Les Saintes Research Articles

Forearc crustal faults as tsunami sources in the upper plate of the Lesser Antilles subduction zone: the case study of the Morne Piton fault system

Abstract. In this study, alternatively to the megathrust, we identify upper-plate normal faults orthogonal to the trench as a possible tsunami source along the Lesser Antilles subduction zone. The Morne Piton fault system is such a trench-perpendicular upper crustal fault at the latitude of Guadeloupe. By means of seismic reflection, high-resolution bathymetry, remotely operated vehicle (ROV) imaging and dating, we reassess the slip rate of the Morne Piton fault since 7 Ma, i.e., its inception, and quantify an average rate of 0.25 mm yr−1 since ca. 1.2 Ma. This result divides by two previous estimations, increases the earthquake time recurrence and lowers the associated hazard. The ROV dive revealed a metric scarp with striae at the toe of the Morne Piton fault system, suggesting a recent fault rupture. We estimate a fault rupture area of ∼ 450–675 km2 and then a magnitude range for a maximum seismic event around Mw 6.5 ± 0.5, making this fault potentially tsunamigenic as the nearby Les Saintes fault responsible for a tsunami following the 2004 Mw 6.3 earthquake. Consequently, we simulate a multi-segment tsunami model representative of a worst-case scenario if all the identified Morne Piton fault segments ruptured together. Our model provides clues for the potential impact of local tsunamis on the surrounding coastal area as well as for local bathymetric controls on tsunami propagation. We illustrate that (i) shallow-water plateaus act as secondary sources and are responsible for a wrapping of the tsunami waves around the island of Marie-Galante; (ii) canyons indenting the shallow-water plateau slope break focus and enhance the wave height in front of the most touristic and populated town of the island; and (iii) the resonance phenomenon is observed within the Les Saintes archipelago, showing that the waves' frequency content is able to perturb the sea level for many hours after the seismic rupture.

K-Ar Geochronology and geochemistry of underwater lava samples from the Subsaintes cruise offshore Les Saintes (Guadeloupe): Insights for the Lesser Antilles arc magmatism

Dating of submarine volcanic systems is key to understand the history of tectonic and volcanic interactions within the Lesser Antilles volcanic arc. In this study, we investigate the radioisotopic dating of submarine volcanic systems located between Les Saintes (Guadeloupe) and Dominica islands in an intra-arc graben bounded to the west by the active Roseau fault. Submarine lava flows and domes have been sampled with the remotely operated vehicle (ROV) Victor6000 controlled onboard the Ifremer's N/O L'Atalante during the 2017 Subsaintes cruise. We sampled distinct volcanic edifices or sets of edifices in the area, in the previously identified Agoucha and Roseau volcanic complexes, and the Coche and Crawen seamounts, in addition to the basement exposed along the Roseau fault scarp. Pre-degassing of these samples before K-Ar dating has been mandatory to strongly limit their atmospheric argon contamination. Based on twelve new K-Ar ages, we find that the earliest volcanism in the area corresponds to the Agoucha volcanic complex with coeval ages of 4.23 ± 0.06 and 4.17 ± 0.06 Ma. These are also the oldest ages obtained for the recent Lesser Antilles arc to the north of Martinique Island. A lava flow sampled along the Roseau fault scarp yielded an age of 4.12 ± 0.06 Ma, further attesting that early phase of submarine volcanism occurred in the area about 1 Ma earlier than the emergence of Les Saintes Islands, which has been dated onland at ~3 Ma. The Roseau volcanic complex was constructed during a relatively long duration of at least 600 kyr, between 3.13 ± 0.05 and 2.52 ± 0.04 Ma, while a much shorter duration is observed for the smaller Coche and Crawen volcanoes, with ages at about 2.2 and 2.0 Ma, respectively. Together with ages of subaerial lavas from Terre-de-Haut in Les Saintes archipelago, these ages suggest that an intense volcanic activity occurred between 3 and 2 Ma in this part of the recent Lesser Antilles arc. The much younger age of 0.274 ± 0.009 Ma obtained here to the north of Colibri volcano, might be related with the northward magmatism of Dominica Island which displays similar timing and geochemistry. Overall, trace elements data show that Crawen, Coche, Agoucha, and, to a lesser extent, Roseau lavas have strong similarities with Basse-Terre, while pyroclastic units, Colibri and some Roseau lavas, are similar to those from Dominica and Les Saintes islands. Finally, this study shows that dating the submarine volcanic activity, which remains mostly unknown and undated, is a key component to understand the formation of volcanic arcs such as the Lesser Antilles arc.

