QuakeIndex

Earthquake · reviewed by a seismologist

M 3.6md

121 km N of San Juan, Puerto Rico

Yes. A magnitude 3.6 earthquake was recorded 121 km N of San Juan, Puerto Rico, at 11:16 pm AST on 22 October 2021 (03:16 UTC), 13 km deep. 2 people have reported feeling it to USGS.

· 13 km deep · released about 4.5 tons of TNT

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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
Magnitude
M 3.6 (md)
Depth
13 km below the surface
Felt
2 reports · strongest reported intensity II
Status
Reviewed by a seismologist

USGS · last changed by USGS · we first saw it 1557 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 71 km (44 mi) from the epicentre. 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.

How big was it?

This earthquake released about 4.5 tons of TNT. Magnitude is logarithmic: each whole step up releases about 32 times more energy, so a magnitude 4.7 would have released about 32 times as much.

  1. Northridge, California 1994 M 6.7 38,000× the energy of this one
  2. Mineral, Virginia 2011 M 5.8 1,700× the energy of this one
  3. Magna, Utah 2020 M 5.7 1,200× the energy of this one
  4. This earthquake M 3.6 about 4.5 tons of TNT
  5. Around the size people start to feel M 3.0 this one released 9.4× 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 4.4 on 2016-10-23 — about 13 times the energy of this one.

Before 2016, the USGS record lists 2 earthquakes of M5 or more within 50 km:

  1. 5.4 106 km N of Brenas, Puerto Rico · 27 km WSW of this epicentre
  2. 5.0 113 km N of Brenas, Puerto Rico · 19 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 19.5631, -66.1645. Map © OpenStreetMap contributors.

Aftershocks so far

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

  1. 3.3 108 km N of San Juan, Puerto Rico
  2. 3.0 73 km N of San Juan, Puerto Rico
  3. 3.5 Puerto Rico region
  4. 3.6 166 km N of San Juan, Puerto Rico
  5. 3.6 114 km NNE of San Juan, Puerto Rico
  6. 3.4 102 km N of San Juan, Puerto Rico
  7. 3.4 75 km N of Brenas, Puerto Rico
  8. 3.4 77 km N of Brenas, Puerto Rico
  9. 3.4 83 km N of Brenas, Puerto Rico
  10. 2.9 82 km N of Brenas, Puerto Rico
  11. 3.0 96 km NNE of San Juan, Puerto Rico
  12. 3.5 87 km N of Brenas, Puerto Rico
  13. 3.4 112 km N of Brenas, Puerto Rico
  14. 3.1 96 km N of Brenas, Puerto Rico
  15. 3.7 103 km N of Brenas, 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.