Earthquake · reviewed by a seismologist
M 3.7mw
Earthquake near Millbrae, CA
No earthquake was likely felt in Millbrae in the 24 hours to 6:09 pm PST (02:09 UTC). The last one was M 2.7, 8 km (5 mi) WNW, at 5:17 pm PDT on 28 October 2026, estimated intensity III (weak) in town; 526 felt reports to USGS. Every earthquake near Millbrae
This page: a magnitude 3.7 earthquake was recorded 2 km (1 mi) north-northeast of Millbrae, CA, at 6:38 pm PDT on 27 October 2023 (01:38 UTC), 12 km deep. 16,471 people have reported feeling it to USGS.
USGS: 2 km NNE of Millbrae, CA
18 km (11 mi) SSE of San Francisco, CA · in South San Francisco, CA
- When
- 6:38 pm PDT on 27 October 2023 ()
- Where
- 2 km (1 mi) north-northeast of Millbrae, CA · earthquakes near Millbrae
- Magnitude
- M 3.7 (mw)
- Depth
- 12 km below the surface
- Felt
- 16,471 reports · strongest reported intensity IV
- Measured shaking
- intensity IV (ShakeMap)
- Nearest
- San Mateo County, 23 km S
- Nearest mapped fault
- Serra 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 224 days ago
Earthquake alerts for Millbrae, CA
Get a notification in this browser when USGS records an earthquake near Millbrae, 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 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 73 km (45 mi) from the epicentre. In Millbrae, 2 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: Millbrae 2 km, intensity III · San Bruno 3 km, intensity III · Burlingame 4 km, intensity III · South San Francisco 5 km, intensity III · San Mateo 8 km, intensity III · Pacifica 10 km, intensity III · Foster City 11 km, intensity III · Daly City 12 km, intensity III. Estimated for each town centre; each link is that town's own record.
How big was it?
This earthquake released about 4.8 tons of TNT. Magnitude is logarithmic: each whole step up releases about 32 times more energy, so a magnitude 4.7 would have released about 32 times as much.
- Northridge, California 1994 M 6.7 35,000× the energy of this one
- Mineral, Virginia 2011 M 5.8 1,600× the energy of this one
- Magna, Utah 2020 M 5.7 1,100× the energy of this one
- This earthquake M 3.7 about 4.8 tons of TNT
- Around the size people start to feel M 3.0 this one released 10× 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 4.5 on 2019-10-15 — about 15 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 · 21 km NW of this epicentre
- 5.3 The 1957 San Francisco, California Earthquake · 11 km WNW 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 37.6178, -122.3770. Map © OpenStreetMap contributors.
Nearby places
| Place | Distance | Direction from the epicentre | |
|---|---|---|---|
| San Mateo County, CA | 23 km (14 mi) | S | earthquakes near San Mateo County |
| Alameda County, CA | 41 km (25 mi) | E | earthquakes near Alameda County |
| Contra Costa County, CA | 50 km (31 mi) | NE | earthquakes near Contra Costa County |
| Marin County, CA | 58 km (36 mi) | NW | earthquakes near Marin County |
| San Francisco County, CA | 59 km (37 mi) | WNW | earthquakes near San Francisco County |
| Santa Cruz County, CA | 75 km (46 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
58 earthquakes have been recorded within 50 km since this one.
- 3.2 5 km WSW of San Francisco Zoo, CA
- 2.2 3 km ESE of Woodside, CA
- 1.5 6 km S of Portola Valley, CA
- 2.1 3 km W of Woodside, CA
- 2.2 6 km S of Alameda, CA
- 1.6 6 km S of Alameda, CA
- 2.3 3 km ESE of Woodside, CA
- 1.6 4 km NE of Portola Valley, CA
- 1.5 6 km E of Santa Venetia, CA
- 1.6 1 km SSE of Pacheco, CA
- 1.5 2 km N of Pleasant Hill, CA
- 1.5 3 km W of Woodside, CA
- 1.8 7 km NW of San Francisco Zoo, CA
- 1.6 2 km ENE of Oakland, CA
- 1.7 8 km NW of Bayview-Montalvin, 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.