First characterization of the cooling of the paleo-geothermal system of Terre-de-Haut (Les Saintes archipelago, Guadeloupe): Application of fluid inclusion and chlorite thermometry

Due to its geodynamic location in the Lesser Antilles arc, Basse-Terre of Guadeloupe displays an active volcanism which is favourable to the development of high-enthalpy geothermal energy. An exhumed analogue of the Bouillante geothermal reservoir has been recently characterized in Terre-de-Haut island (Les Saintes archipelago), giving an opportunity to study the cooling of a natural geothermal system and the related alterations.By coupling chlorite geothermometry and primary fluid inclusions in associated zoned quartz crystals located in N70 trending fractures, new insights on the Terre-de-Haut paleo-geothermal evolution can be inferred by distinguishing three new different episodes during functioning and cooling of this system: (i) a temperature of at least 240–270 °C in fluid inclusions trapped in the quartz core, (ii) chlorite formation at about 120 °C, and (iii) temperatures of ~50 °C - or less - in fluid inclusions of the quartz outer growth zones. Fluid inclusions also reveal that the hydrothermal fluid is of low salinity (2 wt% NaCl), probably of meteoric and sea water origin. Additionally, a second type of fluid inclusions observed in a banded quartz vein indicates at least an episode of a CO2-(H2O) fluid, with traces of H2S. Hence, some similarities can be highlighted between Terre-de-Haut and the Bouillante active geothermal systems in term of the highest temperatures of circulation events and gas composition, despite a difference in fluid origin. This study shows that some alteration episodes also occur at low temperature during the cooling of the geothermal system. Moreover, the N70 trending fractures, that have been identified as drains for the hot temperature fluids, have to be considered for future geothermal exploration.

Simulation of the 2004 tsunami of Les Saintes in Guadeloupe (Lesser Antilles) using new source constraints

The arc of the Lesser Antilles is associated with a significant tectonic activity due to the subduction of the Atlantic oceanic plate under the Caribbean plate. Earthquakes in this context have the potential to trigger landslides and tsunamis due to the important vertical seafloor displacement. The historical tsunamigenic earthquakes in this region are rare, but the damages they may have generated before along the coasts show that they pose a considerable threat to the closest inhabited islands. The most recent tsunamigenic earthquake occurred in 2004 in the area of Les Saintes, along a normal fault system located in the back-arc of the subduction. This $$M_{w}=6.3$$ earthquake generated small waves with 2 m of run-up in several bays of Les Saintes, a group of islands in the South of Guadeloupe. A recent survey conducted in the source area using deep-sea vehicles revealed for the first time an important coseismic slip on the Roseau fault plane, attributed to the 2004 event, which had not been predicted in the seismic inversion models. This event and the dataset on the Roseau fault gives the opportunity to model precisely the earthquake, to compare the simulation results with the observations and to evaluate the impact of the rupture heterogeneity and rupture shallowness on the height of the tsunami waves. Extending our earlier work (Cordrie et al. in OCEANS 2019—Marseille, Jun 2019, Marseille, France, pp 1–9, 2019. https://doi.org/10.1109/OCEANSE.2019.8867447 ) and in order to avoid a loss of quality from the dataset in the modeling of the initial sea-surface deformation especially in shallow depth and near field context, a transfer function of the deformation from the seafloor to the sea surface and different numerical schemes were used. Results on the tsunami height distribution indicate some local tsunami amplification phenomena linked to the bathymetry or the coastline geometry and highlight the most endangered areas of the islands. The simulations give additional constraints on the source, show the impact of the slip heterogeneities on the tsunami and finally provide a complementary estimation of the 2004 coseismic slip intensity.

