Earthquake · reviewed by a seismologist
M 2.3md
Earthquake near Pacifica, CA
No earthquake was likely felt in Pacifica in the 24 hours to 6:45 am PST (14:45 UTC). The last one was M 2.7, 2 km (1 mi) NE, at 5:17 pm PDT on 28 October 2026, estimated intensity III (weak) in town; 526 felt reports to USGS. Every earthquake near Pacifica
This page: a magnitude 2.3 earthquake was recorded in Pacifica, CA, at 9:54 am PDT on 17 September 2023 (16:54 UTC), 8.8 km deep. 9 people have reported feeling it to USGS.
USGS: 1 km E of Pacifica, CA
19 km (12 mi) SSW of San Francisco, CA · 10 km (6 mi) WSW of South San Francisco, CA
- When
- 9:54 am PDT on 17 September 2023 ()
- Where
- in Pacifica, CA · earthquakes near Pacifica
- Magnitude
- M 2.3 (md)
- Depth
- 8.8 km below the surface
- Felt
- 9 reports · strongest reported intensity III
- Nearest
- San Mateo County, 24 km SSE
- Nearest mapped fault
- San Andreas fault, 3 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 1151 days ago
Earthquake alerts for Pacifica, CA
Get a notification in this browser when USGS records an earthquake near Pacifica, 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 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: Pacifica in town, intensity II · San Bruno 6 km, intensity II · South San Francisco 7 km, intensity II · Millbrae 8 km, intensity II · Burlingame 10 km, intensity II · Daly City 10 km, intensity II · San Mateo 14 km, intensity II · Bayview-Hunters Point 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 72 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 5.8 210,000× the energy of this one
- Magna, Utah 2020 M 5.7 150,000× the energy of this one
- Around the size people start to feel M 3.0 13× the energy of this one
- This earthquake M 2.3 about 72 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 4.4 on 2018-01-04 — about 1,600 times the energy of this one.
Before 2016, the USGS record lists 2 earthquakes of M5 or more within 50 km:
- 7.9 The 1906 San Francisco, California Earthquake · 17 km NNW of this epicentre
- 5.3 The 1957 San Francisco, California Earthquake · 6 km N 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 37.6132, -122.4738. Map © OpenStreetMap contributors.
Nearby places
| Place | Distance | Direction from the epicentre | |
|---|---|---|---|
| San Mateo County, CA | 24 km (15 mi) | SSE | earthquakes near San Mateo County |
| Alameda County, CA | 50 km (31 mi) | E | earthquakes near Alameda County |
| San Francisco County, CA | 51 km (32 mi) | WNW | earthquakes near San Francisco County |
| Marin County, CA | 54 km (34 mi) | NNW | earthquakes near Marin County |
| Contra Costa County, CA | 57 km (36 mi) | NE | earthquakes near Contra Costa County |
| Santa Cruz County, CA | 78 km (49 mi) | SSE | earthquakes near Santa Cruz County |
Places and coordinates from the US Census Bureau Gazetteer (2024). Distances are from the epicentre.
Aftershocks so far
52 earthquakes have been recorded within 50 km since this one.
- 1.6 4 km WSW of Colma, CA
- 1.5 1 km N of Millbrae, CA
- 1.9 2 km NNE of Millbrae, CA
- 2.2 4 km WSW of Cupertino, CA
- 2.2 6 km WNW of San Francisco Zoo, CA
- 1.5 6 km WNW of San Francisco Zoo, CA
- 2.1 3 km N of San Lorenzo, CA
- 1.6 7 km ESE of Santa Venetia, CA
- 1.5 2 km ESE of Pacifica, CA
- 1.6 4 km SW of Hillsborough, CA
- 1.6 4 km SW of Hillsborough, CA
- 1.5 2 km NNE of Millbrae, CA
- 1.5 3 km NNE of Millbrae, CA
- 1.7 2 km ENE of Pacifica, CA
- 1.6 3 km NNE of Millbrae, 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.