Earthquake swarms and sea-floor spreading

Abstract

More than 20 earthquake swarms that were detected from the mid-Atlantic ridge and from other parts of the mid-ocean ridge system during the past ten years appear to be related to tectonic, magmatic, or hydrothermal processes near ridge crests. Most of the larger earthquakes associated with the ridge system occur along fracture zones, and their mechanisms are characterized by a predominance of strike-slip faulting. Nearly all the earthquake swarms (sequences of events closely grouped in time and space but without one outstanding main shock) are restricted to the ridge crests themselves and are not found along fracture zones. Earthquakes on ridge crests are characterized by a large component of normal faulting, and many of the swarms may have a similar mechanism. The crestal zone of the mid-ocean ridge system is characterized by sea-floor spreading and by recent volcanism. This study increases the number of regions for which earthquake swarms are associated with areas of historic or recent volcanism; it also suggests a close connection (but not necessarily a direct causal one) between the two phenomena. Earthquake swarms may offer a means of detecting volcanic, hydrothermal, or magmatic processes in progress in submarine areas.