QuakeIndex

Earthquake · reviewed by a seismologist

M 1.7ml

Earthquake near Portola, CA

No earthquake was likely felt in Portola in the 24 hours to 9:51 pm PST (05:51 UTC). The last one was M 2.7, 8 km (5 mi) N, at 8:16 am PST on 10 November 2026, estimated intensity III (weak) in town; 9 felt reports to USGS. Every earthquake near Portola

This page: a magnitude 1.7 earthquake was recorded 19 km (12 mi) northwest of Portola, CA, at 7:00 pm PDT on 7 September 2023 (02:00 UTC), 8.7 km deep.

USGS: 10 km NE of Cromberg, California

79 km (49 mi) WNW of Reno, NV

7:00 pm PDT, Sep 7, 2023 · · 8.7 km deep · released about 11 lb of TNT

Every earthquake near Portola Felt it? Tell USGS Check my area
10 km30 km60 km120 km N Plumas County 18 kmSierra County 41 kmNevada County 72 kmLassen County 87 kmButte County 89 kmYuba County 96 kmPlacer County 97 kmStorey County 109 kmCarson City 115 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
7:00 pm PDT on 7 September 2023 ()
Where
19 km (12 mi) northwest of Portola, CA · earthquakes near Portola
Magnitude
M 1.7 (ml)
Depth
8.7 km below the surface
Felt
no reports yet
Nearest
Plumas County, 18 km WNW
Nearest mapped fault
Mohawk Valley fault, 9 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 1106 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 9 km (6 mi) from the epicentre. In Portola, 19 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.

Earthquakes near other towns within 30 km: East Quincy, Quincy.

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 1,000,000× the energy of this one
  3. Around the size people start to feel M 3.0 89× 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 4.5 on 2016-08-04 — about 15,000 times the energy of this one.

Before 2016, the USGS record lists 4 earthquakes of M5 or more within 50 km:

  1. 5.7 2 km NNE of Canyondam, California · 47 km NW of this epicentre
  2. 5.6 5 km NE of Loyalton, California · 43 km ESE of this epicentre
  3. 5.3 4 km S of Doyle, California · 44 km E of this epicentre
  4. 5.2 3 km N of Blairsden, California · 14 km S 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 39.9329, -120.6226. Map © OpenStreetMap contributors.

Nearby places

PlaceDistanceDirection from the epicentre
Plumas County, CA 18 km (11 mi) WNW earthquakes near Plumas County
Sierra County, CA 41 km (25 mi) SSE earthquakes near Sierra County
Nevada County, CA 72 km (45 mi) S earthquakes near Nevada County
Lassen County, CA 87 km (54 mi) N earthquakes near Lassen County
Butte County, CA 89 km (55 mi) WSW earthquakes near Butte County
Yuba County, CA 96 km (60 mi) SW earthquakes near Yuba County

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

Aftershocks so far

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

  1. 1.9 6 km S of Sierraville, California
  2. 1.8 6 km S of Sierraville, California
  3. 2.1 1 km E of Canyondam, CA
  4. 2.3 1 km E of Johnsville, CA
  5. 1.8 6 km WSW of Greenville, California
  6. 3.4 6 km SW of Canyondam, CA
  7. 2.2 8 km S of Spring Garden, CA
  8. 2.0 2 km SW of Canyondam, CA
  9. 2.2 0 km ESE of Clio, CA
  10. 1.6 0 km N of Whitehawk, California
  11. 2.1 5 km SSW of Canyondam, CA
  12. 1.8 2 km WNW of Canyondam, CA
  13. 2.0 2 km WNW of Canyondam, CA
  14. 1.5 0 km NW of Valley Ranch, California
  15. 2.4 0 km NE of Valley Ranch, 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.