The European Volcano Observatories and their use of the aviation colour code system

Volcano observatories (VOs) around the world are required to maintain surveillance of their volcanoes and inform civil protection and aviation authorities about impending eruptions. They often work through consolidated procedures to respond to volcanic crises in a timely manner and provide a service to the community aimed at reducing the potential impact of an eruption. Within the International Airways Volcano Watch (IAVW) framework of the International Civil Aviation Organisation (ICAO), designated State Volcano Observatories (SVOs) are asked to operate a colour coded system designed to inform the aviation community about the status of a volcano and the expected threats associated. Despite the IAVW documentation defining the different colour-coded levels, operating the aviation colour code in a standardised way is not easy, as sometimes, different SVOs adopt different strategies on how, when, and why to change it. Following two European VOs and Volcanic Ash Advisory Centres (VAACs) workshops, the European VOs agreed to present an overview on how they operate the aviation colour code. The comparative analysis presented here reveals that not all VOs in Europe use this system as part of their operational response, mainly because of a lack of volcanic eruptions since the aviation colour code was officially established, or the absence of a formal designation as an SVO. We also note that the VOs that do regularly use aviation colour code operate it differently depending on the frequency and styles of eruptions, the historical eruptive activity, the nature of the unrest, the monitoring level, institutional norms, previous experiences, and on the agreement they may have with the local Air Transport Navigation providers. This study shows that even though the aviation colour code system was designed to provide a standard, its usage strongly depends on the institutional subjectivity in responding to volcano emergencies. Some common questions have been identified across the different (S)VOs that will need to be addressed by ICAO to have a more harmonised approach and usage of the aviation colour code

Dynamique d'une frontière transformante dans un contexte de collision oblique : étude de la limite nord de la plaque Caraïbe dans la région d'Haïti.

The Northern Caribbean transpressive plate boundary is expressed in Haiti by the partitioning of the deformation between two strike-slip faults and compressive structures. Bathymetric, seismic reflection and receiver-functions studies are methods used here to constrain the structure and the dynamic of the Northern Caribbean transpressive plate boundary offshore and onshore. The bathymetric data acquired during the Haiti-SIS cruises provide a detailed mapping of the geometry and segmentation of the senestrial strike-slip fault systems. The seismic profiles in the Jamaica Passage show that basin structures exist prior to the initiation of the EPGFZ and are cross-cut and folded by the EPGFZ. We identify a distinct crustal domain that we relate to the Caribbean large igneous province. The present deformations offshore show that the EPGFZ is primary strike-slip, with an increasing compressive component of the deformation toward the east. The shortening estimates are very small (2 to 3%) compared to the short-term GPS modeling estimates. Onshore in Haiti, we image the crustal structure from a receiver-functions study. The crustal thickness is ~23 km in the northern part of Haiti, ~22 km in the southern part of Haiti and ~41 km in the middle part, delimiting 3 distinct domains. We propose that these domains correspond to 3 geological distinct terranes: the Cretaceous volcanic arc in the north, the oceanic igneous province in the south, and in between a continental crust underthrusted by dense material. The underthrusted material could be a subducted portion of the Caribbean large igneous province under the Trans-Haitian fold-and-thrust belt.La frontière de plaque transpressive Nord Caraïbe s'exprime dans la région d'Haïti par un partitionnement de la déformation entre deux failles décrochantes et des chevauchements. L'étude de données de bathymétrie, de sismique réflexion, et de fonctions récepteur apporte des contraintes sur la structure et le fonctionnement de cette frontière de plaque en transpression en mer et à terre. Les données de bathymétrie des campagnes Haïti-SIS 1 et 2 nous ont permis de cartographier précisément le grand système de failles décrochantes senestres et leur segmentation. L'étude des profils de sismique réflexion a mis en évidence l'existence de structures pré-existantes à l'activité du décrochement EPGFZ en mer. Nous avons également identifié un domaine crustal distinct, que nous avons relié au plateau océanique Caribéen. L'étude des déformations actuelles en mer nous permet de montrer que la faille EPGFZ est principalement décrochante, avec une composante compressive qui augmente vers l'Est. Les estimations de raccourcissement restent cependant très faibles (2 à 3%) en comparaison des estimations faites par les modélisations GPS. A terre en Haïti, nous avons imagé l'épaisseur crustale grâce à une étude de fonctions récepteur. Les épaisseurs imagées délimitent trois domaines différents. Nous proposons que ces domaines correspondent à trois ensembles géologiques distincts, composés respectivement de l'arc Crétacé des Grandes Antilles au Nord, du plateau océanique Caraïbe au Sud, et d'une croûte continentale au centre. Cette croûte pourrait être sous-charriée par du matériel dense provenant de la subduction d'une portion du plateau océanique Caribéen sous Haïti

