At some convergent boundaries, an oceanic plate collides with a continental plate. Oceanic crust tends to be denser and thinner than continental crust, so the denser oceanic crust gets bent and pulled under, or subducted, beneath the lighter and thicker continental crust. This forms what is called a subduction zone.
I would say that D is the most important reason ie to monitor the location and magnitude of seismic activity to attempt to find patterns which may lead to the ability to predict the next earthquake in the world though individual seismic stations probably monitor more the seismic activity in their own country mostly though perhaps not exclusively.
