QuakeIndex

Earthquake · reviewed by a seismologist

M 1.8md

Earthquake near Saint Helena, CA

No earthquake was likely felt in Saint Helena in the 24 hours to 1:39 pm PST (21:39 UTC). The last one was M 1.7, 11 km (7 mi) SSW, at 12:33 am PDT on 25 October 2026, estimated intensity II (weak) in town. Every earthquake near Saint Helena

This page: a magnitude 1.8 earthquake was recorded 4 km (2 mi) east-northeast of Saint Helena, CA, at 9:19 pm PDT on 20 August 2026 (04:19 UTC), 8.0 km deep.

USGS: 4 km ENE of Saint Helena, CA

82 km (51 mi) N of San Francisco, CA · 25 km (16 mi) ENE of Santa Rosa, CA

9:19 pm PDT, Aug 20, 2026 · · 8.0 km deep · released about 15 lb of TNT

Every earthquake near Saint Helena Felt it? Tell USGS Check my area
10 km30 km60 km120 km N Napa County 9 kmSonoma County 43 kmYolo County 49 kmSolano County 51 kmMarin County 58 kmLake County 72 kmColusa County 76 kmContra Costa County 78 kmSutter County 86 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
9:19 pm PDT on 20 August 2026 ()
Where
4 km (2 mi) east-northeast of Saint Helena, CA · earthquakes near Saint Helena
Magnitude
M 1.8 (md)
Depth
8.0 km below the surface
Felt
no reports yet
Nearest
Napa County, 9 km E
Nearest mapped fault
West Napa fault, 5 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 72 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 11 km (7 mi) from the epicentre. In Saint Helena, 4 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: Angwin 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 15 lb of TNT. Magnitude is logarithmic: each whole step up releases about 32 times more energy, so a magnitude 2.8 would have released about 32 times as much.

  1. Mineral, Virginia 2011 M 5.8 1,000,000× the energy of this one
  2. Magna, Utah 2020 M 5.7 710,000× the energy of this one
  3. Around the size people start to feel M 3.0 63× the energy of this one
  4. This earthquake M 1.8 about 15 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 5.0 on 2016-12-14 — about 65,000 times the energy of this one.

Before 2016, the USGS record lists 3 earthquakes of M5 or more within 50 km:

  1. 6.0 The 2014 South Napa, California Earthquake · 35 km SSE of this epicentre
  2. 5.3 3 km E of Bloomfield, California · 40 km WSW of this epicentre
  3. 5.3 Northern California · 41 km WSW 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 38.5133, -122.4272. Map © OpenStreetMap contributors.

Nearby places

PlaceDistanceDirection from the epicentre
Napa County, CA 9 km (5 mi) E earthquakes near Napa County
Sonoma County, CA 43 km (27 mi) W earthquakes near Sonoma County
Yolo County, CA 49 km (31 mi) ENE earthquakes near Yolo County
Solano County, CA 51 km (31 mi) ESE earthquakes near Solano County
Marin County, CA 58 km (36 mi) SSW earthquakes near Marin County
Lake County, CA 72 km (45 mi) NNW earthquakes near Lake County

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

Aftershocks so far

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

  1. 1.6 6 km W of Cobb, CA
  2. 2.4 9 km WNW of The Geysers, CA
  3. 2.2 3 km S of Anderson Springs, CA
  4. 2.3 3 km S of Anderson Springs, CA
  5. 1.7 8 km NW of The Geysers, CA
  6. 1.7 8 km NW of The Geysers, CA
  7. 2.3 8 km NW of The Geysers, CA
  8. 1.9 8 km NW of The Geysers, CA
  9. 1.6 7 km ENE of Vallejo, CA
  10. 1.7 2 km NW of The Geysers, CA
  11. 1.8 3 km SE of The Geysers, CA
  12. 1.5 0 km SSW of Angwin, CA
  13. 2.0 5 km WNW of Cobb, CA
  14. 2.3 3 km SSW of Cobb, CA
  15. 1.9 2 km E of The Geysers, 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.