QuakeIndex

Earthquake · reviewed by a seismologist

M 1.8md

Earthquake near Patterson, CA

No earthquake was likely felt in Patterson in the 24 hours to 11:06 pm PST (07:06 UTC). The last one was M 2.9, 29 km (18 mi) W, at 9:44 am PDT on 31 October 2026, estimated intensity II (weak) in town. Every earthquake near Patterson

This page: a magnitude 1.8 earthquake was recorded 17 km (11 mi) west-southwest of Patterson, CA, at 10:06 pm PDT on 18 September 2023 (05:06 UTC), 2.5 km deep. 5 people have reported feeling it to USGS.

USGS: 17 km WSW of Patterson, CA

46 km (29 mi) ENE of San Jose, CA · 37 km (23 mi) SSE of Tracy, CA

10:06 pm PDT, Sep 18, 2023 · · 2.5 km deep · released about 13 lb of TNT

Every earthquake near Patterson Felt it? Tell USGS Check my area
10 km30 km60 km120 km N Stanislaus County 32 kmSanta Clara County 40 kmMerced County 58 kmSan Joaquin County 58 kmAlameda County 59 kmSanta Cruz County 76 kmContra Costa County 79 kmSan Benito County 92 kmSan Mateo County 94 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
10:06 pm PDT on 18 September 2023 ()
Where
17 km (11 mi) west-southwest of Patterson, CA · earthquakes near Patterson
Magnitude
M 1.8 (md)
Depth
2.5 km below the surface
Felt
5 reports · strongest reported intensity III
Nearest
Stanislaus County, 32 km ENE
Nearest mapped fault
Great Valley thrust fault system, 12 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 1144 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 13 km (8 mi) from the epicentre. In Patterson, 17 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: Newman.

How big was it?

This earthquake released about 13 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 1,200,000× the energy of this one
  2. Magna, Utah 2020 M 5.7 840,000× the energy of this one
  3. Around the size people start to feel M 3.0 75× the energy of this one
  4. This earthquake M 1.8 about 13 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 5.1 on 2022-10-25 — about 92,000 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. 6.5 Near Morgan Hill, California · 45 km SW of this epicentre
  2. 6.2 Near San Jose, California · 45 km WSW of this epicentre
  3. 6.2 The 1984 Morgan Hill, California Earthquake · 35 km WSW of this epicentre
  4. 6.1 Near San Jose, California · 49 km WSW of this epicentre
  5. 5.8 The 1979 Coyote Lake, California Earthquake · 39 km SSW 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 37.4172, -121.3120. Map © OpenStreetMap contributors.

Nearby places

PlaceDistanceDirection from the epicentre
Stanislaus County, CA 32 km (20 mi) ENE earthquakes near Stanislaus County
Santa Clara County, CA 40 km (25 mi) WSW earthquakes near Santa Clara County
Merced County, CA 58 km (36 mi) ESE earthquakes near Merced County
San Joaquin County, CA 58 km (36 mi) N earthquakes near San Joaquin County
Alameda County, CA 59 km (37 mi) WNW earthquakes near Alameda County
Santa Cruz County, CA 76 km (47 mi) SW earthquakes near Santa Cruz 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. 1.5 15 km E of Alum Rock, CA
  2. 2.4 7 km ENE of Alum Rock, CA
  3. 1.5 10 km SSW of Westley, CA
  4. 2.4 9 km ENE of Gilroy, CA
  5. 1.5 9 km E of Gilroy, CA
  6. 1.6 9 km E of Gilroy, CA
  7. 1.5 18 km WSW of Westley, CA
  8. 2.0 12 km NE of Milpitas, CA
  9. 2.6 16 km E of Seven Trees, CA
  10. 1.7 9 km NNE of Alum Rock, CA
  11. 2.0 24 km SSW of Gustine, CA
  12. 2.1 10 km SE of Sunol, CA
  13. 1.5 8 km SSW of Livermore, CA
  14. 1.5 6 km NNE of Alum Rock, CA
  15. 2.0 14 km ESE of Alum Rock, 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.