TSUNAGI, Japan, July 29 — A magnitude 5.4 earthquake struck 11 kilometres north of this town in southern Japan at 13:19 UTC on Wednesday, at a depth of just 10 kilometres, the U.S. Geological Survey (USGS) reported. No tsunami warning was issued. At least two people have so far reported feeling the shaking, though that number is likely to rise as reports come in from the region.
The quake was a shallow event. Shallow earthquakes — those less than 70 kilometres deep — typically produce stronger shaking at the surface than deeper ones of the same magnitude, because less of the seismic energy dissipates before it reaches the ground.
At 10 kilometres down, this one is firmly in that category. Earthquakes in the magnitude 5 range are classified as moderate; they can cause minor to moderate damage close to the epicentre, especially in areas with less resilient construction. The area around Tsunagi is no stranger to the ground moving.
The USGS records show that within about 300 kilometres of this spot, at least 114 earthquakes of magnitude 5.0 or greater have occurred over the past two decades. The largest in that period was a magnitude 7.1 event in 2024 — the kind of earthquake that can cause serious damage and widespread shaking across a region.
The new quake is significantly smaller but still a reminder of the active tectonics beneath Japan. Seismologists point out that aftershocks are common following an earthquake of this size. Smaller tremors may continue for days or even weeks.
People in the affected area are generally advised to be prepared for further shaking — clear advice, but the kind that can feel abstract until the ground actually moves again. The USGS detected Wednesday’s event through its real-time global seismic monitoring network, which picks up tremors within minutes and feeds the data to scientists and the public worldwide. How does a shallow quake produce such different shaking compared with a deeper one?
The science behind it is straightforward. Seismic waves radiate from the rupture point, called the hypocenter.
When that point is only ten kilometres down, the waves travel a short distance through rock before reaching the surface, carrying more of their original energy. At greater depths — say 50 or 100 kilometres — the waves lose energy as they travel through denser, hotter material, so the surface shaking is weaker for the same magnitude. That’s a key reason why this 5.4, while modest on the scale, could still be felt by people nearby and possibly cause some minor damage to older buildings.
For now, the event is a data point in a long record of seismic activity. The USGS will continue to monitor the region, and anyone in the vicinity should expect that the ground might not be done moving yet.
