QuakeIndex

Earthquake · reviewed by a seismologist

M 2.2md

Earthquake near Union City, CA

No earthquake was likely felt in Union City in the 24 hours to 2:13 pm PST (22:13 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 2.2 earthquake was recorded in Union City, CA, at 8:47 pm PDT on 16 May 2023 (03:47 UTC), 6.8 km deep. 14 people have reported feeling it to USGS.

USGS: 2km ENE of Union City, CA

in Union City, CA · 37 km (23 mi) NNW of San Jose, CA

8:47 pm PDT, May 16, 2023 · · 6.8 km deep · released about 60 lb of TNT

Every earthquake near Union City Felt it? Tell USGS Check my area
10 km30 km60 km120 km N Alameda County 9 kmContra Costa County 36 kmSan Mateo County 39 kmSanta Clara County 50 kmSanta Cruz County 65 kmSan Joaquin County 74 kmSolano County 74 kmMarin County 83 kmStanislaus County 88 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
8:47 pm PDT on 16 May 2023 ()
Where
in Union City, CA · earthquakes near Union City
Magnitude
M 2.2 (md)
Depth
6.8 km below the surface
Felt
14 reports · strongest reported intensity III
Nearest
Alameda County, 9 km NE
Nearest mapped fault
Hayward 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 1273 days ago

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 17 km (11 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: Union City in town, intensity II · Fremont 6 km, intensity II · Newark 9 km, intensity II · Hayward 11 km, intensity II · Dublin 13 km, intensity II · Pleasanton 13 km, intensity II · Castro Valley 13 km, intensity II · San Lorenzo 15 km, intensity II. Estimated for each town centre; each link is that town's own record.

How big was it?

This earthquake released about 60 lb of TNT. Magnitude is logarithmic: each whole step up releases about 32 times more energy, so a magnitude 3.2 would have released about 32 times as much.

  1. Mineral, Virginia 2011 M 5.8 250,000× the energy of this one
  2. Magna, Utah 2020 M 5.7 180,000× the energy of this one
  3. Around the size people start to feel M 3.0 16× the energy of this one
  4. This earthquake M 2.2 about 60 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 5.1 on 2022-10-25 — about 19,000 times the energy of this one.

Before 2016, the USGS record lists 14 earthquakes of M5 or more within 50 km; the five largest:

  1. 6.2 Near San Jose, California · 38 km SSE of this epicentre
  2. 6.2 The 1984 Morgan Hill, California Earthquake · 43 km SE of this epicentre
  3. 6.1 Near San Jose, California · 48 km SSE of this epicentre
  4. 5.8 7 km NNW of Boulder Creek, California · 47 km SSW of this epicentre
  5. 5.8 The 1980 Livermore, California Earthquake · 34 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 37.5992, -121.9978. Map © OpenStreetMap contributors.

Nearby places

PlaceDistanceDirection from the epicentre
Alameda County, CA 9 km (6 mi) NE earthquakes near Alameda County
Contra Costa County, CA 36 km (22 mi) N earthquakes near Contra Costa County
San Mateo County, CA 39 km (24 mi) WSW earthquakes near San Mateo County
Santa Clara County, CA 50 km (31 mi) SSE earthquakes near Santa Clara County
Santa Cruz County, CA 65 km (41 mi) S earthquakes near Santa Cruz County
San Joaquin County, CA 74 km (46 mi) ENE earthquakes near San Joaquin 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.

  1. 1.5 8 km SE of Sunol, CA
  2. 2.2 7 km SW of Brentwood, CA
  3. 2.6 8 km SW of Brentwood, CA
  4. 2.3 2 km NNE of Millbrae, CA
  5. 1.6 7 km SSE of Portola Valley, CA
  6. 1.7 12 km NNE of Alum Rock, CA
  7. 2.4 11 km NNE of Alum Rock, CA
  8. 2.1 11 km NNE of Alum Rock, CA
  9. 2.6 14 km N of Morgan Hill, CA
  10. 1.5 8 km NE of Milpitas, CA
  11. 2.3 9 km NE of Milpitas, CA
  12. 3.6 14 km N of Morgan Hill, CA
  13. 1.7 15 km E of Seven Trees, CA
  14. 2.7 3 km N of Piedmont, CA
  15. 1.8 9 km E of Blackhawk, 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.