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Characterization of site conditions for the RAP-RESIF network in the French West Indies

From March 9, teams from OVSG-IPGP and OVSM-IPGP will be taking part in a geophysical campaign to characterize the sites of seismic stations in the RAP-RESIF network, which will enable better calibration of seismic hazard assessment.

Characterization of site conditions for the RAP-RESIF network in the French West Indies

In March 2020, the French Permanent Accelerometer Network, part of the French Seismological and Geodetic Network, is carrying out a geophysical characterisation campaign of the site conditions under 10 of its seismological stations installed in Martinique and Guadeloupe, and operated by the OVSM-IPGP and the OVSG-IPGP. This campaign is being carried out with the support of the French Ministry for Ecological Transition and Solidarity.

Measurements are scheduled from 9 to 13 March 2020 in Martinique and from March 23rd to 27th  in Guadeloupe. Ten RAP stations will be characterised, with 5 stations per island.

Example of a seismometer installed for an "AVA" measurement (Ambient Vibration Arrays) (RAP-RESIF)

The measurement campaign is being organised by a RAP working group with experience of this type of campaign in mainland France (56 stations characterised since 2012), in conjunction with the Martinique and Guadeloupe observatories.

Example of active MASW (Multi-Analysis Surface-Wave method) measurements (RAP-RESIF)

The geophysical characterisation of accelerometer stations is essential for the correct use of the seismic motion data recorded there. This characterisation involves determining the parameters that qualify the rigidity of the ground on which the station is located: complete profiles of the speed of propagation of shear waves, EC8 regulatory soil class, parameter VS30. The prospecting methods used are non-destructive, the ground is not drilled and these measurements leave no trace. They are based on analysis of the dispersion properties of surface waves. The methodology used and the associated processing correspond to the best practices in the state of the art, and are part of the current international drive to systematically characterise accelerometric stations.

The information obtained will make it possible to better calibrate the choice of seismic motion prediction models used in seismic hazard assessments.

Map of the 10 stations to be characterized in Martinique and Guadeloupe (RAP-RESIF)

The 10 stations selected for the 2020 campaign are among those that have recorded the greatest number of seismic movements generated by earthquakes to date. Other important criteria are the site’s strategic contribution to estimating the seismic hazard and the feasibility of deploying measuring instruments for characterisation.

The participants come from various partner institutes in the RAP-RESIF network: ISTerre in Grenoble, CEA, BRGM, OMP in Toulouse, EOST in Strasbourg, CEREMA in Nice, and of course the IPGP’s volcanological and seismological observatories in Martinique and Guadeloupe. The acquisition plan at each station includes AVA measurements (Ambient Vibration Arrays – passive measurements of surface waves on ambient noise). Temporary seismological stations are deployed for a whole day around each permanent station within a 500 m radius. The protocol also includes MASW (Multi-Analysis Surface-Wave method) measurements, which are active measurements of surface wave propagation, the seismic source simply being a mass struck against a metal slab or beam, and recorded by lines of geophones.

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