M4.9 Earthquake east of the South Sandwich Islands — June 20, 2025
2025-06-20 18:40:27 UTC (2025-06-20) · approx. 5:40 PM UTC-1 local
Aftershock of the M5.2 mainshock.
On June 20, 2025 at 18:40 UTC, a magnitude 4.9 shallow crustal earthquake struck east of the South Sandwich Islands, at a depth of 10.0 km and coordinates -57.9086°, -9.2322°. This earthquake was detected by 44 seismic stations with excellent location accuracy and was assigned a USGS significance rating of 369, placing it among routine seismic activity.
Physical scale: An earthquake of magnitude 4.9 releases seismic energy equivalent to roughly 338 metric tons of TNT. Empirical fault-scaling laws (Wells & Coppersmith, 1994) estimate the subsurface rupture length at approximately 1.4 km — a useful intuition for the size of the slip patch on the fault.
This earthquake is part of an ongoing aftershock sequence following the magnitude 5.2 mainshock that occurred 23 days ago east of the South Sandwich Islands. Since the mainshock, the USGS has recorded 0 aftershocks in this area. Aftershock activity is expected to continue for days to weeks as stresses on surrounding faults redistribute.
The epicenter is located in South Sandwich Islands, a region characterized by the South Sandwich Trench, one of Earth's most remote subduction zones.
Learn more: Magnitude scale · Aftershock sequences
Earthquake Details
-9.2322°E
Technical Information
Common Questions
How strong was the magnitude 4.9 earthquake east of the South Sandwich Islands?
The magnitude 4.9 earthquake that struck east of the South Sandwich Islands on June 20, 2025 at 18:40 UTC had a depth of 10.0 km. For context, this was a light earthquake commonly felt near the epicenter.
Where did the earthquake occur?
The earthquake epicenter was located at -57.9086°, -9.2322°, which is east of the South Sandwich Islands.
Were there aftershocks?
Aftershock activity is monitored continuously by the USGS. Aftershock sequences from magnitude 4.9 earthquakes can continue for several days and gradually diminish over time.
Is this the same earthquake as the M5.2 one earlier?
No. This magnitude 4.9 earthquake is an aftershock of the larger magnitude 5.2 mainshock that occurred earlier east of the South Sandwich Islands. Aftershocks are smaller earthquakes triggered by stress changes from the mainshock.
Actions
Authoritative source: USGS event page (event ID: us6000qlhq). All scientific values on this page are sourced verbatim from the USGS feed.
Cite this page: EarthquakeTracker.org. (2025, June 20, 2025). M4.9 Earthquake east of the South Sandwich Islands — June 20, 2025. Retrieved September 2, 2025 from https://www.earthquaketracker.org/earthquakes/event/us6000qlhq/