M5.4 Earthquake 142 km WSW of Adak, Alaska — September 21, 2024
2024-09-21 17:21:19 UTC (2024-09-21) · approx. 5:21 AM UTC-12 local
Felt by 5 people across nearby locations.
On September 21, 2024 at 17:21 UTC, a magnitude 5.4 shallow crustal earthquake struck 142 km WSW of Adak, Alaska, at a depth of 44.5 km and coordinates 51.2868°, -178.4612°. The earthquake was reported felt by 5 peopleacross nearby locations, with a maximum shaking intensity of Modified Mercalli Intensity (MMI) 2.9 (weak). The USGS PAGER system issued a green alert level for this event, indicating no significant casualties or damage expected. This earthquake was detected by 299 seismic stations with excellent location accuracy and was assigned a USGS significance rating of 450, placing it among routine seismic activity.
Physical scale: An earthquake of magnitude 5.4 releases seismic energy equivalent to roughly 2 kilotons of TNT. Empirical fault-scaling laws (Wells & Coppersmith, 1994) estimate the subsurface rupture length at approximately 3.2 km — 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
Did You Feel It? — community-reported shaking
Aggregated felt-report intensity from 5 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
-178.4612°E
Technical Information
Nearby Earthquakes (Last 7 Days)
Common Questions
How strong was the magnitude 5.4 earthquake near Adak, Alaska?
The magnitude 5.4 earthquake that struck 142 km WSW of Adak, Alaska on September 21, 2024 at 17:21 UTC had a depth of 44.5 km. It was felt by 5 people with maximum shaking intensity of MMI 2.9 (weak). For context, this was a moderate earthquake that could be widely felt.
Where did the earthquake occur?
The earthquake epicenter was located at 51.2868°, -178.4612°, which is 142 km WSW of Adak, Alaska. View all earthquakes in Alaska.
Were there aftershocks?
Aftershock activity is monitored continuously by the USGS. Aftershock sequences from magnitude 5.4 earthquakes can continue for days to weeks 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 5.4 event is significantly smaller than that historical record.
Authoritative source: USGS event page (event ID: us6000ntia). All scientific values on this page are sourced verbatim from the USGS feed.
Cite this page: EarthquakeTracker.org. (2024, September 21, 2024). M5.4 Earthquake 142 km WSW of Adak, Alaska — September 21, 2024. Retrieved July 17, 2026 from https://www.earthquaketracker.org/earthquakes/event/us6000ntia/