QuakeScout
Magnitude6.6

Reviewed by USGSAlaska110y ago

M6.6 earthquake 88 km SSE of Old Harbor, Alaska

Friday, December 21, 1917, 17:54:32 UTC · 56.449°N, 152.838°W

A magnitude 6.6 earthquake struck 88 km SSE of Old Harbor, Alaska on Friday, December 21, 1917, 17:54:32 UTC, at a depth of 15.0 km (shallow). It is the strongest earthquake within 300 km since an M7.1 on November 7, 1912.

Magnitude
6.6
Strong · mw
Depth
15 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

133 kilotons of TNT

That is about 9 times the Hiroshima bomb. It released about 279 times the energy of a magnitude 5.0.

Tectonic setting

57 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

15 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 December 28, 1917. Most nearby activity right after a large earthquake is aftershocks, which usually become less frequent over days and weeks.

M3M4M5M61h6h1d3d7d14d30dMainshock M6.6
Time after the mainshock on a logarithmic scale (first hours stretched), magnitude on the vertical axis. M2.5+ events from USGS.
  1. 6.4103 km SSE of Akhiok, Alaska110y ago · 40 km SW of this epicenter
  2. 6.2173 km SSE of Akhiok, Alaska110y ago · 92 km S of this epicenter

Regional history

Past M5+ earthquakes within 300 km

USGS lists 51 M5.0+ earthquakes within 300 km before this one (catalog from 1900; older records are less complete). The strongest:

  1. 7.9Kodiak Island region, AlaskaOctober 9, 1900 · 154 km NE of this epicenter
  2. 7.14 km ENE of Karluk, AlaskaNovember 7, 1912 · 158 km NW of this epicenter
  3. 6.8Event 48 Novarupta-Mount Katmai area, Alaska PeninsulaJune 10, 1912 · 247 km NW of this epicenter

History · NOAA

Deadliest earthquakes in this area

NOAA’s significant-earthquake database lists 8 damaging, deadly or tsunami-generating earthquakes within 300 km of this epicenter since 1700. The most severe:

  1. 1900M8.3

    Kodiak Island

    9 Oct 1900 · 81 km away · intensity VIII

    Limited damage (under $1M)

  2. 1788M8.0

    Unga Island

    21 Jul 1788 · 62 km away · intensity VII

    Limited damage (under $1M)tsunami

  3. 1792

    Kodiak Island

    1792 · 80 km away · intensity VII

    Limited damage (under $1M)tsunami

  4. 1906M7.6

    Aleutian Islands

    23 Dec 1906 · 79 km away

  5. 1912M7.5

    Alaska Peninsula

    7 Nov 1912 · 176 km away · intensity V

  6. 1854

    Gulf Of Alaska

    27 Jan 1854 · 80 km away · intensity V

    tsunami

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

Nearby trackers

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