QuakeIndex

Earthquake · reviewed by a seismologist

M 2.1md

2 km NE of Millbrae, CA

· 13 km deep · released about 37 lb of TNT

Felt it? Tell USGS Check my area
10 km30 km60 km120 km N San Mateo County 22 kmAlameda County 41 kmContra Costa County 51 kmMarin County 59 kmSan Francisco County 59 kmSanta Cruz County 74 kmSanta Clara County 74 kmSolano County 82 kmNapa 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 2.1 (md)
Depth
13 km below the surface
Felt
3 reports · strongest reported intensity II
Nearest
San Mateo County, 22 km S
Status
Reviewed by a seismologist

USGS · last changed by USGS · we first saw it 187 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 37 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 5.8 410,000× the energy of this one
  2. Magna, Utah 2020 M 5.7 290,000× the energy of this one
  3. Around the size people start to feel M 3.0 26× the energy of this one
  4. This earthquake M 2.1 about 37 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 37.6122, -122.3747. Map © OpenStreetMap contributors.

Nearby places

PlaceDistanceDirection
San Mateo County, CA 22 km (14 mi) N of here earthquakes near San Mateo County
Alameda County, CA 41 km (25 mi) W of here earthquakes near Alameda County
Contra Costa County, CA 51 km (31 mi) SW of here earthquakes near Contra Costa County
Marin County, CA 59 km (37 mi) SE of here earthquakes near Marin County
San Francisco County, CA 59 km (37 mi) ESE of here earthquakes near San Francisco County
Santa Cruz County, CA 74 km (46 mi) NNW of here earthquakes near Santa Cruz County

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

Aftershocks so far

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

  1. 1.9 3 km ESE of Berkeley, CA
  2. 1.8 1 km ENE of Dublin, CA
  3. 1.9 1 km ESE of Pinole, CA
  4. 2.3 2 km SE of Pacifica, CA
  5. 2.5 1 km ESE of Pinole, CA
  6. 1.6 12 km NNW of Boulder Creek, CA
  7. 1.7 4 km NNE of Diablo, CA
  8. 1.5 3 km SSW of San Francisco Zoo, CA
  9. 2.6 3 km SSW of San Francisco Zoo, CA
  10. 1.9 3 km SSW of San Francisco Zoo, CA
  11. 2.9 3 km SSW of San Francisco Zoo, CA
  12. 1.6 1 km WSW of Pleasant Hill, CA
  13. 1.6 4 km WNW of San Francisco Zoo, CA
  14. 1.6 5 km SSW of Clayton, CA
  15. 1.7 6 km WSW of Colma, 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.

For this area

The largest earthquake within 50 km in our catalogue was M 4.5 on 2019-10-15 — it released about 4,000 times the energy of this one.

From the QuakeIndex catalogue, built from the USGS FDSN event service.

On USGS

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