M4.2 Earthquake 55 km SW of Sitka, Alaska — November 23, 2020
2020-11-23 22:19:55 UTC (2020-11-23) · approx. 1:19 PM UTC-9 local
Felt by 126 people across surrounding communities.
On November 23, 2020 at 22:19 UTC, a magnitude 4.2 shallow crustal earthquake struck 55 km SW of Sitka, Alaska, at a depth of 18.5 km and coordinates 56.6987°, -135.9701°. The earthquake was reported felt by 126 peopleacross surrounding communities, with a maximum shaking intensity of Modified Mercalli Intensity (MMI) 2.4 (weak). The USGS PAGER system issued a green alert level for this event, indicating no significant casualties or damage expected. The nearest populated place is Craig (population 1,201).
Physical scale: An earthquake of magnitude 4.2 releases seismic energy equivalent to roughly 30 metric tons of TNT. Empirical fault-scaling laws (Wells & Coppersmith, 1994) estimate the subsurface rupture length at approximately 476 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
Nearest Populated Places
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 126 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 |
|---|
Earthquake Details
-135.9701°E
Technical Information
Nearby Earthquakes (Last 7 Days)
Common Questions
How strong was the magnitude 4.2 earthquake near Sitka, Alaska?
The magnitude 4.2 earthquake that struck 55 km SW of Sitka, Alaska on November 23, 2020 at 22:19 UTC had a depth of 18.5 km. It was felt by 126 people with maximum shaking intensity of MMI 2.4 (weak). For context, this was a light earthquake commonly felt near the epicenter.
Where did the earthquake occur?
The earthquake epicenter was located at 56.6987°, -135.9701°, which is 55 km SW of Sitka, Alaska. The nearest populated place is Craig (population 1,201). View all earthquakes in Alaska.
Were there aftershocks?
Aftershock activity is monitored continuously by the USGS. Aftershock sequences from magnitude 4.2 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 4.2 event is significantly smaller than that historical record.
Authoritative source: USGS event page (event ID: ak020f2thkhg). All scientific values on this page are sourced verbatim from the USGS feed.
Cite this page: EarthquakeTracker.org. (2020, November 23, 2020). M4.2 Earthquake 55 km SW of Sitka, Alaska — November 23, 2020. Retrieved January 14, 2022 from https://www.earthquaketracker.org/earthquakes/event/ak020f2thkhg/