Cartography of Free-Living Amoebae in Soil in Guadeloupe (French West Indies) Using DNA Metabarcoding.

Free-living amoebae (FLA) are ubiquitous protists. Pathogenic FLA such as N. fowleri can be found in hot springs in Guadeloupe, soil being the origin of this contamination. Herein, we analyzed the diversity and distribution of FLA in soil using a targeted metataxonomic analysis. Soil samples (n = 107) were collected from 40 sites. DNA was extracted directly from soil samples or from FLA cultivated at different temperatures (30, 37 and 44 °C). Metabarcoding studies were then conducted through FLA 18SrDNA amplicons sequencing; amplicon sequence variants (ASV) were extracted from each sample and taxonomy assigned against SILVA database using QIIME2 and SHAMAN pipelines. Vermamoeba were detected in DNA extracted directly from the soil, but to detect other FLA an amoebal enrichment step was necessary. V. vermiformis was by far the most represented species of FLA, being detected throughout the islands. Although Naegleria were mainly found in Basse-Terre region, N. fowleri was also detected in Grand Terre and Les Saintes Islands. Acanthamoeba were mainly found in areas where temperature is approx. 30 °C. Vannella and Vahlkampfia were randomly found in Guadeloupe islands. FLA detected in Guadeloupe include both pathogenic genera and genera that can putatively harbor microbial pathogens, therefore posing a potential threat to human health.

Interactions symboliques en milieu insulaire : les roches gravées précolombiennes de Guadeloupe et leur relation au paysage

Située au coeur de la Caraïbe, l’île volcanique de Guadeloupe, ou Basse-Terre, recèle le plus important ensemble d’art rupestre précolombien des Petites Antilles. Ces manifestations graphiques sont généralement attribuées aux communautés céramistes horticoles très mobiles ayant vécu dans les Antilles au Néoindien entre env. 300 av. et 1200 apr. J.-C. Suite aux récentes recherches de terrain menées sur ces sites ornés de plein-air, de nombreuses données nouvelles ont été acquises. Leur analyse spatiale est proposée ici sur des bases quantitatives afin d’aborder les modalités socioculturelles d’ornementation et de fréquentation des sites ornés et, plus largement, le rapport à l’espace insulaire des sociétés précolombiennes ainsi que leurs interactions physiques et symboliques au sein de ce dernier. Les résultats obtenus font ressortir l’existence de plusieurs contextes topographiques distincts du point de vue de l’altitude et de la distance aux ressources en eau douce (source et/ ou rivière). Ils montrent par ailleurs que les sites côtiers occupent préférentiellement les zones du littoral les plus favorables au niveau pluviométrique, mais aussi les plus proches des îles avoisinantes. Une corrélation directe entre la position topographique des sites ornés, le degré d’élaboration et les dimensions des figures qu’ils comprennent est également relevée. Cette corrélation se traduit par une plus forte proportion de grandes figures élaborées aux embouchures et/ ou près de sources côtières comparativement aux sites de plateau et de rivière. Mis en perspective avec les réflexions actuelles sur la dimension archipélique des territoires précolombiens, ceci suggère une utilisation des sites ornés du littoral par une pluralité de groupes différents dans le cadre de leur approvisionnement en eau lors de trajets interinsulaires ou lors de rassemblements périodiques. Par contraste avec l’art rupestre de l’intérieur des terres, la forte proportion de grandes figures élaborées présentes sur les côtes est alors à envisager comme l’expression performative d’un rapport à des espaces partagés et aux autres groupes humains susceptibles de les fréquenter également.

