QuakeIndex

Earthquake · reviewed by a seismologist

M 4.0mw

Earthquake near Modesto, CA

No earthquake was likely felt in Modesto in the 24 hours to 12:26 pm PST (20:26 UTC). The last one was M 3.5, 47 km (29 mi) WSW, at 7:21 am PDT on 27 September 2026, estimated intensity II (weak) in town; 8 felt reports to USGS. Every earthquake near Modesto

This page: a magnitude 4.0 earthquake was recorded 34 km (21 mi) southwest of Modesto, CA, at 5:15 pm PDT on 18 September 2023 (00:15 UTC), less than 1 km deep. 364 people have reported feeling it to USGS.

USGS: 14 km SSW of Westley, CA

50 km (31 mi) ENE of San Jose, CA · 33 km (21 mi) SW of Modesto, CA

5:15 pm PDT, Sep 18, 2023 · · 0.1 km deep · released about 14 tons of TNT

Every earthquake near Modesto Felt it? Tell USGS Check my area
10 km30 km60 km120 km N Stanislaus County 28 kmSanta Clara County 43 kmSan Joaquin County 55 kmMerced County 57 kmAlameda County 60 kmContra Costa County 79 kmSanta Cruz County 80 kmSan Benito County 94 kmSan Mateo County 96 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
5:15 pm PDT on 18 September 2023 ()
Where
34 km (21 mi) southwest of Modesto, CA · earthquakes near Modesto
Magnitude
M 4.0 (mw)
Depth
0.1 km below the surface
Felt
364 reports · strongest reported intensity IV
Measured shaking
intensity V (ShakeMap)
USGS impact alert
green
Nearest
Stanislaus County, 28 km ENE
Nearest mapped fault
Great Valley thrust fault system, 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 923 days ago

This was a small earthquake. Shaking like this is often felt indoors nearby and very rarely causes damage.

At this magnitude and depth, people at rest would likely notice it out to about 95 km (59 mi) from the epicentre. In Modesto, 34 km away, the estimate is intensity III (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: Patterson 14 km, intensity IV · Newman 27 km, intensity III · Gustine 33 km, intensity III · Modesto 34 km, intensity III · Tracy 35 km, intensity III · Morgan Hill 48 km, intensity III. Estimated for each town centre; each link is that town's own record.

How big was it?

This earthquake released about 14 tons of TNT. Magnitude is logarithmic: each whole step up releases about 32 times more energy, so a magnitude 5.0 would have released about 32 times as much.

  1. Northridge, California 1994 M 6.7 12,000× the energy of this one
  2. Mineral, Virginia 2011 M 5.8 560× the energy of this one
  3. Magna, Utah 2020 M 5.7 390× the energy of this one
  4. This earthquake M 4.0 about 14 tons of TNT
  5. Around the size people start to feel M 3.0 this one released 29× more

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 43 times the energy of this one.

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

  1. 6.5 Near Morgan Hill, California · 48 km SW of this epicentre
  2. 6.2 Near San Jose, California · 48 km WSW of this epicentre
  3. 6.2 The 1984 Morgan Hill, California Earthquake · 38 km WSW of this epicentre
  4. 5.8 The 1979 Coyote Lake, California Earthquake · 43 km SSW of this epicentre
  5. 5.7 15 km NE of East Foothills, California · 36 km W 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 37.4418, -121.2848. Map © OpenStreetMap contributors.

Nearby places

PlaceDistanceDirection from the epicentre
Stanislaus County, CA 28 km (18 mi) ENE earthquakes near Stanislaus County
Santa Clara County, CA 43 km (27 mi) SW earthquakes near Santa Clara County
San Joaquin County, CA 55 km (34 mi) N earthquakes near San Joaquin County
Merced County, CA 57 km (35 mi) ESE earthquakes near Merced County
Alameda County, CA 60 km (37 mi) WNW earthquakes near Alameda County
Contra Costa County, CA 79 km (49 mi) NW earthquakes near Contra Costa County

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

Aftershocks so far

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

  1. 2.0 14 km ESE of Alum Rock, CA
  2. 2.5 25 km SSW of Gustine, CA
  3. 2.1 11 km ESE of Alum Rock, CA
  4. 2.8 11 km ESE of Alum Rock, CA
  5. 1.6 24 km SSW of Gustine, CA
  6. 1.7 24 km SSW of Gustine, CA
  7. 2.6 8 km ENE of Alum Rock, CA
  8. 2.6 24 km SSW of Gustine, CA
  9. 1.9 24 km ENE of Alum Rock, CA
  10. 2.1 16 km E of Seven Trees, CA
  11. 2.7 8 km ENE of Alum Rock, CA
  12. 2.2 9 km NE of Alum Rock, CA
  13. 2.0 9 km NE of Alum Rock, CA
  14. 1.6 25 km NE of Hollister, CA
  15. 1.5 25 km NE of Hollister, 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.