QuakeIndex

Earthquake · reviewed by a seismologist

M 3.1md

Earthquake near Guánica, PR

No earthquake was likely felt in Guánica in the 24 hours to 1:37 pm AST (17:37 UTC). The last one was M 2.1, 13 km (8 mi) ENE, at 4:39 pm AST on 9 November 2026, estimated intensity II (weak) in town. Every earthquake near Guánica

This page: a magnitude 3.1 earthquake was recorded 6 km (3 mi) southwest of Guánica, PR, at 6:54 am AST on 20 August 2021 (10:54 UTC), 8.0 km deep. 3 people have reported feeling it to USGS.

USGS: 5 km SW of Guánica, Puerto Rico

35 km (22 mi) W of Ponce, PR

6:54 am AST, Aug 20, 2021 · · 8.0 km deep · released about 1,300 lb of TNT

Every earthquake near Guánica Felt it? Tell USGS Check my area
10 km30 km60 km120 km N Guánica Municipio 3 kmLajas Municipio 11 kmSabana Grande Municipio 16 kmGuayanilla Municipio 17 kmYauco Municipio 19 kmSan Germán Municipio 21 kmPeñuelas Municipio 25 kmCabo Rojo Municipio 25 kmMaricao Municipio 26 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
6:54 am AST on 20 August 2021 ()
Where
6 km (3 mi) southwest of Guánica, PR · earthquakes near Guánica
Magnitude
M 3.1 (md)
Depth
8.0 km below the surface
Felt
3 reports · strongest reported intensity II
Nearest
Guánica Municipio, 3 km ENE
Status
Reviewed by a seismologist

USGS · last changed by USGS · we first saw it 1909 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 40 km (25 mi) from the epicentre. In Guánica, 6 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: Yauco 15 km, intensity III · Guayanilla 19 km, intensity II · San Germán 19 km, intensity II · Magas Arriba 21 km, intensity II · Tallaboa 25 km, intensity II · Pole Ojea 25 km, intensity II · Tallaboa Alta 29 km, intensity II · Puerto Real 29 km, intensity II. Estimated for each town centre; each link is that town's own record.

How big was it?

This earthquake released about 1,300 lb of TNT. Magnitude is logarithmic: each whole step up releases about 32 times more energy, so a magnitude 4.1 would have released about 32 times as much.

  1. Northridge, California 1994 M 6.7 270,000× the energy of this one
  2. Mineral, Virginia 2011 M 5.8 12,000× the energy of this one
  3. Magna, Utah 2020 M 5.7 8,500× the energy of this one
  4. This earthquake M 3.1 about 1,300 lb of TNT
  5. Around the size people start to feel M 3.0 this one released 1.3× 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 6.4 on 2020-01-07 — about 95,000 times the energy of this one.

Before 2016, the USGS record since 1900 lists no earthquake of M5 or more within 50 km.

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 17.9403, -66.9483. Map © OpenStreetMap contributors.

Nearby places

PlaceDistanceDirection from the epicentre
Guánica Municipio, PR 3 km (2 mi) ENE earthquakes near Guánica Municipio
Lajas Municipio, PR 11 km (7 mi) WNW earthquakes near Lajas Municipio
Sabana Grande Municipio, PR 16 km (10 mi) N earthquakes near Sabana Grande Municipio
Guayanilla Municipio, PR 17 km (11 mi) ENE earthquakes near Guayanilla Municipio
Yauco Municipio, PR 19 km (12 mi) NNE earthquakes near Yauco Municipio
San Germán Municipio, PR 21 km (13 mi) NNW earthquakes near San Germán Municipio

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

Aftershocks so far

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

  1. 2.7 16 km W of Puerto Real, Puerto Rico
  2. 2.7 0 km S of Indios, Puerto Rico
  3. 2.6 4 km SE of La Parguera, Puerto Rico
  4. 2.5 0 km SSE of Indios, Puerto Rico
  5. 3.0 1 km S of Indios, Puerto Rico
  6. 2.5 6 km ESE of Pole Ojea, Puerto Rico
  7. 2.5 7 km WSW of La Parguera, Puerto Rico
  8. 2.7 Puerto Rico region
  9. 2.3 13 km S of Guánica, Puerto Rico
  10. 2.6 2 km SW of Guánica, Puerto Rico
  11. 2.6 6 km SSW of Guánica, Puerto Rico
  12. 2.4 7 km WSW of La Parguera, Puerto Rico
  13. 2.5 6 km W of Liborio Negron Torres, Puerto Rico
  14. 2.6 6 km SSW of Pole Ojea, Puerto Rico
  15. 2.1 6 km WSW of La Parguera, 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.