal graben (DIM graben). About 20 Ma ago, at the time of the continental break-up, the emplacement of the OCT started in the east with exhumation of the subcontinental mantle. Farther west, the system was heated up by the strong influence of the Afar hotspot, which led to breakup with much less extension. In the Gulf of Aden (s.str), up to the Shukra El Sheik fracture zone, oceanic spreading started 17.6 Ma ago. West of this fracture zone, oceanic accretion started 10 Ma ago, and 2 Ma ago in the Gulf of Tadjoura. Post-rift deformation of the eastern margins of the Gulf of Aden can be seen in the distal and proximal domains. Indeed, the substantial post-rift uplift of these margins could be associated with either the continental break-up, or activity of the Afar hotspot and related volcanic/magmatic activity. Uplift of the northern proximal margin was still active (e.g. stepped beach rocks exposed at 60 m of 2 Ma; 30 m of 35,200 years; 10 and 2 m) and active volcanoes can be inferred at depths of between 70 and 200 km beneath the margin (at 5-10 km distance from the coast). On the distal margin, heat flow measurements show a high value that is associated with post-rift volcanic activity and the development of a volcano (with flows and sills) shortly after the formation of the OCT. The Afar hotspot is therefore important for several reasons. It allows the localisation of deformation along the Red Sea/Aden system and the rapid opening of the Gulf after the continental break-up; its influence also seems to persist during the post-rift period.
ISSN: 1866-7411

hal-01053089
https://hal.archives-ouvertes.fr/hal-01053089
DOI : 10.1007/s12517-011-0475-4

Éditeur(s) : HAL CCSD Seismological Society of America
Résumé : International audience
Abstract The continuous record of large surface-rupturing earthquakes along the Dead Sea fault brings unprecedented insights for paleoseismic and archaeoseismic research. In most recent studies, paleoseismic trenching documents the late Holocene faulting activity, while tectonic geomorphology addresses the long-term behavior (>10 ka), with a tendency to smooth the effect of individual earthquake rupture events (Mw >7). Here, we combine historical, archaeological, and paleoseismic investigations to build a consolidated catalog of destructive surface-rupturing earthquakes for the last 14 ka along the left-lateral Jordan Valley fault segment. The 120- km-long fault segment limited to the north and the south by major pull-apart basins (the Hula and the Dead Sea, respectively) is mapped in detail and shows five subsegments with narrow stepovers (width < 3 km). We conducted quantitative geomorphology along the fault, measured more than 20 offset drainages, excavated four trenches at two sites, and investigated archaeological sites with seismic damage in the Jordan Valley. Our results in paleoseismic trenching with 28 radiocarbon datings and the archaeoseismology at Tell Saydiyeh, supplemented with a rich historical seismic record, document 12 surface-rupturing events along the fault segment with a mean interval of ∼1160 yr and an average 5 mm=yr slip rate for the last 25 ka. The most complete part of the catalog indicates recurrence intervals that vary from 280 yr to 1500 yr, with a median value of 790 yr, and suggests an episodic behavior for the Jordan Valley fault. Our study allows a better constraint of the seismic cycle and related short-term variations (late Holocene) versus long-term behavior (Holocene and late Pleistocene) of a major continental transform fault.
ISSN: 0037-1106

hal-00747401
https://hal.archives-ouvertes.fr/hal-00747401
DOI : 10.1785/0120100097

Résumé : The maritime economy includes the activities linked to the sea, namely: - Marine resource extraction: living resources and marine minerals, - Exploitation of marine space and of physical properties of marine waters (energy plants - using marine water as a heat sink, marine renewable energies, submarine cable laying, - maritime and coastal construction and public works, maritime transport, Navy), - Exploitation of seascapes (tourism, leisure, boating), - Resource processing (of living resources and oil & gas) - Manufacturing and service industries supplying the above exploitation activities: shipbuilding, ship repair and boat building and their suppliers, oil and gas services, financial services, - Public services: defence; State intervention at sea and public services to maritime activities and to seafarers; public and private activities contributing to the protection of marine and coastal environment; and public research. Since 1997, the French Marine Economic Data report, published by Ifremer, includes a set of key sectoral indicators used to value the economic significance of the French marine-related activities in terms of production and jobs, their role in the national economy, their weight in international competition and the importance of non-market public services. The analysis of the marine sectors is carried out mainly at national scale but regional indicators are also presented when they are available. The European dimension of the activities is also taken into account.

Droits : 2014 Ifremer
http://archimer.ifremer.fr/doc/00253/36455/34990.pdf
DOI:10.13155/36455
http://archimer.ifremer.fr/doc/00253/36455/

