CDSA: A New Seismological Data Center for the French Lesser Antilles

Mendy Bengoubou-Valerius, Sara Bazin, Didier Bertil, François Beauducel, and Alexis Bosson

Seismological Research Letters, 79:1, 90-102, 2008.

Abstract. The Lesser Antilles is an area of high volcanic and earthquake activity, characterized by a 1000 km convergence zone resulting from the Atlantic plate subduction under the Caribbean plate with a slow convergent motion (2 cm/year). This arc has a specific regional setting with important structural heterogeneities which can affect seismic characteristics: oblique subduction in the North, large accretion prism in the South, aseismic ridge sinking in subduction, shallow intraplate active faults close to the volcanic arc. In 2000, the "Centre des Données Sismologiques des Antilles" (CDSA) was created, with the purpose to provide seismological data at public disposal for multiple applications: research, earthquake engineering, and pedagogic. To reach this objective, it is necessary to gather all Martinique and Guadeloupe seismological data, presently scattered between several institutions and in different numerical formats; then, to process data to make them compatible and produce more accurate information on regional and local seismic activity. Numerical signal records and phases arrival times bulletins come mainly from permanent volcanic and seismologic survey networks managed by IPGP Observatories and several accelerometric networks. More than 120 stations from 10 networks with short period, broadband or accelerometric sensors are concerned. With five years of available data, the CDSA data base presents a more homogeneous vision of Lesser Antilles arc seismicity and allows detecting low seismic activity zones, in the north near the Virgin Islands, and in the south between St-Lucia and Grenada. The accuracy improvements of CDSA location, evidenced by the study case of Les Saintes 2004 swarm, is used to better study the relationship between tectonic structures and seismicity around Guadeloupe and Martinique islands, and to better define the subduction slab geometry. Cross-sections perpendicular to the arc reveal that the slab has a nearly constant, 50° dip angle, from St-Lucia to Nevis. As seismic hazard assessment depends from strong ground motion generated by earthquakes, the CDSA data base also includes strong motion records of the region. The underestimation of the peak acceleration values by standard attenuation laws at large distances shows the need to develop new formulae adapted to the Lesser Antilles context.

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