Earthquake · reviewed by a seismologist
M 1.8md
Earthquake near Diablo, CA
No earthquake was likely felt in Diablo in the 24 hours to 3:25 am PST (11:25 UTC). The last one was M 2.5, 18 km (11 mi) NNW, at 1:23 am PST on 2 November 2026, estimated intensity II (weak) in town; 39 felt reports to USGS. Every earthquake near Diablo
This page: a magnitude 1.8 earthquake was recorded in Diablo, CA, at 5:31 am PDT on 12 September 2021 (12:31 UTC), 8.2 km deep.
USGS: 1km NW of Diablo, CA
9 km (6 mi) SE of Walnut Creek, CA · 40 km (25 mi) E of San Francisco, CA
- When
- 5:31 am PDT on 12 September 2021 ()
- Where
- in Diablo, CA · earthquakes near Diablo
- Magnitude
- M 1.8 (md)
- Depth
- 8.2 km below the surface
- Felt
- no reports yet
- Nearest
- Contra Costa County, 9 km N
- Nearest mapped fault
- Calaveras fault, 4 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 1882 days ago
Earthquake alerts for Diablo, 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 10 km (6 mi) from the epicentre. 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: Danville 4 km, intensity II · Alamo 5 km, intensity II · San Ramon 7 km, intensity II. Estimated for each town centre; each link is that town's own record.
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 · 18 km E of this epicentre
- 5.7 15 km NE of East Foothills, California · 48 km SSE of this epicentre
- 5.5 6 km NNE of East Foothills, California · 49 km SSE of this epicentre
- 5.4 9 km NE of Livermore, California · 25 km ESE of this epicentre
- 5.3 The 1957 San Francisco, California Earthquake · 49 km WSW 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 37.8428, -121.9705. Map © OpenStreetMap contributors.
Nearby places
| Place | Distance | Direction from the epicentre | |
|---|---|---|---|
| Contra Costa County, CA | 9 km (5 mi) | N | earthquakes near Contra Costa County |
| Alameda County, CA | 22 km (14 mi) | SSE | earthquakes near Alameda County |
| Solano County, CA | 47 km (29 mi) | N | earthquakes near Solano County |
| San Mateo County, CA | 59 km (37 mi) | SW | earthquakes near San Mateo County |
| San Joaquin County, CA | 62 km (39 mi) | E | earthquakes near San Joaquin County |
| Marin County, CA | 72 km (45 mi) | WNW | earthquakes near Marin County |
Places and coordinates from the US Census Bureau Gazetteer (2024). Distances are from the epicentre.
Aftershocks so far
60 earthquakes have been recorded within 50 km since this one.
- 1.6 1km NE of San Ramon, CA
- 1.8 1km NE of San Ramon, CA
- 2.0 1km NE of San Ramon, CA
- 2.0 1km NE of San Ramon, CA
- 1.5 2km NE of San Ramon, CA
- 3.0 1km NE of San Ramon, CA
- 1.7 1km NE of San Ramon, CA
- 2.3 1km NE of San Ramon, CA
- 2.1 1km NNE of San Ramon, CA
- 2.5 1km NE of San Ramon, CA
- 3.2 2km NE of San Ramon, CA
- 3.9 1km NE of San Ramon, CA
- 1.8 8km WSW of Mountain House, CA
- 2.0 5km E of Fremont, CA
- 2.3 1km W of Kensington, 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.