quarry blast · reviewed by a seismologist
M 1.8ml
Earthquake near Bradbury, CA
No earthquake was likely felt in Bradbury in the 24 hours to 6:08 am PST (14:08 UTC). The last one was M 3.8, 78 km (48 mi) WNW, at 8:00 pm PDT on 29 September 2026, estimated intensity II (weak) in town; 199 felt reports to USGS. Every earthquake near Bradbury
No: USGS classifies this as a quarry blast, not an earthquake. A magnitude 1.8 quarry blast was recorded 5 km (3 mi) northeast of Bradbury, CA, at 12:04 pm PDT on 21 August 2020 (19:04 UTC), less than 1 km deep.
USGS: 5km NE of Bradbury, CA
8 km (5 mi) WNW of Glendora, CA · 48 km (30 mi) ENE of Los Angeles, CA
- When
- 12:04 pm PDT on 21 August 2020 ()
- Where
- 5 km (3 mi) northeast of Bradbury, CA · earthquakes near Bradbury
- Magnitude
- M 1.8 (ml)
- Depth
- -0.8 km below the surface
- Felt
- no reports yet
- Nearest
- Los Angeles County, 31 km W
- 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 2271 days ago
Earthquake alerts for Bradbury, 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 Bradbury, 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: Azusa 5 km, intensity II · Monrovia 7 km, intensity II · Glendora 8 km, intensity II · Covina 11 km, intensity II · Arcadia 11 km, intensity II · Baldwin Park 11 km, intensity II · Sierra Madre 12 km, intensity II · West Covina 12 km, intensity II. Estimated for each town centre; each link is that town's own record.
USGS catalogues this as quarry blast, not an earthquake.
How big was it?
This earthquake released about 16 lb of TNT. Magnitude is logarithmic: each whole step up releases about 32 times more energy, so a magnitude 2.8 would have released about 32 times as much.
- Mineral, Virginia 2011 M 5.8 970,000× the energy of this one
- Magna, Utah 2020 M 5.7 680,000× the energy of this one
- Around the size people start to feel M 3.0 61× the energy of this one
- This earthquake M 1.8 about 16 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 4.4 on 2018-08-29 — about 7,200 times the energy of this one.
Before 2016, the USGS record lists 14 earthquakes of M5 or more within 50 km; the five largest:
- 6.6 1971 San Fernando Earthquake, California · 48 km WNW of this epicentre
- 5.9 The 1987 Whittier Narrows, California Earthquake · 19 km SW of this epicentre
- 5.8 10km SSW of Agua Dulce, CA · 48 km WNW of this epicentre
- 5.8 10km SSW of Agua Dulce, CA · 48 km WNW of this epicentre
- 5.8 The 1991 Sierra Madre, California Earthquake · 12 km NNW 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 34.1800, -117.9275. Map © OpenStreetMap contributors.
Nearby places
| Place | Distance | Direction from the epicentre | |
|---|---|---|---|
| Los Angeles County, CA | 31 km (19 mi) | W | earthquakes near Los Angeles County |
| Orange County, CA | 58 km (36 mi) | SSE | earthquakes near Orange County |
| Ventura County, CA | 113 km (70 mi) | W | earthquakes near Ventura County |
Places and coordinates from the US Census Bureau Gazetteer (2024). Distances are from the epicentre.
Aftershocks so far
48 earthquakes have been recorded within 50 km since this one.
- 1.7 7km SSE of Littlerock, CA
- 1.6 8km SW of Lytle Creek, CA
- 1.9 4km SSW of San Dimas, CA
- 2.1 6km SSW of Pearblossom, CA
- 1.5 1km NNW of La Habra, CA
- 2.1 2km W of Devore, CA
- 1.7 4km SSW of Pinon Hills, CA
- 2.3 3km S of Yorba Linda, CA
- 1.9 5km SSW of Pinon Hills, CA
- 1.6 4km W of South El Monte, CA
- 1.6 3km NNW of Brea, CA
- 1.6 9km SSE of Chino, CA
- 1.5 3km SW of La Mirada, CA
- 2.5 8km NNW of Rancho Cucamonga, CA
- 1.6 4km SSW of Lytle Creek, 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.