QuakeIndex

Earthquake · reviewed by a seismologist

M 2.1ml

Earthquake near Pomona, CA

No earthquake was likely felt in Pomona in the 24 hours to 3:39 pm PST (23:39 UTC). The last one was M 3.2, 16 km (10 mi) ESE, at 5:37 am PDT on 2 September 2026, estimated intensity III (weak) in town; 730 felt reports to USGS. Every earthquake near Pomona

This page: a magnitude 2.1 earthquake was recorded 2 km (1 mi) northwest of Pomona, CA, at 7:55 pm PDT on 21 May 2018 (02:55 UTC), 2.8 km deep. 107 people have reported feeling it to USGS.

USGS: 1km WNW of Pomona, CA

in Pomona, CA · 59 km (37 mi) E of Los Angeles, CA

7:55 pm PDT, May 21, 2018 · · 2.8 km deep · released about 49 lb of TNT

Every earthquake near Pomona Felt it? Tell USGS Check my area
10 km30 km60 km120 km N Orange County 44 kmLos Angeles County 48 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
7:55 pm PDT on 21 May 2018 ()
Where
2 km (1 mi) northwest of Pomona, CA · earthquakes near Pomona
Magnitude
M 2.1 (ml)
Depth
2.8 km below the surface
Felt
107 reports · strongest reported intensity IV
Nearest
Orange County, 44 km S
Nearest mapped fault
Sierra Madre fault, 6 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 3031 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 17 km (11 mi) from the epicentre. In Pomona, 2 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: Pomona 2 km, intensity III · La Verne 4 km, intensity II · San Dimas 6 km, intensity II · Claremont 6 km, intensity II · Diamond Bar 6 km, intensity II · Montclair 7 km, intensity II · Chino Hills 8 km, intensity II · Chino 10 km, intensity II. Estimated for each town centre; each link is that town's own record.

How big was it?

This earthquake released about 49 lb of TNT. Magnitude is logarithmic: each whole step up releases about 32 times more energy, so a magnitude 3.1 would have released about 32 times as much.

  1. Mineral, Virginia 2011 M 5.8 310,000× the energy of this one
  2. Magna, Utah 2020 M 5.7 220,000× the energy of this one
  3. Around the size people start to feel M 3.0 19× the energy of this one
  4. This earthquake M 2.1 about 49 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

No earthquake of M4 or more has been recorded within 50 km since our catalogue begins in 2016.

Before 2016, the USGS record lists 11 earthquakes of M5 or more within 50 km; the five largest:

  1. 6.2 3 km SE of San Bernardino, California · 47 km E of this epicentre
  2. 5.9 The 1987 Whittier Narrows, California Earthquake · 29 km W of this epicentre
  3. 5.8 The 1991 Sierra Madre, California Earthquake · 31 km NW of this epicentre
  4. 5.5 The 1990 Upland, California Earthquake · 11 km NE of this epicentre
  5. 5.4 5km S of Chino Hills, CA · 13 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 34.0672, -117.7692. Map © OpenStreetMap contributors.

Nearby places

PlaceDistanceDirection from the epicentre
Orange County, CA 44 km (27 mi) S earthquakes near Orange County
Los Angeles County, CA 48 km (30 mi) WNW earthquakes near Los Angeles County
San Diego County, CA 148 km (92 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

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

  1. 2.5 2km NE of Villa Park, CA
  2. 1.9 4km SE of Home Gardens, CA
  3. 1.7 1km ENE of Yorba Linda, CA
  4. 1.5 4km SSE of Home Gardens, CA
  5. 2.3 3km SSE of Charter Oak, CA
  6. 1.5 2km SE of Home Gardens, CA
  7. 2.8 3km NW of Fontana, CA
  8. 2.6 13km NE of Trabuco Canyon, CA
  9. 2.0 1km ESE of Loma Linda, CA
  10. 2.4 3km NNE of Rancho Cucamonga, CA
  11. 1.6 1km SSE of Placentia, CA
  12. 2.6 3km SSW of Signal Hill, CA
  13. 1.9 2km WSW of Yorba Linda, CA
  14. 1.7 6km ESE of Ontario, CA
  15. 2.7 6km ESE of Ontario, 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.