M4.8 earthquake 118 km SE of Chignik, Alaska

Tuesday, February 13, 1979, 10:39:39 UTC · 55.692°N, 156.838°W

A magnitude 4.8 earthquake struck 118 km SE of Chignik, Alaska on Tuesday, February 13, 1979, 10:39:39 UTC, at a depth of 33.0 km (shallow). It is the strongest earthquake within 300 km since an M6.7 on February 13, 1979.

Magnitude: 4.8; Light · mb
Depth: 33 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

239 tons of TNT

That is about 1/63 of the Hiroshima bomb. A magnitude 5.0 releases about 2 times more energy.

Tectonic setting

135 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

33 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 M5.0 on February 13, 1979. 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 156 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 10 damaging, deadly or tsunami-generating earthquakes within 300 km of this epicenter since 1700. The most severe:

1900M8.3
Kodiak Island
9 Oct 1900 · 259 km away · intensity VIII
Limited damage (under $1M)
1788M8.0
Unga Island
21 Jul 1788 · 278 km away · intensity VII
Limited damage (under $1M)tsunami
1970M6.0
Andreanof Islands
11 Mar 1970 · 270 km away · intensity V
Limited damage (under $1M)tsunami
1938M8.2
Alaska
10 Nov 1938 · 99 km away · intensity VI
tsunami
1788M8.0
Alaska Peninsula
6 Aug 1788 · 274 km away
tsunami
1906M7.6
Aleutian Islands
23 Dec 1906 · 222 km away

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

Nearby trackers