QuakeIndex

Earthquake · reviewed by a seismologist

M 3.5mw

Earthquake near Borrego Springs, CA

No earthquake was likely felt in Borrego Springs in the 24 hours to 12:56 pm PST (20:56 UTC). The last one was M 4.9, 145 km (90 mi) SE, at 10:27 am PST on 3 November 2026, estimated intensity II (weak) in town; 321 felt reports to USGS. Every earthquake near Borrego Springs

This page: a magnitude 3.5 earthquake was recorded 10 km (6 mi) south of Borrego Springs, CA, at 3:50 am PDT on 28 April 2021 (10:50 UTC), 7.3 km deep. 283 people have reported feeling it to USGS.

USGS: 10km S of Borrego Springs, CA

80 km (50 mi) ENE of San Diego, CA

3:50 am PDT, Apr 28, 2021 · · 7.3 km deep · released about 2.3 tons of TNT

10 km30 km60 km120 km N San Diego County 40 kmRiverside County 72 kmImperial County 97 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
3:50 am PDT on 28 April 2021 ()
Where
10 km (6 mi) south of Borrego Springs, CA · earthquakes near Borrego Springs
Magnitude
M 3.5 (mw)
Depth
7.3 km below the surface
Felt
283 reports · strongest reported intensity III
Measured shaking
intensity IV (ShakeMap)
Nearest
San Diego County, 40 km WSW
Nearest mapped fault
Elsinore 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 1765 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 60 km (37 mi) from the epicentre. In Borrego Springs, 10 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: Borrego Springs 10 km, intensity III · Julian 23 km, intensity III · Pine Valley 40 km, intensity II · San Diego Country Estates 41 km, intensity II · Salton City 42 km, intensity II · Ramona 47 km, intensity II. Estimated for each town centre; each link is that town's own record.

How big was it?

This earthquake released about 2.3 tons of TNT. Magnitude is logarithmic: each whole step up releases about 32 times more energy, so a magnitude 4.5 would have released about 32 times as much.

  1. Northridge, California 1994 M 6.7 75,000× the energy of this one
  2. Mineral, Virginia 2011 M 5.8 3,300× the energy of this one
  3. Magna, Utah 2020 M 5.7 2,400× the energy of this one
  4. This earthquake M 3.5 about 2.3 tons of TNT
  5. Around the size people start to feel M 3.0 this one released 4.7× 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 5.2 on 2016-06-10 — about 410 times the energy of this one.

Before 2016, the USGS record lists 15 earthquakes of M5 or more within 50 km; the five largest:

  1. 6.6 The 1968 Borrego Mountain, California Earthquake · 26 km E of this epicentre
  2. 6.4 The 1954 San Jacinto Fault, California Earthquake · 32 km ENE of this epicentre
  3. 6.0 16km WSW of Oasis, CA · 29 km NNE of this epicentre
  4. 5.7 Eastern San Diego County, California · 27 km E of this epicentre
  5. 5.5 8km NNE of Ocotillo Wells, CA · 27 km E 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 33.1628, -116.3817. Map © OpenStreetMap contributors.

Nearby places

PlaceDistanceDirection from the epicentre
San Diego County, CA 40 km (25 mi) WSW earthquakes near San Diego County
Riverside County, CA 72 km (45 mi) NNE earthquakes near Riverside County
Imperial County, CA 97 km (60 mi) E earthquakes near Imperial County

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

Aftershocks so far

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

  1. 1.6 21km E of Ocotillo Wells, CA
  2. 1.7 13km NNW of Borrego Springs, CA
  3. 2.0 10km S of Borrego Springs, CA
  4. 1.5 8km SW of Salton City, CA
  5. 1.7 9km E of San Diego Country Estates, CA
  6. 1.9 16km ESE of Anza, CA
  7. 3.1 12km NNE of Borrego Springs, CA
  8. 1.6 6km WSW of Salton City, CA
  9. 1.7 12km SSW of Oasis, CA
  10. 1.9 4km NW of Borrego Springs, CA
  11. 3.0 10km NNE of Ocotillo Wells, CA
  12. 1.8 21km ESE of Anza, CA
  13. 1.7 15km SE of Ocotillo Wells, CA
  14. 1.6 18km N of Borrego Springs, CA
  15. 1.6 18km N of Borrego Springs, 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.