Quaternary coral reef complexes as powerful markers of long-term subsidence related to deep processes at subduction zones: Insights from Les Saintes (Guadeloupe, French West Indies)

AbstractGeodetic measurements reveal modern rates of tectonic deformation along subduction zones, but the kinematics of long-term deformation are typically poorly constrained. We explore the use of submarine coral reefs as a record of long-term coastal vertical motion in order to determine deformation rate and discuss its origins. The Lesser Antilles arc results from the subduction of the American plates beneath the Caribbean plate and undergoes regional vertical deformation. Uplifted reefs along forearc islands are markers of the interplay between tectonics and sea-level variations since the late Pleistocene. We compared results from a numerical model of reef-island profile development to high-resolution marine geophysical measurements of Les Saintes reef plateau (Guadeloupe, French West Indies), a ∼20-km-wide, 250-m-thick submerged platform that lies at 45 m below sea level along the volcanic arc, to constrain its vertical deformation history. Models explore different scenarios over wide parameter domains including start time, basement morphology, sea level variations, reef growth rate, subaerial erosion rate, and vertical motion history. The major features of the plateau (its depth, internal structure, unusual double-barrier) is only reproduced in a context of subsidence, with a constant rate of −0.3 to −0.45 mm/yr since the late Pleistocene, or in a context of increasing subsidence, presently of ∼–0.2 mm/yr. Discussed in the framework of the forearc vertical deformation history, this result indicates subsidence is promoted by local faulting, volcanic, and deep subduction processes. Coseismic deformation accumulation could be a mechanism by which deformation builds up in the long-term. We show that subduction can drive long-term subsidence of a volcanic arc, and demonstrate that submarine reefs are powerful markers of long-term vertical motion.

The characterisation of an exhumed high-temperature paleo-geothermal system on Terre-de-Haut Island (the Les Saintes archipelago, Guadeloupe) in terms of clay minerals and petrophysics

The volcanic island of Terre-de-Haut (in the Les Saintes archipelago, Lesser Antilles arc) is described in the literature as an exhumed paleo-geothermal system. Outcropping conditions provide a good, nearly horizontal 2D view of the system. This present study focuses on clay minerals, as they are known to be good markers of hydrothermal alterations worldwide, and on flow pathways. At Terre-de-Haut, the distribution of the clay minerals has a ‘concentric’ zonation with smectite, illite and chlorite comprising the outer part to the inner part of the altered zone, respectively. In the active Bouillante geothermal system, located on Basse-Terre island, 35 km NNW of Terre-de-Haut, drillings have revealed a vertical succession of the same clay minerals: from bottom to top, chlorite above 240 °C, illite above 180 °C and smectite at lower temperatures. Both sites have the same clay minerals and can, therefore, be compared. Within those geothermal systems, pathways for the fluids are encountered at all scales, from the micrometre-scale (µm-scale; through microcracks within phenocrysts and at grain joints) to the metre- and kilometre-scale (m- and km-scale) due to fractures and faults. Petrophysical measurements indicate that fresh rock samples are porous and permeable, allowing hydrothermal alteration on a km-scale. The combination of 1D vertical data at Bouillante and this new 2D horizontal distribution of clay minerals and fractures on Terre-de-Haut allows for a 3D schematic representation of the geothermal systems of the Guadeloupe archipelago and suggests that they are of hectometre-size (hm-size).

