Reviewed by USGSAlaska104y ago
M6.5 earthquake 66 km S of Attu Station, Alaska
Sunday, July 22, 1923, 14:18:06 UTC · 52.251°N, 173.114°E
A magnitude 6.5 earthquake struck 66 km S of Attu Station, Alaska on Sunday, July 22, 1923, 14:18:06 UTC, at a depth of 25.0 km (shallow). It is the strongest earthquake within 300 km since an M6.7 on October 18, 1912.
- Magnitude
- 6.5
- Strong · mw
- Depth
- 25 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: 100 km aftershock search area
In context
How big was it, and why here?
Energy released
82 kilotons of TNT
That is about 5 times the Hiroshima bomb. It released about 172 times the energy of a magnitude 5.0.
Tectonic setting
61 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
25 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 100 km
USGS lists 1 M2.5+ earthquake within 100 km in the following 30 days; the largest was M6.4 on July 31, 1923. 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 9 M5.0+ earthquakes within 300 km before this one (catalog from 1900; older records are less complete). The strongest:
- 7.4151 km S of Attu Station, AlaskaSeptember 2, 1907 · 85 km S of this epicenter
- 7.0167 km WSW of Attu Station, AlaskaApril 10, 1909 · 149 km W of this epicenter
- 6.8129 km SSE of Attu Station, AlaskaNovember 13, 1911 · 72 km SE of this epicenter
- 6.78 km SE of Attu Station, AlaskaOctober 18, 1912 · 61 km N of this epicenter
- 6.6216 km WNW of Attu Station, AlaskaJanuary 6, 1906 · 240 km NW of this epicenter
- 6.3251 km SE of Attu Station, AlaskaDecember 14, 1916 · 221 km SE of this epicenter
- 6.2154 km S of Attu Station, AlaskaApril 29, 1913 · 89 km S of this epicenter
History · NOAA
Deadliest earthquakes in this area
NOAA’s significant-earthquake database lists 2 damaging, deadly or tsunami-generating earthquakes within 300 km of this epicenter since 1700. The most severe:
- 1909M7.8
Aleutian Islands
10 Apr 1909 · 132 km away
- 1898M7.6
Aleutian Islands: Near Islands
29 Jun 1898 · 81 km away
NOAA NCEI Global Significant Earthquake Database. Historical figures are estimates; older records are incomplete.