QuakeIndex

Earthquake · reviewed by a seismologist

M 1.6ml

Earthquake near Rancho Cucamonga, CA

No earthquake was likely felt in Rancho Cucamonga in the 24 hours to 5:55 am PST (13:55 UTC). The last one was M 2.0, 10 km (6 mi) E, at 2:35 am PDT on 23 October 2026, estimated intensity II (weak) in town; 3 felt reports to USGS. Every earthquake near Rancho Cucamonga

This page: a magnitude 1.6 earthquake was recorded 6 km (4 mi) north-northeast of Rancho Cucamonga, CA, at 9:22 am PDT on 21 August 2021 (16:22 UTC), 11 km deep.

USGS: 4km N of Rancho Cucamonga, CA

in Rancho Cucamonga, CA · 79 km (49 mi) ENE of Los Angeles, CA

9:22 am PDT, Aug 21, 2021 · · 11 km deep · released about 7.6 lb of TNT

Every earthquake near Rancho Cucamonga Felt it? Tell USGS Check my area
10 km30 km60 km120 km N Orange County 57 kmLos Angeles County 63 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
9:22 am PDT on 21 August 2021 ()
Where
6 km (4 mi) north-northeast of Rancho Cucamonga, CA · earthquakes near Rancho Cucamonga
Magnitude
M 1.6 (ml)
Depth
11 km below the surface
Felt
no reports yet
Nearest
Orange County, 57 km SSW
Nearest mapped fault
Sierra Madre fault, 1 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 1908 days ago

This was a minor earthquake. Quakes this small are rarely felt and do not cause damage.

At this magnitude and depth, people at rest would likely notice it out to about 1 km (1 mi) from the epicentre. In Rancho Cucamonga, 6 km away, the estimate is intensity II (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.

Earthquakes near other towns within 30 km: San Antonio Heights, Upland, Ontario, Montclair, Fontana, Claremont.

How big was it?

This earthquake released about 7.6 lb of TNT. Magnitude is logarithmic: each whole step up releases about 32 times more energy, so a magnitude 2.6 would have released about 32 times as much.

  1. Mineral, Virginia 2011 M 5.8 2,000,000× the energy of this one
  2. Magna, Utah 2020 M 5.7 1,400,000× the energy of this one
  3. Around the size people start to feel M 3.0 130× the energy of this one
  4. This earthquake M 1.6 about 7.6 lb of TNT

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 4.5 on 2020-09-19 — about 26,000 times the energy of this one.

Before 2016, the USGS record lists 9 earthquakes of M5 or more within 50 km; the five largest:

  1. 6.2 3 km SE of San Bernardino, California · 30 km ESE of this epicentre
  2. 5.9 The 1987 Whittier Narrows, California Earthquake · 48 km WSW of this epicentre
  3. 5.8 The 1991 Sierra Madre, California Earthquake · 41 km WNW of this epicentre
  4. 5.5 The 1990 Upland, California Earthquake · 11 km W of this epicentre
  5. 5.4 5km S of Chino Hills, CA · 29 km SW 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 34.1562, -117.5742. Map © OpenStreetMap contributors.

Nearby places

PlaceDistanceDirection from the epicentre
Orange County, CA 57 km (35 mi) SSW earthquakes near Orange County
Los Angeles County, CA 63 km (39 mi) W earthquakes near Los Angeles County

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

Aftershocks so far

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

  1. 1.6 4km W of Yucaipa, CA
  2. 1.6 5km SSE of Loma Linda, CA
  3. 2.0 4km W of Yucaipa, CA
  4. 1.9 4km SSE of Home Gardens, CA
  5. 1.7 8km NE of Moreno Valley, CA
  6. 1.5 2km SSW of San Dimas, CA
  7. 1.7 4km NNE of Moreno Valley, CA
  8. 2.1 5km W of Devore, CA
  9. 2.2 4km W of Pomona, CA
  10. 1.6 4km NNE of Diamond Bar, CA
  11. 1.7 4km SE of Redlands, CA
  12. 1.5 4km SE of Home Gardens, CA
  13. 1.8 5km SSW of Redlands, CA
  14. 1.6 2km ESE of Anaheim, CA
  15. 1.6 2km ESE of Anaheim, 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.