Nojima Fault

Nojima Fault
by Reggaeman · CC BY-SA 3.0 · source
Name	Nojima Fault
Location	Awaji Island–Kobe region, Hyōgo Prefecture, Japan
Type	Strike-slip fault (left-lateral with oblique components)
Length km	~10
Displacement m	up to 6
Notable events	1995 Great Hanshin (Kobe) earthquake

Nojima Fault The Nojima Fault is a mapped active crustal fault on Awaji Island and the northern Awaji–Kobe area of Hyōgo Prefecture, Japan. It ruptured during the 1995 Great Hanshin (Kobe) earthquake and has since been the focus of intensive study by institutions such as the Geological Survey of Japan, Earthquake Research Committee (Japan), and international teams from the United States Geological Survey and universities including University of Tokyo and Columbia University. The fault is a key feature in understanding seismicity within the Nankai Trough–Japan Trench tectonic context and in regional hazard planning by the Hyōgo Prefectural Government and City of Kobe.

Geology and Structure

The Nojima Fault lies within the forearc region influenced by the subduction of the Philippine Sea Plate beneath the Eurasian Plate and adjacent interactions with the Pacific Plate; it accommodates strain transferred from large plate-boundary structures such as the Nankai megathrust and the Sagami Trough. Geological mapping by the Seismological Society of Japan and trenching investigations by teams from the National Research Institute for Earth Science and Disaster Resilience revealed a predominantly left-lateral strike-slip fault zone with oblique reverse components and a complex splays network cutting Quaternary deposits. Structural studies correlate surface rupture traces with subsurface imbricate thrusts imaged in seismic reflection profiles acquired by the Japan Agency for Marine-Earth Science and Technology and the Hydrographic and Oceanographic Department.

Seismic History

Historical seismicity in the Kobe–Awaji region includes large events recorded in archives maintained by the Imperial Household Agency and documented by scholars at the National Museum of Nature and Science. Paleoseismic trenching by international consortia including researchers from Caltech and University of California, Berkeley has identified multiple Holocene rupture horizons, correlating with regional sequences interpreted alongside catalogues from the International Seismological Centre and the Global Centroid Moment Tensor Project. Pre-instrumental events inferred from stratigraphy have been compared with instrumental records held by the Japan Meteorological Agency and catalogued in global compilations by the United States Geological Survey.

1995 Great Hanshin (Kobe) Earthquake

The fault produced major surface rupture during the magnitude 6.9 earthquake on 17 January 1995, an event extensively investigated by teams from Massachusetts Institute of Technology, Imperial College London, Institut de Physique du Globe de Paris, and the Chinese Academy of Sciences. The earthquake generated widespread urban collapse across Kobe, damage to infrastructure such as the Great Hanshin Expressway, and triggered swift emergency response coordinated by the Self-Defense Forces (Japan) and municipal authorities including the Kobe City Fire Department. Seismological analyses integrated strong-motion records from networks run by the National Research Institute for Earth Science and Disaster Resilience and the Kanazawa University seismic observatory to revise attenuation relationships used by insurers like Sompo Japan Insurance and policy planners at the Ministry of Land, Infrastructure, Transport and Tourism.

Surface Rupture and Displacement

Field mapping by the University of Hyōgo and international partners documented strike-parallel surface ruptures crossing farm fields, roads, and built structures, with net horizontal offsets up to several meters and localized vertical components. Measured displacements informed kinematic models developed at institutions such as University of California, Santa Barbara and Tohoku University, and were incorporated into finite-fault inversions by researchers at the Scripps Institution of Oceanography and the Centre National de la Recherche Scientifique. The rupture trace has been preserved in the Nojima Fault Preservation Museum area (managed in coordination with the Agency for Cultural Affairs), enabling direct comparison of coseismic slip with deeper rupture imaged by reflection surveys conducted by the Japan Oil, Gas and Metals National Corporation.

Monitoring and Research

Continuous and campaign monitoring on and around the fault employs dense GNSS arrays operated by the Geospatial Information Authority of Japan, borehole strainmeters from the International Centre for Earthquake Engineering Research (ICERR), and seismic networks maintained by the Japan Meteorological Agency and university groups such as Nagoya University. Interdisciplinary research programs funded by the Japan Society for the Promotion of Science and international grants from organizations like the National Science Foundation and the European Research Council focus on earthquake physics, rupture propagation, and site amplification linking observations to laboratory studies at facilities including the Rock and Ice Physics Laboratory (University of Tokyo). Collaborative projects also utilize remote sensing from JAXA satellites and LiDAR surveys supported by the Ministry of Education, Culture, Sports, Science and Technology (MEXT).

Hazards and Risk Mitigation

Insights from the Nojima Fault studies have informed seismic building codes enforced by the Ministry of Land, Infrastructure, Transport and Tourism and urban resilience initiatives by the Kobe City Government and Hyōgo Prefectural Government. Post-1995 reforms influenced retrofitting programs implemented through partnerships with engineering firms such as Kajima Corporation and Obayashi Corporation and resilience planning by international bodies like the United Nations Office for Disaster Risk Reduction. Ongoing hazard modeling by teams at Ritsumeikan University and Kyoto University integrates fault slip-rate estimates, paleoseismic recurrence from trenching studies, and ground-motion scenarios used by insurers, emergency managers, and infrastructure operators including the West Japan Railway Company and the Kansai Electric Power Company.

Category:Seismic faults of Japan