LONDON, July 21 — A magnitude 5 earthquake struck the Mid-Indian Ridge at 03:17 UTC on Tuesday, the U.S. Geological Survey (USGS) reported. The quake occurred at a depth of 10 kilometres, making it a shallow event. No tsunami warning was issued.
For all the noise of a moderate tremor on a remote oceanic ridge, the salient point for seismologists is the depth: shallow earthquakes, those less than 70 km down, typically produce stronger shaking at the surface than deeper ones of the same magnitude.
A Seismically Active Stretch
The Mid-Indian Ridge is no stranger to such events. The USGS records show that at least 18 earthquakes of magnitude 5.0 or greater have occurred within roughly 300 km of this location over the past two decades. The strongest among them was a magnitude 5.7 in 2009.
Earthquakes in the magnitude 5 range are classified as moderate. They can cause minor to moderate damage near the epicentre, though in this case the epicentre lies far from populated land.
The USGS detected the event through its real-time global seismic monitoring network, a system that tracks ground motion worldwide.
Aftershocks and Advice
Seismologists note that aftershocks are common following an earthquake of this size. They may continue for days or even weeks. People in the affected area — which, given the remote ocean location, is essentially shipping traffic and research vessels — are generally advised to be prepared for further shaking.
The depth of 10 km is notably shallow. By contrast, many earthquakes at subduction zones occur at depths of 50 km or more.
The shallow depth means the energy release is concentrated nearer the surface, amplifying the shaking over a small area. For all the technical detail, the practical consequence is that any vessel or station in the immediate vicinity would have felt a sharp jolt rather than a rolling motion. The USGS data for this event will be refined in the coming days as more seismic stations report their readings.
No damage reports have been received, which is consistent with the location far at sea. The agency continues to monitor the ridge for further activity.
