M4.0 Earthquake 48 km NW of Nuku‘alofa, Tonga — August 9, 2020
2020-08-09 23:05:03 UTC (2020-08-09) · approx. 11:05 AM UTC-12 local
On August 9, 2020 at 23:05 UTC, a magnitude 4.0 intermediate depth earthquake struck 48 km NW of Nuku‘alofa, Tonga, at a depth of 158.1 km and coordinates -20.7765°, -175.4704°.
Physical scale: An earthquake of magnitude 4.0 releases seismic energy equivalent to roughly 15 metric tons of TNT. Empirical fault-scaling laws (Wells & Coppersmith, 1994) estimate the subsurface rupture length at approximately 347 m — 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 5.0 mainshock that occurred 17 days ago 47 km NW of Houma, 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.
Earthquake Details
-175.4704°E
Technical Information
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Common Questions
How strong was the magnitude 4.0 earthquake near Nuku‘alofa, Tonga?
The magnitude 4.0 earthquake that struck 48 km NW of Nuku‘alofa, Tonga on August 9, 2020 at 23:05 UTC had a depth of 158.1 km. For context, this was a light earthquake commonly felt near the epicenter.
Were there aftershocks?
Aftershock activity is monitored continuously by the USGS. Aftershock sequences from magnitude 4.0 earthquakes can continue for several days and gradually diminish over time.
Is this the same earthquake as the M5.0 one earlier?
No. This magnitude 4.0 earthquake is an aftershock of the larger magnitude 5.0 mainshock that occurred earlier 47 km NW of Houma, Tonga. Aftershocks are smaller earthquakes triggered by stress changes from the mainshock.
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Understanding This Data
Magnitude 4.0 earthquakes are often felt but rarely cause damage.
Authoritative source: USGS event page (event ID: us6000bens). All scientific values on this page are sourced verbatim from the USGS feed.
Cite this page: EarthquakeTracker.org. (2020, August 9, 2020). M4.0 Earthquake 48 km NW of Nuku‘alofa, Tonga — August 9, 2020. Retrieved October 21, 2020 from https://www.earthquaketracker.org/earthquakes/event/us6000bens/