M4.8 Earthquake 2 km SSW of Honmachi, Japan — March 17, 2025

On March 17, 2025 at 20:00 UTC, a magnitude 4.8 shallow crustal earthquake struck 2 km SSW of Honmachi, Japan, at a depth of 20.0 km and coordinates 32.4841°, 130.5885°. This earthquake was detected by 82 seismic stations with excellent location accuracy and was assigned a USGS significance rating of 354, placing it among routine seismic activity.

Physical scale: An earthquake of magnitude 4.8 releases seismic energy equivalent to roughly 239 metric tons of TNT. Empirical fault-scaling laws (Wells & Coppersmith, 1994) estimate the subsurface rupture length at approximately 1.2 km — a useful intuition for the size of the slip patch on the fault.

This earthquake is part of an ongoing aftershock sequence following the magnitude 5.4 mainshock that occurred 14 hours ago 11 km N of Tsunagi, Japan. Since the mainshock, the USGS has recorded 4 aftershocks in this area. Aftershock activity is expected to continue for days to weeks as stresses on surrounding faults redistribute.

The epicenter is located in Japan, a region characterized by the intersection of four tectonic plates — Pacific, Philippine Sea, Eurasian, and North American — creating multiple subduction zones. The nearest mapped fault system is the Japan Trench. View all earthquakes in Japan.

Learn more: Magnitude scale · Aftershock sequences