Éditeur(s) : HAL CCSD
Résumé : International audience
Mylonite bodies are exhumed extensions at depth of shallow structural level brittle faults. They are characterised by intense strain localisation involving large volumes of middle to lower continental crust. The analysis of shear zone geometry and microstructures is a useful tool to decipher deformation kinematics, though finite strain estimation is still relatively qualitative. Timing of the deformation has also been the focus of numerous studies using the complete spectrum of geochronometers. However, only rare examples provide geochronological data that can be unambiguously interpreted and cooling, recrystallisation and neocrystallisation are difficult to tell from each other. Thus, time-scales over which major mylonite zones develop and remain active under ductile conditions as well as their strain rate often remain poorly documented. We investigated two sections across the South-Armorican Shear Zone (SASZ), a crustal-scale pluri-km thick dextral shear zone active during a single tectonic event of late-Variscan age and associated with syntectonic granite emplacement.. Finite strain profiles on these cross-sections, quantified from average Quartz grain-size in 34 samples, show a strong deformation partitioning towards the center of the SASZ, with a decrease, for each section, from 150µm in slightly deformed zones to less than 7-5 µm in the core of the ultramylonite. Furthermore, toward the core of the SASZ, development of a penetrative shear band network progressively eliminates lenses of less deformed rocks and results in homogenisation of the Quartz grain sizes. In parallel, we performed in-situ UV-laser Ar/Ar dating on the fabric-forming white micas. White micas population can be decomposed into inherited muscovites carried by the folation and newly-formed, syn-tectonic substituted phengites located along the shear bands yielding 2 age groups for each sample. Along the profiles, the difference between these two ages evolves from 10-15 Ma in weakly deformed domains to zero toward the SASZ core. In addition, mylonite-forming phengites yielded the same age irrespectively of their position on the section or of the rock strain.. On the regional point of view, this study brings deformation-ages for the late-orogenic evolution of the South Armorican domain. Strain accumulated along the SASZ in a time-span extending to 300-298 Ma, i.e. contemporaneously with the activity of nearby major extensional shear zones. These results support a new model of crustal-scale shear zone activity, where the whole body of the shear zone is active throughout its history (defined as the largest age difference through the section), i.e. the actively deforming zone does not get progressively narrower. The strain distribution nevertheless evolves with time, with an increasingly large fraction partitioned in the ultramylonitic core.
EGU General Assembly
Vienne, Austria

insu-00839320
https://hal-insu.archives-ouvertes.fr/insu-00839320
BIBCODE : 2010EGUGA..12.9881A

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
The Gulf of Cadiz spans the plate boundary between Africa and Eurasia west of the Betic–Rif mountain belt. A narrow east dipping subduction zone descends beneath the Gulf of Cadiz and the straits of Gibraltar. The deep crustal structure of the Gulf and the adjacent SW Iberian and Moroccan margins is constrained by numerous multi-channel seismic reflection and wide-angle seismic surveys. A compilation of these existing studies is presented in the form of depth to basement, sediment thickness, depth to Moho and crustal thickness maps. These structural maps image an E–W trending trough, with thin (< 10 km) crust beneath the Gulf of Cadiz. This trough is filled by an eastward thickening wedge of sediments, reaching a thickness of 10–15 km in the eastern Gulf. These sediments are tectonically deformed, primarily along a series of westward-vergent thrust faults and represent a 200–250 km wide accretionary wedge. The northern and especially the southern limits of the accretionary wedge are marked by sharp morphological lineaments showing evidence of recent deformation. These tectonic limits are situated in an internal position with respect to the Miocene deformation front (external Betic and Rif allocthons), which has been abandoned. At the western boundary of the accretionary wedge, near the adjacent Seine and Horseshoe abyssal plains, an E–W trending basement high (Coral Patch Ridge) can be seen indenting the deformation front in an asymmetric manner. Analog modeling is performed using granular materials accreted against a semicircular backstop (representing the basement of the Rif and Betic mountain belts). The modeling initially produces a symmetric, arcuate accretionary wedge. The ensuing collision of an oblique rigid indenter retards accretion on one side, resulting in an embayment and a locally steeper deformation front. The deformation pattern observed in morphology and high-resolution seismic profiles suggests the accretionary wedge and underlying subduction system is still active. The implications of active subduction for the source region of the 1755 Lisbon earthquake and the regional seismic hazard assessment are discussed.
ISSN: 0040-1951

hal-00424922
http://hal.univ-brest.fr/hal-00424922
http://hal.univ-brest.fr/hal-00424922/document
http://hal.univ-brest.fr/hal-00424922/file/Gutscher_09Tphys_rev.pdf
DOI : 10.1016/j.tecto.2008.11.031