Skinks occur on Terre-de-Bas, Les Saintes (Guadeloupe, French West Indies)

Skinks occur on Terre-de-Bas, Les Saintes (Guadeloupe, French West Indies)

Interactions between active faulting, volcanism, and sedimentary processes at an island arc: Insights from Les Saintes channel, Lesser Antilles arc

AbstractNew high‐resolution marine geophysical data allow to characterize a large normal fault system in the Lesser Antilles arc, and to investigate the interactions between active faulting, volcanism, sedimentary, and mass‐wasting processes. Les Saintes fault system is composed of several normal faults that form a 30 km wide half‐graben accommodating NE‐SW extension. It is bounded by the Roseau fault, responsible for the destructive Mw 6.3 21 November 2004 earthquake. The Roseau fault has been identified from the island of Basse‐Terre to Dominica. It is thus 40 km long, and it could generate Mw 7 earthquakes in the future. Several submarine volcanoes are also recognized. We show that the fault system initiated after the main volcanic construction and subsequently controls the emission of volcanic products. The system propagates southward through damage zones. At the tip of the damage zones, several volcanic cones were recently emplaced probably due to fissures opening in an area of stress increase. A two‐way interaction is observed between active faulting and sedimentary processes. The faults control the development of the main turbiditic system made of kilometer‐wide canyons, as well as the location of sediment ponding. In turn, erosion and sedimentation prevent scarp growth at the seafloor. Faulting also enhances mass‐wasting processes. Since its initiation, the fault system has consequently modified the morphologic evolution of the arc through perturbation of the sedimentary processes and localization of the more recent volcanic activity.

Celebrating the Battle of the Saintes: Imperial News in England and Ireland, 1782

Celebrating the Battle of the Saintes:Imperial News in England and Ireland, 1782* Jennifer McLaren (bio) The same wind that wafted on one of its wings the defeat of the French fleet in the West Indies, attended with a slaughter and carnage hitherto unknown, conveys the happy tidings of ireland’s emancipation on the other, balanced in the calm air of steadiness and unanimity. English valour has triumphed over French pride, and Irish perseverance has broken England’s stubbornness. Freeman’s Journal, 21 May 1782 As news of Admiral George Rodney’s stunning victory over the French fleet at Les Saintes in the Caribbean in April 1782 broke in Ireland, so too did word of Westminster’s repeal of the Dependency of Ireland on Great Britain Act (6. Geo. I, c. 5, also known as the Declaratory Act of 1719). The ebullient pronouncement in the Freeman’s Journal illustrates the apparent contradiction between the applause by patriotic, antigovernment newspapers for Rodney’s imperial victory, and the celebration of Dublin’s independence from Westminster. As Stephen Conway has noted, this enthusiasm for British success seems “odd,” particularly as the Irish Protestant minority had been pulling away from Britain over the course of the American war.1 Yet this paradox, placed against its contemporary networks that passed information from the margins of empire to the metropole and to Ireland, provides an opportunity to examine how imperial news interacted with local politics and shaped imperial sensibilities. Relying [End Page 34] on a comparison of the newspaper coverage of the Saintes and the ensuing celebrations in a selection of London, Dublin, and Belfast newspapers, this essay thus takes the battle—a largely forgotten event in the American war—as a transnational case study in the history of imperial news. The victory at the Saintes has received little scholarly attention. Military historians have analyzed the innovative tactics that Rodney and his captains employed during the battle, but few historians have paused to consider the wider significance of the events of April 1782.2 Until Conway’s essay on the Saintes in a British context and Andrew Jackson O’Shaughnessy’s reexamination of events preceding Yorktown, American and British historiography had largely overlooked the battle. Conway reviewed the celebrations that followed Rodney’s victory in his investigation of the ways in which the American conflict stimulated and redefined a popular sense of Britishness. He argued that the “enthusiastic celebrations of the Saintes … are explicable only when one recognises that Britishness itself was both reconfigured and given a great boost during the American war.”3 O’Shaughnessy examined Rodney and the Saintes in his scholarship on the American Revolution in the context of the British Atlantic. His work has focused on the strategic and practical impact of Rodney’s victory and on other British activities in the Caribbean as they related to developments in the fledgling United States.4 Most recently, Brad Jones included the Saintes in his doctoral thesis on popular loyalism in the British Atlantic during the American revolutionary period. Jones examined how the war and revolutionary ideology affected the ways in which Britons living throughout the Atlantic world understood and articulated their loyalty to Great Britain. According to his assessment, the victory at the Saintes was “constructed as the defining [End Page 35] moment in the American war for Britain’s Atlantic world inhabitants,” who celebrated the victory as exuberantly as those in Britain.5 The Saintes has thus been considered—if minimally—from diverse historiographical perspectives spanning military history, the identity politics of Britain during the American war, and the context of the revolutionary Atlantic. This case study adopts a different approach that is transnational in nature—placing the Saintes and the ensuing celebrations within the framework of new imperial history and “British world” scholarship—two methodologies that have recently begun to converge.6 As Zoë Laidlaw has noted, recent works influenced by new imperial history “range far beyond dissections of metropolitan society and culture, focusing on interactions between widely separated colonial sites, juxtaposing micro and macro, and questioning the relationship between the remarkable and the everyday.”7 In relation to Ireland Niall Whelehan has recently argued that “transnational approaches overlap with...

