Earthquake · reviewed by a seismologist
M 2.3md
Earthquake near Union City, CA
No earthquake was likely felt in Union City in the 24 hours to 8:51 pm PST (04:51 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 2.3 earthquake was recorded 3 km (2 mi) north of Union City, CA, at 4:34 am PDT on 24 May 2017 (11:34 UTC), 6.6 km deep. 7 people have reported feeling it to USGS.
USGS: 2 km N of Union City, California
in Union City, CA · 41 km (25 mi) NNW of San Jose, CA
- When
- 4:34 am PDT on 24 May 2017 ()
- Where
- 3 km (2 mi) north of Union City, CA · earthquakes near Union City
- Magnitude
- M 2.3 (md)
- Depth
- 6.6 km below the surface
- Felt
- 7 reports · strongest reported intensity III
- 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 3458 days ago
Earthquake alerts for Union City, 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 18 km (11 mi) from the epicentre. In Union City, 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: Union City 3 km, intensity II · Hayward 7 km, intensity II · Fremont 9 km, intensity II · Castro Valley 10 km, intensity II · Newark 10 km, intensity II · San Lorenzo 11 km, intensity II · Dublin 12 km, intensity II · Pleasanton 14 km, intensity II. Estimated for each town centre; each link is that town's own record.
How big was it?
This earthquake released about 82 lb of TNT. Magnitude is logarithmic: each whole step up releases about 32 times more energy, so a magnitude 3.3 would have released about 32 times as much.
- Mineral, Virginia 2011 M 5.8 180,000× the energy of this one
- Magna, Utah 2020 M 5.7 130,000× the energy of this one
- Around the size people start to feel M 3.0 12× the energy of this one
- This earthquake M 2.3 about 82 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
No earthquake of M4 or more has been recorded within 50 km since our catalogue begins in 2016.
Before 2016, the USGS record lists 13 earthquakes of M5 or more within 50 km; the five largest:
- 7.9 The 1906 San Francisco, California Earthquake · 48 km WNW of this epicentre
- 6.2 Near San Jose, California · 41 km SSE of this epicentre
- 6.2 The 1984 Morgan Hill, California Earthquake · 46 km SE of this epicentre
- 5.8 7 km NNW of Boulder Creek, California · 49 km SSW of this epicentre
- 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 37.6217, -122.0237. Map © OpenStreetMap contributors.
Nearby places
| Place | Distance | Direction 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) | SSE | 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
59 earthquakes have been recorded within 50 km since this one.
- 1.7 4 km W of Woodside, California
- 1.9 9 km NNE of East Foothills, California
- 1.6 4 km SE of Piedmont, California
- 1.5 2 km S of Loyola, California
- 1.9 0 km NNW of Pleasant Hill, California
- 2.4 8 km NE of Milpitas, California
- 1.6 3 km S of Loyola, California
- 2.0 0 km W of Kensington, California
- 1.7 0 km W of Kensington, California
- 1.8 0 km E of Hayward, California
- 2.0 4 km NNW of Orinda, California
- 2.5 8 km ESE of East Foothills, California
- 2.2 0 km ESE of North Gate, California
- 2.0 4 km NNW of Orinda, California
- 1.6 4 km SW of Danville, California
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.