Éditeur(s) : HAL CCSD
Résumé : In 1996 the European Commission Humanitarian Office (ECHO) launched a regional approach for disaster preparedness, focusing in its first phase on Central America, Caribbean and Southeast Asia (including Bangladesh). The first step in this process was the preparation of a «diagnostic study» that involved a situation review of the countries in these regions with regard to their vulnerabilities, disaster preparedness capacities and national plans or policies for disaster management.The Centre for Research on the Epidemiology of Disasters of the Université Catholique de Louvain (UCL) served as ECHO’s principal technical support with the collaboration of other institutions in Europe and the regions.The present «diagnostic report», covering Central America and the Caribbean, has been carried out by the Centre International pour la Formation et les Echanges en Géosciences (CIFEG) under the supervision of Professor Robert D’Ercole (Université de Savoie, Chambéry).Mr. Thierry Lesales (Université des Antilles et de la Guyane) participated closely in the drafting of this report and was actively involved in the field missions with Mr D’Ercole where they met and interviewed numerous national officials, non-governmental organisations and regional and international bodies. Further assistance was provided by Claudine Misson (CRED) for the interviews and information collected in the Dominican Republic. The report also draws from an earlier mission undertaken by Dr. Philippe Masure (BRGM, France), Christian Bugnion (CRED) and Alexandra Angulo (CRED) who undertook some of the preparatory work for the diagnostic study.This report presents an analysis of the disaster preparedness situation in Central America and the Caribbean and provides some preliminary recommendations regarding priorities and future programme direction. As such it remains primarily a descriptive study. It is expected to form the basis for the formulation of the ECHO Disaster Preparedness Action Plan.
En 1996, la Oficina Humanitaria de la Comunidad Europea (ECHO) lanzó la iniciativa de un enfoque regional en materia de preparación a los desastres, concentrándose inicialmente en las regiones de América Central, Caribe y Asia del Sureste (incluyendo a Bangladesh). La primera fase de este proceso fue la preparación de un « diagnóstico» que implicaba un examen de la situación de los países de cada una de estas regiones en relación a la vulnerabilidad, la capacidad de preparación a los desastres y las políticas y planes nacionales en materia de gestión de desastres.El Centre for Research on the Epidemiology of Disasters (CRED), de la Université Catholique de Louvain (UCL), ha sido el principal apoyo técnico de ECHO para esta iniciativa, con la colaboración y asistencia de otras instituciones en Europa y en las regiones arriba mencionadasEl presente informe que cubre América Central y el Caribe, fue realizado por el International Centre for Training and Exchanges in Geosciences (CIFEG), bajo la dirección del Profesor Robert D'Ercole (Université de Savoie).Thierry Lesales (Université des Antilles et de la Guyane) participó de cerca a la realización de este documento y estuvo activamente implicado junto al Profesor D'Ercole en las misiones que se realizaron en varios países. En el curso de estas misiones, se entrevistaron con numerosos representantes de gobiernos nacionales, de ONGs y de organizaciones regionales e internacionales Se contó igualmente con la asistencia de Claudine Misson (CRED), quien realizó la misión en República Dominicana. El informe se basa igualmente en una misión anterior llevada a cabo por Philippe Masure (BRGM, France), Alexandra Angulo (CRED) y Christian Bugnion (CRED), la cual realizó parte del trabajo preparatorio para el diagnóstico.El informe presenta un análisis de la situación en América Central y el Caribe y provee recomendaciones preliminares para las prioridades y dirección del futuro programa. En el marco de la segunda fase, está destinado a servir de base para la formulación del Plan de Acción de Preparación a los Desastres de ECHO.
Depuis 1994, ECHO (Office Humanitaire de la Commission Européenne, devenu le service de la Commission européenne à l’aide humanitaire et à la protection civile) a financé, à l'échelle mondiale, de nombreuses opérations pour la prévention et la préparation aux catastrophes (catastrophes naturelles principalement) Ces financements ont répondu aux demandes d'ONG et d'organisations internationales qui ont-elles-mêmes mis en oeuvre les projets correspondants. Les évaluations de ces opérations ont donné des appréciations positives. Cependant, ECHO souhaite s'impliquer davantage dans la prévention et la préparation aux catastrophes et mieux cibler ses actions pour une plus grande cohérence d'ensemble.Au cours de la réunion du 16 juillet 1996, le Comité d'Aide Humanitaire a approuvé la nouvelle approche régionale proposée par ECHO pour son programme de prévention, d'atténuation et de préparation aux catastrophes, le DIPECHO (Dlsaster Preparedness ECHO), pour la période 1996—1998. Ce programme doit s'appliquer dans un cadre régional en concentrant d'abord ses financements sur des plans d'action dans les Caraïbes, en Amérique Centrale, en Asie du Sud-Est et au Bangladesh. Par ailleurs, au lieu de répondre exclusivement aux demandes de financements spécifiques d'ONG, d'organisations internationales et de gouvernements, ECHO souhaite préparer des plans d'action et déterminer les partenaires les plus appropriés pour une mise en oeuvre dirigée par ECHO même. En outre, le DIPECHO a pour objet de rendre plus efficace l'action de l'ensemble de l'Union Européenne, par une étroite coordination de son action avec celles de la Commission et des Etats Membres. Il est enfin prévu de faire précéder la préparation des plans d'action par une phase de diagnostic au cours de laquelle seront identifiés, pour chaque région, les risques, les structures et politiques de prévention existantes aux niveaux communautaire, national et régional, ainsi que les appuis extérieurs en cours et à venir. L'objectif est non seulement de déterminer les lacunes, mais également d'évaluer la cohérence et l'efficacité des systèmes de réponse dans leur ensemble......Dans ce contexte, une première mission exploratoire a été réalisée du 30 septembre au 12 octobre 1996 dans les Caraïbes et l'Amérique Centrale (quatre pays visités) et a débouché sur un premier rapport (A. Angulo, Ch. Bugnion, Ph. Masure, "Rapport de mission exploratoire dans les Caraïbes ct en Amérique Centrale pour DIPECHO").Ce rapport apporte de nombreuses informations et en particulier:(1) il définit le cadre conceptuel, insistant, à juste titre, sur le fait que la prévention et la préparation doivent être distinguées de l'aide d'urgence et qu'elles font partie d'un processus continu au même titre que le développement ;(2) il présente les principales organisations régionales et internationales, et leurs activités dans le domaine de la prévention et de la préparation;(3) il met en évidence les grands types de besoins et fournit les premières orientations pour le programme DIPECHO......Le présent rapport, constituant le diagnostic proprement dit, fait suite à une deuxième série de missions effectuées dans la même région. Il vise à compléter les apports de la mission exploratoire, notamment par:(a) une analyse des catastrophes et de leurs conséquences:(b) une évaluation comparée des risques dans la région;(c) une analyse détaillée des réalisations et des besoins en matière de réduction des risques et des conséquences des catastrophes naturelles ;(d) un examen des conditions actuelles pour un programme DIPECHO cohérent, réalisable et efficace, avec, en particulier, la prise en compte de l’organisation actuelle de la prévention et de la préparation dans la région et un état des appuis extérieurs ;- des propositions de lignes d'actions prioritaires pour le DIPECHO......Le diagnostic s'est appuyé sur une importante documentation : travaux scientifiques, études et rapports recueillis auprès du CRED-Université Catholique de Louvain, du CIFEG, du DHA, de l’IDNDR, de divers organismes sur le terrain (notamment le centre de documentation de San José au Costa Rica), et d'universités européennes (Université de Savoie. Chambéry, Université de Lausanne). Mais ce sont avant tout les nombreux entretiens menés lors des missions (près de 200) qui ont donné corps au diagnostic.Treize pays Ont été visités entre le 22/01 et le 07/03/1997 :- République Dominicaine (C Misson);- Costa Rica, Guatemala, Nicaragua et Cuba (R. D'Ercole) ;- Antigua, Barbade, Haïti, Jamaïque, Ste-Lucie, St-Maarten, St-Vincent et le Guyana (Th. Lesales).Leur choix a été déterminé en concertation avec ECHO, le CRED-UCL et le CIFEG. Ils ne recouvrent pas l'ensemble des pays qu'il aurait été théoriquement possible de visiter. Cependant, le choix de pays-clés, les contacts établis avec de nombreux organismes de portée régionale et la documentation consultée, ont permis de bâtir un diagnostic d'ensemble......L'étude comporte trois parties.La 1e partie constitue une analyse des catastrophes en termes de bilan et de risque. Il s'agit, à l'aide de cartes, notamment, de montrer les effets des catastrophes naturelles en Amérique Centrale et dans les Caraïbes, de présenter la répartition et la fréquence des aléas naturels et de procéder à une analyse de critères de vulnérabilité. L'objectif est, enfin, de déterminer des niveaux de risque, à l'échelle de la région, compte tenu des dangers naturels et des critères de vulnérabilité.La 2° partie est l'étude des actions entreprises dans la région, ces dernières années, afin de réduire les risques et les conséquences des catastrophes. Cette étude permet de dégager des lacunes et des besoins. Les différentes composantes entrant dans le processus de réduction des catastrophes sont retenues : recherche scientifique et technique, prévention stricto sensu, préparation, information / formation. L'accent est également placé sur les modes actuels d'application des politiques de réduction des risques : de l'approche sectorielle à l'approche intégrée.La 3e partie traite des conditions actuelles pour la mise en oeuvre d'un programme DIPECHO cohérent et efficace. Quatre aspects fondamentaux sont analysés: les particularités régionales et nationales (l'hétérogénéité et ses conséquences); les faiblesses et qualités institutionnelles aux différents échelons géographiques: les caractéristiques des organismes susceptibles de contribuer à la mise en oeuvre du DIPECHO; le rôle actuel et en perspective de la Communauté Européenne et des Etats Membres.Chaque partie comporte une conclusion partielle La conclusion générale reprend les idées force des conclusions intermédiaires ct débouche sur des lignes d'actions prioritaires recommandées pour le DIPECHO......L'étude confiée au CIFEG par le CRED-UCL et ECHO a été coordonnée par Robert D'Ercole (Département de Géographie, Université de Savoie, Chambéry, France). Elle a bénéficié de la collaboration de Thierry Lesales (Département de Géographie, Université des Antilles et de la Guyane, Martinique, France) et de Patrick Pigeon (Département de Géographie, Université de Savoie, Chambéry, France). Ont également contribué à la réalisation de celle étude: Claudine Misson (CRED-UCL, Belgique), Jean-Claude Napias (CIFEG, directeur), Jacques Giri (CIFEG, président), Sylvie Orlyk (CIFEG, secrétariat).
https://hal.archives-ouvertes.fr/hal-01196496

