Reviewed by USGSCalifornia42y ago
M4.2 earthquake 251 km W of Ferndale, California
Sunday, September 16, 1984, 21:36:24 UTC · 40.343°N, 127.215°W
A magnitude 4.2 earthquake struck 251 km W of Ferndale, California on Sunday, September 16, 1984, 21:36:24 UTC, at a depth of 10.0 km (shallow).
- Magnitude
- 4.2
- Light · mb
- Depth
- 10 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
30 tons of TNT
That is about 1/500 of the Hiroshima bomb. A magnitude 5.0 releases about 16 times more energy.
Tectonic setting
10 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
10 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 3 M2.5+ earthquakes within 50 km in the following 30 days; the largest was M4.5 on September 20, 1984. 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 137 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 · 165 km NE of this epicenter
- 7.2The 1980 Eureka, California EarthquakeNovember 8, 1980 · 264 km E of this epicenter
- 7.1The 1923 Humboldt County, California EarthquakeJanuary 22, 1923 · 185 km E of this epicenter
- 6.8123 km W of Ferndale, CaliforniaNovember 25, 1954 · 128 km E of this epicenter
- 6.884 km W of Ferndale, CaliforniaFebruary 9, 1941 · 169 km E of this epicenter
- 6.8off the coast of Northern CaliforniaJuly 6, 1934 · 164 km NE of this epicenter
- 6.7217 km W of Ferndale, CaliforniaSeptember 10, 1984 · 37 km NE of this epicenter
- 6.552 km WNW of Big Lagoon, CaliforniaJuly 15, 1918 · 237 km NE 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 2 recorded deaths. The most severe:
- 1954M6.6
Humboldt County
21 Dec 1954 · 286 km away
1 death$2 million damage
- 1932M6.5
Eureka
6 Jun 1932 · 251 km away · intensity VIII
1 deathModerate damage ($1–5M)
- 1980M7.2
North Coast
8 Nov 1980 · 264 km away · intensity VII
$2 million damage
- 1865
Fort Humboldt, Eureka
1 Oct 1865 · 240 km away · intensity IX
Moderate damage ($1–5M)
- 1922M7.6
Northern
31 Jan 1922 · 162 km away
Limited damage (under $1M)
- 1923M7.1
Northern
22 Jan 1923 · 185 km away · intensity VIII
Limited damage (under $1M)tsunami
NOAA NCEI Global Significant Earthquake Database. Historical figures are estimates; older records are incomplete.