M4.0 Earthquake 257 km WSW of Adak, Alaska — September 21, 2021
2021-09-21 18:48:39 UTC (2021-09-21) · approx. 6:48 AM UTC+12 local
On September 21, 2021 at 18:48 UTC, a magnitude 4.0 intermediate depth earthquake struck 257 km WSW of Adak, Alaska, at a depth of 106.2 km and coordinates 51.4661°, 179.7056°.
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.
Earthquake Details
179.7056°E
Technical Information
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Common Questions
How strong was the magnitude 4.0 earthquake near Adak, Alaska?
The magnitude 4.0 earthquake that struck 257 km WSW of Adak, Alaska on September 21, 2021 at 18:48 UTC had a depth of 106.2 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.
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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: us7000fe4u). All scientific values on this page are sourced verbatim from the USGS feed.
Cite this page: EarthquakeTracker.org. (2021, September 21, 2021). M4.0 Earthquake 257 km WSW of Adak, Alaska — September 21, 2021. Retrieved December 3, 2021 from https://www.earthquaketracker.org/earthquakes/event/us7000fe4u/