Microearthquakes near the eastern end of St Paul's Fracture Zone

Abstract

Summary. Four ocean-bottom seismographs were deployed near the eastern end of the St Paul's Fracture Zone in 1974 December. Microearthquakes were observed both along the fracture zone and in the median valley of the Mid-Atlantic Ridge. Seventy-six of them have been located and reliable depths obtained for 51. The range of depths observed suggests that the thickness of the lithosphere close to the ridge axis is 7 km. The absence of earthquakes on the ridge axis between 1 and 5 km depth may be the result of a highly cracked crust and thus indicates the depth to which hydrothermal fluids penetrate.