QuakeScout
Magnitude5.1

Reviewed by USGSAlaska40y ago

M5.1 earthquake 68 km SW of Unalaska, Alaska

Saturday, April 11, 1987, 16:22:09 UTC · 53.406°N, 167.213°W

A magnitude 5.1 earthquake struck 68 km SW of Unalaska, Alaska on Saturday, April 11, 1987, 16:22:09 UTC, at a depth of 33.0 km (shallow). It is the strongest earthquake within 300 km since an M5.7 on April 9, 1987.

Magnitude
5.1
Moderate · mb
Depth
33 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: 75 km aftershock search area

In context

How big was it, and why here?

Energy released

674 tons of TNT

That is about 1/22 of the Hiroshima bomb. It released about 1 times the energy of a magnitude 5.0.

Tectonic setting

126 km

from the nearest mapped plate boundary, between the North American and Pacific plates. Earthquakes this far from a boundary happen on faults inside a plate, often less frequently but sometimes strongly.

Depth: shallow

33 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 75 km

USGS lists 3 M2.5+ earthquakes within 75 km in the following 30 days; the largest was M4.5 on April 12, 1987. Most nearby activity right after a large earthquake is aftershocks, which usually become less frequent over days and weeks.

M3M4M51h6h1d3d7d14d30dMainshock M5.1
Time after the mainshock on a logarithmic scale (first hours stretched), magnitude on the vertical axis. M2.5+ events from USGS.
  1. 3.938 km WSW of Dutch Harbor, Alaska40y ago · 45 km N of this epicenter
  2. 4.476 km SW of Unalaska, Alaska40y ago · 15 km W of this epicenter
  3. 4.563 km SW of Unalaska, Alaska40y ago · 16 km NW of this epicenter

Regional history

Past M5+ earthquakes within 300 km

USGS lists 339 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 · 290 km E of this epicenter
  2. 7.881 km E of Nikolski, AlaskaJuly 2, 1965 · 53 km SW of this epicenter
  3. 7.4133 km WNW of Nikolski, AlaskaApril 18, 1916 · 229 km W of this epicenter
  4. 7.139 km S of Akutan, AlaskaMarch 22, 1957 · 104 km NE of this epicenter
  5. 7.135 km SW of Nikolski, AlaskaMarch 11, 1957 · 154 km SW of this epicenter
  6. 7.0203 km SSE of Unalaska, AlaskaAugust 22, 1940 · 180 km SE of this epicenter
  7. 6.980 km SW of Nikolski, AlaskaMarch 9, 1957 · 196 km SW of this epicenter

History · NOAA

Deadliest earthquakes in this area

NOAA’s significant-earthquake database lists 11 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 · 290 km away · intensity VI

    168 deaths$26 million damagetsunami

  2. 1965M6.5

    Aleutian Islands: Fox Islands

    2 Jul 1965 · 47 km away

    Limited damage (under $1M)tsunami

  3. 1917M7.9

    Alaska Peninsula

    31 May 1917 · 198 km away · intensity V

  4. 1902M7.8

    Aleutian Islands: Fox Islands

    1 Jan 1902 · 114 km away

  5. 1907M7.8

    Aleutian Islands

    2 Sep 1907 · 191 km away

  6. 1916M7.5

    Aleutian Islands: Fox Islands

    18 Apr 1916 · 185 km away

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

Nearby trackers

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