Earthquake · automatic estimate, may change
M 2.1md
Earthquake near Portola Valley, CA
No earthquake was likely felt in Portola Valley in the 24 hours to 3:13 am PST (11:13 UTC). The last one was M 1.9, 6 km (4 mi) N, at 4:14 pm PDT on 11 October 2026, estimated intensity II (weak) in town; 1 felt report to USGS. Every earthquake near Portola Valley
This page: a magnitude 2.1 earthquake was recorded 6 km (4 mi) south-southeast of Portola Valley, CA, at 11:56 am PDT on 3 October 2025 (18:56 UTC), 8.6 km deep. 1 person has reported feeling it to USGS. The magnitude and location are an automatic first estimate and may change.
USGS: 6 km SSE of Portola Valley, CA
10 km (6 mi) SW of Palo Alto, CA · 36 km (22 mi) W of San Jose, CA
- When
- 11:56 am PDT on 3 October 2025 ()
- Where
- 6 km (4 mi) south-southeast of Portola Valley, CA · earthquakes near Portola Valley
- Magnitude
- M 2.1 (md)
- Depth
- 8.6 km below the surface
- Felt
- 1 report · strongest reported intensity III
- Nearest
- San Mateo County, 17 km NW
- Nearest mapped fault
- San Andreas fault, 3 km from its surface trace — near is not the same as on
- Status
- Automatic — a machine’s first estimate, which may change
USGS · last changed by USGS · we first saw it 406 days ago
Earthquake alerts for Portola Valley, 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 16 km (10 mi) from the epicentre. In Portola Valley, 6 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: Los Altos 11 km, intensity II · Mountain View 13 km, intensity II · Palo Alto 14 km, intensity II · Menlo Park 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 51 lb of TNT. Magnitude is logarithmic: each whole step up releases about 32 times more energy, so a magnitude 3.1 would have released about 32 times as much.
- Mineral, Virginia 2011 M 5.8 300,000× the energy of this one
- Magna, Utah 2020 M 5.7 210,000× the energy of this one
- Around the size people start to feel M 3.0 19× the energy of this one
- This earthquake M 2.1 about 51 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 23,000 times the energy of this one.
Before 2016, the USGS record lists 17 earthquakes of M5 or more within 50 km; the five largest:
- 6.9 The 1989 Loma Prieta, California Earthquake · 44 km SE of this epicentre
- 6.3 16 km SW of Davenport, California · 46 km SSW of this epicentre
- 6.2 Near San Jose, California · 37 km E of this epicentre
- 6.2 The 1984 Morgan Hill, California Earthquake · 48 km E of this epicentre
- 6.1 Near San Jose, California · 40 km ESE 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 37.3283, -122.2167. Map © OpenStreetMap contributors.
Nearby places
| Place | Distance | Direction from the epicentre | |
|---|---|---|---|
| San Mateo County, CA | 17 km (10 mi) | NW | earthquakes near San Mateo County |
| Santa Cruz County, CA | 40 km (25 mi) | SSE | earthquakes near Santa Cruz County |
| Alameda County, CA | 44 km (28 mi) | NE | earthquakes near Alameda County |
| Santa Clara County, CA | 48 km (30 mi) | ESE | earthquakes near Santa Clara County |
| Contra Costa County, CA | 70 km (43 mi) | NNE | earthquakes near Contra Costa County |
| San Francisco County, CA | 84 km (53 mi) | WNW | earthquakes near San Francisco County |
Places and coordinates from the US Census Bureau Gazetteer (2024). Distances are from the epicentre.
Aftershocks so far
28 earthquakes have been recorded within 50 km since this one.
- 2.2 3 km ESE of Union City, CA
- 1.7 11 km E of Alum Rock, CA
- 1.7 4 km SE of Pacifica, CA
- 1.8 3 km SE of Pacifica, CA
- 1.6 5 km SE of Oakland, CA
- 2.4 5 km SE of Oakland, CA
- 2.0 8 km E of Alum Rock, CA
- 2.0 3 km S of Sunol, CA
- 2.4 1 km E of Woodside, CA
- 1.6 1 km ESE of Woodside, CA
- 2.6 1 km ESE of Woodside, CA
- 2.2 1 km E of Woodside, CA
- 2.0 1 km ENE of Woodside, CA
- 2.5 1 km E of Woodside, CA
- 2.2 1 km E of Woodside, 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.