QuakeScout
Magnitude2.7

Reviewed by USGSAlaska5y ago

M2.7 earthquake 99 km SE of False Pass, Alaska

Saturday, April 17, 2021, 23:26:00 UTC · 54.167°N, 162.433°W

A magnitude 2.7 earthquake struck 99 km SE of False Pass, Alaska on Saturday, April 17, 2021, 23:26:00 UTC, at a depth of 20.5 km (shallow).

Magnitude
2.7
Minor · ml
Depth
21 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

169 kg of TNT

That is about 1/88,990 of the Hiroshima bomb. A magnitude 5.0 releases about 2,818 times more energy.

Tectonic setting

85 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

21 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 M3.3 on May 9, 2021. Most nearby activity right after a large earthquake is aftershocks, which usually become less frequent over days and weeks.

M31h6h1d3d7d14d30dMainshock M2.7
Time after the mainshock on a logarithmic scale (first hours stretched), magnitude on the vertical axis. M2.5+ events from USGS.
  1. 3.384 km SSE of False Pass, Alaska5y ago · 25 km W of this epicenter
  2. 2.597 km SSE of False Pass, Alaska5y ago · 20 km SW of this epicenter
  3. 2.798 km SSE of False Pass, Alaska5y ago · 33 km SW of this epicenter

Regional history

Past M5+ earthquakes within 300 km

USGS lists 379 M5.0+ earthquakes within 300 km before this one (catalog from 1900; older records are less complete). The strongest:

  1. 8.6The 1946 Unimak Island, Alaska EarthquakeApril 1, 1946 · 79 km S of this epicenter
  2. 8.21938 Semidi Islands, Alaska EarthquakeNovember 10, 1938 · 296 km NE of this epicenter
  3. 7.82020 Perryville, Alaska EarthquakeJuly 22, 2020 · 267 km NE of this epicenter
  4. 7.62020 Sand Point, Alaska EarthquakeOctober 19, 2020 · 188 km E of this epicenter
  5. 7.454 km SE of Sand Point, AlaskaMay 31, 1917 · 188 km NE of this epicenter
  6. 7.190 km SE of King Cove, AlaskaMay 14, 1948 · 95 km NE of this epicenter
  7. 7.139 km S of Akutan, AlaskaMarch 22, 1957 · 223 km W of this epicenter

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:

  1. 1946M8.6

    Unimak Island

    1 Apr 1946 · 79 km away · intensity VI

    168 deaths$26 million damagetsunami

  2. 2020M7.8

    Alaska

    22 Jul 2020 · 267 km away · intensity VII

    Limited damage (under $1M)tsunami

  3. 1938M8.2

    Alaska

    10 Nov 1938 · 298 km away · intensity VI

    tsunami

  4. 1788M8.0

    Alaska Peninsula

    6 Aug 1788 · 131 km away

    tsunami

  5. 2020M7.6

    Alaska

    19 Oct 2020 · 188 km away · intensity IX

    tsunami

  6. 1948M7.5

    Alaska Peninsula

    14 May 1948 · 100 km away

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

Nearby trackers

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