Dynamic of a transform boundary in an oblique collision context : the Northen Caribbean plate boundary in the Haiti aera

The Northern Caribbean transpressive plate boundary is expressed in Haiti by the partitioning of the deformation between two strike-slip faults and compressive structures. Bathymetric, seismic reflection and receiver-functions studies are methods used here to constrain the structure and the dynamic of the Northern Caribbean transpressive plate boundary offshore and onshore. The bathymetric data acquired during the Haiti-SIS cruises provide a detailed mapping of the geometry and segmentation of the senestrial strike-slip fault systems. The seismic profiles in the Jamaica Passage show that basin structures exist prior to the initiation of the EPGFZ and are cross-cut and folded by the EPGFZ. We identify a distinct crustal domain that we relate to the Caribbean large igneous province. The present deformations offshore show that the EPGFZ is primary strike-slip, with an increasing compressive component of the deformation toward the east. The shortening estimates are very small (2 to 3%) compared to the short-term GPS modeling estimates. Onshore in Haiti, we image the crustal structure from a receiver-functions study. The crustal thickness is ~23 km in the northern part of Haiti, ~22 km in the southern part of Haiti and ~41 km in the middle part, delimiting 3 distinct domains. We propose that these domains correspond to 3 geological distinct terranes: the Cretaceous volcanic arc in the north, the oceanic igneous province in the south, and in between a continental crust underthrusted by dense material. The underthrusted material could be a subducted portion of the Caribbean large igneous province under the Trans-Haitian fold-and-thrust belt.La frontière de plaque Nord Caraïbe est une région en collision oblique qui sépare la plaque Nord Amérique de la plaque Caraïbe. Dans la région d’Haïti, la transpression qui en résulte s’exprime par un partitionnement de la déformation entre d’une part deux failles décrochantes majeures et d’autre part des chevauchements. Cette frontière de plaque connaît une sismicité importante dont le dernier exemple en date est le séisme meurtrier du 12 Janvier 2010 de magnitude 7. Ce dernier a eu lieu près de Port-au-Prince et a mis en évidence l’importance de la transpression dans cette zone. L’étude complémentaire de données de bathymétrie, de sismique réflexion, et de fonctions récepteur apporte des contraintes sur la structure et le fonctionnement de cette frontière de plaque en transpression en mer et à terre. Dans un premier temps, les données de bathymétrie acquises durant les campagnes Haïti-SIS 1 et Haïti-SIS 2 nous ont permis de réaliser une cartographie précise du grand système de failles décrochantes senestres et de leur segmentation. Nos estimations de l’aléa sismique associé à ces décrochements indiquent que les futurs séismes en mer pourraient atteindre des magnitudes de 7 à 8. L’étude des profils de sismique réflexion nous a ensuite permis de mettre en évidence l’existence de structures pré-existantes à l’activité du décrochement Enriquillo- Plantain-Garden (EPGFZ) en mer dans le Passage de la Jamaïque. Ces structure préexistantes sont associées à la tectonique extensive de la marge continentale passive Est du système Cayman. Elles sont ensuite recoupées et déformées par le décrochement EPGFZ. L’activité d’EPGFZ permet la création d’un bassin asymétrique au centre du Passage de la Jamaïque. Nous avons également identifié un domaine crustal distinct au sud du Passage de la Jamaïque, que nous avons relié au plateau océanique Caribéen. La cartographie des deux domaines crustaux identifiés en mer montre que leur frontière ne coïncide pas avec la trace d’EPGFZ. L’étude des déformations actuelles en mer dans le Passage de la Jamaïque et dans le Golfe de la Gonâve nous permet de montrer que la faille EPGFZ est principalement décrochante, avec une composante compressive qui augmente vers l’Est. Dans le Golfe de la Gonâve, plusieurs plis et chevauchements sont identifiés. Les estimations de raccourcissement restent cependant très faibles (2 à 3%) en comparaison des estimations faites par les modélisations GPS. La transpression semble donc être accommodée de manière diffuse au travers de la frontière de plaque. A terre en Haïti, nous avons imagé l’épaisseur crustale grâce à une étude de fonctions récepteur. La croûte imagée est épaisse d’environ 23 km au Nord d’Haïti, d’environ 22 km au Sud et d’environ 41 km au centre, délimitant ainsi trois grands domaines différents. Nous proposons que ces domaines correspondent à trois ensembles géologiques distincts, composés respectivement de l’arc volcanique Crétacé des Grandes Antilles au Nord, du plateau océanique Caraïbe au Sud, et d’une croûte continentale au centre. Cette croûte pourrait être constituée de trois écailles crustales et être sous-plaquée par du matériel dense. Le sous-plaquage dense pourrait correspondre à la subduction d’une portion du plateau océanique Caribéen sous la chaîne Trans-Haïtienne. Nous proposons une reconstitution géodynamique qui précise la mise en place et le fonctionnement de la frontière de plaque transpressive Nord Caraïbe en Haïti depuis le Maastrichtien (70 Ma) jusqu’au Pleistocène (2 Ma)

