M4.9 Earthquake south of Tonga — July 27, 2026

On July 27, 2026 at 01:34 UTC, a magnitude 4.9 shallow crustal earthquake struck south of Tonga, at a depth of 10.0 km and coordinates -24.5389°, -175.2032°. This earthquake was detected by 40 seismic stations with good location accuracy and was assigned a USGS significance rating of 369, placing it among routine seismic activity.

Physical scale: An earthquake of magnitude 4.9 releases seismic energy equivalent to roughly 338 metric tons of TNT. Empirical fault-scaling laws (Wells & Coppersmith, 1994) estimate the subsurface rupture length at approximately 1.4 km — a useful intuition for the size of the slip patch on the fault.

Active aftershock sequence: This earthquake is the mainshock of an ongoing aftershock sequence. In the 2 hours since the mainshock, the USGS has recorded 5 aftershocks within 20 km of the epicenter, including 5 of magnitude 3.0 or greater. The strongest aftershock was a magnitude 5.1 event 1 hour ago. Aftershock sequences from mainshocks of magnitude 4.9 typically continue for several days and gradually diminish over time, though occasional larger aftershocks remain possible.

The epicenter is located in Tonga, a region characterized by the Tonga-Kermadec subduction zone, where the Pacific Plate descends at up to 240 mm per year — the fastest plate convergence on Earth. The nearest mapped fault system is the Tonga Trench. View all earthquakes in Tonga.

Learn more: Magnitude scale · Aftershock sequences