Reviewed by USGSAlaska4y ago
M2.5 earthquake 174 km SE of Chignik, Alaska
Monday, October 25, 2021, 23:28:04 UTC · 55.346°N, 156.179°W
A magnitude 2.5 earthquake struck 174 km SE of Chignik, Alaska on Monday, October 25, 2021, 23:28:04 UTC, at a depth of 37.7 km (shallow).
- Magnitude
- 2.5
- Minor · ml
- Depth
- 38 km
- Shallow
- Felt reports
- 0
- Did You Feel It?
- Est. shaking
- —
- No ShakeMap
- PAGER alert
- None
- Not issued
- Tsunami
- No flag
- USGS feed
Outlined circle: this earthquakeDashed circle: 50 km aftershock search area
In context
How big was it, and why here?
Energy released
85 kg of TNT
That is about 1/177,558 of the Hiroshima bomb. A magnitude 5.0 releases about 5,623 times more energy.
Tectonic setting
82 km
from the nearest mapped plate boundary, between the North American and Pacific plates. Earthquakes cluster along boundaries like this one, where plates collide, pull apart or slide past each other.
Depth: shallow
38 km
Shallow earthquakes (under 70 km) produce the strongest surface shaking for their size, so they are the ones most likely to cause damage near the epicenter.
Did You Feel It?
Where it was felt
No “Did You Feel It?” reports have been published for this event yet. If you felt it, you can add your report on the USGS website.
I felt it — report to USGS ↗USGS PAGER estimate
Who was exposed to shaking
USGS publishes PAGER impact estimates for significant earthquakes, usually within an hour. No PAGER estimate is available for this event.
After the main event
Aftershocks within 50 km
USGS lists 4 M2.5+ earthquakes within 50 km in the following 30 days; the largest was M3.9 on November 1, 2021. Most nearby activity right after a large earthquake is aftershocks, which usually become less frequent over days and weeks.
Regional history
Past M5+ earthquakes within 300 km
USGS lists 356 M5.0+ earthquakes within 300 km before this one (catalog from 1900; older records are less complete). The strongest:
- 8.21938 Semidi Islands, Alaska EarthquakeNovember 10, 1938 · 128 km W of this epicenter
- 8.22021 Chignik, Alaska EarthquakeJuly 29, 2021 · 108 km W of this epicenter
- 7.82020 Perryville, Alaska EarthquakeJuly 22, 2020 · 156 km W of this epicenter
- 7.62020 Sand Point, Alaska EarthquakeOctober 19, 2020 · 235 km W of this epicenter
- 7.454 km SE of Sand Point, AlaskaMay 31, 1917 · 238 km W of this epicenter
- 7.14 km ENE of Karluk, AlaskaNovember 7, 1912 · 273 km NE of this epicenter
- 7.0113 km ESE of Chignik, AlaskaMay 4, 1923 · 66 km NW of this epicenter
- 7.026 km SSE of Karluk, AlaskaDecember 6, 1999 · 249 km NE of this epicenter
History · NOAA
Deadliest earthquakes in this area
NOAA’s significant-earthquake database lists 11 damaging, deadly or tsunami-generating earthquakes within 300 km of this epicenter since 1700. The most severe:
- 1900M8.3
Kodiak Island
9 Oct 1900 · 256 km away · intensity VIII
Limited damage (under $1M)
- 1788M8.0
Unga Island
21 Jul 1788 · 269 km away · intensity VII
Limited damage (under $1M)tsunami
- 2020M7.8
Alaska
22 Jul 2020 · 156 km away · intensity VII
Limited damage (under $1M)tsunami
- 1970M6.0
Andreanof Islands
11 Mar 1970 · 277 km away · intensity V
Limited damage (under $1M)tsunami
- 1938M8.2
Alaska
10 Nov 1938 · 139 km away · intensity VI
tsunami
- 2021M8.2
Alaska Peninsula
29 Jul 2021 · 105 km away · intensity VIII
tsunami
NOAA NCEI Global Significant Earthquake Database. Historical figures are estimates; older records are incomplete.