The 2015 Magnitude 7.0 Earthquake on the Southern Mid-Atlantic Ridge

The southern Mid-Atlantic Ridge forms a divergent tectonic boundary separating the South American and African plates. This segment of the global mid-ocean ridge system exhibits seafloor spreading rates of approximately 3–4 cm per year, producing new oceanic crust through basaltic volcanism and normal faulting. The ridge axis lies at depths of 2,500–3,500 m, offset by transform faults that accommodate lateral plate motion. On 17 June 2015 at 12:51 UTC, a magnitude 7.0 earthquake occurred at a focal depth of 10 km along the southern Mid-Atlantic Ridge. The event was centered directly on the ridge axis and represents the sole magnitude 7.0 or greater earthquake recorded in the region since 1 January 2000. Its shallow depth and strike-slip to normal-faulting mechanism are consistent with extensional stresses at a slow-spreading ridge. The Mid-Atlantic Ridge was first recognized as a continuous submarine feature during 19th-century sounding expeditions. Detailed bathymetric mapping by Bruce Heezen and Marie Tharp in the 1950s revealed its central rift valley and fracture zones, providing key evidence for seafloor spreading and plate tectonics. Modern multibeam sonar and satellite altimetry have refined the ridge’s segmentation, confirming persistent transform offsets and episodic volcanic activity. Seismic monitoring indicates that large events remain infrequent on this portion of the ridge. The 2015 earthquake released strain accumulated over decades of plate divergence without generating a tsunami, owing to its remote oceanic location and moderate energy release. Post-event studies using hydroacoustic and teleseismic data confirmed rupture propagation along a north–south trending fault plane aligned with the ridge axis. Ongoing geophysical surveys continue to monitor microseismicity and crustal accretion along the southern Mid-Atlantic Ridge, contributing to improved models of oceanic plate boundary processes.

References

USGS Earthquake Catalog (event parameters)
NOAA National Centers for Environmental Information (ridge bathymetry)
National Geographic Society archives (historical ridge mapping)