hal-01196496
https://hal.archives-ouvertes.fr/hal-01196496
https://hal.archives-ouvertes.fr/hal-01196496/document
https://hal.archives-ouvertes.fr/hal-01196496/file/D%27Ercole%20et%20al%201997%20Diagnostic%20DIPECHO%20Caraibes%20compressed.pdf

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
This study analyzes the active tectonics within the northwestern and southeastern extensions of the Pambak-Sevan-Syunik fault (PSSF), a major right-lateral strike-slip fault cutting through Armenia. Quantifying the deformations in terms of geometry, kinematics, slip rates and earthquake activity, using cosmogenic 3He, OSL/IRSL and radiocarbon dating techniques, reveal different behaviors between the two regions. Within the northwestern extension, in the region of Amasia, the PSSF bends to the west and splits into two main WNW–ESE trending reverse faults defining a compressional pop-up structure. We estimate an uplift rate and a shortening rate of 0.5 ± 0.1 mm/y and 1.4 ± 0.6 mm/y, respectively. This suggests that most of the ∼2 mm/y right lateral movement of the PSSF seems to be absorbed within the Amasia pop-structure. Within the southeastern extension, the PSSF shows signs of dying out within the Tsghuk Volcano region at the southernmost tip of the Syunik graben. There, the tectonic activity is characterized by a very slow NS trending normal faulting associated with a slight right-lateral movement. Slip rates analyses (i.e. vertical slip rate, EW stretching rate at 90° to the fault, and right-lateral slip rate of ∼0.2 mm/y, ∼0.1 mm/y and ∼0.05 mm/y, respectively) lead to the conclusion that the right lateral movement observed further north along the PSSF is mainly transferred within other active faults further west within the Karabagh (Hagari fault or other structures further northwestwards). Comparing our slip rates with those estimated from GPS data suggests that most of the deformation is localized and seismic, at least within the Tsghuk region. The geometrical and kinematic pattern observed within the two terminations of the PSSF suggests that the fault and its surrounding crustal blocks are presently rotating anticlockwise, as also observed within the GPS velocity field. This is consistent with the recent kinematic models proposed for the Caucasus-Kura-South Caspian region and brings a new insight into the present geodynamics of Armenia.
ISSN: 1040-6182

hal-01307342
https://hal.archives-ouvertes.fr/hal-01307342
DOI : 10.1016/j.quaint.2015.05.021

