QuakeIndex

Earthquake · reviewed by a seismologist

M 2.1md

Earthquake near San Lorenzo, CA

No earthquake was likely felt in San Lorenzo in the 24 hours to 5:55 pm PST (01:55 UTC). The last one was M 2.4, 19 km (12 mi) ENE, at 4:29 pm PDT on 19 October 2026, estimated intensity II (weak) in town; 5 felt reports to USGS. Every earthquake near San Lorenzo

This page: a magnitude 2.1 earthquake was recorded 9 km (5 mi) west-southwest of San Lorenzo, CA, at 9:30 pm PDT on 25 September 2023 (04:30 UTC), 7.8 km deep. 3 people have reported feeling it to USGS.

USGS: 10 km WSW of San Lorenzo, CA

24 km (15 mi) SE of San Francisco, CA · 9 km (6 mi) SSW of San Leandro, CA

9:30 pm PDT, Sep 25, 2023 · · 7.8 km deep · released about 46 lb of TNT

Every earthquake near San Lorenzo Felt it? Tell USGS Check my area
10 km30 km60 km120 km N Alameda County 27 kmSan Mateo County 28 kmContra Costa County 39 kmSanta Clara County 65 kmMarin County 66 kmSanta Cruz County 71 kmSan Francisco County 73 kmSolano County 75 kmSan Joaquin County 89 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
9:30 pm PDT on 25 September 2023 ()
Where
9 km (5 mi) west-southwest of San Lorenzo, CA · earthquakes near San Lorenzo
Magnitude
M 2.1 (md)
Depth
7.8 km below the surface
Felt
3 reports · strongest reported intensity III
Nearest
Alameda County, 27 km E
Nearest mapped fault
Hayward fault, 12 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 1134 days ago

This was a minor earthquake. Quakes this small are rarely felt and do not cause damage.

At this magnitude and depth, people at rest would likely notice it out to about 16 km (10 mi) from the epicentre. In San Lorenzo, 9 km away, the estimate is intensity II (weak). 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: San Lorenzo 9 km, intensity II · Foster City 10 km, intensity II · San Leandro 11 km, intensity II · San Mateo 12 km, intensity II · Hayward 13 km, intensity II · Castro Valley 13 km, intensity II · Belmont 14 km, intensity II · Burlingame 14 km, intensity II. Estimated for each town centre; each link is that town's own record.

How big was it?

This earthquake released about 46 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 5.8 330,000× the energy of this one
  2. Magna, Utah 2020 M 5.7 230,000× the energy of this one
  3. Around the size people start to feel M 3.0 21× the energy of this one
  4. This earthquake M 2.1 about 46 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 4.5 on 2019-10-15 — about 3,200 times the energy of this one.

Before 2016, the USGS record lists 9 earthquakes of M5 or more within 50 km; the five largest:

  1. 7.9 The 1906 San Francisco, California Earthquake · 32 km WNW of this epicentre
  2. 5.8 7 km NNW of Boulder Creek, California · 50 km S of this epicentre
  3. 5.8 The 1980 Livermore, California Earthquake · 46 km ENE of this epicentre
  4. 5.7 15 km NE of East Foothills, California · 50 km ESE of this epicentre
  5. 5.5 6 km NNE of East Foothills, California · 45 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 37.6332, -122.2155. Map © OpenStreetMap contributors.

Nearby places

PlaceDistanceDirection from the epicentre
Alameda County, CA 27 km (17 mi) E earthquakes near Alameda County
San Mateo County, CA 28 km (17 mi) SSW earthquakes near San Mateo County
Contra Costa County, CA 39 km (24 mi) NE earthquakes near Contra Costa County
Santa Clara County, CA 65 km (41 mi) SE earthquakes near Santa Clara County
Marin County, CA 66 km (41 mi) NW earthquakes near Marin County
Santa Cruz County, CA 71 km (44 mi) SSE earthquakes near Santa Cruz County

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

Aftershocks so far

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

  1. 2.2 6 km WNW of San Francisco Zoo, CA
  2. 1.5 6 km WNW of San Francisco Zoo, CA
  3. 2.1 3 km N of San Lorenzo, CA
  4. 2.0 12 km NE of Milpitas, CA
  5. 1.6 7 km ESE of Santa Venetia, CA
  6. 1.5 2 km ESE of Pacifica, CA
  7. 1.7 2 km NNE of Saratoga, CA
  8. 1.6 4 km SW of Hillsborough, CA
  9. 1.7 9 km NNE of Alum Rock, CA
  10. 1.6 4 km SW of Hillsborough, CA
  11. 1.5 2 km NNE of Millbrae, CA
  12. 2.1 10 km SE of Sunol, CA
  13. 1.5 8 km SSW of Livermore, CA
  14. 1.5 3 km NNE of Millbrae, CA
  15. 1.7 2 km ENE 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.