M4.0 earthquake 36 km SSW of Ferndale, California

Sunday, June 21, 1981, 06:20:39 UTC · 40.294°N, 124.484°W

A magnitude 4.0 earthquake struck 36 km SSW of Ferndale, California on Sunday, June 21, 1981, 06:20:39 UTC, at a depth of 22.3 km (shallow).

Magnitude: 4.0; Light · ml
Depth: 22 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

15 tons of TNT

That is about 1/998 of the Hiroshima bomb. A magnitude 5.0 releases about 32 times more energy.

Tectonic setting

2 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

22 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 10 M2.5+ earthquakes within 50 km in the following 30 days; the largest was M4.6 on July 17, 1981. Most nearby activity right after a large earthquake is aftershocks, which usually become less frequent over days and weeks.

Time after the mainshock on a logarithmic scale (first hours stretched), magnitude on the vertical axis. M2.5+ events from USGS.

Regional history

Past M5+ earthquakes within 300 km

USGS lists 132 M5.0+ earthquakes within 300 km before this one (catalog from 1900; older records are less complete). The strongest:

History · NOAA

Deadliest earthquakes in this area

NOAA’s significant-earthquake database lists 18 damaging, deadly or tsunami-generating earthquakes within 300 km of this epicenter since 1700, which together caused about 3 recorded deaths. The most severe:

1969M4.8
Santa Rosa
2 Oct 1969 · 255 km away · intensity VIII
1 death$8 million damage
1954M6.6
Humboldt County
21 Dec 1954 · 79 km away
1 death$2 million damage
1932M6.5
Eureka
6 Jun 1932 · 51 km away · intensity VIII
1 deathModerate damage ($1–5M)
1980M7.2
North Coast
8 Nov 1980 · 94 km away · intensity VII
$2 million damage
1898M6.5
Sonoma County
31 Mar 1898 · 294 km away · intensity VIII
Moderate damage ($1–5M)tsunami
1892M6.2
Winters
21 Apr 1892 · 298 km away · intensity IX
Moderate damage ($1–5M)

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

Nearby trackers