M3.5 earthquake 20 km WSW of Petrolia, CA

Wednesday, September 16, 2026, 14:34:52 UTC · 40.285°N, 124.519°W

A magnitude 3.5 earthquake struck 20 km WSW of Petrolia, CA on Wednesday, September 16, 2026, 14:34:52 UTC, at a depth of 20.1 km (shallow). USGS received 18 “Did You Feel It?” reports, with a maximum reported intensity of III (weak).

Magnitude: 3.5; Minor · mw
Depth: 20 km; Shallow
Felt reports: 18; Max intensity III
Est. shaking: III; Weak (ShakeMap)
PAGER alert: None; Not issued
Tsunami: No flag; USGS feed

Outlined circle: this earthquakeDashed circle: 50 km aftershock search areaColoured lines: estimated shaking intensity (USGS ShakeMap)

In context

How big was it, and why here?

Energy released

3 tons of TNT

That is about 1/5,240 of the Hiroshima bomb. A magnitude 5.0 releases about 166 times more energy.

Tectonic setting

3 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

20 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
95536<br>0.293	III · Weak	5	36 km
95558<br>0.320	III · Weak	2	32 km
95540<br>0.320	II · Weak	2	51 km
95589<br>0.330	III · Weak	1	56 km
95562<br>0.330	II · Weak	1	43 km
95565<br>0.330	II · Weak	1	49 km
95570<br>0.330	I · Not felt	1	103 km
95503<br>0.330	I · Not felt	1	62 km
95547<br>0.330	I · Not felt	1	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 since this event; the largest was M3.0 on September 21, 2026. 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 249 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 28 damaging, deadly or tsunami-generating earthquakes within 300 km of this epicenter since 1700, which together caused about 6 recorded deaths. The most severe:

2022M6.4
Humboldt County
20 Dec 2022 · 28 km away · intensity VIII
2 deaths$250 million damage
2014M6.0
Napa, Vallejo
24 Aug 2014 · 298 km away · intensity VIII
1 death$700 million damage
1969M4.8
Santa Rosa
2 Oct 1969 · 256 km away · intensity VIII
1 death$8 million damage
1954M6.6
Humboldt County
21 Dec 1954 · 82 km away
1 death$2 million damage
1932M6.5
Eureka
6 Jun 1932 · 53 km away · intensity VIII
1 deathModerate damage ($1–5M)
1992M7.1
Humboldt County: Ferndale, Petrolia
25 Apr 1992 · 19 km away · intensity VIII
$75 million damagetsunami

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

Nearby trackers