Reviewed by USGSCalifornia45y ago
M2.5 earthquake 105 km W of Ferndale, California
Monday, August 17, 1981, 03:47:53 UTC · 40.402°N, 125.483°W
A magnitude 2.5 earthquake struck 105 km W of Ferndale, California on Monday, August 17, 1981, 03:47:53 UTC, at a depth of 4.0 km (shallow).
- Magnitude
- 2.5
- Minor · md
- Depth
- 4 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
91 kg of TNT
That is about 1/165,707 of the Hiroshima bomb. A magnitude 5.0 releases about 5,248 times more energy.
Tectonic setting
6 km
from the nearest mapped plate boundary, between the Pacific and Juan de Fuca plates. Earthquakes cluster along boundaries like this one, where plates collide, pull apart or slide past each other.
Depth: shallow
4 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 September 11, 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 131 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 · 88 km N of this epicenter
- 7.2The 1980 Eureka, California EarthquakeNovember 8, 1980 · 131 km NE of this epicenter
- 7.1The 1923 Humboldt County, California EarthquakeJanuary 22, 1923 · 39 km E of this epicenter
- 6.8123 km W of Ferndale, CaliforniaNovember 25, 1954 · 20 km W of this epicenter
- 6.884 km W of Ferndale, CaliforniaFebruary 9, 1941 · 33 km NE of this epicenter
- 6.8off the coast of Northern CaliforniaJuly 6, 1934 · 83 km N of this epicenter
- 6.552 km WNW of Big Lagoon, CaliforniaJuly 15, 1918 · 121 km NE of this epicenter
- 6.568 km W of Ferndale, CaliforniaOctober 3, 1941 · 37 km E of this epicenter
History · NOAA
Deadliest earthquakes in this area
NOAA’s significant-earthquake database lists 12 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 · 143 km away
1 death$2 million damage
- 1932M6.5
Eureka
6 Jun 1932 · 107 km away · intensity VIII
1 deathModerate damage ($1–5M)
- 1980M7.2
North Coast
8 Nov 1980 · 131 km away · intensity VII
$2 million damage
- 1865
Fort Humboldt, Eureka
1 Oct 1865 · 106 km away · intensity IX
Moderate damage ($1–5M)
- 1922M7.6
Northern
31 Jan 1922 · 66 km away
Limited damage (under $1M)
- 1923M7.1
Northern
22 Jan 1923 · 39 km away · intensity VIII
Limited damage (under $1M)tsunami
NOAA NCEI Global Significant Earthquake Database. Historical figures are estimates; older records are incomplete.