The complex northern termination of the Tonga.Kermadec island arc is an excellent example of a tear in an oceanic plate. The research will study earthquake locations and focal mechanisms in this tectonically active area. The observations will be used to develop a comprehensive model of lithospheric structure and dynamics of plate interaction and will be compared with observations from other arc terminations. The research bears on fundamental questions of earthquake and tsunami risk in the Southwest Pacific and thus has application to the National Earthquake Hazard Reduction Program.