Tectonic evolution of Les Saintes archipelago (Guadeloupe, French West Indies): relation with the Lesser Antilles arc system

Abstract In this paper, we provide the first structural map of Les Saintes archipelago (Guadeloupe, Lesser Antilles). The finite strain pattern displays four families of fault systems characterized by their statistical structural orientations: N000-N020, N050-N070, N090-N110 and N130-N140 trending fault systems. Our onshore results thus underline a fault network much more complex than the one depicted by the previous offshore geophysical investigations around Les Saintes archipelago, which show only N120-N150 trending system. According to the available K-Ar dating of the volcanic rocks and the relative chronology of the faults defined in the field, we determine the deformation history in Les Saintes islands since the last 3 Ma. The four highlighted trending fault systems are already active since the Pliocene and are consistent with the present-day extensional tectonics in the Guadeloupe archipelago compatible with the reactivation of inherited structures at the active arc scale. We interpret the tectonic evolution of Les Saintes islands as the result of interplay between subduction of aseismic ridges (Tiburon and Barracuda ridges) and oblique convergence. Furthermore, we recognized an exhumed geothermal paleo-system in Terre-de-Haut island which is a good analogue of the present-day active Bouillante geothermal system. Its duration is estimated at 400 k.y. during the Pliocene.

First report of a skink population in Les Saintes (Guadeloupe, FWI)

First report of a skink population in Les Saintes (Guadeloupe, FWI)

Initial sub-aerial volcanic activity along the central Lesser Antilles inner arc: New K–Ar ages from Les Saintes volcanoes

We present new groundmass K–Ar ages obtained using the Cassignol–Gillot technique, together with whole-rock major and trace elements, from Les Saintes islands (Terre-de-Haut and Terre-de-Bas). They are located along the northern Lesser Antilles inner arc, between Basse-Terre Island (western Guadeloupe) to the North and Dominica Island to the South. Ages reveal that the main volcanic phase in Terre-de-Haut occurred between 2.98±0.04 and 2.00±0.03Ma, and show that the onset of sub-aerial volcanism in Terre-de-Haut is slightly older (~0.2Myr) than that of northern Basse-Terre. Volcanism in Les Saintes resumed to the west, with the rapid construction of Terre-de-Bas Island at 0.888±0.009Ma. Major elements analyses show that most lavas from Les Saintes belong to a sub-alkaline medium-K magmatic series and are mainly andesites, with relatively rare basaltic andesites and dacites. Rare earth elements spectra reveal a strong enrichment in light elements, as observed for Dominica lavas, and significantly higher than observed for Basse-Terre lavas. Noticeably, Terre-de-Bas spectra display more enriched patterns relative to those from Terre-de-Haut lavas, suggesting a lower degree of partial melting or a stronger sedimentary component incorporated to the subducting slab. Overall, geochemical signatures of Les Saintes and Dominica magmas display common characteristics, which we interpret as reflecting strong petrogenetic affinities, while both are significantly different from that of Basse-Terre lavas. Finally, this study provides a precise timing of subaerial volcanism of Les Saintes Islands, which can be used to better constrain through time the development of the tectonic half-graben where these islands lie, which is part of the arc-parallel en-echelon faults system accommodating the oblique convergence of the North American plate from Montserrat to Dominica. In addition, these results reveal that the initiation of Terre-de-Haut volcanism is presently the oldest dated volcanism from the northern part of the Lesser Antilles active arc.