Éditeur(s) : HAL CCSD
Résumé : The territory of Armenia was located in the collision zone between Arabia and Eurasia, and is the seat of active intercontinental deformations, which was attested by the many historical earthquakes that have occurred in this region. All these destructive earthquakes show a strong regional seismic activity, and therefore it is important to evaluate the seismic hazard associated with active structures that generates this seismicity.This study presents the results of the analysis of the active tectonics within the northwestern and southeastern extensions of the Pambak-Sevan-Syunik fault (PSSF), a major right-lateral strike-slip fault cutting through Armenia (NW - SE). Quantifying the deformations in terms of geometry, kinematics, slip rates and earthquake activity, using cosmogenic 3He, OSL/IRSL and radiocarbon dating techniques, reveal different behaviors between the two regions.Within the northwestern extension, in the region of Amassia, the PSSF bends to the west and splits into two main WNW-ESE trending reverse faults defining a compressional pop-up structure. We estimate an uplift rate and a shortening rate of 0.5 ± 0.1 mm/y and 1.4 ± 0.6 mm/y, respectively. This suggests that most of the ~2 mm/y right lateral movement of the PSSF seems to be absorbed within the Amasia pop-structure.Within the southeastern extension, in the region of Tsghuk volcano, the PSSF shows signs of dying out at the southernmost tip of the Syunik graben. A very slow NS trending normal faulting associated with a slight right-lateral movement characterizes the tectonic activity in the region of Tsghuk volcano. We estimate vertical slip rates, EW stretching rate, and right-lateral slip rate of ~0.2 mm/y, ~0.1 mm/y and ~0.05 mm/y, respectively. These results lead to the conclusion that the right lateral movement observed further north along the PSSF is mainly transferred within other active faults further west within the Karabagh (Hagari fault or other structures further northwestwards).
L’Arménie se situe dans la zone de collision entre Arabie et Eurasie et est le siège d’une déformation intracontinental active comme l’atteste les nombreux tremblements de terre historiques qui s’y sont produits. Tous ces séismes, destructeurs, attestent d’une forte activité sismique régionale, et il est par conséquent important d'évaluer l’aléa sismique associé aux structures actives qui génère cette sismicité.Le travail présenté ici, expose les résultats de l’analyse de la tectonique active au niveau des terminaisons nord-ouest et sud-est de la faille de Pambak-Sevan-Syunik (PSSF), une des failles décrochant majeure qui traverse l'Arménie du NW au SE. La quantification des déformations en termes de géométrie, cinématique, vitesse de glissement et paléosismicité, en utilisant les méthodes de datation 3He cosmogénique, OSL/IRSL et radiocarbone, révèlent des comportements différents entre les deux régions.Au niveau de la terminaison nord-ouest, dans la région d’Amassia, la faille PSSF s’incurve vers l'ouest et se subdivise en deux branches de direction WNW-ESE, et de cinématique inverse, définissant une structure en pop-up. Nous estimons une vitesse de soulèvement de 0.5 ± 0.1 mm/an et une vitesse de raccourcissement NNE-SSW de 1.4 ± 0.6 mm/an. Ces résultats suggère que l’essentiel des ~2 mm/an de mouvement dextre estimés le long de la faille de PSSF sont absorbés au niveau du pop-up d’Amassia.Au niveau de la terminaison sud-est, dans la région du volcan Tsghuk, la faille PSSF semble disparaitre. Le peu d’activité tectonique est caractérisée par des failles normales sub-méridiennes associées à une légère composante décrochant dextre. Nous déterminons une vitesse de glissement vertical de ~0,2 mm/an, une vitesse d’extension ~EW de ~0,1 mm/an associée à une composante dextre de ~0,05 mm/an. Ces résultats suggèrent que le mouvement dextre observé le long de la faille de PSSF plus au nord, a été transféré sur d'autres failles plus à l'ouest dans le Karabakh (faille Hagari ou autres structures situés encore plus au NW).
https://tel.archives-ouvertes.fr/tel-01621440

NNT : 2016MONTT152
tel-01621440
https://tel.archives-ouvertes.fr/tel-01621440
https://tel.archives-ouvertes.fr/tel-01621440v2/document
https://tel.archives-ouvertes.fr/tel-01621440/file/2016_MKRTCHYAN_archivage.pdf

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
Big storm events represent a major risk for populations and infrastructures settled on coastal lowlands. In the Western Mediterranean, where human societies colonized and occupied the coastal areas since the Ancient times, the variability of storm activity for the past three millennia was investigated with a multi-proxy sedimentological and geochemical study from a lagoonal sequence. Mappings of the geochemistry and magnetic susceptibility of detrital sources in the watershed of the lagoon and from the coastal barriers were undertaken in order to track the terrestrial or coastal/marine origin of sediments deposited into the lagoon. The multi-proxy analysis shows that coarser material, low magnetic susceptibility, and high strontium content characterize the sedimentological signature of the paleostorm levels identified in the lagoonal sequence. A comparison with North Atlantic and Western Mediterranean paleoclimate proxies shows that the phases of high storm activity occurred during cold periods, suggesting a climatically-controlled mechanism for the occurrence of these storm periods. Besides, an in-phase storm activity pattern is found between the Western Mediterranean and Northern Europe. Spectral analyses performed on the Sr content revealed a new 270-year solar-driven pattern of storm cyclicity. For the last 3000 years, this 270-year cycle defines a succession of ten major storm periods (SP) with a mean duration of 96 ± 54 yr. Periods of higher storm activity are recorded from >680 to 560 cal yr BC (SP10, end of the Iron Age Cold Period), from 140 to 820 cal yr AD (SP7 to SP5) with a climax of storminess between 400 and 800 cal yr AD (Dark Ages Cold Period), and from 1230 to >1800 cal yr AD (SP3 to SP1, Little Ice Age). Periods of low storm activity occurred from 560 cal yr BC to 140 cal yr AD (SP9 and SP8, Roman Warm Period) and from 820 to 1230 cal yr AD (SP4, Medieval Warm Period).
ISSN: 0277-3791

hal-01277796
https://hal.archives-ouvertes.fr/hal-01277796
DOI : 10.1016/j.quascirev.2015.10.009

