QuakeIndex

Earthquake · reviewed by a seismologist

M 2.1md

Earthquake near San Sebastián, PR

No earthquake was likely felt in San Sebastián in the 24 hours to 5:58 am AST (09:58 UTC). The last one was M 3.4, 50 km (31 mi) N, at 9:00 pm AST on 27 October 2026, estimated intensity II (weak) in town. Every earthquake near San Sebastián

This page: a magnitude 2.1 earthquake was recorded 2 km (1 mi) east of San Sebastián, PR, at 3:41 pm AST on 27 September 2018 (19:41 UTC), 8.0 km deep. 1 person has reported feeling it to USGS.

USGS: 2 km E of San Sebastián, Puerto Rico

96 km (60 mi) W of San Juan, PR · 24 km (15 mi) NE of Mayagüez, PR

3:41 pm AST, Sep 27, 2018 · · 8.0 km deep · released about 44 lb of TNT

Every earthquake near San Sebastián Felt it? Tell USGS Check my area
10 km30 km60 km120 km N San Sebastián Municipio 0 kmLas Marías Municipio 12 kmLares Municipio 12 kmMoca Municipio 13 kmQuebradillas Municipio 15 kmCamuy Municipio 17 kmIsabela Municipio 17 kmAñasco Municipio 18 kmMaricao Municipio 18 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
3:41 pm AST on 27 September 2018 ()
Where
2 km (1 mi) east of San Sebastián, PR · earthquakes near San Sebastián
Magnitude
M 2.1 (md)
Depth
8.0 km below the surface
Felt
1 report · strongest reported intensity II
Nearest
San Sebastián Municipio, 0 km S
Status
Reviewed by a seismologist

USGS · last changed by USGS · we first saw it 2968 days ago

This was a minor earthquake. Quakes this small are rarely felt and do not cause damage.

At this magnitude and depth, people at rest would likely notice it out to about 15 km (9 mi) from the epicentre. In San Sebastián, 2 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: San Sebastián 2 km, intensity II · Lares 11 km, intensity II. Estimated for each town centre; each link is that town's own record.

How big was it?

This earthquake released about 44 lb of TNT. Magnitude is logarithmic: each whole step up releases about 32 times more energy, so a magnitude 3.1 would have released about 32 times as much.

  1. Mineral, Virginia 2011 M 5.8 340,000× the energy of this one
  2. Magna, Utah 2020 M 5.7 240,000× the energy of this one
  3. Around the size people start to feel M 3.0 22× the energy of this one
  4. This earthquake M 2.1 about 44 lb of TNT

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 1,900 times the energy of this one.

Before 2016, the USGS record lists 8 earthquakes of M5 or more within 50 km; the five largest:

  1. 7.1 24 km NNW of San Antonio, Puerto Rico · 47 km NNW of this epicentre
  2. 6.3 6 km WNW of Aguadilla, Puerto Rico · 28 km WNW of this epicentre
  3. 6.1 15 km WNW of San Antonio, Puerto Rico · 37 km NW of this epicentre
  4. 6.1 18 km NNW of San Antonio, Puerto Rico · 40 km NNW of this epicentre
  5. 5.8 12 km N of Garrochales, Puerto Rico · 50 km ENE 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 18.3351, -66.9683. Map © OpenStreetMap contributors.

Nearby places

PlaceDistanceDirection from the epicentre
San Sebastián Municipio, PR 0 km (0 mi) S earthquakes near San Sebastián Municipio
Las Marías Municipio, PR 12 km (7 mi) S earthquakes near Las Marías Municipio
Lares Municipio, PR 12 km (8 mi) ESE earthquakes near Lares Municipio
Moca Municipio, PR 13 km (8 mi) WNW earthquakes near Moca Municipio
Quebradillas Municipio, PR 15 km (9 mi) NNE earthquakes near Quebradillas Municipio
Camuy Municipio, PR 17 km (10 mi) NE earthquakes near Camuy Municipio

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

Aftershocks so far

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

  1. 2.0 3 km WNW of Mayagüez, Puerto Rico
  2. 2.3 9 km NNE of Carrizales, Puerto Rico
  3. 2.3 3 km NNE of Espino, Puerto Rico
  4. 2.0 5 km S of Magas Arriba, Puerto Rico
  5. 2.4 1 km SSW of Boquerón, Puerto Rico
  6. 1.7 Mona Passage
  7. 1.6 12 km NE of Sabana Grande, Puerto Rico
  8. 1.8 6 km W of Hormigueros, Puerto Rico
  9. 2.5 3 km N of Sabana Eneas, Puerto Rico
  10. 1.6 1 km SE of Palmarejo, Puerto Rico
  11. 2.4 24 km N of Isabela, Puerto Rico
  12. 2.1 1 km N of Fuig, Puerto Rico
  13. 2.1 1 km E of Fuig, Puerto Rico
  14. 1.9 3 km SE of Maria Antonia, Puerto Rico
  15. 2.3 19 km SW of Stella, 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.