This project will deploy an array of 14 three-component ocean- bottom seismometers to record earthquakes for a period of about eight weeks at two sites along the northern Mid-Atlantic Ridge. The objectives are to: (1) locate the hypocenters of earthquakes within the median valley; (2) conduct source mechanism studies of located earthquakes; (3) invert P and S wave travel time and attenuation differences; and (4) define the relationships among earthquakes locations and source characteristics, and structural heterogeneity to segment length, median valley width, axial topographic relief and mantle Bouguer anomaly.