Microearthquake Study of the Mid-Atlantic Ridge near 37° N, using Sonobuoys

IN view of the successful use of telemetering radio sonobuoys for detecting and locating microearthquakes in the Gulf of California¹, we carried out a similar survey of the Mid-Atlantic Ridge, in the region near latitude 37° N, during May and June of this year. Our object was to study the level of distribution of seismicity; in particular, we hoped to locate some earthquakes sufficiently accurately that we could associate them with local physiographic features, and draw conclusions about the present tectonic activity of this section of the ridge. Teleseismic study of the mid-ocean ridge suffers from two basic limitations: the epicentral locations are not sufficiently accurate to allow more than a general correlation of seismic activity with the median rift (where present) and with the transform faults offsetting the ridge segments², and it is not generally possible to locate earthquakes of magnitude less than about 4 (ref. 3). Ocean bottom seismometers have also been used to study ridge seismicity, but the results to date have been fairly limited.