M5.8 Earthquake 280 km SW of Vaini, Tonga — August 17, 2021
2021-08-17 17:24:49 UTC (2021-08-17) · approx. 5:24 AM UTC-12 local
Felt by 2 people across nearby locations.
On August 17, 2021 at 17:24 UTC, a magnitude 5.8 intermediate depth earthquake struck 280 km SW of Vaini, Tonga, at a depth of 157.0 km and coordinates -23.0367°, -177.0395°. The earthquake was reported felt by 2 peopleacross nearby locations, with a maximum shaking intensity of Modified Mercalli Intensity (MMI) 3.1 (light). The USGS PAGER system issued a green alert level for this event, indicating no significant casualties or damage expected.
Physical scale: An earthquake of magnitude 5.8 releases seismic energy equivalent to roughly 8 kilotons of TNT. Empirical fault-scaling laws (Wells & Coppersmith, 1994) estimate the subsurface rupture length at approximately 6.1 km — a useful intuition for the size of the slip patch on the fault.
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
ShakeMap — predicted shaking intensity
Modeled ground-motion intensity contoured on the Modified Mercalli scale (MMI). Computed by the USGS from the moment-tensor solution and regional ground-motion prediction equations.
Source: U.S. Geological Survey ShakeMap. View interactive ShakeMap on USGS
Did You Feel It? — community-reported shaking
Aggregated felt-report intensity from 2 citizen responses to the USGS Did You Feel It? system. Each colored zone represents the average MMI from reports in that area.
Source: U.S. Geological Survey Did You Feel It?. View on USGS · submit your own report
Population exposure (USGS PAGER)
Estimated population that experienced each level of shaking. Based on the USGS PAGER rapid impact assessment, which combines ShakeMap output with global population grids.
| Shaking intensity (MMI) | Description | Population exposed |
|---|---|---|
| MMI 3 | weak | 5,736 |
Earthquake Details
-177.0395°E
Technical Information
Nearby Earthquakes (Last 7 Days)
Common Questions
How strong was the magnitude 5.8 earthquake near Vaini, Tonga?
The magnitude 5.8 earthquake that struck 280 km SW of Vaini, Tonga on August 17, 2021 at 17:24 UTC had a depth of 157.0 km. It was felt by 2 people with maximum shaking intensity of MMI 3.1 (light). For context, this was a moderate earthquake that could be widely felt.
Where did the earthquake occur?
The earthquake epicenter was located at -23.0367°, -177.0395°, which is 280 km SW of Vaini, Tonga. View all earthquakes in Tonga.
Were there aftershocks?
Aftershock activity is monitored continuously by the USGS. Aftershock sequences from magnitude 5.8 earthquakes can continue for days to weeks and gradually diminish over time.
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 5.8 event is significantly smaller than that historical record.
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Location
Authoritative source: USGS event page (event ID: us6000f7ki). All scientific values on this page are sourced verbatim from the USGS feed.
Cite this page: EarthquakeTracker.org. (2021, August 17, 2021). M5.8 Earthquake 280 km SW of Vaini, Tonga — August 17, 2021. Retrieved December 22, 2025 from https://www.earthquaketracker.org/earthquakes/event/us6000f7ki/