M3.9 Earthquake 121 km S of Sand Point, Alaska — July 16, 2023
2023-07-16 20:07:22 UTC (2023-07-16) · approx. 9:07 AM UTC-11 local
On July 16, 2023 at 20:07 UTC, a magnitude 3.9 shallow crustal earthquake struck 121 km S of Sand Point, Alaska, at a depth of 35.0 km and coordinates 54.2568°, -160.7432°.
Physical scale: An earthquake of magnitude 3.9 releases seismic energy equivalent to roughly 11 metric tons of TNT. Empirical fault-scaling laws (Wells & Coppersmith, 1994) estimate the subsurface rupture length at approximately 296 m — 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 5.1 mainshock that occurred 24 days ago 90 km S of Sand Point, Alaska. Since the mainshock, the USGS has recorded 13 aftershocks in this area. Aftershock activity is expected to continue for days to weeks as stresses on surrounding faults redistribute.
Earthquake Details
-160.7432°E
Technical Information
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Common Questions
How strong was the magnitude 3.9 earthquake near Sand Point, Alaska?
The magnitude 3.9 earthquake that struck 121 km S of Sand Point, Alaska on July 16, 2023 at 20:07 UTC had a depth of 35.0 km. For context, this was a minor earthquake typically detected only by instruments.
Were there aftershocks?
Aftershock activity is monitored continuously by the USGS. Aftershock sequences from magnitude 3.9 earthquakes can continue for several days and gradually diminish over time.
Is this the same earthquake as the M5.1 one earlier?
No. This magnitude 3.9 earthquake is an aftershock of the larger magnitude 5.1 mainshock that occurred earlier 90 km S of Sand Point, Alaska. Aftershocks are smaller earthquakes triggered by stress changes from the mainshock.
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Understanding This Data
Magnitude 3.9 earthquakes are typically only recorded by instruments.
Authoritative source: USGS event page (event ID: us7000kgvj). All scientific values on this page are sourced verbatim from the USGS feed.
Cite this page: EarthquakeTracker.org. (2023, July 16, 2023). M3.9 Earthquake 121 km S of Sand Point, Alaska — July 16, 2023. Retrieved September 28, 2023 from https://www.earthquaketracker.org/earthquakes/event/us7000kgvj/