M 7.4 - 18 km WNW of Basse-Pointe, Martinique

Tectonic Summary

The November 29, 2007, M 7.4 Martinique earthquake occurred as the result of oblique normal faulting at an intermediate depth, approximately 156 km beneath the Lesser Antilles Island Arc of the eastern Caribbean Sea. Focal mechanism solutions indicate that oblique rupture occurred on either a near-vertical north-south normal fault or shallowly dipping east-striking normal fault. At the location of the earthquake, the South America plate subducts to the west-northwest beneath the Caribbean plate at a velocity of about 20 mm/yr. The earthquake occurred within the subducted South America plate in response to stresses generated by the plate’s slow distortion at depth, rather than on the thrust fault that constitutes the interface the between the Caribbean and South America plates. Slip on a fault aligned with either nodal plane of the focal mechanism solution would accommodate the down-dip extension of the South America slab that is implied by the normal-component of the faulting solution.

Earthquakes like this event, with focal depths between 70 and 300 km, are commonly termed “intermediate-depth” earthquakes. Intermediate-depth earthquakes represent deformation within subducted slabs rather than at the shallow plate interface between subducting and overriding tectonic plates. They typically cause less damage on the ground surface above their foci than is the case with similar-magnitude shallow-focus earthquakes, but large intermediate-depth earthquakes may be felt at great distance from their epicenters. The subducted South America plate is seismically active to depths of almost 200 km beneath the Lesser Antilles Island Arc near Martinique.

The November 29th event was the first earthquake of M 7 or larger to have occurred within its 400 km vicinity since the M 7.5 event in October 1974, about 250 km to the north. No fatalities were reported from that earthquake, though several people were injured and some building damage was documented.

Hayes et al. (2016) Tectonic summaries of magnitude 7 and greater earthquakes from 2000 to 2015, USGS Open-File Report 2016-1192. (5.2 MB PDF)