Organization of Volcanic Observatories
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Observatoire Volcanologique de la Montagne Pelée
(Institut de Physique du Globe de Paris)
Morne des Cadets
Fonds St Denis
97250 Saint Pierre
|Telephone :||0596 78 41 41|
|Telefax :||0596 55 80 80|
Jean-Pierre VIODE - Research engineer
Patrick TUCHAIS - Engineer
Claude MELEZAN - Technical assistant
Myrtha JEAN-BAPTISTE - Secretary
Marie-Amélie UNN-TOC - Secretary
Montagne Pelée Observatory is one of the three French volcanological observatories with Soufrière de Guadeloupe and Piton de la Fournaise (Réunion) observatories. The headquarters of French volcanological observatories is at the Institut de Physique du Globe de Paris. Montagne Pelée Observatory has operated since 1903, the first seismometer was set up in 1932.
SEISMIC NETWORKS AND DATA PROCESSING.
The seismic networks set up on the La Martinique island are composed of 15 stations, which are designed to record seismic activity directly linked to the Montagne Pelée volcano but also to the subduction of the Atlantic plate beneath the Caribbean one, which can give rise to major earthquakes.
a) Volcanologic network
For the permanent monitoring of the volcano 6 stations have been installed on and around it. The stations belong to three types :
- One vertical component station - telemetred to the observatory by voice-grade radio after amplification and frequency modulation of the seismic signal by IPGP instruments (5 stations).
- Analog three component station - One station of this type is installed at Morne des cadets observatory, 8,5 km off the summit.
- Digital three component stations - (1). This station uses Lennartz PCM 5800 digital instrument, which by gain ranging have a dynamic range of 120 dB, and digital wide band telemetry to the observatory. This station has operated since 1989 directly on the summit of the volcano. It constrains the focus depth of earthquakes by unclipped S-readings on horizontal components.
All stations are equipped with Mark Product L4-C 1 Hz seismometers with calibration coils and powered by solar panels.
b. Fort-de-France network
A small aperture array of 5 vertical telemetered stations monitors the local seismicity located in and around the Fort-de-France Bay for microtectonic studies and site effects measurements in this area. The four stations are locally received by a 4 channels PCM 5800 encoder and digitally transmitted to the observatory as an unique digital stream.
c. - Regional network
Several other vertical stations transmit in real-time to the observatory, one in the eastern cap of La Caravelle, two others in the southern part of La Martinique.
Some stations operated by SRU (Trinidad) and IPGP on other islands are also used for regional studies, as well as stations of La Soufrière Observatory in Guadeloupe.
d. Recording and processing.
All seismic signals are transmitted continuously and in real-time to the observatory, some through one-channel radio repeater or TV-frequency transposer. Records are in :
One five-channels stripchart paper recorder displays continuously at 2.5 mm/s the signals of five stations.
- On 128-channel IASPEI PC system which digitizes received signals, displays them on screen and records them on HD when a STA/LTA threshold criterium is reached. One channel is dedicated to time signals from a GPS Clock. The PC is linked in a LAN network with others PC which allows the analysis of the recorded data without loss of recording time. Presently the software analysis package of IASPEI is used, in conjunction with a Windows program: " Winquake " developed at the Observatory.
- On audio-tape after digitization by one 16-channel 12-bit PCM Schlumberger multiplexers, analog detection by coincidence by IPGP electronics. This system is now only used as a back-up of the IASPEI one.
- On audio-tape for the Lennartz PCM 5800 system. The digital signals of the two Lennartz instruments in the field are digitally mixed at the observatory and recorded on audio tape. The same Lennartz unit can be used to retrieve the seismic signals.
The records (paper and files on HD) are read daily, and hypocenters and usual parameters of seismicity are locally computed. Regular bulletins are monthly issued by the observatory ; further analysis are carried out at IPGP.
The monitoring of the ground deformation of Montagne Pelée began in 1976. The ground deformation networks have been progressively expanded since.
Spirit level tilt stations (Dry Tilt).
The spirit level tilt measurements are made with precise optical level Wild NA2 equipped with a micrometer. Four stations are set up. The stations are routinely measured.
From West to East across the Volcano there is a levelling track with 20 benchmarks, they are measured every two years.
Ten reflectors on Montagne Pelée are routinely monitored from the observatory. The surveillance network is measured every month an AGA 600 Laser geodimeter (now in stand by).
Four stations using silica pendulums are telemetered (since 1989) with permanent control of temperature (daily variations). A network of four stations has been set up around the volcano. Value are sent every 30 minutes to a PC by packet mode transmission (AX 25 Protocol). The realtime visualisation of the datas is made via a Windows interface (CLINOX25 Program)
DIFFERENTIAL MAGNETIC NETWORK
A permanent network of nine magnetic stations (seven on the volcano and two near the observatory) has been set up since summer 1984. These stations are equipped with a Littlemore or Geometrics magnetometer, values are telemetered every minute to an AT286 computer and compared to the Observatory reference station. The data are sent every night to IPG in Paris for research work.
Each month, hot spring waters and hot drill hole waters are collected for analysis.
A data-logger at the bottom of the drill hole records temperature, water level, pH and conductivity.
Information updated 1997
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