QuakeScout
Magnitude4.5

Reviewed by USGSAlaska5y ago

M4.5 earthquake 152 km S of False Pass, Alaska

Wednesday, October 6, 2021, 03:42:21 UTC · 53.488°N, 163.494°W

A magnitude 4.5 earthquake struck 152 km S of False Pass, Alaska on Wednesday, October 6, 2021, 03:42:21 UTC, at a depth of 10.8 km (shallow). It is the strongest earthquake within 300 km since an M4.7 on September 12, 2021.

Magnitude
4.5
Light · mb
Depth
11 km
Shallow
Felt reports
0
Did You Feel It?
Est. shaking
I
Not felt (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

85 tons of TNT

That is about 1/178 of the Hiroshima bomb. A magnitude 5.0 releases about 6 times more energy.

Tectonic setting

39 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

11 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 M4.4 on October 6, 2021. Most nearby activity right after a large earthquake is aftershocks, which usually become less frequent over days and weeks.

M3M41h6h1d3d7d14d30dMainshock M4.5
Time after the mainshock on a logarithmic scale (first hours stretched), magnitude on the vertical axis. M2.5+ events from USGS.
  1. 4.4153 km S of False Pass, Alaska5y ago · 2 km SW of this epicenter
  2. 3.3154 km S of False Pass, Alaska5y ago · 3 km SE of this epicenter
  3. 4.4147 km S of False Pass, Alaska5y ago · 5 km N of this epicenter

Regional history

Past M5+ earthquakes within 300 km

USGS lists 448 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 · 44 km E of this epicenter
  2. 7.881 km E of Nikolski, AlaskaJuly 2, 1965 · 282 km W of this epicenter
  3. 7.62020 Sand Point, Alaska EarthquakeOctober 19, 2020 · 281 km NE of this epicenter
  4. 7.454 km SE of Sand Point, AlaskaMay 31, 1917 · 288 km NE of this epicenter
  5. 7.190 km SE of King Cove, AlaskaMay 14, 1948 · 196 km NE of this epicenter
  6. 7.139 km S of Akutan, AlaskaMarch 22, 1957 · 154 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 · 44 km away · intensity VI

    168 deaths$26 million damagetsunami

  2. 1965M6.5

    Aleutian Islands: Fox Islands

    2 Jul 1965 · 275 km away

    Limited damage (under $1M)tsunami

  3. 1788M8.0

    Alaska Peninsula

    6 Aug 1788 · 233 km away

    tsunami

  4. 1902M7.8

    Aleutian Islands: Fox Islands

    1 Jan 1902 · 294 km away

  5. 2020M7.6

    Alaska

    19 Oct 2020 · 281 km away · intensity IX

    tsunami

  6. 1948M7.5

    Alaska Peninsula

    14 May 1948 · 198 km away

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

Nearby trackers

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