The Holocene drowned reef of Les Saintes plateau as witness of a long-term tectonic subsidence along the Lesser Antilles volcanic arc in Guadeloupe

Resulting from the interplay between tectonics and eustatism, reef terraces are powerful markers of vertical movements at a scale of 1000 to 100,000 years. In the Lesser Antilles, they grow around every island of the archipelago and record both local and subduction-related tectonics. The recent acquisition and interpretation of very high-resolution bathymetry of Les Saintes submarine plateau, French West Indies, together with seismic reflection profiles, are a unique opportunity to study one of these submarine structures, at metric to kilometric scales, addressing the questions of its nature, age and growth environment, but also of the control of active tectonics on its formation. The 20 km wide Les Saintes reef plateau lies at about 45 mbsl. It is crosscut by NW–SE striking, north-dipping normal faults that belong to Les Saintes fault system and graben, which produced a Mw 6.3 earthquake in 2004. The plateau is composed of four 20 m thick reef units, piled up in “layer cake” morphology down to 110 mbsl. The upper unit has a fresh morphology and presents typical reef features, like barrier and lagoon, spurs and grooves, pinnacles, etc. From its morphology we propose that it grew during the Holocene last transgression. Below, the three other units likely formed during Pleistocene sea level highstands and were eroded during the low stands, as evidenced in seismic reflection profiles. This scenario would imply that Les Saintes plateau formed in a context of subsidence with a rate we evaluate to be of the order of tenths of mm/yr. Probably linked to local tectonics, we believe that this deformation is also related to plate-scale subduction processes, similarly to deformations occurring on the other islands of the Guadeloupe archipelago.

High-frequency directivity effects: evidence from analysis of the Les Saintes records

The main-shock (Mw, 6.3) and the aftershocks of the ‘Les Saintes’ earthquake sequence (French Indies) were analyzed to quantify high-frequency directivity effects. A correction method was applied to isolate source spectra within a large frequency range (0.5 to 25 Hz). Most of the aftershocks source spectra are fully consistent with a Brune spectrum point-source shape and do not show any azimuthal dependence. The main-shock (Mw, 6.3) and the two largest aftershocks (Mw, 5.8, 5.3) show, however, a clear azimuthal dependence that indicates significant directivity effect. The discrepancy of the radiated spectral energy and the change in the corner frequencies introduced by directivity effects show that such an effect is significant at high frequency (from 1 to 25 Hz). Our data suggest that the amplitudes in the main-shock Fourier spectrum at directive sites are around a factor of 2.5 higher with respect to anti-directive sites.

Colonisation and diversification of the Zenaida Dove (Zenaida aurita) in the Antilles: phylogeography, contemporary gene flow and morphological divergence.

