QuakeIndex

Earthquake · reviewed by a seismologist

M 3.1ml

31 km SW of Portola Valley, CA

· 14 km deep · released about 1,400 lb of TNT

Felt it? Tell USGS Check my area
10 km30 km60 km120 km N San Mateo County 28 kmSanta Cruz County 45 kmSanta Clara County 70 kmAlameda County 72 kmSan Francisco County 79 kmContra Costa County 95 kmMarin County 100 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
Magnitude
M 3.1 (ml)
Depth
14 km below the surface
Felt
238 reports · strongest reported intensity IV
Nearest
San Mateo County, 28 km NNE
Status
Reviewed by a seismologist

USGS · last changed by USGS · we first saw it 345 days ago

This was a small earthquake. Shaking like this is often felt indoors nearby and very rarely causes damage. 238 people have reported feeling it to USGS.

How big was it?

This earthquake released about 1,400 lb of TNT. Magnitude is logarithmic: each whole step up releases about 32 times more energy, so a magnitude 4.1 would have released about 32 times as much.

  1. Northridge, California 1994 M 6.7 240,000× the energy of this one
  2. Mineral, Virginia 2011 M 5.8 11,000× the energy of this one
  3. Magna, Utah 2020 M 5.7 7,700× the energy of this one
  4. This earthquake M 3.1 about 1,400 lb of TNT
  5. Around the size people start to feel M 3.0 this one released 1.5× 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.

Where

Epicentre 37.1757, -122.4753. Map © OpenStreetMap contributors.

Nearby places

PlaceDistanceDirection
San Mateo County, CA 28 km (17 mi) SSW of here earthquakes near San Mateo County
Santa Cruz County, CA 45 km (28 mi) WNW of here earthquakes near Santa Cruz County
Santa Clara County, CA 70 km (43 mi) W of here earthquakes near Santa Clara County
Alameda County, CA 72 km (45 mi) SW of here earthquakes near Alameda County
San Francisco County, CA 79 km (49 mi) SE of here earthquakes near San Francisco County
Contra Costa County, CA 95 km (59 mi) SSW of here earthquakes near Contra Costa County

Places and coordinates from the US Census Bureau Gazetteer (2024). Distances are from the epicentre.

Aftershocks so far

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

  1. 2.1 2 km NE of Millbrae, CA
  2. 1.6 3 km SE of Pacifica, CA
  3. 2.0 3 km SE of Pacifica, CA
  4. 2.3 10 km SW of Bonny Doon, CA
  5. 2.1 3 km SE of Pacifica, CA
  6. 1.8 24 km WNW of Boulder Creek, CA
  7. 2.1 3 km SE of Pacifica, CA
  8. 1.8 3 km SE of Pacifica, CA
  9. 1.6 3 km SE of Pacifica, CA
  10. 1.5 3 km SE of Pacifica, CA
  11. 2.0 2 km SE of Pacifica, CA
  12. 1.5 3 km SE of Pacifica, CA
  13. 1.6 2 km SE of Pacifica, CA
  14. 1.6 4 km SE of Pacifica, CA
  15. 1.6 2 km SE of Pacifica, 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.