Reviewed by USGSAlaska5y ago
M4.0 earthquake 140 km SSE of Chignik, Alaska
Friday, October 15, 2021, 02:50:28 UTC · 55.222°N, 157.218°W
A magnitude 4.0 earthquake struck 140 km SSE of Chignik, Alaska on Friday, October 15, 2021, 02:50:28 UTC, at a depth of 38.8 km (shallow). The USGS PAGER alert is green: low likelihood of casualties and damage.
- Magnitude
- 4.0
- Light · ml
- Depth
- 39 km
- Shallow
- Felt reports
- 0
- Did You Feel It?
- Est. shaking
- II
- Weak (ShakeMap)
- PAGER alert
- Green
- Impact estimate
- Tsunami
- No flag
- USGS feed
Outlined circle: this earthquakeDashed circle: 50 km aftershock search areaColoured lines: estimated shaking intensity (USGS ShakeMap)
In context
How big was it, and why here?
Energy released
15 tons of TNT
That is about 1/998 of the Hiroshima bomb. A magnitude 5.0 releases about 32 times more energy.
Tectonic setting
96 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
39 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 populated area was estimated to feel noticeable shaking.
After the main event
Aftershocks within 50 km
USGS lists 8 M2.5+ earthquakes within 50 km in the following 30 days; the largest was M4.2 on October 17, 2021. Most nearby activity right after a large earthquake is aftershocks, which usually become less frequent over days and weeks.
- 3.0Alaska Peninsula4y ago · 9 km W of this epicenter
- 2.7134 km SE of Chignik, Alaska4y ago · 26 km NE of this epicenter
- 2.9106 km ESE of Perryville, Alaska4y ago · 37 km NW of this epicenter
- 2.6144 km SE of Perryville, Alaska4y ago · 8 km SW of this epicenter
- 2.6131 km SSE of Chignik, Alaska4y ago · 10 km N of this epicenter
- 3.0122 km SE of Chignik, Alaska5y ago · 48 km NE of this epicenter
- 3.0126 km SE of Perryville, Alaska5y ago · 28 km W of this epicenter
- 4.2137 km SE of Perryville, Alaska5y ago · 30 km SW of this epicenter
Regional history
Past M5+ earthquakes within 300 km
USGS lists 350 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 · 61 km W of this epicenter
- 8.22021 Chignik, Alaska EarthquakeJuly 29, 2021 · 45 km W of this epicenter
- 7.82020 Perryville, Alaska EarthquakeJuly 22, 2020 · 89 km W of this epicenter
- 7.62020 Sand Point, Alaska EarthquakeOctober 19, 2020 · 169 km SW of this epicenter
- 7.454 km SE of Sand Point, AlaskaMay 31, 1917 · 171 km W of this epicenter
- 7.190 km SE of King Cove, AlaskaMay 14, 1948 · 262 km W of this epicenter
- 7.0113 km ESE of Chignik, AlaskaMay 4, 1923 · 74 km N of this epicenter
- 7.071 km SE of King Cove, AlaskaMay 30, 1991 · 290 km W 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:
- 2020M7.8
Alaska
22 Jul 2020 · 89 km away · intensity VII
Limited damage (under $1M)tsunami
- 1938M8.2
Alaska
10 Nov 1938 · 78 km away · intensity VI
tsunami
- 2021M8.2
Alaska Peninsula
29 Jul 2021 · 41 km away · intensity VIII
tsunami
- 1788M8.0
Alaska Peninsula
6 Aug 1788 · 242 km away
tsunami
- 1906M7.6
Aleutian Islands
23 Dec 1906 · 274 km away
- 2020M7.6
Alaska
19 Oct 2020 · 169 km away · intensity IX
tsunami
NOAA NCEI Global Significant Earthquake Database. Historical figures are estimates; older records are incomplete.