TOKYO, July 28 — A magnitude 5.6 earthquake struck 16 kilometers northeast of Tsunagi, Japan, at 08:08 UTC on July 28, according to the U.S. Geological Survey. The quake occurred at a depth of 10 kilometers, placing it in the shallow category that seismologists say typically produces stronger shaking at the surface than deeper events of the same magnitude. No tsunami warning was issued following the event, officials said.
The temblor struck in a region long accustomed to seismic activity. Records show at least 111 earthquakes of magnitude 5.0 or greater have occurred within roughly 300 kilometers of this location over the past two decades.
The largest among them was a magnitude 7.1 event in 2024. At magnitude 5.6, this is what seismologists classify as a moderate earthquake. Such events are capable of causing minor to moderate damage near the epicenter, though the precise extent of any damage or injuries from this particular quake was not immediately available.
Shallow earthquakes, those less than 70 kilometers deep, release their energy closer to the surface, which amplifies ground motion in populated areas. The USGS detected the event through its real-time global seismic monitoring network, which tracks earthquakes worldwide as they happen.
The network relies on a distributed array of seismometers that feed data to analysis centers, allowing scientists to determine location, depth, and magnitude within minutes of an event. Seismologists note that aftershocks are common following an earthquake of this size and may continue for days or even weeks. People in the affected area are generally advised to be prepared for further shaking, a standard precaution in earthquake-prone regions.
Japan sits at the convergence of four tectonic plates — the Pacific, Philippine Sea, Eurasian, and North American plates — making it one of the most seismically active countries on earth. The Pacific Plate subducts beneath the Okhotsk microplate along the Japan Trench, while the Philippine Sea Plate slides beneath the Eurasian Plate along the Nankai Trough. These subduction zones generate frequent earthquakes, some of them massive.
The 2011 Tohoku earthquake, magnitude 9.0, occurred along the Japan Trench and triggered a devastating tsunami. The depth of an earthquake is a critical factor in determining its potential for destruction.
Shallow events, those less than 70 kilometers deep, account for most damaging earthquakes because the seismic waves have less distance to travel before reaching the surface. A magnitude 5.6 quake at 10 kilometers depth, while moderate in energy release, can still rattle buildings and cause objects to fall, particularly in structures not designed to modern seismic codes. The magnitude scale is logarithmic, meaning each whole-number increase represents about 32 times more energy release.
A magnitude 6.0 earthquake releases roughly 32 times the energy of a magnitude 5.0. The 2024 magnitude 7.1 event in the same region released many hundreds of times more energy than today’s quake, underscoring the range of seismic threats this area faces.
