Earthquake · reviewed by a seismologist
M 1.8md
Earthquake near Blackhawk, CA
No earthquake was likely felt in Blackhawk in the 24 hours to 3:35 am PST (11:35 UTC). The last one was M 2.1, 5 km (3 mi) WNW, at 7:18 am PDT on 31 October 2026, estimated intensity II (weak) in town; 1 felt report to USGS. Every earthquake near Blackhawk
This page: a magnitude 1.8 earthquake was recorded 9 km (6 mi) east of Blackhawk, CA, at 11:47 am PDT on 27 May 2021 (18:47 UTC), 13 km deep.
USGS: 9km E of Blackhawk, CA
13 km (8 mi) ENE of San Ramon, CA · 58 km (36 mi) N of San Jose, CA
- When
- 11:47 am PDT on 27 May 2021 ()
- Where
- 9 km (6 mi) east of Blackhawk, CA · earthquakes near Blackhawk
- Magnitude
- M 1.8 (md)
- Depth
- 13 km below the surface
- Felt
- no reports yet
- Nearest
- Contra Costa County, 17 km NW
- Nearest mapped fault
- Greenville fault, 2 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 1994 days ago
Earthquake alerts for Blackhawk, CA
Get a notification in this browser when USGS records an earthquake near Blackhawk, CA. No account or email needed.
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 1 km (1 mi) from the epicentre. In Blackhawk, 9 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: Diablo, Byron, Livermore, Brentwood, San Ramon, Danville.
How big was it?
This earthquake released about 13 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 1,100,000× the energy of this one
- Magna, Utah 2020 M 5.7 810,000× the energy of this one
- Around the size people start to feel M 3.0 72× the energy of this one
- This earthquake M 1.8 about 13 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 2019-10-15 — about 11,000 times the energy of this one.
Before 2016, the USGS record lists 6 earthquakes of M5 or more within 50 km; the five largest:
- 5.8 The 1980 Livermore, California Earthquake · 4 km NE of this epicentre
- 5.7 15 km NE of East Foothills, California · 39 km SSE of this epicentre
- 5.5 6 km NNE of East Foothills, California · 43 km S of this epicentre
- 5.4 9 km NE of Livermore, California · 12 km SE of this epicentre
- 5.3 6 km E of East Foothills, California · 48 km S 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 37.8193, -121.8053. Map © OpenStreetMap contributors.
Nearby places
| Place | Distance | Direction from the epicentre | |
|---|---|---|---|
| Contra Costa County, CA | 17 km (11 mi) | NW | earthquakes near Contra Costa County |
| Alameda County, CA | 21 km (13 mi) | SSW | earthquakes near Alameda County |
| San Joaquin County, CA | 49 km (30 mi) | ENE | earthquakes near San Joaquin County |
| Solano County, CA | 51 km (32 mi) | NNW | earthquakes near Solano County |
| San Mateo County, CA | 67 km (42 mi) | SW | earthquakes near San Mateo County |
| Santa Clara County, CA | 67 km (42 mi) | S | earthquakes near Santa Clara County |
Places and coordinates from the US Census Bureau Gazetteer (2024). Distances are from the epicentre.
Aftershocks so far
57 earthquakes have been recorded within 50 km since this one.
- 1.6 5km E of Vallejo, CA
- 1.9 10km NE of Milpitas, CA
- 1.7 5km NW of Dublin, CA
- 2.6 6km S of Livermore, CA
- 2.4 11km NE of Milpitas, CA
- 1.8 5km ENE of Vallejo, CA
- 1.7 8km SSW of Livermore, CA
- 1.8 3km SW of Alamo, CA
- 1.9 3km SW of Clayton, CA
- 1.8 1km ENE of Alamo, CA
- 1.7 5km WNW of Dublin, CA
- 1.5 5km E of Fremont, CA
- 1.6 1km NE of Berkeley, CA
- 2.1 8km ENE of Alum Rock, CA
- 2.0 1km NNW of Pleasant Hill, 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.