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| Fuji River fault system | |
|---|---|
| Name | Fuji River fault system |
| Location | Shizuoka Prefecture, Yamanashi Prefecture, Nagano Prefecture, Mount Fuji |
| Coordinates | 35°N 138°E |
| Length | ~40–70 km |
| Type | Strike-slip and reverse-oblique |
| Status | Active |
| Notable events | 1707 Hōei earthquake (regional context), 1854 Ansei-Tōkai earthquake (regional context) |
Fuji River fault system
The Fuji River fault system is an active crustal fault complex in central Honshū that lies along the drainage of the Fuji River and adjacent piedmonts of Mount Fuji. It links geomorphic features across Suruga Bay, the Kiso Mountains, and the Southern Alps and plays a role in strain partitioning between the Philippine Sea Plate and the Eurasian Plate. The system influences basin evolution near Shizuoka City and Fujinomiya and is a focus for seismic hazard studies coordinated by agencies such as the Japan Meteorological Agency and the Geological Survey of Japan.
The fault system traverses the forearc and inner arc of central Japan where the Nankai Trough subduction of the Philippine Sea Plate beneath the Eurasian Plate produces complex deformation. It abuts major structures including the Itoigawa-Shizuoka Tectonic Line, the Suruga Trough, and the Median Tectonic Line domain, and interacts with volcanic edifices such as Mount Hakone and Mount Fuji. Regional uplift, sedimentation in the Fuji River basin, and Quaternary terraces reflect activity that is contemporaneous with late Pleistocene and Holocene geomorphic change documented by the University of Tokyo and the National Institute of Advanced Industrial Science and Technology.
The system comprises multiple strands with strike-slip to oblique-reverse motion, including a western strand near the Abe River fan, a central strand aligned with the Fuji River channel, and an eastern strand approaching Suruga Bay. Segmentation is defined by bends, step-overs, and relay ramps that connect to faults mapped by the Geospatial Information Authority of Japan. Individual segments range from a few kilometers to tens of kilometers in length and cut Pleistocene terraces, Holocene alluvium, and volcanic deposits from Mount Fuji and older cones of the Mount Ashitaka group.
Tectonic evolution of the fault system reflects interplay between subduction-related compression and lateral extrusion driven by the Pacific Plate and the North American Plate interactions in northern Honshū. Paleogeographic reconstructions link episodes of activity to regional events such as the 1707 Hōei earthquake and the 1854 Ansei-Tōkai earthquake, though these events were dominated by subduction interface rupture. Uplift rates inferred from marine terraces and fluvial terraces near Numazu and Shimizu Port indicate late Quaternary deformation consistent with ongoing shortening and right-lateral shear accommodated along the system.
Instrumental seismicity catalogues maintained by the Japan Meteorological Agency and the National Research Institute for Earth Science and Disaster Resilience record microseismicity beneath the basin and along mapped faults. Historical accounts from the Edo period and modern seismic networks attribute felt intensities in Shizuoka Prefecture and Yamanashi Prefecture to both crustal and subduction earthquakes, complicating attribution. Notable nearby earthquakes that inform recurrence models include events recorded in the 18th and 19th centuries and local earthquakes in the 20th century detected by the Hi-net seismic array.
Trenching studies conducted by teams from the University of Tokyo, Tohoku University, and the National Institute of Advanced Industrial Science and Technology reveal stratigraphic evidence for multiple Holocene surface-rupturing events. Radiocarbon dating of organic layers and tephrochronology tied to Mount Fuji and Aso tephra provide age control for paleoearthquakes. Estimated slip rates vary by segment but commonly fall in the range of millimeters per year, derived from offset terraces, channel migrations, and cumulative displacement tables compiled by the Geological Survey of Japan. These rates inform probabilistic rupture models used in seismic hazard assessments by the Building Research Institute.
Seismic hazard maps produced by the Cabinet Office (Japan) and the Japan Seismic Hazard Information Station incorporate the fault system into scenario earthquakes that affect Tokyo Metropolitan Area supply chains and transportation corridors such as the Tōkaidō Main Line and the Tōkaidō Shinkansen. Urban areas including Fujinomiya, Fuji City, and Shizuoka City face combined hazards of ground shaking, liquefaction in alluvial plains, and secondary hazards from dam and road disruptions. Mitigation measures promoted by municipal governments and the Ministry of Land, Infrastructure, Transport and Tourism include land-use zoning, seismic retrofitting of lifeline structures, early warning integrations with the Japan Meteorological Agency earthquake early warning system, and community preparedness programs run by local fire departments and municipal authorities.
Investigations employ a multidisciplinary toolkit: high-resolution mapping by the Geospatial Information Authority of Japan, airborne LiDAR surveys by the Remote Sensing Technology Center of Japan, shallow trenching and stratigraphic logging, radiocarbon dating at facilities like the Institute for Cosmic Ray Research, and geodetic measurements using continuous GNSS networks maintained by the Geospatial Information Authority of Japan and campaign GPS surveys by university teams. Active-source seismic reflection and borehole logging complement ambient noise tomography from the Hi-net and dense temporary deployments. Data integration supports fault rupture simulations using physics-based codes developed at institutions such as the Earthquake Research Institute, University of Tokyo.
Category:Seismic faults of Japan