QuakeIndex

Earthquake · reviewed by a seismologist

M 1.6ml

Earthquake near San Dimas, CA

No earthquake was likely felt in San Dimas in the 24 hours to 6:54 am PST (14:54 UTC). The last one was M 3.2, 23 km (14 mi) ESE, at 5:37 am PDT on 2 September 2026, estimated intensity II (weak) in town; 730 felt reports to USGS. Every earthquake near San Dimas

This page: a magnitude 1.6 earthquake was recorded 3 km (2 mi) south-southwest of San Dimas, CA, at 9:58 am PDT on 21 March 2023 (16:58 UTC), 15 km deep. 1 person has reported feeling it to USGS.

USGS: 3km SSW of San Dimas, CA

5 km (3 mi) WNW of Pomona, CA · 56 km (34 mi) E of Los Angeles, CA

9:58 am PDT, Mar 21, 2023 · · 15 km deep · released about 8.1 lb of TNT

Every earthquake near San Dimas Felt it? Tell USGS Check my area
10 km30 km60 km120 km N Los Angeles County 43 kmOrange County 45 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
9:58 am PDT on 21 March 2023 ()
Where
3 km (2 mi) south-southwest of San Dimas, CA · earthquakes near San Dimas
Magnitude
M 1.6 (ml)
Depth
15 km below the surface
Felt
1 report · strongest reported intensity I
Nearest
Los Angeles County, 43 km WNW
Nearest mapped fault
Sierra Madre fault, 5 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 1332 days ago

This was a minor earthquake. Quakes this small are rarely felt and do not cause damage.

At this magnitude and depth it was probably too small to be felt, even directly above it. In San Dimas, 3 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: Charter Oak, La Verne, Diamond Bar, Pomona, Covina, Glendora.

How big was it?

This earthquake released about 8.1 lb of TNT. Magnitude is logarithmic: each whole step up releases about 32 times more energy, so a magnitude 2.6 would have released about 32 times as much.

  1. Mineral, Virginia 2011 M 5.8 1,900,000× the energy of this one
  2. Magna, Utah 2020 M 5.7 1,300,000× the energy of this one
  3. Around the size people start to feel M 3.0 120× the energy of this one
  4. This earthquake M 1.6 about 8.1 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 2020-09-19 — about 24,000 times the energy of this one.

Before 2016, the USGS record lists 10 earthquakes of M5 or more within 50 km; the five largest:

  1. 5.9 The 1987 Whittier Narrows, California Earthquake · 25 km W of this epicentre
  2. 5.8 The 1991 Sierra Madre, California Earthquake · 27 km NW of this epicentre
  3. 5.5 The 1990 Upland, California Earthquake · 13 km ENE of this epicentre
  4. 5.4 5km S of Chino Hills, CA · 15 km SSE of this epicentre
  5. 5.2 3km W of Lytle Creek, CA · 32 km NE 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 34.0813, -117.8128. Map © OpenStreetMap contributors.

Nearby places

PlaceDistanceDirection from the epicentre
Los Angeles County, CA 43 km (27 mi) WNW earthquakes near Los Angeles County
Orange County, CA 45 km (28 mi) S earthquakes near Orange County
San Diego County, CA 152 km (94 mi) SE earthquakes near San Diego 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. 1.9 7km SW of Pearblossom, CA
  2. 1.5 5km SSE of Home Gardens, CA
  3. 1.7 4km NE of Yorba Linda, CA
  4. 1.6 10km WSW of Corona, CA
  5. 1.9 7km SW of Pearblossom, CA
  6. 1.6 7km SW of Pearblossom, CA
  7. 2.2 6km NE of Sierra Madre, CA
  8. 1.7 2km WNW of Silver Lake, CA
  9. 1.6 6km SE of Chino Hills, CA
  10. 1.8 3km SW of Chino Hills, CA
  11. 2.7 6km SE of Chino Hills, CA
  12. 1.6 5km SE of Home Gardens, CA
  13. 1.9 6km NE of Sierra Madre, CA
  14. 2.6 6km NE of Sierra Madre, CA
  15. 3.1 6km NE of Sierra Madre, 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.