QuakeIndex

Earthquake · reviewed by a seismologist

M 1.6md

Earthquake near San Ramon, CA

No earthquake was likely felt in San Ramon in the 24 hours to 10:40 pm PST (06:40 UTC). The last one was M 2.1, 6 km (4 mi) NNE, at 7:18 am PDT on 31 October 2026, estimated intensity II (weak) in town; 1 felt report to USGS. Every earthquake near San Ramon

This page: a magnitude 1.6 earthquake was recorded 3 km (2 mi) southwest of San Ramon, CA, at 9:30 pm PDT on 17 October 2023 (04:30 UTC), 8.9 km deep. 2 people have reported feeling it to USGS.

USGS: 3 km SW of San Ramon, CA

19 km (12 mi) E of Oakland, CA · 7 km (4 mi) W of San Ramon, CA

9:30 pm PDT, Oct 17, 2023 · · 8.9 km deep · released about 7.1 lb of TNT

Every earthquake near San Ramon Felt it? Tell USGS Check my area
10 km30 km60 km120 km N Alameda County 15 kmContra Costa County 18 kmSan Mateo County 50 kmSolano County 56 kmSanta Clara County 66 kmSan Joaquin County 67 kmMarin County 72 kmSanta Cruz County 84 kmNapa County 87 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 17 October 2023 ()
Where
3 km (2 mi) southwest of San Ramon, CA · earthquakes near San Ramon
Magnitude
M 1.6 (md)
Depth
8.9 km below the surface
Felt
2 reports · strongest reported intensity I
Nearest
Alameda County, 15 km SSE
Nearest mapped fault
Calaveras fault, 3 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 1114 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 6 km (4 mi) from the epicentre. In San Ramon, 3 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 Ramon 3 km, intensity II · Danville 7 km, intensity II. Estimated for each town centre; each link is that town's own record.

How big was it?

This earthquake released about 7.1 lb of TNT. Magnitude is logarithmic: each whole step up releases about 32 times more energy, so a magnitude 2.6 would have released about 32 times as much.

  1. Mineral, Virginia 2011 M 5.8 2,100,000× the energy of this one
  2. Magna, Utah 2020 M 5.7 1,500,000× the energy of this one
  3. Around the size people start to feel M 3.0 130× the energy of this one
  4. This earthquake M 1.6 about 7.1 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 21,000 times the energy of this one.

Before 2016, the USGS record lists 8 earthquakes of M5 or more within 50 km; the five largest:

  1. 7.9 The 1906 San Francisco, California Earthquake · 48 km W of this epicentre
  2. 5.8 The 1980 Livermore, California Earthquake · 23 km ENE of this epicentre
  3. 5.7 15 km NE of East Foothills, California · 42 km SE of this epicentre
  4. 5.5 6 km NNE of East Foothills, California · 42 km SSE of this epicentre
  5. 5.4 9 km NE of Livermore, California · 27 km E 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 37.7633, -122.0072. Map © OpenStreetMap contributors.

Nearby places

PlaceDistanceDirection from the epicentre
Alameda County, CA 15 km (10 mi) SSE earthquakes near Alameda County
Contra Costa County, CA 18 km (11 mi) NNE earthquakes near Contra Costa County
San Mateo County, CA 50 km (31 mi) SW earthquakes near San Mateo County
Solano County, CA 56 km (35 mi) N earthquakes near Solano County
Santa Clara County, CA 66 km (41 mi) SSE earthquakes near Santa Clara County
San Joaquin County, CA 67 km (42 mi) ENE earthquakes near San Joaquin County

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

Aftershocks so far

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

  1. 1.5 5 km E of Vallejo, CA
  2. 1.7 2 km ESE of Oakland, CA
  3. 2.1 1 km SSE of Los Altos Hills, CA
  4. 2.5 2 km SSE of Los Altos Hills, CA
  5. 1.7 5 km S of San Ramon, CA
  6. 1.8 5 km S of San Ramon, CA
  7. 1.5 5 km S of San Ramon, CA
  8. 1.7 8 km SSW of Martinez, CA
  9. 2.2 5 km S of San Ramon, CA
  10. 1.7 4 km ENE of Discovery Bay, CA
  11. 1.6 4 km WSW of Colma, CA
  12. 1.5 1 km N of Millbrae, CA
  13. 1.9 2 km NNE of Millbrae, CA
  14. 2.4 7 km ENE of Alum Rock, CA
  15. 1.7 5 km WNW of Byron, 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.