Ocean-bottom seismograph observations on the Mid-Atlantic Ridge near 45 N

This paper describes the results obtained from the deployment of an array of ocean-bottom seismographs on the Mid-Atlantic Ridge near 45° N. Seismicity is restricted to a zone only 5 km wide near the centre of the Median Valley. The large scatter of epicentres determined using teleseismic data can be reconciled with this zone. The observed activity includes aftershock and swarm-like sequences but in terms of b value these, and teleseismically observed events, belong to the same population. The results are in agreement with a caldera collapse model of the Median Valley with movement restricted to the innermost faults.