Caribbean avifaunal biogeography has been mainly studied based on mitochondrial DNA. Here, we investigated both past and recent island differentiation and micro-evolutionary changes in the Zenaida Dove (Zenaida aurita) based on combined information from one mitochondrial (Cytochrome c Oxydase subunit I, COI) and 13 microsatellite markers and four morphological characters. This Caribbean endemic and abundant species has a large distribution, and two subspecies are supposed to occur: Z. a. zenaida in the Greater Antilles (GA) and Z. a. aurita in the Lesser Antilles (LA). Doves were sampled on two GA islands (Puerto Rico and the British Virgin Islands) and six LA islands (Saint Barthélemy, Guadeloupe, Les Saintes, Martinique, Saint Lucia and Barbados). Eleven COI haplotypes were observed that could be assembled in two distinct lineages, with six specific to GA, four to LA, the remaining one occurring in all islands. However, the level of divergence between those two lineages was too moderate to fully corroborate the existence of two subspecies. Colonisation of the studied islands appeared to be a recent process. However, both phenotypic and microsatellite data suggest that differentiation is already under way between all of them, partly associated with the existence of limited gene flow. No isolation by distance was observed. Differentiation for morphological traits was more pronounced than for neutral markers. These results suggest that despite recent colonisation, genetic drift and/or restricted gene flow are promoting differentiation for neutral markers. Variation in selective pressures between islands may explain the observed phenotypic differentiation.

New Phytoseiid mites of the FrenchWest Indies, with description of a new species, and new records (Acari: Mesostigmata)

The authors report results of several surveys carried out to collect phytoseiid mites, between April 2008 and January 2009, in crops and natural surrounding vegetation in several locations of Guadeloupe, La Désirade, Les Saintes and Martinique. A catalogue of 11 new species for Guadeloupe, La Désirade, Les Saintes and Martinique is provided with some information on their biology, when available, and biogeography. New locations for six additional species rarely recorded in the West Indies are also provided. Among the 11 new species, one species new to Science, named Transeius mariae-angeae, is described.

Empirical model for rapid macroseismic intensities prediction in Guadeloupe and Martinique

We describe a simple model for prediction of macroseismic intensities adapted to Guadeloupe and Martinique (Lesser Antilles), based on a combination of peak ground acceleration (PGA) predictive equation and a forward relation between acceleration and intensity. The PGA predictive equation is built from a 3-parameter functional form constrained by measurements from permanent accelerometer stations, mostly associated with Les Saintes crustal earthquake (21/11/2004, M w = 6.3 ) and its many aftershocks. The forward intensity model is checked on a database of recent instrumental events of various origins with magnitudes 1.6 to 7.4, distances from 4 to 300 km, and observed intensities from I to VIII. Global sigma residual equals 0.8 in the MSK scale, suggesting a larger applicability range than the intermediate PGA predictive equation. The model is presently used by the French Lesser Antilles observatories to produce automatic reports for earthquakes potentially felt.

Tectonic context of moderate to large historical earthquakes in the Lesser Antilles and mechanical coupling with volcanoes

[1] The oblique convergence between North American and Caribbean plates is accommodated in a bookshelf faulting manner by active, oblique-normal faults in the northern part of the Lesser Antilles arc. In the last 20 years, two M > 6 earthquakes occurred along a large, arc parallel, en echelon fault system, the 16 March 1985 in Redonda and 21 November 2004 in Les Saintes. A better understanding of active faulting in this region permit us to review the location and magnitude of historical earthquakes by using a regional seismic attenuation law. Several others moderate earthquakes may have occurred along the en echelon fault system implying a strong seismic hazard along the arc. These faults control the effusion of volcanic products and some earthquakes seem to be correlated in time with volcanic unrest. Shallow earthquakes on intraplate faults induced normal stress and pressure changes around neighboring volcano and may have triggered volcanic activity. The Redonda earthquake could have initiated the 1995 eruption of Montserrat's Soufriere Hills by compressing its plumbing system. Conversely, pressure changes under the volcano increased Coulomb stress changes and brought some faults closer to failure, promoting seismicity. We also discuss the magnitude of the largest 11 January 1839 and 8 February 1843 megathrust interplate earthquakes. We calculate that they have increased the stress on some overriding intraplate faults and the extensional strain beneath several volcanoes. This may explain an increase of volcanic and seismic activity in the second half of the 19th century culminating with the devastating, 1902 Mount Pelee eruption.