A Deep focus earthquakes is one that occurs deeper beneath the subduction zone called Wadati-Benioff zone having a focus greater than 300 km deep and magnitudes greater than 6, Because of these, they can only be measured using the Moment Magnitude scale which can measure earthquakes with magnitude over 10
Here there is a forceful collision of the tectonic plates as they slide over each other within the continental and oceanic plates boundaries causing the release of great energy,with extreme heat and pressure causing the rocks to flow instead of breaking and faulting of the rocks
Deep focus earthquakes are very dangerous although occurring 20 - 30 years along a fault line are responsible for the many destructive tsunamis that happen.
That is true that is a plate boundary that most earth quakes happen and most of them are low level earth quakes and very rarely are there big earth quakes
