M5.6 earthquake 152 km E of Atka, Alaska

Monday, September 19, 2011, 08:14:14 UTC · 52.037°N, 171.982°W

A magnitude 5.6 earthquake struck 152 km E of Atka, Alaska on Monday, September 19, 2011, 08:14:14 UTC, at a depth of 31.0 km (shallow). It is the strongest earthquake within 300 km since an M6.9 on September 2, 2011.

Magnitude: 5.6; Moderate · mww
Depth: 31 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: 75 km aftershock search area

In context

How big was it, and why here?

Energy released

4 kilotons of TNT

That is about 1/4 of the Hiroshima bomb. It released about 8 times the energy of a magnitude 5.0.

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

31 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 75 km

USGS lists 64 M2.5+ earthquakes within 75 km in the following 30 days; the largest was M4.8 on October 8, 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 813 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 12 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 · 258 km away
2 deathsSevere damage ($5–24M)tsunami
1986M8.0
Aleutian Islands: Adak
7 May 1986 · 201 km away · intensity VI
Moderate damage ($1–5M)tsunami
1901M7.8
Aleutian Islands: Fox Islands
31 Dec 1901 · 93 km away
Limited damage (under $1M)tsunami
1907M7.8
Aleutian Islands
2 Sep 1907 · 165 km away
1929M7.8
Aleutian Islands: Fox Islands
7 Mar 1929 · 179 km away · intensity V
tsunami
1916M7.5
Aleutian Islands: Fox Islands
18 Apr 1916 · 194 km away

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

Nearby trackers