Median Valley Seismology: The Mid-Atlantic Ridge near 45 N

Two ocean bottom seismographs have been operated on the Mid-Atlantic Ridge near 45° N. Earthquakes up to ML= 3·8 were observed in a total of eight days recording and the seismicity was found to be largely confined to the Median Valley. The observations are related to other geological and geophysical work in the area and to the teleseismically reported activity there during the last 10 years. A number of models of the structure and seismicity of the ridge axis are discussed. The most plausible model which can account for the observations indicates a magma chamber at a depth of about 3 km beneath the Median Valley floor.