Reviewed by USGSCalifornia46y ago
M2.9 earthquake 9 km WNW of McKinleyville, California
Monday, April 20, 1981, 06:22:34 UTC · 40.974°N, 124.209°W
A magnitude 2.9 earthquake struck 9 km WNW of McKinleyville, California on Monday, April 20, 1981, 06:22:34 UTC, at a depth of 46.5 km (shallow).
- Magnitude
- 2.9
- Minor · md
- Depth
- 46 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: 50 km aftershock search area
In context
How big was it, and why here?
Energy released
349 kg of TNT
That is about 1/43,086 of the Hiroshima bomb. A magnitude 5.0 releases about 1,365 times more energy.
Tectonic setting
61 km
from the nearest mapped plate boundary, between the Juan de Fuca and North American plates. Earthquakes cluster along boundaries like this one, where plates collide, pull apart or slide past each other.
Depth: shallow
46 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 50 km
USGS lists 1 M2.5+ earthquake within 50 km in the following 30 days; the largest was M2.9 on May 16, 1981. 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 134 M5.0+ earthquakes within 300 km before this one (catalog from 1900; older records are less complete). The strongest:
- 7.4123 km W of Big Lagoon, CaliforniaJanuary 31, 1922 · 120 km W of this epicenter
- 7.2The 1980 Eureka, California EarthquakeNovember 8, 1980 · 16 km N of this epicenter
- 7.1The 1923 Humboldt County, California EarthquakeJanuary 22, 1923 · 88 km SW of this epicenter
- 6.8123 km W of Ferndale, CaliforniaNovember 25, 1954 · 139 km SW of this epicenter
- 6.884 km W of Ferndale, CaliforniaFebruary 9, 1941 · 96 km W of this epicenter
- 6.8off the coast of Northern CaliforniaJuly 6, 1934 · 117 km W of this epicenter
- 6.552 km WNW of Big Lagoon, CaliforniaJuly 15, 1918 · 58 km NW of this epicenter
- 6.568 km W of Ferndale, CaliforniaOctober 3, 1941 · 90 km SW of this epicenter
History · NOAA
Deadliest earthquakes in this area
NOAA’s significant-earthquake database lists 13 damaging, deadly or tsunami-generating earthquakes within 300 km of this epicenter since 1700, which together caused about 2 recorded deaths. The most severe:
- 1954M6.6
Humboldt County
21 Dec 1954 · 30 km away
1 death$2 million damage
- 1932M6.5
Eureka
6 Jun 1932 · 28 km away · intensity VIII
1 deathModerate damage ($1–5M)
- 1980M7.2
North Coast
8 Nov 1980 · 16 km away · intensity VII
$2 million damage
- 1975M5.6
Oroville
1 Aug 1975 · 285 km away · intensity VIII
$3 million damage
- 1865
Fort Humboldt, Eureka
1 Oct 1865 · 25 km away · intensity IX
Moderate damage ($1–5M)
- 1922M7.6
Northern
31 Jan 1922 · 108 km away
Limited damage (under $1M)
NOAA NCEI Global Significant Earthquake Database. Historical figures are estimates; older records are incomplete.