The earthquakes along the coasts of Asia and Australia are almost exclusively appearing along the plate boundaries. There's multiple plate boundaries in this regions, with lot of subduction going on, where the Australian, Pacific, Philippine, Eurasian plate, interact between each other, thus causing a lot of geologic activity. The constant movement of the plates causes lot of rocks to break deep into the crust, which in turn causes adjustments deep into the crust, and that results in the releasing of lot of force, manifested with strong vibrations, better known as earthquakes. The earthquakes can appear either on the land on in the sea/ocean, and they can have devastating consequences if they are strong ones.