QuakeScout
Magnitude6.3

Reviewed by USGSAlaska87y ago

M6.3 earthquake 80 km S of Attu Station, Alaska

Saturday, May 4, 1940, 07:24:08 UTC · 52.139°N, 172.969°E

A magnitude 6.3 earthquake struck 80 km S of Attu Station, Alaska on Saturday, May 4, 1940, 07:24:08 UTC, at a depth of 25.0 km (shallow). It is the strongest earthquake within 300 km since an M7.0 on April 16, 1940.

Magnitude
6.3
Strong · mw
Depth
25 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: 100 km aftershock search area

In context

How big was it, and why here?

Energy released

41 kilotons of TNT

That is about 3 times the Hiroshima bomb. It released about 86 times the energy of a magnitude 5.0.

Tectonic setting

45 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

25 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 100 km

USGS lists 2 M2.5+ earthquakes within 100 km in the following 30 days; the largest was M6.4 on May 11, 1940. Most nearby activity right after a large earthquake is aftershocks, which usually become less frequent over days and weeks.

M3M4M5M61h6h1d3d7d14d30dMainshock M6.3
Time after the mainshock on a logarithmic scale (first hours stretched), magnitude on the vertical axis. M2.5+ events from USGS.
  1. 6.0151 km SSE of Attu Station, Alaska87y ago · 85 km SE of this epicenter
  2. 6.467 km S of Attu Station, Alaska87y ago · 29 km NE of this epicenter

Regional history

Past M5+ earthquakes within 300 km

USGS lists 28 M5.0+ earthquakes within 300 km before this one (catalog from 1900; older records are less complete). The strongest:

  1. 7.993 km NW of Attu Station, AlaskaDecember 17, 1929 · 153 km N of this epicenter
  2. 7.4151 km S of Attu Station, AlaskaSeptember 2, 1907 · 71 km S of this epicenter
  3. 7.2238 km SSE of Attu Station, AlaskaSeptember 8, 1939 · 187 km SE of this epicenter
  4. 7.024 km E of Attu Station, AlaskaApril 16, 1940 · 88 km NE of this epicenter
  5. 7.080 km SSE of Attu Station, AlaskaApril 16, 1940 · 56 km E of this epicenter
  6. 7.0167 km WSW of Attu Station, AlaskaApril 10, 1909 · 140 km W of this epicenter
  7. 6.8129 km SSE of Attu Station, AlaskaNovember 13, 1911 · 70 km SE of this epicenter
  8. 6.895 km SE of Attu Station, AlaskaFebruary 22, 1935 · 90 km E of this epicenter

History · NOAA

Deadliest earthquakes in this area

NOAA’s significant-earthquake database lists 3 damaging, deadly or tsunami-generating earthquakes within 300 km of this epicenter since 1700. The most severe:

  1. 1909M7.8

    Aleutian Islands

    10 Apr 1909 · 140 km away

  2. 1929M7.8

    Aleutian Islands: Near Islands

    17 Dec 1929 · 108 km away

  3. 1898M7.6

    Aleutian Islands: Near Islands

    29 Jun 1898 · 68 km away

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

Nearby trackers

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