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 5:25 pm AST (21:25 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 15 km (10 mi) north of Isabela, PR, at 10:07 pm AST on 7 July 2021 (02:07 UTC), 76 km deep.

USGS: 15 km N of Isabela, Puerto Rico

37 km (23 mi) NW of Arecibo, PR · 105 km (65 mi) WNW of San Juan, PR

10:07 pm AST, Jul 7, 2021 · · 76 km deep · released about 1.8 tons of TNT

Every earthquake near Isabela Felt it? Tell USGS Check my area
10 km30 km60 km120 km N Isabela Municipio 17 kmAguadilla Municipio 22 kmQuebradillas Municipio 22 kmCamuy Municipio 28 kmMoca Municipio 30 kmHatillo Municipio 33 kmAguada Municipio 34 kmSan Sebastián Municipio 35 kmAñasco Municipio 41 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
10:07 pm AST on 7 July 2021 ()
Where
15 km (10 mi) north of Isabela, PR · earthquakes near Isabela
Magnitude
M 3.4 (md)
Depth
76 km below the surface
Felt
no reports yet
Nearest
Isabela Municipio, 17 km S
Status
Reviewed by a seismologist

USGS · last changed by USGS · we first saw it 1953 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 it was probably too small to be felt, even directly above it. In Isabela, 15 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.

Earthquakes near other towns within 30 km: Rafael Hernandez, Mora, Quebradillas, Aceitunas, Cacao, Caban.

How big was it?

This earthquake released about 1.8 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 95,000× the energy of this one
  2. Mineral, Virginia 2011 M 5.8 4,300× the energy of this one
  3. Magna, Utah 2020 M 5.7 3,000× the energy of this one
  4. This earthquake M 3.4 about 1.8 tons of TNT
  5. Around the size people start to feel M 3.0 this one released 3.7× 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 5.1 on 2019-09-24 — about 330 times the energy of this one.

Before 2016, the USGS record lists 14 earthquakes of M5 or more within 50 km; the five largest:

  1. 7.7 45 km N of San Antonio, Puerto Rico · 31 km NNW of this epicentre
  2. 7.1 24 km NNW of San Antonio, Puerto Rico · 18 km WNW of this epicentre
  3. 6.4 32 km NW of Aguadilla, Puerto Rico · 38 km W of this epicentre
  4. 6.3 6 km WNW of Aguadilla, Puerto Rico · 30 km SW of this epicentre
  5. 6.1 15 km WNW of San Antonio, Puerto Rico · 24 km WSW 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 18.6401, -67.0280. Map © OpenStreetMap contributors.

Nearby places

PlaceDistanceDirection from the epicentre
Isabela Municipio, PR 17 km (11 mi) S earthquakes near Isabela Municipio
Aguadilla Municipio, PR 22 km (13 mi) SW earthquakes near Aguadilla Municipio
Quebradillas Municipio, PR 22 km (14 mi) SSE earthquakes near Quebradillas Municipio
Camuy Municipio, PR 28 km (17 mi) SE earthquakes near Camuy Municipio
Moca Municipio, PR 30 km (18 mi) S earthquakes near Moca Municipio
Hatillo Municipio, PR 33 km (20 mi) SE earthquakes near Hatillo 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. 3.4 59 km N of San Antonio, Puerto Rico
  2. 3.4 38 km NNW of San Antonio, Puerto Rico
  3. 2.0 6 km W of Maricao, Puerto Rico
  4. 3.5 40 km N of Carrizales, Puerto Rico
  5. 3.3 43 km NW of San Antonio, Puerto Rico
  6. 3.2 42 km NW of San Antonio, Puerto Rico
  7. 2.5 6 km SE of Espino, Puerto Rico
  8. 3.4 42 km N of San Antonio, Puerto Rico
  9. 3.3 50 km N of Isabela, Puerto Rico
  10. 3.5 Mona Passage
  11. 3.1 Puerto Rico region
  12. 3.2 5 km SW of Stella, Puerto Rico
  13. 2.4 19 km N of Quebradillas, Puerto Rico
  14. 3.1 45 km NW of Aguadilla, Puerto Rico
  15. 3.3 26 km N of Hatillo, 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.