Éditeur(s) : HAL CCSD
Résumé : This thesis aims to analyze the active tectonics and the seismic hazard for three main cities of NW Iran (Tehran, Tabriz and Zandjan) using morphotectonics and paleoseismology. Within the Tehran capital, we focused our analysis on the Mosha-North Tehran (M-NT) active fault system. Our investigations show that this fault system is mainly dominated by left-lateral faulting. Along the eastern part of the M-NT fault system, we found evidences of at least seven strong (M>7) paleoearthquakes during the past 10 ka (recurrence interval : 1100-1400 yrs). Our study along the central portion of the fault system (in Abali region) suggests that it corresponds probably to the source of the 1830 AD historical earthquake (M=7.1, Io= IX). Within Tabriz region, we studied the SE segment of the North Tabriz fault. We found evidences of at least three strong events, which occurred during the past 33.5 ka. The North Tabriz dextral fault corresponds to the central portion of a fault system (TFS), and contains two fault segments (NW and SE). Our paleoseismological analysis shows a variation of the slip rate, which decreases from NW to SE along the strike-slip fault. The western (Mishu) and eastern (Bozghush) terminations of the fault system correspond to oblique-compression zones. TFS belongs to the eastern portion of a regional fault system (GSKT), linking the active extension within the central part of the collision and the active compression to the East. Finally, we focus on the Zandjan area, where no important historical seismicitiy is recorded. There, based on morphotectonics analysis we discovered a large active fault network, whose southeastern part affects the Zandjan city. To conclude this work, we replace our observations within the general geodynamic framework of the Arabia- Eurasia collision. One of the striking pictures is the occurrence of opposite kinematics along the M-NT (and other range parallel faults within the south Central Alborz) and the North Tabriz fault systems that have the same trend. This shows the rapid variation of the regional stress field in the Northern Iran.
L'objectif de ce mémoire de thèse est l'étude de la tectonique récente et l'évaluation de l'aléa sismique pour trois villes importante, Téhéran, Tabriz et Zandjan, situées dans le nord-ouest de l'Iran. Dans la capitale de l'Iran, Téhéran, nous nous sommes concentrés sur le système de faille active de Mosha-Nord Téhéran. Nos travaux démontrent que ce système est essentiellement décrochant sénestre. Nos analyses paléosismologiques sur la portion est de ce système (dans la vallée de Tar) montrent au minimum les évidences de sept grands événements sismiques (M>7) pendant les derniers 10000 ans (l'intervalle de récurrence est de 1100 à 1400 ans). Les études que nous avons mené dans la partie centrale de ce système (région d'Abali) révèlent qu'il pourrait être la source du dernier événement sismique ayant affecté la ville de Téhéran en 1830 AD. Dans la région de Tabriz, nous nous sommes intéressés au segment SE de la faille décrochante dextre de Nord Tabriz où nous avons trouvé les évidences de trois grands séismes pendant les derniers 33500 ans. Nos études montrent que la faille Nord Tabriz qui est la portion centrale d'un système de faille (TFS) est constituée par deux segments NW et SE dextres. Notre étude paléosismologique suggère une variation de la vitesse qui diminue du NW vers SE le long de ces segments. Les extrémités ouest (Mishu) et est (Bozghush) de ce système correspondent à des zones compressives qui absorbent les déplacements horizontaux sur les segments NW et SE. D'un point de vue général la TFS est une partie d'un système de failles régionales (GSKT) qui relie une zone d'extension active dans la partie centrale de la collision Arabie-Eurasie et une zone de compression active à l'Est. Enfin, à Zandjan qui est une ville située dans une région de lacune sismique, nous avons découvert un important réseau de failles actives. Le tracé sud-est de ce réseau de failles passe par la ville de Zandjan. En conclusion, les localisations et les cinématiques des systèmes de faille étudiés sont discutées dans le cadre géodynamique général de la collision Arabie-Eurasie. On remarquera que la faille majeure de Nord Tabriz qui correspond essentiellement à un décrochement dextre a la même direction NW-SE que les décrochements sénestres présents dans la chaîne de l'Alborz (les failles de : Mosha, Talaghan et Manjil). Cette observation nécessite une variation de la direction de compression entre ces deux régions.
https://tel.archives-ouvertes.fr/tel-00539739

tel-00539739
https://tel.archives-ouvertes.fr/tel-00539739
https://tel.archives-ouvertes.fr/tel-00539739/document
https://tel.archives-ouvertes.fr/tel-00539739/file/thesesoleymani.pdf

