Earthquake · reviewed by a seismologist
M 1.7md
Earthquake near Byron, CA
No earthquake was likely felt in Byron in the 24 hours to 3:03 am PST (11:03 UTC). The last one was M 3.5, 53 km (33 mi) SSE, at 7:21 am PDT on 27 September 2026, estimated intensity II (weak) in town; 8 felt reports to USGS. Every earthquake near Byron
This page: a magnitude 1.7 earthquake was recorded 3 km (2 mi) north-northwest of Byron, CA, at 7:11 am PDT on 21 July 2021 (14:11 UTC), 4.0 km deep.
USGS: 3km NNW of Byron, CA
8 km (5 mi) SE of Brentwood, CA · 68 km (42 mi) NNE of San Jose, CA
- When
- 7:11 am PDT on 21 July 2021 ()
- Where
- 3 km (2 mi) north-northwest of Byron, CA · earthquakes near Byron
- Magnitude
- M 1.7 (md)
- Depth
- 4.0 km below the surface
- Felt
- no reports yet
- Nearest
- Contra Costa County, 27 km W
- Nearest mapped fault
- Greenville fault, 16 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 1940 days ago
Earthquake alerts for Byron, CA
Get a notification in this browser when USGS records an earthquake near Byron, 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 11 km (7 mi) from the epicentre. In Byron, 3 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: Discovery Bay 4 km, intensity II · Brentwood 6 km, intensity II. Estimated for each town centre; each link is that town's own record.
How big was it?
This earthquake released about 9.3 lb of TNT. Magnitude is logarithmic: each whole step up releases about 32 times more energy, so a magnitude 2.7 would have released about 32 times as much.
- Mineral, Virginia 2011 M 5.8 1,600,000× the energy of this one
- Magna, Utah 2020 M 5.7 1,100,000× the energy of this one
- Around the size people start to feel M 3.0 100× the energy of this one
- This earthquake M 1.7 about 9.3 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 16,000 times the energy of this one.
Before 2016, the USGS record lists 4 earthquakes of M5 or more within 50 km:
- 5.8 The 1980 Livermore, California Earthquake · 12 km WSW of this epicentre
- 5.7 15 km NE of East Foothills, California · 46 km S of this epicentre
- 5.4 9 km NE of Livermore, California · 17 km SSW of this epicentre
- 5.1 11 km E of Blackhawk, California · 15 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 37.8950, -121.6478. Map © OpenStreetMap contributors.
Nearby places
| Place | Distance | Direction from the epicentre | |
|---|---|---|---|
| Contra Costa County, CA | 27 km (17 mi) | W | earthquakes near Contra Costa County |
| San Joaquin County, CA | 33 km (21 mi) | E | earthquakes near San Joaquin County |
| Alameda County, CA | 36 km (22 mi) | SW | earthquakes near Alameda County |
| Solano County, CA | 49 km (30 mi) | NNW | earthquakes near Solano County |
| Sacramento County, CA | 67 km (42 mi) | NNE | earthquakes near Sacramento County |
| Stanislaus County, CA | 68 km (42 mi) | ESE | earthquakes near Stanislaus County |
Places and coordinates from the US Census Bureau Gazetteer (2024). Distances are from the epicentre.
Aftershocks so far
53 earthquakes have been recorded within 50 km since this one.
- 2.0 9km SW of Brentwood, CA
- 1.6 1km SW of Alamo, CA
- 1.6 10km NE of Milpitas, CA
- 1.5 3km SSW of Clayton, CA
- 1.9 1km S of San Ramon, CA
- 1.6 9km SE of Sunol, CA
- 1.6 5km SW of Clayton, CA
- 2.8 16km SSE of Livermore, CA
- 2.1 4km WSW of Alamo, CA
- 2.1 6km SSW of Moraga, CA
- 1.9 5km SW of Pacheco, CA
- 1.8 2km SE of Pacheco, CA
- 1.6 1km S of Blackhawk, CA
- 2.7 0km N of Byron, CA
- 2.0 19km NE of Alum Rock, 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.