QuakeIndex

Earthquake · reviewed by a seismologist

M 3.4mw

Earthquake near Fontana, CA

No earthquake was likely felt in Fontana in the 24 hours to 7:07 am PST (15:07 UTC). The last one was M 1.6, 5 km (3 mi) W, at 6:17 am PDT on 26 October 2026, estimated intensity II (weak) in town. Every earthquake near Fontana

This page: a magnitude 3.4 earthquake was recorded 6 km (4 mi) northwest of Fontana, CA, at 1:22 am PDT on 3 July 2021 (08:22 UTC), 4.7 km deep. 1,244 people have reported feeling it to USGS.

USGS: 4km NNW of Fontana, CA

in Fontana, CA · 87 km (54 mi) E of Los Angeles, CA

1:22 am PDT, Jul 3, 2021 · · 4.7 km deep · released about 2 tons of TNT

Every earthquake near Fontana Felt it? Tell USGS Check my area
10 km30 km60 km120 km N Orange County 58 kmLos Angeles County 72 km
Distance rings around the epicentre, with the nearest towns at their true direction and later quakes as coloured dots. Not a shaking map — see the USGS ShakeMap for that.
When
1:22 am PDT on 3 July 2021 ()
Where
6 km (4 mi) northwest of Fontana, CA · earthquakes near Fontana
Magnitude
M 3.4 (mw)
Depth
4.7 km below the surface
Felt
1,244 reports · strongest reported intensity IV
Measured shaking
intensity IV (ShakeMap)
Nearest
Orange County, 58 km SSW
Nearest mapped fault
Sierra Madre fault, 3 km from its surface trace — near is not the same as on
Status
Reviewed by a seismologist

USGS · last changed by USGS · we first saw it 1696 days ago

This was a small earthquake. Shaking like this is often felt indoors nearby and very rarely causes damage.

At this magnitude and depth, people at rest would likely notice it out to about 58 km (36 mi) from the epicentre. In Fontana, 6 km away, the estimate is intensity III (weak). Estimated from magnitude, depth and distance with the intensity equation USGS Did You Feel It? uses; felt reports, where there are any, are the measurement.

Likely felt in: Fontana 6 km, intensity III · Rialto 11 km, intensity III · Rancho Cucamonga 11 km, intensity III · Muscoy 13 km, intensity III · Upland 16 km, intensity III · Colton 17 km, intensity III · Rubidoux 17 km, intensity III · Ontario 18 km, intensity III. Estimated for each town centre; each link is that town's own record.

How big was it?

This earthquake released about 2 tons of TNT. Magnitude is logarithmic: each whole step up releases about 32 times more energy, so a magnitude 4.4 would have released about 32 times as much.

  1. Northridge, California 1994 M 6.7 86,000× the energy of this one
  2. Mineral, Virginia 2011 M 5.8 3,800× the energy of this one
  3. Magna, Utah 2020 M 5.7 2,700× the energy of this one
  4. This earthquake M 3.4 about 2 tons of TNT
  5. Around the size people start to feel M 3.0 this one released 4.1× more

Energy from the Gutenberg–Richter relation (log10E = 1.5M + 4.8), rounded to two figures; bar length is magnitude, which is already a logarithm of energy. Magnitudes of past earthquakes from the USGS catalogue.

For this area

The largest earthquake within 50 km since 2016 was M 4.4 on 2018-08-29 — about 29 times the energy of this one.

Before 2016, the USGS record lists 13 earthquakes of M5 or more within 50 km; the five largest:

  1. 6.2 3 km SE of San Bernardino, California · 21 km ESE of this epicentre
  2. 6.0 The 1910 Lake Elsinore, California Earthquake · 49 km S of this epicentre
  3. 5.8 The 1991 Sierra Madre, California Earthquake · 50 km WNW of this epicentre
  4. 5.6 7km ENE of Running Springs, CA · 42 km ENE of this epicentre
  5. 5.5 The 1990 Upland, California Earthquake · 20 km W of this epicentre

Since 2016: the QuakeIndex catalogue (US, M1.5+), built from the USGS FDSN event service. Before 2016: USGS ComCat, M5+ from 1900. Distances are between epicentres. This is the record, not a forecast.

Where

Epicentre 34.1333, -117.4800. Map © OpenStreetMap contributors.

Nearby places

PlaceDistanceDirection from the epicentre
Orange County, CA 58 km (36 mi) SSW earthquakes near Orange County
Los Angeles County, CA 72 km (45 mi) W earthquakes near Los Angeles County
San Bernardino County, CA 144 km (89 mi) NE earthquakes near San Bernardino County

Places and coordinates from the US Census Bureau Gazetteer (2024). Distances are from the epicentre.

Aftershocks so far

50 earthquakes have been recorded within 50 km since this one.

  1. 2.6 5km SE of Loma Linda, CA
  2. 1.7 4km SE of Yucaipa, CA
  3. 1.6 4km SW of Highland, CA
  4. 1.9 4km SE of Home Gardens, CA
  5. 1.7 5km NNW of Beaumont, CA
  6. 2.0 3km E of Loma Linda, CA
  7. 1.7 4km SE of Home Gardens, CA
  8. 1.7 2km ESE of Loma Linda, CA
  9. 1.7 4km N of Fontana, CA
  10. 1.6 4km N of Fontana, CA
  11. 1.8 3km SSE of Devore, CA
  12. 1.6 4km N of Rancho Cucamonga, CA
  13. 1.7 6km SSE of Home Gardens, CA
  14. 1.5 5km NNE of Fontana, CA
  15. 1.8 1km NNW of La Puente, CA

Counted from the QuakeIndex database, which ingests the USGS feed every 30 seconds · as of . QuakeIndex does not forecast aftershocks. When USGS issues an operational aftershock forecast it appears on the USGS event page.

On USGS

QuakeIndex does not issue warnings. For earthquake early warning see ShakeAlert.