M5.1 Earthquake 125 km SE of Perryville, Alaska — August 18, 2020
2020-08-18 18:28:33 UTC (2020-08-18) · approx. 7:28 AM UTC-11 local
On August 18, 2020 at 18:28 UTC, a magnitude 5.1 shallow crustal earthquake struck 125 km SE of Perryville, Alaska, at a depth of 14.3 km and coordinates 55.0200°, -157.9389°. The USGS PAGER system issued a green alert level for this event, indicating no significant casualties or damage expected. The nearest populated place is Sand Point (population 976).
Physical scale: An earthquake of magnitude 5.1 releases seismic energy equivalent to roughly 674 metric tons of TNT. Empirical fault-scaling laws (Wells & Coppersmith, 1994) estimate the subsurface rupture length at approximately 2.0 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
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
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
-157.9389°E
Technical Information
Nearby Earthquakes (Last 7 Days)
Common Questions
How strong was the magnitude 5.1 earthquake near Perryville, Alaska?
The magnitude 5.1 earthquake that struck 125 km SE of Perryville, Alaska on August 18, 2020 at 18:28 UTC had a depth of 14.3 km. For context, this was a moderate earthquake that could be widely felt.
Where did the earthquake occur?
The earthquake epicenter was located at 55.0200°, -157.9389°, which is 125 km SE of Perryville, Alaska. The nearest populated place is Sand Point (population 976). View all earthquakes in Alaska.
Were there aftershocks?
Aftershock activity is monitored continuously by the USGS. Aftershock sequences from magnitude 5.1 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 5.1 event is significantly smaller than that historical record.
Authoritative source: USGS event page (event ID: ak020amc11hi). All scientific values on this page are sourced verbatim from the USGS feed.
Cite this page: EarthquakeTracker.org. (2020, August 18, 2020). M5.1 Earthquake 125 km SE of Perryville, Alaska — August 18, 2020. Retrieved December 22, 2025 from https://www.earthquaketracker.org/earthquakes/event/ak020amc11hi/