Hadal trenches uniquely preserve exceptional sedimentary archives of past geological events, yet their depositional processes remain poorly constrained. The Japan Trench captures complex earthquake-triggered event beds that record repeated sediment-gravity flows that deliver terrigenous and biogenic material into the trench, influencing both paleoseismic reconstruction and deep-sea carbon cycling on multi-millennial timescales. Classical event stratigraphy treats these event beds as the product of a brief, isochronous process. This study aims to build on this concept to enable the documentation of relative depositional timing within a single event bed. Within four well documented historical earthquake-triggered beds recovered during IODP Expedition 386 and linked to megathrust earthquakes (CE 2011 Tohoku-Oki, CE 1454 Kyotoku, CE 869 Jogan, and ~2.3 ka), we develop a systematic, facies-based framework to identify event-internal characteristics. This integrated approach resolves sedimentary structures—physical, chemical and biogenic characteristics—by combining visual core description with high-resolution 2D and 3D imaging (X-ray computed tomography and X-ray radiography), grain-size measurements, and geochemical datasets (X-ray fluorescence). Six event-internal facies (F1–F6), bounded by hemipelagic facies (F0), form a fining-upward sequence that records the shift from high-energy, non-cohesive, bedload-dominated flows to low-energy, cohesive, suspension-dominated deposition. This shift is marked by a 32 µm grain-size threshold that separates coarse-grained (F1–F3; >32 µm) from fine-grained (F4–F6;