QuakeIndex

Earthquake · reviewed by a seismologist

M 2.9md

Earthquake near Portola Valley, CA

No earthquake was likely felt in Portola Valley in the 24 hours to 9:32 pm PST (05:32 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 2.9 earthquake was recorded in Portola Valley, CA, at 11:09 pm PST on 19 January 2023 (07:09 UTC), 7.3 km deep. 133 people have reported feeling it to USGS.

USGS: 1km SE of Portola Valley, CA

8 km (5 mi) WSW of Palo Alto, CA · 37 km (23 mi) WNW of San Jose, CA

11:09 pm PST, Jan 19, 2023 · · 7.3 km deep · released about 630 lb of TNT

Every earthquake near Portola Valley Felt it? Tell USGS Check my area
10 km30 km60 km120 km N San Mateo County 14 kmAlameda County 41 kmSanta Cruz County 45 kmSanta Clara County 50 kmContra Costa County 65 kmSan Francisco County 81 kmMarin County 88 kmSolano County 102 kmSan Joaquin County 105 km
Distance rings around the epicentre, with the nearest towns at their true direction and later quakes as coloured dots. Not a shaking map — see the USGS ShakeMap for that.
When
11:09 pm PST on 19 January 2023 ()
Where
in Portola Valley, CA · earthquakes near Portola Valley
Magnitude
M 2.9 (md)
Depth
7.3 km below the surface
Felt
133 reports · strongest reported intensity V
Nearest
San Mateo County, 14 km WNW
Nearest mapped fault
San Andreas fault, under 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 1317 days ago

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 30 km (19 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: Menlo Park 10 km, intensity III · Los Altos 10 km, intensity III · Palo Alto 11 km, intensity III · Redwood City 12 km, intensity III · Mountain View 13 km, intensity III · East Palo Alto 13 km, intensity III · San Carlos 15 km, intensity II · Sunnyvale 17 km, intensity II. Estimated for each town centre; each link is that town's own record.

How big was it?

This earthquake released about 630 lb of TNT. Magnitude is logarithmic: each whole step up releases about 32 times more energy, so a magnitude 3.9 would have released about 32 times as much.

  1. Mineral, Virginia 2011 M 5.8 24,000× the energy of this one
  2. Magna, Utah 2020 M 5.7 17,000× the energy of this one
  3. Around the size people start to feel M 3.0 1.5× the energy of this one
  4. This earthquake M 2.9 about 630 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 16 earthquakes of M5 or more within 50 km; the five largest:

  1. 6.9 The 1989 Loma Prieta, California Earthquake · 49 km SE of this epicentre
  2. 6.2 Near San Jose, California · 39 km ESE of this epicentre
  3. 6.2 The 1984 Morgan Hill, California Earthquake · 49 km E of this epicentre
  4. 6.1 Near San Jose, California · 42 km ESE of this epicentre
  5. 5.8 7 km NNW of Boulder Creek, California · 22 km SSE 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 37.3742, -122.2262. Map © OpenStreetMap contributors.

Nearby places

PlaceDistanceDirection from the epicentre
San Mateo County, CA 14 km (8 mi) WNW earthquakes near San Mateo County
Alameda County, CA 41 km (26 mi) NE earthquakes near Alameda County
Santa Cruz County, CA 45 km (28 mi) SSE earthquakes near Santa Cruz County
Santa Clara County, CA 50 km (31 mi) ESE earthquakes near Santa Clara County
Contra Costa County, CA 65 km (41 mi) NNE earthquakes near Contra Costa County
San Francisco County, CA 81 km (50 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

55 earthquakes have been recorded within 50 km since this one.

  1. 1.7 2km S of San Ramon, CA
  2. 1.6 5km WSW of Colma, CA
  3. 2.3 5km WSW of Colma, CA
  4. 2.0 8km NE of Alum Rock, CA
  5. 1.7 9km E of Alum Rock, CA
  6. 1.8 10km NE of Milpitas, CA
  7. 1.6 4km WSW of San Francisco Zoo, CA
  8. 2.5 12km ESE of Alum Rock, CA
  9. 1.6 12km ESE of Alum Rock, CA
  10. 1.7 12km ESE of Alum Rock, CA
  11. 2.4 12km ESE of Alum Rock, CA
  12. 2.2 3km NNE of San Leandro, CA
  13. 3.0 3km NNE of San Leandro, CA
  14. 2.7 3km NNE of San Leandro, CA
  15. 3.0 3km NNE of San Leandro, 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

QuakeIndex does not issue warnings. For earthquake early warning see ShakeAlert.