Reviewed by USGSAlaska104y ago
M6.4 earthquake 124 km SSW of Attu Station, Alaska
Tuesday, July 31, 1923, 15:07:59 UTC · 51.823°N, 172.458°E
A magnitude 6.4 earthquake struck 124 km SSW of Attu Station, Alaska on Tuesday, July 31, 1923, 15:07:59 UTC, at a depth of 15.0 km (shallow). It is the strongest earthquake within 300 km since an M6.5 on July 22, 1923.
- Magnitude
- 6.4
- Strong · mw
- Depth
- 15 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 earthquake
In context
How big was it, and why here?
Energy released
60 kilotons of TNT
That is about 4 times the Hiroshima bomb. It released about 126 times the energy of a magnitude 5.0.
Tectonic setting
2 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
15 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 has not published any M2.5+ earthquake within 100 km in the 30 days after this event.
Regional history
Past M5+ earthquakes within 300 km
USGS lists 10 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 · 43 km SE of this epicenter
- 7.0167 km WSW of Attu Station, AlaskaApril 10, 1909 · 115 km NW of this epicenter
- 6.8129 km SSE of Attu Station, AlaskaNovember 13, 1911 · 89 km E of this epicenter
- 6.78 km SE of Attu Station, AlaskaOctober 18, 1912 · 121 km NE of this epicenter
- 6.6216 km WNW of Attu Station, AlaskaJanuary 6, 1906 · 238 km NW of this epicenter
- 6.566 km S of Attu Station, AlaskaJuly 22, 1923 · 65 km NE of this epicenter
- 6.3251 km SE of Attu Station, AlaskaDecember 14, 1916 · 251 km E 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 · 175 km away
- 1898M7.6
Aleutian Islands: Near Islands
29 Jun 1898 · 37 km away
NOAA NCEI Global Significant Earthquake Database. Historical figures are estimates; older records are incomplete.