M4.5 Earthquake 87 km SSW of Nikolski, Alaska — October 20, 2023
2023-10-20 19:39:39 UTC (2023-10-20) · approx. 8:39 AM UTC-11 local
On October 20, 2023 at 19:39 UTC, a magnitude 4.5 shallow crustal earthquake struck 87 km SSW of Nikolski, Alaska, at a depth of 20.9 km and coordinates 52.2323°, -169.4305°. This earthquake was detected by 101 seismic stations with good location accuracy and was assigned a USGS significance rating of 312, placing it among routine seismic activity.
Physical scale: An earthquake of magnitude 4.5 releases seismic energy equivalent to roughly 85 metric tons of TNT. Empirical fault-scaling laws (Wells & Coppersmith, 1994) estimate the subsurface rupture length at approximately 767 m — a useful intuition for the size of the slip patch on the fault.
The epicenter is located in Alaska, a region characterized by Pacific Plate subduction beneath the North American Plate, producing frequent megathrust and crustal earthquakes along the Aleutian arc. The nearest mapped fault system is the Aleutian megathrust. View all earthquakes in Alaska.
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
Earthquake Details
-169.4305°E
Technical Information
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Common Questions
How strong was the magnitude 4.5 earthquake near Nikolski, Alaska?
The magnitude 4.5 earthquake that struck 87 km SSW of Nikolski, Alaska on October 20, 2023 at 19:39 UTC had a depth of 20.9 km. For context, this was a light earthquake commonly felt near the epicenter.
Where did the earthquake occur?
The earthquake epicenter was located at 52.2323°, -169.4305°, which is 87 km SSW of Nikolski, Alaska. View all earthquakes in Alaska.
Were there aftershocks?
Aftershock activity is monitored continuously by the USGS. Aftershock sequences from magnitude 4.5 earthquakes can continue for several days and gradually diminish over time.
Has Alaska had earthquakes this big before?
The largest recorded earthquake in Alaska was the M9.2 Great Alaska earthquake of March 27, 1964. Today's magnitude 4.5 event is significantly smaller than that historical record.
Authoritative source: USGS event page (event ID: us6000lh09). All scientific values on this page are sourced verbatim from the USGS feed.
Cite this page: EarthquakeTracker.org. (2023, October 20, 2023). M4.5 Earthquake 87 km SSW of Nikolski, Alaska — October 20, 2023. Retrieved December 26, 2023 from https://www.earthquaketracker.org/earthquakes/event/us6000lh09/