M4.9 earthquake 108 km SSW of False Pass, Alaska

Tuesday, September 12, 2023, 21:48:57 UTC · 53.962°N, 164.079°W

A magnitude 4.9 earthquake struck 108 km SSW of False Pass, Alaska on Tuesday, September 12, 2023, 21:48:57 UTC, at a depth of 46.8 km (shallow). It is the strongest earthquake within 300 km since an M5.0 on September 10, 2023.

Magnitude: 4.9; Light · mb
Depth: 47 km; Shallow
Felt reports: 0; Did You Feel It?
Est. shaking: III; Weak (ShakeMap)
PAGER alert: None; Not issued
Tsunami: No flag; USGS feed

Outlined circle: this earthquakeDashed circle: 50 km aftershock search areaColoured lines: estimated shaking intensity (USGS ShakeMap)

In context

How big was it, and why here?

Energy released

338 tons of TNT

That is about 1/45 of the Hiroshima bomb. A magnitude 5.0 releases about 1 times more energy.

Tectonic setting

103 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

47 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 11 M2.5+ earthquakes within 50 km in the following 30 days; the largest was M3.3 on September 15, 2023. 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 470 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 11 damaging, deadly or tsunami-generating earthquakes within 300 km of this epicenter since 1700, which together caused about 169 recorded deaths. The most severe:

1946M8.6
Unimak Island
1 Apr 1946 · 97 km away · intensity VI
168 deaths$26 million damagetsunami
2023M7.2
Alaska Peninsula
16 Jul 2023 · 223 km away · intensity VI
1 deathtsunami
1965M6.5
Aleutian Islands: Fox Islands
2 Jul 1965 · 252 km away
Limited damage (under $1M)tsunami
1788M8.0
Alaska Peninsula
6 Aug 1788 · 230 km away
tsunami
1902M7.8
Aleutian Islands: Fox Islands
1 Jan 1902 · 287 km away
2020M7.6
Alaska
19 Oct 2020 · 298 km away · intensity IX
tsunami

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

Nearby trackers