M4.9 Earthquake 40 km NNW of Neiafu, Tonga — September 30, 2021
2021-09-30 15:37:55 UTC (2021-09-30) · approx. 3:37 AM UTC-12 local
Aftershock of the M5.3 mainshock.
On September 30, 2021 at 15:37 UTC, a magnitude 4.9 intermediate depth earthquake struck 40 km NNW of Neiafu, Tonga, at a depth of 79.8 km and coordinates -18.3347°, -174.1720°.
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.
This earthquake is part of an ongoing aftershock sequence following the magnitude 5.3 mainshock that occurred 12 days ago 26 km NW of Neiafu, 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
-174.1720°E
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Common Questions
How strong was the magnitude 4.9 earthquake near Neiafu, Tonga?
The magnitude 4.9 earthquake that struck 40 km NNW of Neiafu, Tonga on September 30, 2021 at 15:37 UTC had a depth of 79.8 km. For context, this was a light earthquake commonly felt near the epicenter.
Where did the earthquake occur?
The earthquake epicenter was located at -18.3347°, -174.1720°, which is 40 km NNW of Neiafu, Tonga. View all earthquakes in Tonga.
Were there aftershocks?
Aftershock activity is monitored continuously by the USGS. Aftershock sequences from magnitude 4.9 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 4.9 earthquake is an aftershock of the larger magnitude 5.3 mainshock that occurred earlier 26 km NW of Neiafu, 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 4.9 event is significantly smaller than that historical record.
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Authoritative source: USGS event page (event ID: us6000fsa1). All scientific values on this page are sourced verbatim from the USGS feed.
Cite this page: EarthquakeTracker.org. (2021, September 30, 2021). M4.9 Earthquake 40 km NNW of Neiafu, Tonga — September 30, 2021. Retrieved December 4, 2021 from https://www.earthquaketracker.org/earthquakes/event/us6000fsa1/