QuakeIndex

Earthquake · reviewed by a seismologist

M 1.7md

Earthquake near Saint Helena, CA

No earthquake was likely felt in Saint Helena in the 24 hours to 11:22 pm PST (07:22 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 1.7 earthquake was recorded in Saint Helena, CA, at 3:42 am PDT on 8 September 2017 (10:42 UTC), 9.3 km deep.

USGS: 1 km W of Saint Helena, California

81 km (50 mi) N of San Francisco, CA · 20 km (12 mi) ENE of Santa Rosa, CA

3:42 am PDT, Sep 8, 2017 · · 9.3 km deep · released about 11 lb of TNT

Every earthquake near Saint Helena Felt it? Tell USGS Check my area
10 km30 km60 km120 km N Napa County 14 kmSonoma County 38 kmYolo County 55 kmSolano County 55 kmMarin County 55 kmLake County 71 kmColusa County 78 kmContra Costa County 80 kmSutter County 90 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
3:42 am PDT on 8 September 2017 ()
Where
in Saint Helena, CA · earthquakes near Saint Helena
Magnitude
M 1.7 (md)
Depth
9.3 km below the surface
Felt
no reports yet
Nearest
Napa County, 14 km E
Nearest mapped fault
West Napa fault, under 1 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 3351 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 8 km (5 mi) from the epicentre. 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.

Earthquakes near other towns within 30 km: Deer Park, Angwin, Kenwood, Calistoga, Yountville, Eldridge.

How big was it?

This earthquake released about 11 lb of TNT. Magnitude is logarithmic: each whole step up releases about 32 times more energy, so a magnitude 2.7 would have released about 32 times as much.

  1. Mineral, Virginia 2011 M 5.8 1,400,000× the energy of this one
  2. Magna, Utah 2020 M 5.7 970,000× the energy of this one
  3. Around the size people start to feel M 3.0 86× the energy of this one
  4. This earthquake M 1.7 about 11 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 89,000 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 · 36 km SSE of this epicentre
  2. 5.3 3 km E of Bloomfield, California · 35 km SW of this epicentre
  3. 5.3 Northern California · 36 km SW 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 38.5047, -122.4918. Map © OpenStreetMap contributors.

Nearby places

PlaceDistanceDirection from the epicentre
Napa County, CA 14 km (9 mi) E earthquakes near Napa County
Sonoma County, CA 38 km (24 mi) W earthquakes near Sonoma County
Yolo County, CA 55 km (34 mi) ENE earthquakes near Yolo County
Solano County, CA 55 km (34 mi) ESE earthquakes near Solano County
Marin County, CA 55 km (34 mi) SSW earthquakes near Marin County
Lake County, CA 71 km (44 mi) NNW earthquakes near Lake County

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

Aftershocks so far

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

  1. 1.5 4 km SSW of Oakville, California
  2. 1.6 7 km W of Cobb, California
  3. 2.5 14 km NNW of Moskowite Corner, California
  4. 1.8 5 km WSW of Cobb, California
  5. 1.8 7 km W of Cobb, California
  6. 2.9 11 km NE of Angwin, California
  7. 1.6 9 km W of Cobb, California
  8. 2.0 7 km W of Cobb, California
  9. 1.6 8 km W of Cobb, California
  10. 2.8 9 km WNW of Cobb, California
  11. 1.6 0 km SE of Angwin, California
  12. 2.0 5 km WNW of Cobb, California
  13. 1.8 5 km N of Healdsburg, California
  14. 1.7 7 km W of Cobb, California
  15. 1.8 10 km W of Cobb, California

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.