Dynamic of a transform boundary in an oblique collision context : the Northen Caribbean plate boundary in the Haiti aera

La frontière de plaque transpressive Nord Caraïbe s'exprime dans la région d'Haïti par un partitionnement de la déformation entre deux failles décrochantes et des chevauchements. L'étude de données de bathymétrie, de sismique réflexion, et de fonctions récepteur apporte des contraintes sur la structure et le fonctionnement de cette frontière de plaque en transpression en mer et à terre. Les données de bathymétrie des campagnes Haïti-SIS 1 et 2 nous ont permis de cartographier précisément le grand système de failles décrochantes senestres et leur segmentation. L'étude des profils de sismique réflexion a mis en évidence l'existence de structures pré-existantes à l'activité du décrochement EPGFZ en mer. Nous avons également identifié un domaine crustal distinct, que nous avons relié au plateau océanique Caribéen. L'étude des déformations actuelles en mer nous permet de montrer que la faille EPGFZ est principalement décrochante, avec une composante compressive qui augmente vers l'Est. Les estimations de raccourcissement restent cependant très faibles (2 à 3%) en comparaison des estimations faites par les modélisations GPS. A terre en Haïti, nous avons imagé l'épaisseur crustale grâce à une étude de fonctions récepteur. Les épaisseurs imagées délimitent trois domaines différents. Nous proposons que ces domaines correspondent à trois ensembles géologiques distincts, composés respectivement de l'arc Crétacé des Grandes Antilles au Nord, du plateau océanique Caraïbe au Sud, et d'une croûte continentale au centre. Cette croûte pourrait être sous-charriée par du matériel dense provenant de la subduction d'une portion du plateau océanique Caribéen sous Haïti.The Northern Caribbean transpressive plate boundary is expressed in Haiti by the partitioning of the deformation between two strike-slip faults and compressive structures. Bathymetric, seismic reflection and receiver-functions studies are methods used here to constrain the structure and the dynamic of the Northern Caribbean transpressive plate boundary offshore and onshore. The bathymetric data acquired during the Haiti-SIS cruises provide a detailed mapping of the geometry and segmentation of the senestrial strike-slip fault systems. The seismic profiles in the Jamaica Passage show that basin structures exist prior to the initiation of the EPGFZ and are cross-cut and folded by the EPGFZ. We identify a distinct crustal domain that we relate to the Caribbean large igneous province. The present deformations offshore show that the EPGFZ is primary strike-slip, with an increasing compressive component of the deformation toward the east. The shortening estimates are very small (2 to 3%) compared to the short-term GPS modeling estimates. Onshore in Haiti, we image the crustal structure from a receiver-functions study. The crustal thickness is ~23 km in the northern part of Haiti, ~22 km in the southern part of Haiti and ~41 km in the middle part, delimiting 3 distinct domains. We propose that these domains correspond to 3 geological distinct terranes: the Cretaceous volcanic arc in the north, the oceanic igneous province in the south, and in between a continental crust underthrusted by dense material. The underthrusted material could be a subducted portion of the Caribbean large igneous province under the Trans-Haitian fold-and-thrust belt

A Significant Increase in Interplate Seismicity near Major Historical Earthquakes Offshore Martinique (FWI)

