World Organization of Volcanic Observatories
Observatoire Volcanologique et Sismologique de Guadeloupe
(Institut de Physique du Globe de Paris)
French West Indies
|Telephone :||+590 (0)590 991133|
|Telefax :||+590 (0)590 991134|
Céline Dessert - Head of Soufriére volcano Observatory at Guadeloupe
Christian Anténor-Habazac - Electronics engineer / Technical manager
Gilbert Hammouya - Gas and water chemistry engineer
Thierry Kitou - Electronics engineer
Alexis Bosson - Computer engineer assistant
Olivier Crispi - Gas and water chemistry engineer assistant
Christian Lambert - Mechanic and field assistant
Pascal Rival - Laboratory and field assistant
Bertrand Figaro - Seismology and field assistant
Veronique Daniel - Secretary
Sylvie Pierrot - Secretary (temporary)
Observatoire Volcanologique et Sismologique in Guadeloupe (OVSG) is one of the three French volcanological observatories with Montagne Pelée (Martinique) and Piton de la Fournaise (Réunion) observatories. It is in charge of the monitoring of La Soufrière volcano and regional seismicity around the Guadeloupe archipelago. The head of the French volcanological observatories is at the Institut de Physique du Globe de Paris.
A basic geophysical laboratory was created in 1948 in Saint-Claude on the flanks of Soufrière volcano responsible for installing and maintaining a handful of seismic stations. Upgrade and modernization of the volcano monitoring network began with the onset of significant seismic unrest in 1975 which turned out to be premonitory to the violent and long-lasting phreatic eruption of 1976-1977. As a result of this eruption whose consequences could have been much more severe, a substantial program of basic volcano research as well as a comprehensive multidisciplinary volcano monitoring network has been supported since then by the French government.
During the 1976 eruption, seismic monitoring equipment was moved to a crisis site near the sea in the thick protective walls of the XVIth century Fort Delgres, while administrative staff mainly stayed in Saint-Claude. The Observatory was finally moved in 1993 to a single operational site on top of the extinct Houëlmont volcanic plug at an elevation of 430 m and at a distance of about 8 km from the active volcano summit. The current modern Observatory houses all monitoring and data processing installations, a chemistry analytical lab, offices, a small library, a survival crisis cellar, observational tower, as well as technical lab space and living quarters for visiting scientists. Current staff (about 10 resident and visiting) include researchers, electronic, chemical, and computer engineers, technicians, and administrative all part of the French ministry of Education and Research.
The Soufrière of Guadeloupe Volcano Observatory is responsible for operating and maintaining the surveillance network, and for data processing, analysis, and archival. These data is available to IPGP and other collaborators. The Observatory is also in charge of informing the official authorities and elected officials in Guadeloupe concerned by risk prevention, mitigation, and emergency planning and management, as well as informing the population via a public monthly information bulletin and regular media communications. The Observatory also actively participates in research programs, collaborative monitoring programs in the Caribbean (Montserrat, Dominica), and training activities related to dissemination of scientific volcano-related information and applied aspects of volcano hazard preparedness and prevention. The recent increase in fumarolic activity and low-energy shallow level seismicity since 1997 prompted a significant upgrade in the monitoring network, development national research programs, and public information as well as renewed interests by Civil Protection authorities to set up contingency mitigation and emergency plans.
The Soufrière monitoring lies on several scientific disciplines lasting from geophysics and geochemistry to geological observations. The current network includes about 70 telemetered permanent stations with continuous or semi-continuous recording, and about 250 sites measured manually in the field with varying acquisition periods (see network maps below).
The seismic networks set up on the Guadeloupean islands are composed of 39 stations, which are designed to record seismic activity directly linked to the Soufrière volcano but also to the subduction of the Atlantic plate beneath the Caribbean one, which can give rise to major earthquakes (1843, M ~ 8). Usually it records every year between 500-1000 regional and local earthquakes related to the subduction zone, about 10 of them are felt by guadeloupean population. On November 21th 2004, an intraplaque shallow event of magnitude 6.3 occured between Les Saintes Archipelago and Dominica. One child was killed, about 45 people injured and several public building and houses were damaged in Guadeloupe. The event was followed by more than 23,000 aftershocks (the biggest one on February 14th, 2005) and it still continues on August 2005.
