QuakeIndex

Earthquake · reviewed by a seismologist

M 3.1md

111 km N of San Juan, Puerto Rico

Yes. A magnitude 3.1 earthquake was recorded 111 km N of San Juan, Puerto Rico, at 9:21 am AST on 4 December 2017 (13:21 UTC), 33 km deep.

· 33 km deep · released about 1,600 lb of TNT

Felt it? Tell USGS Check my area
10 km30 km60 km120 km N Dorado Municipio 112 kmToa Baja Municipio 113 kmCataño Municipio 114 kmLoíza Municipio 115 kmSan Juan Municipio 117 kmVega Baja Municipio 118 kmVega Alta Municipio 118 kmCarolina Municipio 120 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 3.1 (md)
Depth
33 km below the surface
Felt
no reports yet
Nearest
Dorado Municipio, 112 km S
Status
Reviewed by a seismologist

USGS · last changed by USGS · we first saw it 3179 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 29 km (18 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 1,600 lb of TNT. Magnitude is logarithmic: each whole step up releases about 32 times more energy, so a magnitude 4.2 would have released about 32 times as much.

  1. Northridge, California 1994 M 6.7 210,000× the energy of this one
  2. Mineral, Virginia 2011 M 5.8 9,400× the energy of this one
  3. Magna, Utah 2020 M 5.7 6,700× the energy of this one
  4. This earthquake M 3.1 about 1,600 lb of TNT
  5. Around the size people start to feel M 3.0 this one released 1.7× 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 4.4 on 2016-10-23 — about 75 times the energy of this one.

Before 2016, the USGS record lists 3 earthquakes of M5 or more within 50 km:

  1. 5.4 106 km N of Brenas, Puerto Rico · 32 km W of this epicentre
  2. 5.1 92 km N of Suárez, Puerto Rico · 44 km ESE of this epicentre
  3. 5.0 113 km N of Brenas, Puerto Rico · 26 km W 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 19.4700, -66.0810. Map © OpenStreetMap contributors.

Nearby places

PlaceDistanceDirection from the epicentre
Dorado Municipio, PR 112 km (70 mi) S earthquakes near Dorado Municipio
Toa Baja Municipio, PR 113 km (70 mi) S earthquakes near Toa Baja Municipio
Cataño Municipio, PR 114 km (71 mi) S earthquakes near Cataño Municipio
Loíza Municipio, PR 115 km (71 mi) S earthquakes near Loíza Municipio
San Juan Municipio, PR 117 km (72 mi) S earthquakes near San Juan Municipio
Vega Baja Municipio, PR 118 km (73 mi) SSW earthquakes near Vega Baja Municipio

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

Aftershocks so far

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

  1. 3.4 71 km NNE of San Juan, Puerto Rico
  2. 3.2 82 km N of San Juan, Puerto Rico
  3. 3.2 93 km N of Loíza, Puerto Rico
  4. 3.3 98 km N of Suárez, Puerto Rico
  5. 2.6 80 km N of San Juan, Puerto Rico
  6. 2.8 92 km N of San Juan, Puerto Rico
  7. 3.1 91 km N of Brenas, Puerto Rico
  8. 3.0 116 km N of San Juan, Puerto Rico
  9. 3.0 86 km N of Brenas, Puerto Rico
  10. 2.9 96 km N of San Juan, Puerto Rico
  11. 2.9 86 km N of San Juan, Puerto Rico
  12. 2.8 69 km N of Brenas, Puerto Rico
  13. 3.1 102 km N of San Juan, Puerto Rico
  14. 3.2 113 km N of Brenas, Puerto Rico
  15. 2.6 104 km N of Brenas, Puerto Rico

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.