M8.2 Earthquake near 2021 Chignik, Alaska Earthquake — July 29, 2021
2021-07-29 06:15:49 UTC (2021-07-29) · approx. 7:15 PM UTC-11 local
Felt by 512 people across surrounding communities. Maximum shaking intensity MMI 7.4 (severe).
On July 29, 2021 at 06:15 UTC, a magnitude 8.2 shallow crustal earthquake struck near 2021 Chignik, Alaska Earthquake, at a depth of 35.0 km and coordinates 55.3635°, -157.8876°. The earthquake was reported felt by 512 peopleacross surrounding communities, with a maximum shaking intensity of Modified Mercalli Intensity (MMI) 7.4 (severe). The USGS PAGER system issued a yellow alert level for this event, indicating local impact possible. The nearest populated place is Sand Point (population 976).
Physical scale: An earthquake of magnitude 8.2 releases seismic energy equivalent to roughly 30.1 megatons of TNT. Empirical fault-scaling laws (Wells & Coppersmith, 1994) estimate the subsurface rupture length at approximately 274 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
What the Shaking Felt Like
At MMI 7.4 (severe), people in the most strongly affected areas would have experienced: Very strong shaking. Difficult to stand. Damage to weak structures; slight damage to well-built structures. Furniture broken. Fallen plaster and loose bricks.
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 512 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 |
|---|---|---|
| MMI 3 | weak | 153,758 |
| MMI 4 | light | 24,669 |
| MMI 5 | moderate | 1,487 |
| MMI 6 | strong | 145 |
| MMI 7 | very strong | 1,734 |
Earthquake Details
-157.8876°E
Technical Information
Nearby Earthquakes (Last 7 Days)
Common Questions
How strong was the magnitude 8.2 earthquake near 2021 Chignik, Alaska Earthquake?
The magnitude 8.2 earthquake that struck near 2021 Chignik, Alaska Earthquake on July 29, 2021 at 06:15 UTC had a depth of 35.0 km. It was felt by 512 people with maximum shaking intensity of MMI 7.4 (severe). For context, this was a strong earthquake capable of causing significant damage.
Where did the earthquake occur?
The earthquake epicenter was located at 55.3635°, -157.8876°, which is near 2021 Chignik, Alaska Earthquake. 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 8.2 earthquakes can continue for months to years 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 8.2 event is within one magnitude unit of that historical record.
Authoritative source: USGS event page (event ID: ak0219neiszm). All scientific values on this page are sourced verbatim from the USGS feed.
Cite this page: EarthquakeTracker.org. (2021, July 29, 2021). M8.2 Earthquake near 2021 Chignik, Alaska Earthquake — July 29, 2021. Retrieved April 15, 2026 from https://www.earthquaketracker.org/earthquakes/event/ak0219neiszm/