M6.7 earthquake 217 km W of Ferndale, California

Monday, September 10, 1984, 03:14:10 UTC · 40.503°N, 126.831°W

A magnitude 6.7 earthquake struck 217 km W of Ferndale, California on Monday, September 10, 1984, 03:14:10 UTC, at a depth of 10.0 km (shallow). It is the strongest earthquake within 300 km since an M7.2 on November 8, 1980.

Magnitude: 6.7; Strong · mw
Depth: 10 km; Shallow
Felt reports: 0; Did You Feel It?
Est. shaking: V; Moderate (ShakeMap)
PAGER alert: None; Not issued
Tsunami: No flag; USGS feed

Outlined circle: this earthquakeDashed circle: 100 km aftershock search areaColoured lines: estimated shaking intensity (USGS ShakeMap)

In context

How big was it, and why here?

Energy released

169 kilotons of TNT

That is about 11 times the Hiroshima bomb. It released about 355 times the energy of a magnitude 5.0.

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

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 100 km

USGS lists 21 M2.5+ earthquakes within 100 km in the following 30 days; the largest was M5.0 on September 11, 1984. 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 139 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 11 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 · 251 km away
1 death$2 million damage
1932M6.5
Eureka
6 Jun 1932 · 216 km away · intensity VIII
1 deathModerate damage ($1–5M)
1980M7.2
North Coast
8 Nov 1980 · 227 km away · intensity VII
$2 million damage
1865
Fort Humboldt, Eureka
1 Oct 1865 · 204 km away · intensity IX
Moderate damage ($1–5M)
1922M7.6
Northern
31 Jan 1922 · 125 km away
Limited damage (under $1M)
1923M7.1
Northern
22 Jan 1923 · 152 km away · intensity VIII
Limited damage (under $1M)tsunami

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

Nearby trackers