M3.9 Earthquake 180 km WSW of Adak, Alaska — February 19, 2021
2021-02-19 23:03:04 UTC (2021-02-19) · approx. 11:03 AM UTC-12 local
On February 19, 2021 at 23:03 UTC, a magnitude 3.9 shallow crustal earthquake struck 180 km WSW of Adak, Alaska, at a depth of 36.9 km and coordinates 51.1557°, -178.9693°.
Physical scale: An earthquake of magnitude 3.9 releases seismic energy equivalent to roughly 11 metric tons of TNT. Empirical fault-scaling laws (Wells & Coppersmith, 1994) estimate the subsurface rupture length at approximately 296 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 5.3 mainshock that occurred 19 days ago 151 km WSW of Adak, Alaska. Since the mainshock, the USGS has recorded 27 aftershocks in this area. Aftershock activity is expected to continue for days to weeks as stresses on surrounding faults redistribute.
Earthquake Details
-178.9693°E
Technical Information
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Common Questions
How strong was the magnitude 3.9 earthquake near Adak, Alaska?
The magnitude 3.9 earthquake that struck 180 km WSW of Adak, Alaska on February 19, 2021 at 23:03 UTC had a depth of 36.9 km. For context, this was a minor earthquake typically detected only by instruments.
Were there aftershocks?
Aftershock activity is monitored continuously by the USGS. Aftershock sequences from magnitude 3.9 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 3.9 earthquake is an aftershock of the larger magnitude 5.3 mainshock that occurred earlier 151 km WSW of Adak, Alaska. Aftershocks are smaller earthquakes triggered by stress changes from the mainshock.
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Understanding This Data
Magnitude 3.9 earthquakes are typically only recorded by instruments.
Authoritative source: USGS event page (event ID: us6000djjf). All scientific values on this page are sourced verbatim from the USGS feed.
Cite this page: EarthquakeTracker.org. (2021, February 19, 2021). M3.9 Earthquake 180 km WSW of Adak, Alaska — February 19, 2021. Retrieved May 4, 2021 from https://www.earthquaketracker.org/earthquakes/event/us6000djjf/