Reviewed by USGSAlaska11y ago
M4.3 earthquake in Rat Islands, Aleutian Islands, Alaska
Wednesday, October 21, 2015, 07:45:52 UTC · 50.827°N, 179.186°E
A magnitude 4.3 earthquake struck in Rat Islands, Aleutian Islands, Alaska on Wednesday, October 21, 2015, 07:45:52 UTC, at a depth of 20.6 km (shallow).
- Magnitude
- 4.3
- Light · mb
- Depth
- 21 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
43 tons of TNT
That is about 1/354 of the Hiroshima bomb. A magnitude 5.0 releases about 11 times more energy.
Tectonic setting
30 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
21 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 2 M2.5+ earthquakes within 50 km in the following 30 days; the largest was M3.2 on November 12, 2015. 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 949 M5.0+ earthquakes within 300 km before this one (catalog from 1900; older records are less complete). The strongest:
- 8.71965 Western Aleutian Islands (Hawadax/Rat Islands) EarthquakeFebruary 4, 1965 · 58 km NW of this epicenter
- 8.31906 Western Aleutian Islands (Hawadax/Rat Islands) EarthquakeAugust 17, 1906 · 134 km NW of this epicenter
- 7.977 km WSW of Adak, AlaskaJune 10, 1996 · 236 km E of this epicenter
- 7.9Rat Islands, Aleutian Islands, AlaskaJune 23, 2014 · 118 km N of this epicenter
- 7.8Rat Islands, Aleutian Islands, AlaskaNovember 17, 2003 · 52 km NW of this epicenter
- 7.6Rat Islands, Aleutian Islands, AlaskaMarch 30, 1965 · 110 km SW of this epicenter
- 7.4265 km WSW of Adak, AlaskaFebruary 4, 1965 · 73 km NE of this epicenter
- 7.388 km WSW of Adak, AlaskaJuly 7, 1929 · 226 km E of this epicenter
History · NOAA
Deadliest earthquakes in this area
NOAA’s significant-earthquake database lists 13 damaging, deadly or tsunami-generating earthquakes within 300 km of this epicenter since 1700. The most severe:
- 1965M8.7
Aleutian Islands: Rat Islands
4 Feb 1965 · 58 km away · intensity VI
Under $1 million damagetsunami
- 1906M8.3
Aleutian Islands: Rat Islands
17 Aug 1906 · 134 km away
- 1905M7.9
Andreanof Islands
14 Feb 1905 · 160 km away
- 1996M7.9
Andreanof Islands
10 Jun 1996 · 236 km away · intensity VI
tsunami
- 2014M7.9
Aleutian Islands
23 Jun 2014 · 118 km away · intensity VI
tsunami
- 2003M7.8
Aleutian Islands: Rat Islands
17 Nov 2003 · 52 km away
tsunami
NOAA NCEI Global Significant Earthquake Database. Historical figures are estimates; older records are incomplete.