M4.0 Earthquake 153 km SSE of Chignik, Alaska — July 29, 2021
2021-07-29 23:38:15 UTC (2021-07-29) · approx. 1:38 PM UTC-10 local
On July 29, 2021 at 23:38 UTC, a magnitude 4.0 shallow crustal earthquake struck 153 km SSE of Chignik, Alaska, at a depth of 16.2 km and coordinates 55.1396°, -157.0834°.
Physical scale: An earthquake of magnitude 4.0 releases seismic energy equivalent to roughly 15 metric tons of TNT. Empirical fault-scaling laws (Wells & Coppersmith, 1994) estimate the subsurface rupture length at approximately 347 m — a useful intuition for the size of the slip patch on the fault.
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
-157.0834°E
Technical Information
Nearby Earthquakes (Last 7 Days)
Common Questions
How strong was the magnitude 4.0 earthquake near Chignik, Alaska?
The magnitude 4.0 earthquake that struck 153 km SSE of Chignik, Alaska on July 29, 2021 at 23:38 UTC had a depth of 16.2 km. For context, this was a light earthquake commonly felt near the epicenter.
Were there aftershocks?
Aftershock activity is monitored continuously by the USGS. Aftershock sequences from magnitude 4.0 earthquakes can continue for several days and gradually diminish over time.
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Understanding This Data
Magnitude 4.0 earthquakes are often felt but rarely cause damage.
Authoritative source: USGS event page (event ID: ak0219nos0s4). All scientific values on this page are sourced verbatim from the USGS feed.
Cite this page: EarthquakeTracker.org. (2021, July 29, 2021). M4.0 Earthquake 153 km SSE of Chignik, Alaska — July 29, 2021. Retrieved October 3, 2021 from https://www.earthquaketracker.org/earthquakes/event/ak0219nos0s4/