M3.8 Earthquake 4 km SW of Indios, Puerto Rico — September 20, 2021
2021-09-20 21:58:25 UTC (2021-09-20) · approx. 5:58 PM UTC-4 local
Felt by 20 people across nearby locations.
On September 20, 2021 at 21:58 UTC, a magnitude 3.8 shallow crustal earthquake struck 4 km SW of Indios, Puerto Rico, at a depth of 11.0 km and coordinates 17.9653°, -66.8490°. The earthquake was reported felt by 20 peopleacross nearby locations, with a maximum shaking intensity of Modified Mercalli Intensity (MMI) 3.1 (light). This earthquake was detected by 25 seismic stations with moderate location accuracy and was assigned a USGS significance rating of 225, placing it among routine seismic activity.
Physical scale: An earthquake of magnitude 3.8 releases seismic energy equivalent to roughly 6.6 metric tons of TNT. Empirical fault-scaling laws (Wells & Coppersmith, 1994) estimate the subsurface rupture length at approximately 237 m — a useful intuition for the size of the slip patch on the fault.
The epicenter is located in Puerto Rico, a region characterized by the Puerto Rico Trench oblique subduction zone and the Muertos Trough, with complex Caribbean–North American plate interactions. The nearest mapped fault system is the Puerto Rico Trench. View all earthquakes in Puerto Rico.
Learn more: Magnitude scale · Aftershock sequences
ShakeMap — predicted shaking intensity
Modeled ground-motion intensity contoured on the Modified Mercalli scale (MMI). Computed by the USGS from the moment-tensor solution and regional ground-motion prediction equations.
Source: U.S. Geological Survey ShakeMap. View interactive ShakeMap on USGS
Did You Feel It? — community-reported shaking
Aggregated felt-report intensity from 20 citizen responses to the USGS Did You Feel It? system. Each colored zone represents the average MMI from reports in that area.
Source: U.S. Geological Survey Did You Feel It?. View on USGS · submit your own report
Earthquake Details
-66.8490°E
Technical Information
Nearby Earthquakes (Last 7 Days)
Common Questions
How strong was the magnitude 3.8 earthquake near Indios, Puerto Rico?
The magnitude 3.8 earthquake that struck 4 km SW of Indios, Puerto Rico on September 20, 2021 at 21:58 UTC had a depth of 11.0 km. It was felt by 20 people with maximum shaking intensity of MMI 3.1 (light). For context, this was a minor earthquake typically detected only by instruments.
Where did the earthquake occur?
The earthquake epicenter was located at 17.9653°, -66.8490°, which is 4 km SW of Indios, Puerto Rico. View all earthquakes in Puerto Rico.
Were there aftershocks?
Aftershock activity is monitored continuously by the USGS. Aftershock sequences from magnitude 3.8 earthquakes can continue for several days and gradually diminish over time.
Has Puerto Rico had earthquakes this big before?
The largest recorded earthquake in Puerto Rico was the M7.3 offshore earthquake of October 11, 1918. Today's magnitude 3.8 event is significantly smaller than that historical record.
Authoritative source: USGS event page (event ID: pr2021263005). All scientific values on this page are sourced verbatim from the USGS feed.
Cite this page: EarthquakeTracker.org. (2021, September 20, 2021). M3.8 Earthquake 4 km SW of Indios, Puerto Rico — September 20, 2021. Retrieved December 3, 2021 from https://www.earthquaketracker.org/earthquakes/event/pr2021263005/