On this map of earthquakes near Japan,why do shallow earthquakes occur to the east and deeper earthquakes occur to the west?

Question

Quizplus · Accepted Answer

The subduction zone dips to the west, meaning that the tectonic plate to the east is being forced downward into the mantle at a shallow angle, causing shallower earthquakes to occur there. As the plate descends deeper into the mantle towards the west, more pressure and heat build up, resulting in deeper earthquakes occurring in that region.

On This Map of Earthquakes near Japan,why Do Shallow Earthquakes