QuakeIndex

Earthquake · reviewed by a seismologist

M 3.4md

Earthquake near Isabela, PR

No earthquake was likely felt in Isabela in the 24 hours to 8:47 pm AST (00:47 UTC). The last one was M 3.4, 31 km (19 mi) N, at 9:00 pm AST on 27 October 2026, estimated intensity II (weak) in town. Every earthquake near Isabela

This page: a magnitude 3.4 earthquake was recorded 23 km (14 mi) north-northeast of Isabela, PR, at 10:30 pm AST on 17 September 2021 (02:30 UTC), 12 km deep. 1 person has reported feeling it to USGS.

USGS: 22 km NNE of Isabela, Puerto Rico

96 km (59 mi) WNW of San Juan, PR · 32 km (20 mi) NW of Arecibo, PR

10:30 pm AST, Sep 17, 2021 · · 12 km deep · released about 1.7 tons of TNT

Every earthquake near Isabela Felt it? Tell USGS Check my area
10 km30 km60 km120 km N Quebradillas Municipio 24 kmIsabela Municipio 24 kmCamuy Municipio 27 kmHatillo Municipio 30 kmAguadilla Municipio 33 kmMoca Municipio 38 kmArecibo Municipio 38 kmSan Sebastián Municipio 39 kmAguada Municipio 44 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
10:30 pm AST on 17 September 2021 ()
Where
23 km (14 mi) north-northeast of Isabela, PR · earthquakes near Isabela
Magnitude
M 3.4 (md)
Depth
12 km below the surface
Felt
1 report · strongest reported intensity II
Nearest
Quebradillas Municipio, 24 km S
Status
Reviewed by a seismologist

USGS · last changed by USGS · we first saw it 1881 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 54 km (34 mi) from the epicentre. In Isabela, 23 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.

Likely felt in: Isabela 23 km, intensity II · Quebradillas 23 km, intensity II · Hatillo 24 km, intensity II · Rafael Hernandez 29 km, intensity II · Arecibo 32 km, intensity II · Aguadilla 38 km, intensity II · San Sebastián 39 km, intensity II · Lares 43 km, intensity II. Estimated for each town centre; each link is that town's own record.

How big was it?

This earthquake released about 1.7 tons of TNT. Magnitude is logarithmic: each whole step up releases about 32 times more energy, so a magnitude 4.4 would have released about 32 times as much.

  1. Northridge, California 1994 M 6.7 100,000× the energy of this one
  2. Mineral, Virginia 2011 M 5.8 4,600× the energy of this one
  3. Magna, Utah 2020 M 5.7 3,200× the energy of this one
  4. This earthquake M 3.4 about 1.7 tons of TNT
  5. Around the size people start to feel M 3.0 this one released 3.5× 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 5.1 on 2019-09-24 — about 350 times the energy of this one.

Before 2016, the USGS record lists 17 earthquakes of M5 or more within 50 km; the five largest:

  1. 7.7 45 km N of San Antonio, Puerto Rico · 32 km NW of this epicentre
  2. 7.1 24 km NNW of San Antonio, Puerto Rico · 28 km W of this epicentre
  3. 6.4 32 km NW of Aguadilla, Puerto Rico · 49 km W of this epicentre
  4. 6.4 61 km N of Hatillo, Puerto Rico · 42 km NNE of this epicentre
  5. 6.3 6 km WNW of Aguadilla, Puerto Rico · 41 km SW 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 18.6826, -66.9213. Map © OpenStreetMap contributors.

Nearby places

PlaceDistanceDirection from the epicentre
Quebradillas Municipio, PR 24 km (15 mi) S earthquakes near Quebradillas Municipio
Isabela Municipio, PR 24 km (15 mi) SSW earthquakes near Isabela Municipio
Camuy Municipio, PR 27 km (17 mi) SSE earthquakes near Camuy Municipio
Hatillo Municipio, PR 30 km (19 mi) SSE earthquakes near Hatillo Municipio
Aguadilla Municipio, PR 33 km (20 mi) SW earthquakes near Aguadilla Municipio
Moca Municipio, PR 38 km (23 mi) SSW earthquakes near Moca Municipio

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

Aftershocks so far

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

  1. 2.6 25 km N of Garrochales, Puerto Rico
  2. 2.7 13 km NNW of Camuy, Puerto Rico
  3. 3.0 51 km N of Isabela, Puerto Rico
  4. 3.0 19 km N of Camuy, Puerto Rico
  5. 3.3 64 km N of Carrizales, Puerto Rico
  6. 2.9 10 km NNE of Arecibo, Puerto Rico
  7. 2.8 24 km NW of San Antonio, Puerto Rico
  8. 2.5 45 km NNW of San Antonio, Puerto Rico
  9. 3.5 1 km E of Arecibo, Puerto Rico
  10. 3.7 60 km N of Isabela, Puerto Rico
  11. 3.5 58 km N of Hatillo, Puerto Rico
  12. 3.4 59 km N of San Antonio, Puerto Rico
  13. 3.2 67 km N of Isabela, Puerto Rico
  14. 3.4 38 km NNW of San Antonio, Puerto Rico
  15. 3.5 40 km N of Carrizales, 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.