M4.6 earthquake 93 km W of Ferndale, California

Friday, December 23, 2005, 21:38:32 UTC · 40.427°N, 125.346°W

A magnitude 4.6 earthquake struck 93 km W of Ferndale, California on Friday, December 23, 2005, 21:38:32 UTC, at a depth of 3.2 km (shallow). USGS received 54 “Did You Feel It?” reports, with a maximum reported intensity of IV (light). It is the strongest earthquake within 300 km since an M4.9 on June 19, 2005.

Magnitude: 4.6; Light · mw
Depth: 3 km; Shallow
Felt reports: 54; Max intensity IV
Est. shaking: II; Weak (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

133 tons of TNT

That is about 1/113 of the Hiroshima bomb. A magnitude 5.0 releases about 4 times more energy.

Tectonic setting

9 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

3 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

Reports sent by people to USGS, grouped by place (most reports first). Intensity uses the Modified Mercalli scale (I–X): what people felt, not the magnitude.

Place	Intensity	Reports	Distance
95540<br>0.269	III · Weak	8	104 km
95503<br>0.293	II · Weak	5	110 km
95536<br>0.302	III · Weak	4	93 km
94583<br>0.302	III · Weak	4	414 km
95560<br>0.311	IV · Light	3	128 km
95542<br>0.311	III · Weak	3	130 km
95589<br>0.311	III · Weak	3	122 km
95565<br>0.311	III · Weak	3	111 km
95558<br>0.311	III · Weak	3	96 km
95562<br>0.311	III · Weak	3	102 km
95501<br>0.320	II · Weak	2	108 km
95521<br>0.330	III · Weak	1	120 km

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 M2.8 on December 27, 2005. 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.

2.899 km W of Ferndale, California21y ago · 6 km W of this epicenter

Regional history

Past M5+ earthquakes within 300 km

USGS lists 187 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 17 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 · 131 km away
1 death$2 million damage
1932M6.5
Eureka
6 Jun 1932 · 96 km away · intensity VIII
1 deathModerate damage ($1–5M)
1992M7.1
Humboldt County: Ferndale, Petrolia
25 Apr 1992 · 87 km away · intensity VIII
$75 million damagetsunami
1980M7.2
North Coast
8 Nov 1980 · 120 km away · intensity VII
$2 million damage
1991M6.2
Honeydew, Whitethorn, Petrolia
17 Aug 1991 · 87 km away · intensity VII
Moderate damage ($1–5M)
1994M5.5
Eureka, Samoa, Arcata, Blue Lake
26 Dec 1994 · 94 km away · intensity VII
$2 million damage

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

Nearby trackers