M4.1 earthquake 11km SSW of Ferndale, CA

Thursday, August 25, 2005, 02:27:44 UTC · 40.482°N, 124.309°W

A magnitude 4.1 earthquake struck 11km SSW of Ferndale, CA on Thursday, August 25, 2005, 02:27:44 UTC, at a depth of 26.7 km (shallow). USGS received 261 “Did You Feel It?” reports, with a maximum reported intensity of IV (light).

Magnitude: 4.1; Light · mw
Depth: 27 km; Shallow
Felt reports: 261; Max intensity IV
Est. shaking: IV; Light (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

22 tons of TNT

That is about 1/683 of the Hiroshima bomb. A magnitude 5.0 releases about 22 times more energy.

Tectonic setting

21 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

27 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
95521<br>0.110	II · Weak	61	54 km
95540<br>0.137	III · Weak	40	32 km
95501<br>0.146	II · Weak	36	45 km
95503<br>0.153	III · Weak	33	41 km
95536<br>0.230	IV · Light	14	27 km
95562<br>0.236	IV · Light	13	30 km
95519<br>0.248	II · Weak	11	62 km
95551<br>0.277	IV · Light	7	33 km
95565<br>0.293	III · Weak	5	35 km
95542<br>0.293	III · Weak	5	61 km
95528<br>0.302	III · Weak	4	43 km
95524<br>0.302	II · Weak	4	51 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 5 M2.5+ earthquakes within 50 km in the following 30 days; the largest was M3.4 on September 10, 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.

Regional history

Past M5+ earthquakes within 300 km

USGS lists 191 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 23 damaging, deadly or tsunami-generating earthquakes within 300 km of this epicenter since 1700, which together caused about 5 recorded deaths. The most severe:

1993M6.0
Klamath Falls
21 Sep 1993 · 280 km away · intensity VII
2 deaths$8 million damage
1969M4.8
Santa Rosa
2 Oct 1969 · 264 km away · intensity VIII
1 death$8 million damage
1954M6.6
Humboldt County
21 Dec 1954 · 54 km away
1 death$2 million damage
1932M6.5
Eureka
6 Jun 1932 · 28 km away · intensity VIII
1 deathModerate damage ($1–5M)
1992M7.1
Humboldt County: Ferndale, Petrolia
25 Apr 1992 · 13 km away · intensity VIII
$75 million damagetsunami
2000M5.0
Napa
3 Sep 2000 · 285 km away · intensity VII
$50 million damage

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

Nearby trackers