Reviewed by USGSAlaska11y ago
M2.5 earthquake 85 km SSE of Atka, Alaska
Friday, November 20, 2015, 22:23:48 UTC · 51.536°N, 173.556°W
A magnitude 2.5 earthquake struck 85 km SSE of Atka, Alaska on Friday, November 20, 2015, 22:23:48 UTC, at a depth of 5.8 km (shallow).
- Magnitude
- 2.5
- Minor · ml
- Depth
- 6 km
- Shallow
- Felt reports
- 0
- Max intensity I
- 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
85 kg of TNT
That is about 1/177,558 of the Hiroshima bomb. A magnitude 5.0 releases about 5,623 times more energy.
Tectonic setting
65 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
6 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 3 M2.5+ earthquakes within 50 km in the following 30 days; the largest was M3.8 on December 18, 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 914 M5.0+ earthquakes within 300 km before this one (catalog from 1900; older records are less complete). The strongest:
- 8.61957 Atka, Alaska EarthquakeMarch 9, 1957 · 143 km W of this epicenter
- 8.01986 Atka, Alaska EarthquakeMay 7, 1986 · 84 km W of this epicenter
- 7.977 km WSW of Adak, AlaskaJune 10, 1996 · 282 km W of this epicenter
- 7.8234 km SSW of Nikolski, AlaskaMarch 7, 1929 · 272 km E of this epicenter
- 7.65 km WNW of Adak, AlaskaFebruary 14, 1905 · 220 km W of this epicenter
- 7.4133 km WNW of Nikolski, AlaskaApril 18, 1916 · 288 km NE of this epicenter
- 7.388 km WSW of Adak, AlaskaJuly 7, 1929 · 290 km W of this epicenter
- 7.346 km SSW of Adak, AlaskaJune 10, 1996 · 228 km W 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, which together caused about 2 recorded deaths. The most severe:
- 1957M8.6
Alaska
9 Mar 1957 · 143 km away
2 deathsSevere damage ($5–24M)tsunami
- 1986M8.0
Aleutian Islands: Adak
7 May 1986 · 84 km away · intensity VI
Moderate damage ($1–5M)tsunami
- 1901M7.8
Aleutian Islands: Fox Islands
31 Dec 1901 · 176 km away
Limited damage (under $1M)tsunami
- 1996M7.9
Andreanof Islands
10 Jun 1996 · 282 km away · intensity VI
tsunami
- 1907M7.8
Aleutian Islands
2 Sep 1907 · 287 km away
- 1929M7.8
Aleutian Islands: Fox Islands
7 Mar 1929 · 254 km away · intensity V
tsunami
NOAA NCEI Global Significant Earthquake Database. Historical figures are estimates; older records are incomplete.