Complex sentence: The epicenter of this earthquake lies just to the west of the Japan Trench, the surface expression of the west-dipping subduction zone that forms part of the convergent boundary between the Pacific and Eurasian plates.
Split into simpler sentences: The epicenter of lies just to the west of the Japan Trench, the surface expression of the west-dipping subduction zone. The trench forms part of the convergent boundary between the Pacific and Eurasian plates.