International audienceUnderstanding the processes that may be at the origin of major earthquakes in subduction zones is highly challenging, especially in the case of slowly converging areas such as the Lesser Antilles subduction zone. Our study reveals a recorded increase in seismicity rate and cumulative seismic moment over the last two decades offshore Martinique island and, particularly, in the presumed rupture area of the major historical 1839 earthquake. This sustained seismicity is shared between extensive intermediate depth activity since the 2007 Mw 7.4 earthquake that occurred about 20 km north of Martinique and a compressive seismic cluster located in the seismogenic zone of the subduction zone. We also observe a downward migration of the seismicity along the plate interface up to a 60–65 km depth and a recorded increase in the magnitudes of the earthquakes. All these observations may indicate ongoing changes along the plate boundary interface near the area of the historical major rupture of 1839, although more detailed statistical studies and additional data are necessary to confirm this trend

How transpressive is the northern Caribbean plate boundary?

International audienceTranspressive deformation at the northern Caribbean plate boundary is accommodated mostly by two major strikeslipfaults, but the amount and location of accommodation of the compressional component of deformation is still debated.We collected marine geophysical data including multi-beam bathymetry and multichannel seismic reflection profiles alongthis plate boundary around Hispaniola, in the Jamaica Passage and in the Gulf of Gonâve. The data set allows us to imagethe offshore active strike-slip faults as well as the compressional structures. We confirm that the Enriquillo-Plantain-GardenFault Zone (EPGFZ) in the Jamaica Passage has a primary strike-slip motion, as indicated by active left-lateral strike-sliprelatedstructures, i.e.: restraining bend, asymmetrical basin, en echelon pressures ridges and horsetail splay. Based ontopographic cross-sections across the EPGFZ, we image a very limited compressional component, if any, for at least thewestern part of the Jamaica Passage. Toward the east of the Jamaica Passage, the fault trace becomes more complex and weidentify adjacent compressional structures. In the Gulf of Gonâve, distributed folding and thrust faulting of the most recentsediments indicate active pervasive compressional tectonics. Estimates of shortening in the Jamaica Passage and in the Gulfof Gonâve indicate an increase of the compressional component of deformation towards the east, which nonetheless remainsvery small compared to that inferred from block modelling based on GPS measurement

The northern Caribbean plate boundary in the Jamaica Passage: structure and seismic stratigraphy

International audienceMultibeam bathymetry data and multichannel seismic reflection profiles have been collected at the end of 2012 along the Enriquillo-Plantain-Garden Fault Zone (EPGFZ) in the Jamaica Passage, between Jamaica and Hispaniola. Analysis of the data set reveals the tectonic evolution and the stratigraphic complexity of the northern Caribbean boundary. Stratigraphic correlations with previous marine and on land studies are proposed to place the identified seismic sequences in their regional tectonic history. Two distinct crustal domains are interpreted. Typical stratigraphic sequences for the rifted blocks of the Eastern Cayman Trough margin are identified in five basins of the Jamaica Passage, highlighting the eastward limit of the Cayman Trough margin. These inherited basins are deformed and folded during a first phase of compression that could correspond to the regional tectonic rearrangement recorded in the early Miocene (about 20 Ma). A distinct crustal domain that we propose to relate to the Carib Beds (Caribbean typical reflectors A′′,B′′ and V) is identified in the southern part of the Jamaica Passage, indicating that the Caribbean Large Igneous Province could extend up to the extreme northeast part of theLower Nicaragua Rise. The left-lateral EPGFZ currently cuts acrosstwo pre-existing basins, the Morantand Matley basins. During the activity of the EPGFZ, these basins are deformed and folded indicating a second phase of compression. In contrast, the Navassa basin, located in the middle of the Jamaica Passage, results from the strike-slip motion of the EPGFZ and is interpreted as an asymmetricalbasin bordered by the EPGFZonly on its northern sid

Building a Natural-Hazard-Resilient High-Quality Seismic Network: How WI Network Sustained Hurricanes Maria and Irma

