M4.0 earthquake 83 km SSW of Sand Point, Alaska

Sunday, September 27, 2020, 04:08:21 UTC · 54.642°N, 160.980°W

A magnitude 4.0 earthquake struck 83 km SSW of Sand Point, Alaska on Sunday, September 27, 2020, 04:08:21 UTC, at a depth of 30.8 km (shallow).

Magnitude: 4.0; Light · mb
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: 50 km aftershock search area

In context

How big was it, and why here?

Energy released

15 tons of TNT

That is about 1/998 of the Hiroshima bomb. A magnitude 5.0 releases about 32 times more energy.

Tectonic setting

110 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

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 50 km

USGS lists 20 M2.5+ earthquakes within 50 km in the following 30 days; the largest was M4.4 on October 4, 2020. 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 354 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, which together caused about 168 recorded deaths. The most severe:

1946M8.6
Unimak Island
1 Apr 1946 · 176 km away · intensity VI
168 deaths$26 million damagetsunami
2020M7.8
Alaska
22 Jul 2020 · 160 km away · intensity VII
Limited damage (under $1M)tsunami
1938M8.2
Alaska
10 Nov 1938 · 191 km away · intensity VI
tsunami
1788M8.0
Alaska Peninsula
6 Aug 1788 · 40 km away
tsunami
2020M7.6
Alaska
19 Oct 2020 · 87 km away · intensity IX
tsunami
1948M7.5
Alaska Peninsula
14 May 1948 · 16 km away

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

Nearby trackers