QuakeScout
Magnitude7.6

Reviewed by USGSAlaska Earthquake6y ago

M7.6 earthquake 2020 Sand Point, Alaska Earthquake

Monday, October 19, 2020, 20:54:38 UTC · 54.602°N, 159.626°W

A magnitude 7.6 earthquake struck 2020 Sand Point, Alaska Earthquake on Monday, October 19, 2020, 20:54:38 UTC, at a depth of 28.4 km (shallow). USGS received 321 “Did You Feel It?” reports, with a maximum reported intensity of IX (violent). The USGS PAGER alert is yellow: some casualties and damage are possible. It is the strongest earthquake within 300 km since an M7.8 on July 22, 2020.

Tsunami flagUSGS sets this flag for large events in oceanic regions so tsunami warning centers review them. It does not by itself mean a tsunami occurred. Check tsunami.gov and local authorities for official messages.

Magnitude
7.6
Major · mww
Depth
28 km
Shallow
Felt reports
321
Max intensity IX
Est. shaking
VII
Very strong (ShakeMap)
PAGER alert
Yellow
Impact estimate
Tsunami
Flag
Check tsunami.gov

Outlined circle: this earthquakeDashed circle: 200 km aftershock search areaColoured lines: estimated shaking intensity (USGS ShakeMap)

In context

How big was it, and why here?

Energy released

3.8 megatons of TNT

That is about 252 times the Hiroshima bomb. It released about 7,943 times the energy of a magnitude 5.0.

Tectonic setting

84 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

28 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

Reports sent by people to USGS, grouped by place (most reports first). Intensity uses the Modified Mercalli scale (I–X): what people felt, not the magnitude.

PlaceIntensityReportsDistance
99603<br>0.156II · Weak32751 km
99577<br>0.168II · Weak28958 km
99516<br>0.190II · Weak22931 km
99501<br>0.194II · Weak21937 km
99507<br>0.213II · Weak17935 km
99628<br>0.230III · Weak14481 km
99685<br>0.242III · Weak12470 km
99567<br>0.242II · Weak12976 km
99661<br>0.248VII · Very strong11103 km
99502<br>0.255II · Weak10925 km
99613<br>0.269III · Weak8499 km
99654<br>0.269II · Weak8963 km
I felt it — report to USGS ↗

USGS PAGER estimate

Who was exposed to shaking

Modelled from the ShakeMap and population data. Alert level yellow: some casualties and damage are possible.

VII · Very strong shaking
1,700 people
IV · Light shaking
1,100 people
III · Weak shaking
16,000 people
II · Weak shaking
12,000 people

Estimated shaking in nearby towns

  • Sand PointPopulation 976VII · Very strong
  • AkutanPopulation 1,000III · Weak
  • Dutch HarborPopulation 4,400III · Weak
  • DillinghamPopulation 2,300III · Weak
  • UnalaskaPopulation 4,400III · Weak
  • Kodiak StationPopulation 1,300II · Weak
  • KodiakPopulation 6,100II · Weak

After the main event

Aftershocks within 200 km

USGS lists 1,284 M2.5+ earthquakes within 200 km in the following 30 days; the largest was M5.1 on November 5, 2020. Most nearby activity right after a large earthquake is aftershocks, which usually become less frequent over days and weeks.

M3M4M5M6M71h6h1d3d7d14d30dMainshock M7.6
Time after the mainshock on a logarithmic scale (first hours stretched), magnitude on the vertical axis. M2.5+ events from USGS.
  1. 2.7127 km SSE of Sand Point, Alaska5y ago · 34 km S of this epicenter
  2. 2.9south of Alaska5y ago · 31 km S of this epicenter
  3. 3.0108 km SSE of Sand Point, Alaska5y ago · 14 km S of this epicenter
  4. 2.7104 km SSE of Sand Point, Alaska5y ago · 23 km SW of this epicenter
  5. 3.3151 km SSE of Sand Point, Alaska5y ago · 62 km S of this epicenter
  6. 3.5203 km SSE of King Cove, Alaska5y ago · 187 km SW of this epicenter
  7. 3.5127 km SSE of Sand Point, Alaska5y ago · 34 km S of this epicenter
  8. 3.088 km SSE of Sand Point, Alaska5y ago · 13 km NW of this epicenter

Regional history

Past M5+ earthquakes within 300 km

USGS lists 336 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 · 243 km SW of this epicenter
  2. 8.21938 Semidi Islands, Alaska EarthquakeNovember 10, 1938 · 112 km NE of this epicenter
  3. 7.82020 Perryville, Alaska EarthquakeJuly 22, 2020 · 84 km NE of this epicenter
  4. 7.454 km SE of Sand Point, AlaskaMay 31, 1917 · 47 km N of this epicenter
  5. 7.190 km SE of King Cove, AlaskaMay 14, 1948 · 99 km W of this epicenter
  6. 7.0113 km ESE of Chignik, AlaskaMay 4, 1923 · 227 km NE of this epicenter
  7. 7.071 km SE of King Cove, AlaskaMay 30, 1991 · 128 km W of this epicenter

History · NOAA

Deadliest earthquakes in this area

NOAA’s significant-earthquake database lists 9 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 · 243 km away · intensity VI

    168 deaths$26 million damagetsunami

  2. 2020M7.8

    Alaska

    22 Jul 2020 · 84 km away · intensity VII

    Limited damage (under $1M)tsunami

  3. 1938M8.2

    Alaska

    10 Nov 1938 · 126 km away · intensity VI

    tsunami

  4. 1788M8.0

    Alaska Peninsula

    6 Aug 1788 · 99 km away

    tsunami

  5. 2020M7.6

    Alaska

    19 Oct 2020 · 0 km away · intensity IX

    tsunami

  6. 1948M7.5

    Alaska Peninsula

    14 May 1948 · 89 km away

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

Nearby trackers

Closest city pages