Microearthquakes on the Galapagos Spreading Centre and the Seismicity of Fast‐Spreading Ridges

Abstract

Fast‐spreading centres such as the East Pacific Rise and the Galapagos spreading centre often show hiatuses hundreds of kilometres in length in WWSSN (World Wide Standardized Seismic Network) recorded seismic activity. Sonobuoys were deployed over a seismically quiet segment of the Galapagos spreading centre to measure the seismicity at close range. During 45 h of reliable recording time we detected an average of 15 microearthquakes per hour with a maximum of 80 microearthquakes in one hour. The events were part of a swarm which occurred within a few kilometres of the ridge crest axis. Magnitudes ranged from m=−0.4 to m=+0.8. Although fast‐spreading ridges have few large earthquakes, they may be the sites of significant microearthquake and earthquake swarm activity. Copyright © 1974, Wiley Blackwell. All rights reserved