Earthquake · automatic estimate, may change
M 1.3md
Earthquake near Portola Valley, CA
USGS: 11 km SSE of Portola Valley, CA
13 km (8 mi) SSW of Palo Alto, CA · 34 km (21 mi) W of San Jose, CA
- When
- 5:57 am PDT on 28 September 2026 ()
- Where
- 11 km (7 mi) SSE of Portola Valley, CA · earthquakes near Portola Valley
- Magnitude
- M 1.3 (md)
- Depth
- 1.9 km below the surface
- Felt
- no reports yet
- Nearest
- San Mateo County, 20 km NW
- Nearest mapped fault
- San Andreas fault, 4 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 5 days ago
A magnitude 1.3 earthquake was recorded 11 km (7 mi) SSE of Portola Valley, CA, at 5:57 am PDT on 28 September 2026 (12:57 UTC). This was a minor earthquake. Quakes this small are rarely felt and do not cause damage.
Earthquakes near other towns within 30 km: Loyola, Los Altos Hills, Ladera, Los Altos, Mountain View, Stanford.
How big was it?
This earthquake released about 2.3 lb of TNT. Magnitude is logarithmic: each whole step up releases about 32 times more energy, so a magnitude 2.3 would have released about 32 times as much.
- Mineral, Virginia 2011 M 5.8 6,500,000× the energy of this one
- Magna, Utah 2020 M 5.7 4,600,000× the energy of this one
- Around the size people start to feel M 3.0 410× the energy of this one
- This earthquake M 1.3 about 2.3 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 500,000 times the energy of this one.
Before 2016, the USGS record lists 18 earthquakes of M5 or more within 50 km; the five largest:
- 6.9 The 1989 Loma Prieta, California Earthquake · 40 km SE of this epicentre
- 6.3 16 km SW of Davenport, California · 43 km SSW of this epicentre
- 6.2 Near San Jose, California · 35 km E of this epicentre
- 6.2 The 1984 Morgan Hill, California Earthquake · 46 km E of this epicentre
- 6.1 Near San Jose, California · 37 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 37.2928, -122.1982. Map © OpenStreetMap contributors.
Nearby places
| Place | Distance | Direction from the epicentre | |
|---|---|---|---|
| San Mateo County, CA | 20 km (13 mi) | NW | earthquakes near San Mateo County |
| Santa Cruz County, CA | 35 km (22 mi) | SSE | earthquakes near Santa Cruz County |
| Santa Clara County, CA | 46 km (28 mi) | E | earthquakes near Santa Clara County |
| Alameda County, CA | 47 km (29 mi) | NNE | earthquakes near Alameda County |
| Contra Costa County, CA | 73 km (45 mi) | NNE | earthquakes near Contra Costa County |
| San Francisco County, CA | 88 km (55 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
5 earthquakes have been recorded within 50 km since this one.
- 1.0 4 km WSW of Cupertino, CA
- 1.1 5 km WSW of Cupertino, CA
- 1.2 2 km NE of Pacifica, CA
- 1.3 11 km SW of Loyola, CA
- 1.2 15 km E of Seven Trees, 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.