QuakeIndex

Earthquake · reviewed by a seismologist

M 1.7ml

Earthquake near San Dimas, CA

No earthquake was likely felt in San Dimas in the 24 hours to 3:44 am PST (11:44 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 1.7 earthquake was recorded 7 km (4 mi) north-northeast of San Dimas, CA, at 8:30 am PST on 30 December 2018 (16:30 UTC), 14 km deep.

USGS: 7km NNE of San Dimas, CA

6 km (4 mi) ENE of Glendora, CA · 60 km (37 mi) ENE of Los Angeles, CA

8:30 am PST, Dec 30, 2018 · · 14 km deep · released about 12 lb of TNT

Every earthquake near San Dimas Felt it? Tell USGS Check my area
10 km30 km60 km120 km N Los Angeles County 44 kmOrange County 55 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
8:30 am PST on 30 December 2018 ()
Where
7 km (4 mi) north-northeast of San Dimas, CA · earthquakes near San Dimas
Magnitude
M 1.7 (ml)
Depth
14 km below the surface
Felt
no reports yet
Nearest
Los Angeles County, 44 km W
Nearest mapped fault
Sierra Madre fault, 2 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 2870 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, 7 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: La Verne, Glendora, Charter Oak, Claremont, Citrus, Azusa.

How big was it?

This earthquake released about 12 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 1,200,000× the energy of this one
  2. Magna, Utah 2020 M 5.7 870,000× the energy of this one
  3. Around the size people start to feel M 3.0 78× the energy of this one
  4. This earthquake M 1.7 about 12 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 4.4 on 2018-08-29 — about 9,100 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. 6.2 3 km SE of San Bernardino, California · 49 km E of this epicentre
  2. 5.9 The 1987 Whittier Narrows, California Earthquake · 29 km WSW of this epicentre
  3. 5.8 The 1991 Sierra Madre, California Earthquake · 22 km WNW of this epicentre
  4. 5.5 The 1990 Upland, California Earthquake · 9 km ESE of this epicentre
  5. 5.4 5km S of Chino Hills, CA · 24 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 34.1678, -117.7877. Map © OpenStreetMap contributors.

Nearby places

PlaceDistanceDirection from the epicentre
Los Angeles County, CA 44 km (27 mi) W earthquakes near Los Angeles County
Orange County, CA 55 km (34 mi) S earthquakes near Orange County

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

Aftershocks so far

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

  1. 1.6 2km E of Colton, CA
  2. 1.7 4km SE of Home Gardens, CA
  3. 1.8 8km ESE of Yorba Linda, CA
  4. 2.2 8km ESE of Yorba Linda, CA
  5. 3.6 8km ESE of Yorba Linda, CA
  6. 2.2 7km SSW of Lytle Creek, CA
  7. 1.6 7km SSW of Lytle Creek, CA
  8. 1.8 3km NNW of Orange, CA
  9. 1.5 4km SW of Fontana, CA
  10. 1.8 4km SW of Fontana, CA
  11. 1.8 2km WNW of Fontana, CA
  12. 2.1 4km SW of Fontana, CA
  13. 1.6 4km SE of Home Gardens, CA
  14. 2.0 4km SW of Fontana, CA
  15. 2.1 4km SW of Fontana, 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.