QuakeIndex

Earthquake · reviewed by a seismologist

M 3.7md

85 km N of Culebra, Puerto Rico

Yes. A magnitude 3.7 earthquake was recorded 85 km N of Culebra, Puerto Rico, at 2:38 am AST on 23 September 2021 (06:38 UTC), 56 km deep.

· 56 km deep · released about 4.8 tons of TNT

10 km30 km60 km120 km N Culebra Municipio 84 kmFajardo Municipio 86 kmLuquillo Municipio 94 kmRío Grande Municipio 99 kmCeiba Municipio 101 kmLoíza Municipio 103 kmVieques Municipio 108 kmCanóvanas Municipio 108 kmCarolina Municipio 109 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
Magnitude
M 3.7 (md)
Depth
56 km below the surface
Felt
no reports yet
Nearest
Culebra Municipio, 84 km S
Status
Reviewed by a seismologist

USGS · last changed by USGS · we first saw it 1804 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 48 km (30 mi) from the epicentre. 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.

How big was it?

This earthquake released about 4.8 tons of TNT. Magnitude is logarithmic: each whole step up releases about 32 times more energy, so a magnitude 4.7 would have released about 32 times as much.

  1. Northridge, California 1994 M 6.7 35,000× the energy of this one
  2. Mineral, Virginia 2011 M 5.8 1,600× the energy of this one
  3. Magna, Utah 2020 M 5.7 1,100× the energy of this one
  4. This earthquake M 3.7 about 4.8 tons of TNT
  5. Around the size people start to feel M 3.0 this one released 10× 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 5.0 on 2021-02-06 — about 95 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. 6.1 91 km N of Charlotte Amalie, U.S. Virgin Islands · 42 km ENE of this epicentre
  2. 6.0 112 km N of Charlotte Amalie, U.S. Virgin Islands · 43 km NE of this epicentre
  3. 5.6 112 km N of Charlotte Amalie, U.S. Virgin Islands · 47 km NE of this epicentre
  4. 5.1 107 km N of Charlotte Amalie, U.S. Virgin Islands · 38 km NE of this epicentre
  5. 5.1 122 km NNE of Vieques, Puerto Rico · 39 km NNW 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 19.0746, -65.2213. Map © OpenStreetMap contributors.

Nearby places

PlaceDistanceDirection from the epicentre
Culebra Municipio, PR 84 km (52 mi) S earthquakes near Culebra Municipio
Fajardo Municipio, PR 86 km (53 mi) SSW earthquakes near Fajardo Municipio
Luquillo Municipio, PR 94 km (58 mi) SSW earthquakes near Luquillo Municipio
Río Grande Municipio, PR 99 km (61 mi) SW earthquakes near Río Grande Municipio
Ceiba Municipio, PR 101 km (62 mi) SSW earthquakes near Ceiba Municipio
Loíza Municipio, PR 103 km (64 mi) SW earthquakes near Loíza Municipio

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

Aftershocks so far

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

  1. 3.8 83 km N of Cruz Bay, U.S. Virgin Islands
  2. 3.4 81 km N of Culebra, Puerto Rico
  3. 3.5 84 km NNE of Luquillo, Puerto Rico
  4. 3.5 106 km N of Charlotte Amalie, U.S. Virgin Islands
  5. 3.7 102 km NNW of Charlotte Amalie, U.S. Virgin Islands
  6. 3.0 66 km N of Charlotte Amalie, U.S. Virgin Islands
  7. 3.5 74 km N of Culebra, Puerto Rico
  8. 3.7 75 km N of Charlotte Amalie, U.S. Virgin Islands
  9. 4.0 66 km N of Culebra, Puerto Rico
  10. 3.7 67 km N of Culebra, Puerto Rico
  11. 3.6 Puerto Rico region
  12. 3.4 86 km N of Culebra, Puerto Rico
  13. 3.6 63 km N of Charlotte Amalie, U.S. Virgin Islands
  14. 3.2 44 km NNW of Charlotte Amalie, U.S. Virgin Islands
  15. 3.4 75 km NNW of Charlotte Amalie, U.S. Virgin Islands

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.