QuakeIndex

Earthquake · reviewed by a seismologist

M 2.3md

Earthquake near Grass Valley, CA

No earthquake was likely felt in Grass Valley in the 24 hours to 5:56 am PST (13:56 UTC). The last one was M 5.6, 187 km (116 mi) W, at 8:10 am PDT on 24 June 2026, estimated intensity II (weak) in town; 5,311 felt reports to USGS. Every earthquake near Grass Valley

This page: a magnitude 2.3 earthquake was recorded 50 km (31 mi) northeast of Grass Valley, CA, at 1:12 am PST on 23 February 2020 (09:12 UTC), less than 1 km deep.

USGS: 22km SW of Whitehawk, CA

1:12 am PST, Feb 23, 2020 · · -1.0 km deep · released about 98 lb of TNT

Every earthquake near Grass Valley Felt it? Tell USGS Check my area
10 km30 km60 km120 km N Sierra County 16 kmNevada County 31 kmPlumas County 47 kmPlacer County 57 kmYuba County 64 kmButte County 77 kmEl Dorado County 89 kmCarson City 95 kmStorey County 103 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
1:12 am PST on 23 February 2020 ()
Where
50 km (31 mi) northeast of Grass Valley, CA · earthquakes near Grass Valley
Magnitude
M 2.3 (md)
Depth
-1.0 km below the surface
Felt
no reports yet
Nearest
Sierra County, 16 km E
Nearest mapped fault
Mohawk Valley fault, 19 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 2453 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 20 km (12 mi) from the epicentre. In Grass Valley, 50 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.

How big was it?

This earthquake released about 98 lb of TNT. Magnitude is logarithmic: each whole step up releases about 32 times more energy, so a magnitude 3.3 would have released about 32 times as much.

  1. Mineral, Virginia 2011 M 5.8 150,000× the energy of this one
  2. Magna, Utah 2020 M 5.7 110,000× the energy of this one
  3. Around the size people start to feel M 3.0 9.8× the energy of this one
  4. This earthquake M 2.3 about 98 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

No earthquake of M4 or more has been recorded within 50 km since our catalogue begins in 2016.

Before 2016, the USGS record lists 7 earthquakes of M5 or more within 50 km; the five largest:

  1. 5.9 West of Downieville, California · 26 km WSW of this epicentre
  2. 5.9 9 km NW of Truckee, California · 44 km ESE of this epicentre
  3. 5.6 5 km NE of Loyalton, California · 47 km ENE of this epicentre
  4. 5.3 11 km N of Soda Springs, California · 31 km ESE of this epicentre
  5. 5.2 3 km N of Blairsden, California · 27 km NNE 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 39.5752, -120.7118. Map © OpenStreetMap contributors.

Nearby places

PlaceDistanceDirection from the epicentre
Sierra County, CA 16 km (10 mi) E earthquakes near Sierra County
Nevada County, CA 31 km (19 mi) S earthquakes near Nevada County
Plumas County, CA 47 km (29 mi) NNW earthquakes near Plumas County
Placer County, CA 57 km (35 mi) S earthquakes near Placer County
Yuba County, CA 64 km (40 mi) WSW earthquakes near Yuba County
Butte County, CA 77 km (48 mi) W earthquakes near Butte County

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

Aftershocks so far

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

  1. 3.0 19km NW of Truckee, CA
  2. 4.7 19km NW of Truckee, CA
  3. 1.7 15 km SSE of Sierraville, California
  4. 2.7 20km NW of Truckee, CA
  5. 3.1 19km NW of Truckee, CA
  6. 1.5 15 km SSE of Sierraville, California
  7. 2.4 16km SW of Loyalton, CA
  8. 2.3 11km N of Truckee, CA
  9. 1.9 22km SSW of Whitehawk, CA
  10. 2.0 3km WSW of Whitehawk, CA
  11. 1.7 2 km ENE of East Quincy, California
  12. 1.6 16 km NNW of Truckee, California
  13. 1.8 3 km SSE of Sattley, California
  14. 2.1 18km WSW of Loyalton, CA
  15. 2.7 10km SSE of Beckwourth, 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.