QuakeIndex

Earthquake · reviewed by a seismologist

M 2.1md

1km SE of Portola Valley, CA

· 7.2 km deep · released about 41 lb of TNT

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 104 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 2.1 (md)
Depth
7.2 km below the surface
Felt
3 reports · strongest reported intensity IV
Nearest
San Mateo County, 14 km WNW
Status
Reviewed by a seismologist

USGS · last changed by USGS · we first saw it 1343 days ago

This was a minor earthquake. Quakes this small are rarely felt and do not cause damage. 3 people have reported feeling it to USGS.

How big was it?

This earthquake released about 41 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.

  1. Mineral, Virginia 2011 M 5.8 370,000× the energy of this one
  2. Magna, Utah 2020 M 5.7 260,000× the energy of this one
  3. Around the size people start to feel M 3.0 23× the energy of this one
  4. This earthquake M 2.1 about 41 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.

Where

Epicentre 37.3772, -122.2238. Map © OpenStreetMap contributors.

Nearby places

PlaceDistanceDirection
San Mateo County, CA 14 km (9 mi) ESE of here earthquakes near San Mateo County
Alameda County, CA 41 km (25 mi) SW of here earthquakes near Alameda County
Santa Cruz County, CA 45 km (28 mi) NNW of here earthquakes near Santa Cruz County
Santa Clara County, CA 50 km (31 mi) WNW of here earthquakes near Santa Clara County
Contra Costa County, CA 65 km (40 mi) SSW of here earthquakes near Contra Costa County
San Francisco County, CA 81 km (50 mi) ESE of here 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. 2.0 5km NE of Alum Rock, CA
  2. 1.6 9km NE of Milpitas, CA
  3. 2.1 9km E of Alum Rock, CA
  4. 2.3 9km E of Alum Rock, CA
  5. 1.9 7km NE of Alum Rock, CA
  6. 1.5 8km NE of Alum Rock, CA
  7. 2.2 7km SSE of Sunol, CA
  8. 1.7 2km S of San Ramon, CA
  9. 1.6 5km WSW of Colma, CA
  10. 2.3 5km WSW of Colma, CA
  11. 2.0 8km NE of Alum Rock, CA
  12. 1.7 9km E of Alum Rock, CA
  13. 1.8 10km NE of Milpitas, CA
  14. 1.6 4km WSW of San Francisco Zoo, CA
  15. 2.5 12km ESE of Alum Rock, 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.