Éditeur(s) : HAL CCSD
Résumé : The aim of this thesis is to analyze the variations in slip rates along strike-slip faults, in intracontinental domain, producing large earthquakes (M > 7.5). To illustrate these variations, this work has focused in two area located in the most tectonically active continental domains in the world: in the western part of Mongolia (Bogd and Bulnay faults) and in the northern part of Iran (Astaneh and Tabriz faults). Using morphotectonic and paleoseismological analyses, the kinematics, the slip rates and the recurrence times have been estimated and allow us to describe the characteristics of seismic cycle along these faults. In Mongolia, the slip rates are estimated at ~ 1,2 and ~ 2,6 mm/yr along the Bogd and the Bulnay faults, respectively, with no variations of geological slip rates over the late Pleistocene-Holocene period. These two faults present characteristic slips and similar recurrence times between large earthquakes. The paleoseismological investigations suggest that a cluster occurred 3000 years ago, similar to the seismic cluster recorded in Mongolia during the XX century. In Iran, the slip rate was estimated to 2 mm/yr along the Astaneh fault and the recurrence times are ranging from 1600 to 2200 years, associated with offsets comprised between 3 and 4,5 m. We have also estimated a slip rate of ~ 7 mm/yr along the Tabriz fault, in agreement with the present day rate estimated by GPS, suggesting no variations in the slip rate over the past 45 ka.
Ce travail de thèse a pour but d'analyser les variations de vitesses sur des grandes failles décrochantes en contexte intracontinental, capables de produire des séismes de très fortes magnitudes (M > 7.5). Afin d'illustrer ces variations d'activités, cette analyse a été effectuée sur deux zones d'études situées en domaine continental et sismiquement actives: la région ouest de la Mongolie (failles de Bogd et Bolnay) et le nord de l'Iran (failles d'Astaneh et de Tabriz). À partir d'une approche morphotectonique et paléosismologique, les cinématiques, les vitesses de failles et les intervalles de récurrence entre les séismes majeurs ont été estimés, permettant d'analyser les caractéristiques du cycle sismique sur chacune des failles. En Mongolie, les failles de Bogd et Bolnay présentent respectivement des vitesses de ~ 1,2 et 2,6 mm/an, qui semblent être constantes sur la période Pleistocène supérieur-Holocène. Ces deux failles présentent également des glissements caractéristiques et des intervalles de temps similaires entre les séismes majeurs. Les analyses paléosismologiques suggèrent qu'un essaim sismique comparable à celui enregistré au XXème siècle a eu lieu il y a environ 3000 ans. En Iran, une vitesse géologique de 2 mm/an a été estimée sur la faille d'Astaneh et les données paléosismologiques suggèrent des intervalles de récurrence de 1800 ans, associés à des déplacements en surface compris entre 3 et 4,5 m. Nous avons également estimé une vitesse de 7 mm/an sur la faille de Tabriz, en accord avec les données GPS, suggérant que la vitesse sur cette faille est constante depuis 45 ka.
https://tel.archives-ouvertes.fr/tel-00591794

tel-00591794
https://tel.archives-ouvertes.fr/tel-00591794
https://tel.archives-ouvertes.fr/tel-00591794/document
https://tel.archives-ouvertes.fr/tel-00591794/file/these_rizza.pdf

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
We present a new set of brittle microtectonic measurements carried out in the Pliocene and Quaternary rocks outcropping in several key sectors of the western Betic and Rif orogen, the so-called Gibraltar orogenic arc. This data set, along with available earthquake focal mechanisms and borehole breakouts, allowed us to compile the Pliocene and Quaternary stress map of this area. This map provides new constraints for tectonic models and the present-day tectonic activity of the proposed active eastward subduction of oceanic lithosphere beneath the Gibraltar Arc and roll-back. The horizontal maximum compressive stress (S-Hmax) is NW-SE in the Betic Orogen and N-S/NNW-SSE in the southern Rif Cordillera. There is a significant consistency between S-Hmax and the displacement field deduced from GPS measurements with respect to the African plate: both appear to reflect the NW-SE convergence between the African and the European plates that is perturbed in the Rif. We propose that part of the eastern Rif behaves as a quasi-rigid block welded to the stable African plate. This block is bounded by important faults that localized most of the deformation disturbing the stress and surface displacement field. Pliocene to Quaternary N-S to NW-SE Africa-Europe plate convergence seem to be associated to the reorganization of the remnant Early Miocene subduction system in a continental-continental collision framework. Three-dimensional reconstruction of available seismic tomography plotted against the intermediate seismicity shows that only part of the old subduction system, whose orientation ranges from N20 degrees E to N100 degrees E, remains active: the portion ranging from N30 degrees E to N40 degrees E, orthogonal to the regional convergence. (C) 2011 Elsevier Ltd. All rights reserved.
ISSN: 0264-3707

hal-00671033
https://hal.archives-ouvertes.fr/hal-00671033
DOI : 10.1016/j.jog.2010.12.003

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
Absolute earthquake hypocenter locations have been determined in the area offshore eastern Taiwan, at the Southernmost Ryukyu subduction zone. Location process is run within a 3D velocity model by combining the Taiwanese and neighboring Japanese networks and using the 3D MAXI technique. The study focuses on the most active seismic cluster in the Taiwan region that occurs in the forearc domain offshore eastern Taiwan. Earthquakes distribute mainly along 2 active planes. The first one aligns along the subduction interface and the second one, shallower affects the overriding margin. Focal mechanisms within the shallow group indicate that nodal planes are either compatible with high-angle back-thrusts or low-angle thrusts. The active seismic deformation exclusively indicates reverse faulting revealing that the forearc basement undergoes trench-perpendicular strong compression. By integrating the seismological image into the regional context, we favor the hypothesis in which the dense seismicity occurring offshore marks the activity of en-échelon high-angle reverse faults accommodating the uplift of a broken piece of Ryukyu Arc basement, called Hoping Basement Rise. The uplift is inferred to be caused by the subduction of an oceanic relief, either exotic block, seamount or oceanic crust sliver. Our favored solution satisfies the narrowness of epicenter's cluster along the Hoping Canyon, and the observation of high-angle active faults on seismic lines crossing the area. Furthermore, this solution is compatible with the active uplift of the Hoping Rise demonstrated from morphological and sedimentological data. We do not exclude the branching of the high-angle reverse faults system onto a splay fault connected with the subduction interface but further investigations are needed to map precisely the 3D distribution of active faults that break the margin.
ISSN: 0040-1951

hal-00407726
https://hal.archives-ouvertes.fr/hal-00407726
DOI : 10.1016/j.tecto.2007.11.018

