Japan's Government Earthquake Research Committee said a magnitude-5.6 earthquake that struck Yamanashi Prefecture on June 26, 2026, likely originated within the Philippine Sea Plate [1].

This finding helps scientists understand the specific tectonic mechanisms driving seismic activity near Mount Fuji. Identifying whether a quake is an internal-plate event or a boundary rupture is critical for assessing future risks in the region.

The earthquake occurred at approximately 22:30 JST on June 26, 2026 [3]. The strongest shaking was recorded in Fujikawaguchiko Town, located in the Fuji Five Lakes area of eastern Yamanashi Prefecture, where the intensity reached Shindo 6-lower [2].

Following the event, the research committee, chaired by 小原, held an emergency meeting on June 27, 2026 [4]. During this session, the committee analyzed seismic data to determine the rupture's location. The analysis indicated that the quake was an internal-plate event, meaning the rupture occurred inside the Philippine Sea Plate itself rather than at the boundary where it meets the continental plate [1].

Geological data shows the Philippine Sea Plate is currently colliding with the continental plate. The committee said the seismic signatures of this specific event point to a rupture within the plate's interior [1].

Officials continue to monitor the area for aftershocks. The committee's focus remains on the interaction between these plates to better predict the behavior of the region's complex fault systems [1].

“The earthquake likely originated within the Philippine Sea Plate.”

The classification of this event as an internal-plate earthquake suggests that the stress accumulation within the Philippine Sea Plate is reaching a breaking point, independent of the primary subduction boundary. This adds a layer of complexity to the seismic profile of the Fuji Five Lakes region, as it indicates multiple potential sources of significant tremors beyond the well-known plate boundaries.