QuakeIndex

Earthquake · reviewed by a seismologist

M 3.4md

Earthquake near Las Marias, PR

No earthquake was likely felt in Las Marias in the 24 hours to 6:04 pm AST (22:04 UTC). The last one was M 3.5, 12 km (8 mi) NNE, at 12:03 am AST on 6 November 2026, estimated intensity II (weak) in town. Every earthquake near Las Marias

This page: a magnitude 3.4 earthquake was recorded 3 km (2 mi) north-northeast of Las Marias, PR, at 7:42 pm AST on 21 October 2017 (23:42 UTC), 7.0 km deep. 2 people have reported feeling it to USGS.

USGS: 3 km NNE of Las Marias, Puerto Rico

13 km (8 mi) N of Mayagüez, PR · 113 km (70 mi) W of San Juan, PR

7:42 pm AST, Oct 21, 2017 · · 7.0 km deep · released about 1.8 tons of TNT

Every earthquake near Las Marias Felt it? Tell USGS Check my area
10 km30 km60 km120 km N Añasco Municipio 4 kmAguada Municipio 8 kmMoca Municipio 9 kmRincón Municipio 13 kmSan Sebastián Municipio 17 kmAguadilla Municipio 18 kmLas Marías Municipio 19 kmHormigueros Municipio 21 kmIsabela Municipio 22 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
7:42 pm AST on 21 October 2017 ()
Where
3 km (2 mi) north-northeast of Las Marias, PR · earthquakes near Las Marias
Magnitude
M 3.4 (md)
Depth
7.0 km below the surface
Felt
2 reports · strongest reported intensity III
Nearest
Añasco Municipio, 4 km S
Status
Reviewed by a seismologist

USGS · last changed by USGS · we first saw it 3227 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 56 km (35 mi) from the epicentre. In Las Marias, 3 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: Aguada 9 km, intensity III · Aguadilla 12 km, intensity III · Rincón 12 km, intensity III · Mayagüez 13 km, intensity III · San Sebastián 15 km, intensity III · Rafael Hernandez 18 km, intensity III · Isabela 23 km, intensity II · Quebradillas 27 km, intensity II. Estimated for each town centre; each link is that town's own record.

How big was it?

This earthquake released about 1.8 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 4.3 on 2017-10-14 — about 24 times the energy of this one.

Before 2016, the USGS record lists 10 earthquakes of M5 or more within 50 km; the five largest:

  1. 7.1 24 km NNW of San Antonio, Puerto Rico · 43 km N of this epicentre
  2. 6.4 32 km NW of Aguadilla, Puerto Rico · 42 km NW of this epicentre
  3. 6.3 6 km WNW of Aguadilla, Puerto Rico · 16 km NNW of this epicentre
  4. 6.1 15 km WNW of San Antonio, Puerto Rico · 28 km NNW of this epicentre
  5. 6.1 18 km NNW of San Antonio, Puerto Rico · 36 km N 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 18.3183, -67.1341. Map © OpenStreetMap contributors.

Nearby places

PlaceDistanceDirection from the epicentre
Añasco Municipio, PR 4 km (2 mi) S earthquakes near Añasco Municipio
Aguada Municipio, PR 8 km (5 mi) NW earthquakes near Aguada Municipio
Moca Municipio, PR 9 km (5 mi) NE earthquakes near Moca Municipio
Rincón Municipio, PR 13 km (8 mi) W earthquakes near Rincón Municipio
San Sebastián Municipio, PR 17 km (11 mi) E earthquakes near San Sebastián Municipio
Aguadilla Municipio, PR 18 km (11 mi) N earthquakes near Aguadilla Municipio

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

Aftershocks so far

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

  1. 2.5 16 km SW of Stella, Puerto Rico
  2. 1.9 Mona Passage
  3. 2.2 Puerto Rico region
  4. 3.1 17 km NW of Rincón, Puerto Rico
  5. 2.6 Mona Passage
  6. 2.2 2 km S of Guánica, Puerto Rico
  7. 2.7 21 km SW of Stella, Puerto Rico
  8. 1.6 0 km SE of Fuig, Puerto Rico
  9. 2.0 15 km SSW of Stella, Puerto Rico
  10. 2.7 11 km E of Maricao, Puerto Rico
  11. 1.7 2 km SE of Maria Antonia, Puerto Rico
  12. 2.3 3 km WNW of Santo Domingo, Puerto Rico
  13. 2.7 19 km NW of San Antonio, Puerto Rico
  14. 2.5 11 km WNW of Puerto Real, Puerto Rico
  15. 2.2 5 km NNW of Puerto Real, 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.