International audienceAbstract Between 2008 and 2014, the Institut de Physique du Globe de Paris (IPGP) and the University of the West Indies, Seismic Research Centre (UWI-SRC) designed and built a regional seismic network across the Lesser Antilles. One of the goals of the network is to provide real-time seismic data to the tsunami warning centers in the framework of the Intergovernmental Coordination Group working toward the establishment of a tsunami and other coastal hazards early warning system (ICG-CARIBE-EWS) for the Caribbean and adjacent regions (McNamara et al., 2016). In an area prone to hurricanes, earthquakes, tsunamis, and volcanic eruptions, we chose different techniques and technologies to ensure that our cooperated network could survive and keep providing data in case of major natural hazards. The Nanometrics very small aperture terminal (VSAT) technology is at the heart of the system. It allows for duplicated data collection at the three observatories (Trinidad, Martinique, and Guadeloupe; Anglade et al., 2015). In 2017, the network design and implementation were put to the test with Saffir–Simpson category 5 hurricanes Irma and Maria that went, respectively, through the north and central portion of the Lesser Antilles, mainly impacting the sites operated by volcanological and seismological observatories of IPGP in Martinique (Observatoire Volcanologique et Sismologique de Martinique [OVSM]) and in Guadeloupe (Observatoire Volcanologique et Sismologique de Guadeloupe [OVSG]). Our concepts proved to be valid with a major data shortage of less than 12 hr and only two stations having sustained heavy damage. In this article, we review the strengths and weaknesses of the initial design and discuss various steps that can be taken to enhance the ability of our cooperated network to provide timely real-time seismic data to tsunami warning centers under any circumstances

Spatial Variations in Crustal and Mantle Anisotropy Across the North American-Caribbean Boundary on Haiti

International audienceHaiti, on the island of Hispaniola, is situated across the North American-Caribbean plate boundary at the transition point between oblique subduction in the east and a transform plate boundary in the west. Here we use shear wave splitting measurements from S waves of local (0-50 km) and intermediate depth (50-150 km) earthquakes as well as SK(K)S phases from teleseismic earthquakes to ascertain good spatial and vertical resolution of the azimuthal anisotropic structure. This allows us to place new constraints on the pattern of deformation in the crust and mantle beneath this transitional region. SK(K)S results are dominated by plate boundary parallel (E-W) fast directions with~1.9 s delay times, indicating subslab trench parallel mantle flow is continuing westward along the plate boundary. Intermediate depth earthquakes originating within the subducting North American plate show a mean fast polarization direction of 065°and delay time of 0.46 s, subparallel to the relative plate motion between the Caribbean and North American plates (070°). We suggest a basal shear zone within the lower ductile crust and upper lithospheric mantle as being a potential major source of anisotropy above the subducting slab. Upper crustal anisotropy is isolated using shear wave splitting measurements on local seismicity, which show consistent delay times on the order of 0.2 s. The fast polarization directions indicate that the crustal anisotropy is controlled by the fault networks in close proximity to the major strike-slip faults, which bisect the north and south of Haiti, and by the regional stress field where faulting is less pervasive

The tectonics and active faulting of Haiti from seismicity and tomography

Oblique convergence of the Caribbean and North American plates has partitioned strain across a major transpressional fault system that bisects the island of Hispaniola. The devastating MW 7.0, 2010 earthquake that struck southern Haiti, rupturing an unknown fault, highlighted our limited understanding of regional fault segmentation and its link to plate boundary deformation. Here we assess seismic activity and fault structures across Haiti using data from 33 broadband seismic stations deployed for 16‐months. We use travel‐time tomography to obtain relocated hypocenters and models of Vp and Vp/Vs crustal structure. Earthquake locations reveal two clusters of seismic activity. The first corresponds to aftershocks of the 2010 earthquake and delineates faults associated with that rupture. The second cluster shows shallow activity north of Lake Enriquillo (Dominican Republic), interpreted to have occurred on a north‐dipping thrust fault. Crustal seismic velocities show a narrow low‐velocity region with an increased Vp/Vs ratio (1.80‐1.85) dipping underneath the Massif de la Selle, which coincides with a southward‐dipping zone of hypocenters to a depth of 20 km beneath southern Haiti. Our observations of seismicity and crustal structure in southern Haiti suggests a transition in the Enriquillo fault system from a near vertical strike‐slip fault along the Southern Peninsula to a southward‐dipping oblique‐slip fault along the southern border of the Cul‐de‐Sac‐Enriquillo basin. This result, consistent with recent geodetic results but at odds with the classical seismotectonic interpretation of the Enriquillo fault system, is an important constraint in our understanding of regional seismic hazard