Reviewed by USGSAlaska3y ago
M2.5 earthquake 85 km S of False Pass, Alaska
Thursday, September 21, 2023, 17:12:55 UTC · 54.084°N, 163.468°W
A magnitude 2.5 earthquake struck 85 km S of False Pass, Alaska on Thursday, September 21, 2023, 17:12:55 UTC, at a depth of 35.0 km (shallow).
- Magnitude
- 2.5
- Minor · ml
- Depth
- 35 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
99 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
35 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 M3.6 on October 19, 2023. 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 457 M5.0+ earthquakes within 300 km before this one (catalog from 1900; older records are less complete). The strongest:
- 8.6The 1946 Unimak Island, Alaska EarthquakeApril 1, 1946 · 78 km SE of this epicenter
- 7.62020 Sand Point, Alaska EarthquakeOctober 19, 2020 · 256 km E of this epicenter
- 7.454 km SE of Sand Point, AlaskaMay 31, 1917 · 252 km NE of this epicenter
- 7.22023 Sand Point, Alaska EarthquakeJuly 16, 2023 · 179 km E of this epicenter
- 7.190 km SE of King Cove, AlaskaMay 14, 1948 · 160 km E of this epicenter
- 7.139 km S of Akutan, AlaskaMarch 22, 1957 · 155 km W of this epicenter
- 7.071 km SE of King Cove, AlaskaMay 30, 1991 · 132 km NE of this epicenter
- 7.0203 km SSE of Unalaska, AlaskaAugust 22, 1940 · 253 km SW of this epicenter
History · NOAA
Deadliest earthquakes in this area
NOAA’s significant-earthquake database lists 10 damaging, deadly or tsunami-generating earthquakes within 300 km of this epicenter since 1700, which together caused about 169 recorded deaths. The most severe:
- 1946M8.6
Unimak Island
1 Apr 1946 · 78 km away · intensity VI
168 deaths$26 million damagetsunami
- 2023M7.2
Alaska Peninsula
16 Jul 2023 · 181 km away · intensity VI
1 deathtsunami
- 1965M6.5
Aleutian Islands: Fox Islands
2 Jul 1965 · 294 km away
Limited damage (under $1M)tsunami
- 1788M8.0
Alaska Peninsula
6 Aug 1788 · 189 km away
tsunami
- 2020M7.6
Alaska
19 Oct 2020 · 256 km away · intensity IX
tsunami
- 1948M7.5
Alaska Peninsula
14 May 1948 · 167 km away
NOAA NCEI Global Significant Earthquake Database. Historical figures are estimates; older records are incomplete.