A significant increase in interplate seismicity near major historical earthquakes offshore Martinique (FWI)

(Corbeau et al., 2021)

Understanding the processes that may be at the origin of major earthquakes in subduction zones is highly challenging for scientists, especially in the case of slowly converging areas such as the Lesser Antilles subduction zone which produce only few seismic events to analyze.

We have studied the seismicity recorded by the OVSM-IPGP from 2000 until the end of 2019 offshore Martinique Island.

Our study reveals a recorded increase in seismicity rate and cumulative seismic moment over the last two decades and, particularly, in the presumed rupture area of the major (M 7.5 to 8) historical 1839 earthquake (Figure 1).

Figure 1: General map of the Lesser Antilles arc where the North-American tectonic plate (NAM) subducts under the Caribbean tectonic plate (CAR) at about 19 mm/yr (DeMets et al., 2000). Gray ellipses indicate the locations of the presumed rupture zones associated with the two largest historical earthquakes of 1839 (M 7.5 to 8) and 1843 (M 8 to 8.5) in the Lesser Antilles arc (Feuillet et al., 2011). The red line A-B indicates the location of the seismic cross-section shown in Figure 2A

This sustained seismicity is shared along the subduction interface between two distinct zones: the intermediate depth zone, from 120 to 180 km depth, where the seismic rate is high since the occurrence of the 2007 Mw 7.4 earthquake; and the seismogenic zone of the subduction, from 20 to 70 km depth, where a seismic cluster clearly occurs since 2015 (Figure 2A).

Figure 2: A. Seismicity of the last two decades recorded by the OVSM-IPGP around Martinique and presented along the transect A-B of Figure 1. The seismicity is distributing along the subduction interface between the seismogenic zone (in light red, at about 20 to 70 km depth) and the intermediate depth zone (in light blue, at about 120 to 180 km depth). B. Graph showing the increase of the seismicity during the last two decades in the seismic cluster of the seismogenic zone. We can note the occurrence of earthquakes of magnitude above 5 since 2015.

An increase in the magnitudes recorded in the cluster was also observed (Figure 2B), associated with a downward migration of the hypocenters along the seismogenic zone of the plate interface up to 60–65 km depths. All these observations may indicate ongoing changes along the plate boundary interface of the Lesser Antilles subduction zone, offshore Martinique, near the area of the historical major rupture of 1839.

Although these observations have been previously proposed to be major earthquake intermediate-term precursors in other subduction zones, more detailed statistical studies and additional data are necessary to confirm this trend and to estimate seismic hazards in the Lesser Antilles.

Sources

Corbeau, J.1,2, O.L. Gonzalez3, N. Feuillet1, A.M. Lejeune1,2,4, F. Fontaine1,2, V. Clouard1,2,5, J.-M. Saurel1 and the OVSM Team1,2, (2021). A significant increase in the interplate seismicity near major historical earthquakes offshore Martinique (FWI). Bull. Seismol. Soc. Am.,  https://doi.org/10.1785/0120200377

1 Université de Paris, Institut de Physique du Globe de Paris (IPGP), Centre National de la Recherche Scientifique (CNRS), Paris, France

2 Observatoire Volcanologique et Sismologique de Martinique, Institut de

Physique du Globe de Paris (OVSM-IPGP), Saint-Pierre, France

3 Centro Nacional de Investigaciones Sismológicas (CENAIS), Ministerio de Ciencia, Tecnología y Medio Ambiente, Cuba

4 Sorbonne Université, Institut des Sciences de la Terre Paris (ISTeP), Centre National de la Recherche Scientifique (CNRS), Paris, France

5Géosciences Environnement Toulouse (GET), Observatoire Midi Pyrénées, Université Paul Sabatier, CNRS, IRD, Toulouse, France

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