M3.1 earthquake 123 km SE of Atka, Alaska

Monday, September 26, 2011, 13:12:46 UTC · 51.536°N, 172.751°W

A magnitude 3.1 earthquake struck 123 km SE of Atka, Alaska on Monday, September 26, 2011, 13:12:46 UTC, at a depth of 20.0 km (shallow).

Magnitude: 3.1; Minor · ml
Depth: 20 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

674 kg of TNT

That is about 1/22,353 of the Hiroshima bomb. A magnitude 5.0 releases about 708 times more energy.

Tectonic setting

54 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

20 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 6 M2.5+ earthquakes within 50 km in the following 30 days; the largest was M4.6 on October 23, 2011. Most nearby activity right after a large earthquake is aftershocks, which usually become less frequent over days and weeks.

Time after the mainshock on a logarithmic scale (first hours stretched), magnitude on the vertical axis. M2.5+ events from USGS.

Regional history

Past M5+ earthquakes within 300 km

USGS lists 845 M5.0+ earthquakes within 300 km before this one (catalog from 1900; older records are less complete). The strongest:

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, which together caused about 2 recorded deaths. The most severe:

1957M8.6
Alaska
9 Mar 1957 · 199 km away
2 deathsSevere damage ($5–24M)tsunami
1986M8.0
Aleutian Islands: Adak
7 May 1986 · 140 km away · intensity VI
Moderate damage ($1–5M)tsunami
1901M7.8
Aleutian Islands: Fox Islands
31 Dec 1901 · 120 km away
Limited damage (under $1M)tsunami
1907M7.8
Aleutian Islands
2 Sep 1907 · 237 km away
1929M7.8
Aleutian Islands: Fox Islands
7 Mar 1929 · 200 km away · intensity V
tsunami
1916M7.5
Aleutian Islands: Fox Islands
18 Apr 1916 · 271 km away

NOAA NCEI Global Significant Earthquake Database. Historical figures are estimates; older records are incomplete.

Nearby trackers