M4.8 Earthquake 174 km NE of Neiafu, Tonga — September 23, 2021
2021-09-23 18:32:31 UTC (2021-09-23) · approx. 6:32 AM UTC-12 local
Aftershock of the M5.3 mainshock.
On September 23, 2021 at 18:32 UTC, a magnitude 4.8 shallow crustal earthquake struck 174 km NE of Neiafu, Tonga, at a depth of 10.0 km and coordinates -17.3678°, -173.0187°.
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 5.3 mainshock that occurred 3 days ago 155 km SSE of Hihifo, Tonga. Since the mainshock, the USGS has recorded 0 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 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
Earthquake Details
-173.0187°E
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Common Questions
How strong was the magnitude 4.8 earthquake near Neiafu, Tonga?
The magnitude 4.8 earthquake that struck 174 km NE of Neiafu, Tonga on September 23, 2021 at 18:32 UTC had a depth of 10.0 km. For context, this was a light earthquake commonly felt near the epicenter.
Where did the earthquake occur?
The earthquake epicenter was located at -17.3678°, -173.0187°, which is 174 km NE of Neiafu, Tonga. View all earthquakes in Tonga.
Were there aftershocks?
Aftershock activity is monitored continuously by the USGS. Aftershock sequences from magnitude 4.8 earthquakes can continue for several days and gradually diminish over time.
Is this the same earthquake as the M5.3 one earlier?
No. This magnitude 4.8 earthquake is an aftershock of the larger magnitude 5.3 mainshock that occurred earlier 155 km SSE of Hihifo, Tonga. Aftershocks are smaller earthquakes triggered by stress changes from the mainshock.
Has Tonga had earthquakes this big before?
The largest recorded earthquake in Tonga was the M8.1 Tonga Trench earthquake of June 26, 1917. Today's magnitude 4.8 event is significantly smaller than that historical record.
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Authoritative source: USGS event page (event ID: us7000ff7i). All scientific values on this page are sourced verbatim from the USGS feed.
Cite this page: EarthquakeTracker.org. (2021, September 23, 2021). M4.8 Earthquake 174 km NE of Neiafu, Tonga — September 23, 2021. Retrieved December 3, 2021 from https://www.earthquaketracker.org/earthquakes/event/us7000ff7i/