Éditeur(s) : HAL CCSD European Geosciences Union (EGU)
Résumé : International audience
Pollen and clay mineralogical analyses of a Holocene sequence from Sebkha Boujmel (southern Tunisia) traces the climatic and environmental dynamics in the lower arid bioclimatic zone over the last 8000 years. During the Mid- to Late Holocene transition, between 8 and 3 ka, a succession of five wet/dry oscillations is recorded. An intense arid event occurs between 5.7 and 4.6 ka. This episode marks the onset of a long-term aridification trend with a progressive retreat of Mediterranean woody xerophytic vegetation and of grass steppes. It ends with the establishment of pre-desert ecosystems around 3 ka. The millennial-scale climate change recorded in the data from Sebkha Boujmel is consistent with records from the south and east Mediterranean, as well as with climatic records from the desert region for the end of the African Humid Period (AHP). Eight centennial climatic events are recorded at Sebkha Boujmel and these are contemporary with those recorded in the Mediterranean and in the Sahara. They indicate a clear coupling between the southern Mediterranean and the Sahara before 3 ka. The event at 4.2 ka is not evidenced and the link between events recorded in Sebkha Boujmel and the North Atlantic Cooling events is clearer from 3 ka onwards. These variations indicate the importance of climatic determinism in the structuring of landscapes, with the establishment of the arid climatic conditions of the Late Holocene. It is only from 3 ka onwards that the dynamic of plant associations is modified by both human activity and climatic variability. The climatic episodes identified during the historic period indicate strong regionalisation related to the differential impact of the North Atlantic Oscillation (NAO) and the Mediterranean Oscillation (MO) on the Mediterranean basin. The local human impact on regional ecosystems is recorded in the form of episodes of intensification of pastoral and/or agricultural activities. The development of olive production and of several taxa associated with agriculture attest to increasing sedentism among human populations during Classical Antiquity. The significant increase in Artemisia (wormwood) between 1.1 and 0.8 ka (850–1150 AD) is linked to intensive pastoral activity, associated with heightened interannual and/or seasonal climatic instability. A complete re-shaping of the landscape is recorded during the 20th century. The remarkable expansion of the olive tree, and the deterioration of regional ecosystems with the spread of desert species, is linked to recent local socio-economic changes in Tunisia.
ISSN: 1814-9324

hal-01319967
https://hal.archives-ouvertes.fr/hal-01319967
https://hal.archives-ouvertes.fr/hal-01319967/document
https://hal.archives-ouvertes.fr/hal-01319967/file/cp-12-1339-2016.pdf
DOI : 10.5194/cp-12-1339-2016

Éditeur(s) : HAL CCSD Oxford University Press (OUP): Policy P - Oxford Open Option A Oxford University Press (OUP)
Résumé : International audience
The Pyrenean mountain range is a slowly deforming belt with continuous and moderate seismic activity. To quantify its deformation field, we present the velocity field estimated from a GPS survey of the Pyrenees spanning 18 yr. The PotSis and ResPyr networks, including a total of 85 GPS sites, were installed and first measured in 1992 and 1995–1997, respectively, and remeasured in 2008 and 2010. We obtain a deformation field with velocities less than 1 mm yr−1 across the range. The estimated velocities for individual stations do not differ significantly from zero with 95 per cent confidence. Even so, we estimate a maximum extensional horizontal strain rate of 2.0 ± 1.7 nanostrain per year in a N–S direction in the western part of the range. We do not interpret the vertical displacements due to their large uncertainties. In order to compare the horizontal strain rates with the seismic activity, we analyse a set of 194 focal mechanisms using three methods: (i) the ‘r’ factor relating their P and T axes, (ii) the stress tensors obtained by fault slip inversion and (iii) the strain-rate tensors. Stress and strain-rate tensors are estimated for: (i) the whole data set, (ii) the eastern and western parts of the range separately, and (iii) eight zones, which are defined based on the seismicity and the tectonic patterns of the Pyrenees. Each of these analyses reveals a lateral variation of the deformation style from compression and extension in the east to extension and strike-slip in the west of the range. Although the horizontal components of the strain-rate tensors estimated from the seismic data are slightly smaller in magnitude than those computed from the GPS velocity field, they are consistent within the 2σ uncertainties. Furthermore, the orientations of their principal axes agree with the mapped active faults.
ISSN: 0956-540X

hal-01171752
https://hal.archives-ouvertes.fr/hal-01171752
DOI : 10.1093/gji/ggv052

Éditeur(s) : HAL CCSD Elsevier
Résumé : We use a triangular representation of the plunges of P, B, and Taxes to compare the different ways tectonic regime is inferred from earthquake focal mechanisms in recent works. We argue that P, B, and Taxes provide a reasonable estimate of principal stress directions when faulting is close to Andersonian conditions, and that this can be estimated from the location on a triangular diagram. We analyze the geometrical relationship between the plunges of P, B, and Taxes on one hand, and the rake of slip and dip of nodal planes on the other hand. We show that the rake and dip level curves correspond to trajectories of the vertical direction along great and small circles with respect to the frame of the P, B. and Taxes. This shows that dip-slip faulting is compatible with vertical P or Taxes, but does not require it, and instead requires horizontal B axes. It also shows that strike-slip faulting does not require vertical B axes, but P and Taxes with equal plunges. This also reveals that focal mechanisms where P, B, and Taxes all have moderate plunge correspond to two very different types of nodal planes: a steeply dipping one with oblique slip and a moderately dipping one with strike-slip. Seismically active and moderately dipping strike-slip faults are to be found among these events.
ISSN: 0040-1951

hal-00486367
https://hal.archives-ouvertes.fr/hal-00486367
DOI : 10.1016/j.tecto.2009.03.006