QuakeIndex

Earthquake · reviewed by a seismologist

M 3.3mw

Earthquake near Union City, CA

No earthquake was likely felt in Union City in the 24 hours to 2:52 am PST (10:52 UTC). The last one was M 1.9, 9 km (6 mi) NNE, at 10:32 am PST on 2 November 2026, estimated intensity II (weak) in town. Every earthquake near Union City

This page: a magnitude 3.3 earthquake was recorded 3 km (2 mi) north of Union City, CA, at 6:22 pm PST on 21 December 2022 (02:22 UTC), 3.8 km deep. 1,651 people have reported feeling it to USGS.

USGS: 3km N of Union City, CA

in Union City, CA · 41 km (25 mi) NNW of San Jose, CA

6:22 pm PST, Dec 21, 2022 · · 3.8 km deep · released about 1.5 tons of TNT

Every earthquake near Union City Felt it? Tell USGS Check my area
10 km30 km60 km120 km N Alameda County 10 kmContra Costa County 34 kmSan Mateo County 38 kmSanta Clara County 53 kmSanta Cruz County 68 kmSolano County 72 kmSan Joaquin County 75 kmMarin County 79 kmSan Francisco County 89 km
Distance rings around the epicentre, with the nearest towns at their true direction and later quakes as coloured dots. Not a shaking map — see the USGS ShakeMap for that.
When
6:22 pm PST on 21 December 2022 ()
Where
3 km (2 mi) north of Union City, CA · earthquakes near Union City
Magnitude
M 3.3 (mw)
Depth
3.8 km below the surface
Felt
1,651 reports · strongest reported intensity IV
Nearest
Alameda County, 10 km ENE
Nearest mapped fault
Hayward fault, 1 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 604 days ago

This was a small earthquake. Shaking like this is often felt indoors nearby and very rarely causes damage.

At this magnitude and depth, people at rest would likely notice it out to about 54 km (34 mi) from the epicentre. In Union City, 3 km away, the estimate is intensity III (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: Union City 3 km, intensity III · Hayward 7 km, intensity III · Fremont 9 km, intensity III · Castro Valley 10 km, intensity III · Newark 10 km, intensity III · San Lorenzo 11 km, intensity III · Dublin 12 km, intensity III · Pleasanton 14 km, intensity III. Estimated for each town centre; each link is that town's own record.

How big was it?

This earthquake released about 1.5 tons of TNT. Magnitude is logarithmic: each whole step up releases about 32 times more energy, so a magnitude 4.3 would have released about 32 times as much.

  1. Northridge, California 1994 M 6.7 110,000× the energy of this one
  2. Mineral, Virginia 2011 M 5.8 4,900× the energy of this one
  3. Magna, Utah 2020 M 5.7 3,500× the energy of this one
  4. This earthquake M 3.3 about 1.5 tons of TNT
  5. Around the size people start to feel M 3.0 this one released 3.2× more

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 5.1 on 2022-10-25 — about 380 times the energy of this one.

Before 2016, the USGS record lists 13 earthquakes of M5 or more within 50 km; the five largest:

  1. 7.9 The 1906 San Francisco, California Earthquake · 48 km WNW of this epicentre
  2. 6.2 Near San Jose, California · 41 km SSE of this epicentre
  3. 6.2 The 1984 Morgan Hill, California Earthquake · 46 km SE of this epicentre
  4. 5.8 7 km NNW of Boulder Creek, California · 49 km SSW of this epicentre
  5. 5.8 The 1980 Livermore, California Earthquake · 33 km NE 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 37.6202, -122.0250. Map © OpenStreetMap contributors.

Nearby places

PlaceDistanceDirection from the epicentre
Alameda County, CA 10 km (6 mi) ENE earthquakes near Alameda County
Contra Costa County, CA 34 km (21 mi) N earthquakes near Contra Costa County
San Mateo County, CA 38 km (24 mi) SW earthquakes near San Mateo County
Santa Clara County, CA 53 km (33 mi) SE earthquakes near Santa Clara County
Santa Cruz County, CA 68 km (42 mi) S earthquakes near Santa Cruz County
Solano County, CA 72 km (45 mi) N earthquakes near Solano County

Places and coordinates from the US Census Bureau Gazetteer (2024). Distances are from the epicentre.

Aftershocks so far

56 earthquakes have been recorded within 50 km since this one.

  1. 1.6 2km S of San Ramon, CA
  2. 1.6 12km ENE of Milpitas, CA
  3. 1.6 12km ENE of Milpitas, CA
  4. 1.6 12km ENE of Milpitas, CA
  5. 1.9 3km E of Hayward, CA
  6. 1.7 15km E of Seven Trees, CA
  7. 2.0 2km ESE of Berkeley, CA
  8. 1.5 6km WNW of Sunol, CA
  9. 2.2 4km WSW of Colma, CA
  10. 1.8 5km WSW of Colma, CA
  11. 1.8 15km E of Seven Trees, CA
  12. 2.2 16km E of Seven Trees, CA
  13. 1.9 6km SSE of Portola Valley, CA
  14. 2.4 16km E of Seven Trees, CA
  15. 1.8 2km SE of Pacheco, 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

QuakeIndex does not issue warnings. For earthquake early warning see ShakeAlert.