a) Volcanological network
For the permanent monitoring of the volcano, 18 permanent stations have been installed on and around it in a polygon of 100 km² on the Basse-Terre island. The stations belong to four types:
b) Regional network
21 other stations are installed to cover the Guadeloupe archipelago: Grande-Terre, La Désirade, Marie-Galante islands but also some surrounding islands like Montserrat, Antigua, and Dominica. These data increase the detection capacity of the networks but also the accuracy of the location for earthquakes occuring along the subduction slab, mostly eastward of Guadeloupe, and in the Pointe-à-Pitre Bay. The equipment belong to three type:
Some stations operated by Seismic Research Unit (Trinidad) on other islands are also used for regional studies (Nevis), as well as stations of Montagne Pelée Observatory in Martinique (IPGP).
c) Recording and processing
Except for the accelerometer network in trigger mode, all seismic signals are transmitted continuously and in real time toward the observatory, some through radio repeaters. Records are in continuous mode, 100 Hz sampling, using IASPEI SUDS format and GEOSIG native format, 2 or 5-min duration files, and saved every day on two full CD-R (with automatic process).
Between 1975 and 2003, two five-channels stripchart paper recorder (Sefram) were used to display continuously at 2.5 mm/s the sismograms of five stations of both networks (volcanologic and regional). They are now replaced by computer processes using Matlab routines and HTTP interface with automatic alarms on saturated events (possibly felt by population). The records are daily read by an operator. Location of hypocenters and usual parameters of seismicity are locally computed. Data are archived and automatically processed with preset time scales of 24h, 30 days, 1 year and 10 years comprehensive graphics for simulated helicorders (one per component), bulletins (number, energy, Guttenberg-Richer diagrams) and hypocenter maps and profiles at different geographic scales. Regular bulletins are monthly issued by the observatory; further analysis are carried out at IPGP.
Since the end of 2004, maximum horizontal ground accelerations (PGA) are estimated for the main cities of Guadeloupe immediately after a seismic event.This simulation is based on a local attenuation law named "B-Cube" [Beauducel et al., 2004], that took advantage of the numerous strong-motion records associated to Les Saintes crisis.
The observation of the ground deformation of Soufrière began in 1976. The networks have been progressively improved and are now using different scale and sensitivity instruments:
All these data are processed using real-time automatic graphic routines showing parameter trends with preset time scales of 24h, 30 days, 1 year and 10 years. Manual measurements are integrated into the database using HTTP forms.
Fluid circulations within the volcanic edifice are monitored with monthly thermo-mineral springs and gas fumaroles sampling, in order to evaluate the composition of the volcanic fluids:
All these data are entered into the database using HTTP forms and processed using real-time automatic graphic routines showing all parameter trends with preset time scales of 1 year and 10 years.
During 1993 a bidirectional radio-linked magnetic network has been settled on Soufrière volcano, extended in 2000 and complemented with a ground self-potential station:
All these data are processed using real-time automatic graphic routines showing absolute and relative parameter trends with preset time scales of 24h, 30 days, 1 year and 10 years.
Thanks to IPGP and collaboration with other universities, a team of about 50 scientists and technicians affiliated with the Office of Volcano Observatories participates actively in the development of new monitoring equipment, processing and analysis of the data. In this framework, frequent surveys and experiments in geophysics (electrical and seismic tomography, …), chemistry, and volcanology (deposits and other geological mapping, …) are carried on to complement the permanent monitoring network.
The Observatory maintains an extensive computer network with automatic data processing, storage and transmition to IPGP for all of the telemetered and manual data. A recent development of automated processing routines allows immediate access via an internet server to the status of the monitoring network, to complete numerical and graphical data set, as well as to key quantitative indicators of volcano activity. This original system has been effective since 2001 and was adapted for Montagne Pelée Observatory in 2003. It consists in a single Linux server (dual processors 2.4 MHz, 1.5 Mb RAM and 150 Gb SCSI-W3 disks) and home-made scripts written in Matlab, Perl and Shell. Main characteristics are the following:
a) Data bank
b) Data processing
c) Acquisition control
d) Routine schedule
e) Web interface
Inputs and outputs of this system is managed through a restricted access Web site with a fixed architecture and dynamic pages generated by the Matlab routines themselves or Perl CGI scripts. The Web site contains hundreds pages and graphics, and thousands cross-links. It leads to several usefull tools for observatory managment:
Information updated May 2014