Surrections cosismiques et subsidence intersismique enregistrées par des coraux à Mallicolo (Vanuatu, Pacifique sud-ouest)

Abstract

Evidence of successive periods of uplift and subsidence is present on the western coast of Malekula Island, Vanuatu, in the southwest Pacific. These vertical motions are recorded in coral growth. Corals grew on the outer rim of an ancient reef flat uplifted by the 1965 earthquake and afterwards eroded by sea waves. The occurrence of corals on this reef flat implies that it had been submerged since 1965. The whole unit is now uplifted following the 1994 earthquake. This timing of events suggests that the last submersion of the reef flat resulted from the accumulation of the strain, the relaxation of which caused the 1994 earthquake. Vertical displacements modelled using a dislocation model partly agree with this interpretation, suggesting that some aseismic motions might have occurred.