Reviewed by USGSAlaska40y ago
M5.0 earthquake 63 km SE of Akhiok, Alaska
Monday, July 21, 1986, 15:24:45 UTC · 56.592°N, 153.361°W
A magnitude 5.0 earthquake struck 63 km SE of Akhiok, Alaska on Monday, July 21, 1986, 15:24:45 UTC, at a depth of 33.0 km (shallow). It is the strongest earthquake within 300 km since an M6.8 on June 19, 1986.
- Magnitude
- 5.0
- 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
477 tons of TNT
That is about 1/32 of the Hiroshima bomb. Each whole step in magnitude is about 32 times more energy.
Tectonic setting
90 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
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 2 M2.5+ earthquakes within 75 km in the following 30 days; the largest was M3.6 on July 24, 1986. Most nearby activity right after a large earthquake is aftershocks, which usually become less frequent over days and weeks.
Regional history
Past M5+ earthquakes within 300 km
USGS lists 256 M5.0+ earthquakes within 300 km before this one (catalog from 1900; older records are less complete). The strongest:
- 7.9Kodiak Island region, AlaskaOctober 9, 1900 · 169 km NE of this epicenter
- 7.14 km ENE of Karluk, AlaskaNovember 7, 1912 · 127 km NW of this epicenter
- 7.0113 km ESE of Chignik, AlaskaMay 4, 1923 · 227 km W of this epicenter
- 6.9143 km ESE of Chignik, AlaskaFebruary 13, 1951 · 201 km SW of this epicenter
- 6.9171 km SW of Akhiok, AlaskaFebruary 6, 1964 · 182 km SW of this epicenter
- 6.8100 km SSE of Old Harbor, AlaskaJune 19, 1986 · 40 km SE 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. The most severe:
- 1900M8.3
Kodiak Island
9 Oct 1900 · 56 km away · intensity VIII
Limited damage (under $1M)
- 1788M8.0
Unga Island
21 Jul 1788 · 50 km away · intensity VII
Limited damage (under $1M)tsunami
- 1970M6.0
Andreanof Islands
11 Mar 1970 · 106 km away · intensity V
Limited damage (under $1M)tsunami
- 1792
Kodiak Island
1792 · 94 km away · intensity VII
Limited damage (under $1M)tsunami
- 1906M7.6
Aleutian Islands
23 Dec 1906 · 44 km away
- 1912M7.5
Alaska Peninsula
7 Nov 1912 · 141 km away · intensity V
NOAA NCEI Global Significant Earthquake Database. Historical figures are estimates; older records are incomplete.