M2.8 earthquake 111 km E of Chignik, Alaska

Monday, October 18, 2021, 01:34:49 UTC · 56.279°N, 156.608°W

A magnitude 2.8 earthquake struck 111 km E of Chignik, Alaska on Monday, October 18, 2021, 01:34:49 UTC, at a depth of 30.1 km (shallow). USGS received 1 “Did You Feel It?” report, with a maximum reported intensity of II (weak).

Magnitude: 2.8; Minor · ml
Depth: 30 km; Shallow
Felt reports: 1; Max intensity II
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

239 kg of TNT

That is about 1/63,000 of the Hiroshima bomb. A magnitude 5.0 releases about 1,995 times more energy.

Tectonic setting

183 km

from the nearest mapped plate boundary, between the North American and Pacific plates. Earthquakes this far from a boundary happen on faults inside a plate, often less frequently but sometimes strongly.

Depth: shallow

30 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

Reports sent by people to USGS, grouped by place (most reports first). Intensity uses the Modified Mercalli scale (I–X): what people felt, not the magnitude.

Place	Intensity	Reports	Distance
99515<br>0.330	II · Weak	1	662 km

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 17 M2.5+ earthquakes within 50 km in the following 30 days; the largest was M3.5 on November 4, 2021. 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 421 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 13 damaging, deadly or tsunami-generating earthquakes within 300 km of this epicenter since 1700. The most severe:

1900M8.3
Kodiak Island
9 Oct 1900 · 211 km away · intensity VIII
Limited damage (under $1M)
1788M8.0
Unga Island
21 Jul 1788 · 235 km away · intensity VII
Limited damage (under $1M)tsunami
2020M7.8
Alaska
22 Jul 2020 · 183 km away · intensity VII
Limited damage (under $1M)tsunami
1970M6.0
Andreanof Islands
11 Mar 1970 · 213 km away · intensity V
Limited damage (under $1M)tsunami
1792
Kodiak Island
1792 · 293 km away · intensity VII
Limited damage (under $1M)tsunami
1938M8.2
Alaska
10 Nov 1938 · 141 km away · intensity VI
tsunami

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

Nearby trackers