Earthquake · reviewed by a seismologist
M 1.9ml
Earthquake near Ontario, CA
No earthquake was likely felt in Ontario in the 24 hours to 10:24 am PST (18:24 UTC). The last one was M 1.7, 8 km (5 mi) SE, at 2:48 pm PDT on 9 October 2026, estimated intensity II (weak) in town. Every earthquake near Ontario
This page: a magnitude 1.9 earthquake was recorded 5 km (3 mi) east-southeast of Ontario, CA, at 6:54 am PST on 4 December 2021 (14:54 UTC), 3.7 km deep. 7 people have reported feeling it to USGS.
USGS: 3km ESE of Ontario, CA
in Ontario, CA · 74 km (46 mi) E of Los Angeles, CA
- When
- 6:54 am PST on 4 December 2021 ()
- Where
- 5 km (3 mi) east-southeast of Ontario, CA · earthquakes near Ontario
- Magnitude
- M 1.9 (ml)
- Depth
- 3.7 km below the surface
- Felt
- 7 reports · strongest reported intensity III
- Nearest
- Orange County, 44 km SSW
- Nearest mapped fault
- Red Hill-Etiwanda Avenue fault, 8 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 1802 days ago
Earthquake alerts for Ontario, CA
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Alerts are on for .
Not a warning. An alert comes after USGS publishes a quake, usually minutes after the shaking. For early warning use ShakeAlert, through your phone's Wireless Emergency Alerts or the MyShake app.
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 14 km (9 mi) from the epicentre. In Ontario, 5 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.
Likely felt in: Ontario 5 km, intensity II · Rancho Cucamonga 7 km, intensity II · Upland 8 km, intensity II · Chino 8 km, intensity II · Montclair 9 km, intensity II · Eastvale 9 km, intensity II · Claremont 12 km, intensity II · Norco 13 km, intensity II. Estimated for each town centre; each link is that town's own record.
How big was it?
This earthquake released about 20 lb of TNT. Magnitude is logarithmic: each whole step up releases about 32 times more energy, so a magnitude 2.9 would have released about 32 times as much.
- Mineral, Virginia 2011 M 5.8 760,000× the energy of this one
- Magna, Utah 2020 M 5.7 540,000× the energy of this one
- Around the size people start to feel M 3.0 48× the energy of this one
- This earthquake M 1.9 about 20 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 9,800 times the energy of this one.
Before 2016, the USGS record lists 15 earthquakes of M5 or more within 50 km; the five largest:
- 6.2 3 km SE of San Bernardino, California · 32 km E of this epicentre
- 6.0 The 1910 Lake Elsinore, California Earthquake · 42 km SSE of this epicentre
- 5.9 The 1987 Whittier Narrows, California Earthquake · 44 km W of this epicentre
- 5.8 The 1991 Sierra Madre, California Earthquake · 44 km NW of this epicentre
- 5.5 The 1990 Upland, California Earthquake · 14 km NW 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 34.0398, -117.6040. Map © OpenStreetMap contributors.
Nearby places
| Place | Distance | Direction from the epicentre | |
|---|---|---|---|
| Orange County, CA | 44 km (27 mi) | SSW | earthquakes near Orange County |
| Los Angeles County, CA | 63 km (39 mi) | WNW | earthquakes near Los Angeles County |
| San Diego County, CA | 137 km (85 mi) | SE | earthquakes near San Diego County |
Places and coordinates from the US Census Bureau Gazetteer (2024). Distances are from the epicentre.
Aftershocks so far
55 earthquakes have been recorded within 50 km since this one.
- 1.5 4km SE of Redlands, CA
- 1.9 6km SSE of Lytle Creek, CA
- 1.7 4km SSE of Home Gardens, CA
- 1.5 2km NW of Loma Linda, CA
- 1.8 3km SSW of San Bernardino, CA
- 1.5 3km ESE of Loma Linda, CA
- 1.8 8km N of Glendora, CA
- 2.6 2km S of Redlands, CA
- 1.5 4km SSW of Redlands, CA
- 1.6 2km NNW of Fontana, CA
- 1.5 2km E of Home Gardens, CA
- 1.5 4km SE of Home Gardens, CA
- 1.7 6km WNW of Fontana, CA
- 3.6 13km NE of Trabuco Canyon, CA
- 1.7 4km NNW of Fontana, 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
- The official USGS event page — the source of record for every value above
- Did you feel it? Report it to USGS — reports go to USGS, not to us
- ShakeMap for this event, when USGS has produced one
QuakeIndex does not issue warnings. For earthquake early warning see ShakeAlert.