M3.9 Earthquake 20 km E of Castle Rock, Washington — September 5, 2026
2026-09-05 11:09:28 UTC (1 hour ago) · approx. 3:09 AM UTC-8 local
Felt by 467 people across surrounding communities.
On September 5, 2026 at 11:09 UTC, a magnitude 3.9 shallow crustal earthquake struck 20 km E of Castle Rock, Washington, at a depth of 17.2 km and coordinates 46.2450°, -122.6448°. The earthquake was reported felt by 467 peopleacross surrounding communities, with a maximum shaking intensity of Modified Mercalli Intensity (MMI) 3.6 (light). This earthquake was detected by 42 seismic stations with excellent location accuracy and was assigned a USGS significance rating of 440, placing it among routine seismic activity.
Physical scale: An earthquake of magnitude 3.9 releases seismic energy equivalent to roughly 12 metric tons of TNT. Empirical fault-scaling laws (Wells & Coppersmith, 1994) estimate the subsurface rupture length at approximately 315 m — a useful intuition for the size of the slip patch on the fault.
The epicenter is located in Washington, a region characterized by the Cascadia Subduction Zone, where the Juan de Fuca Plate subducts beneath North America and is capable of producing M9+ megathrust earthquakes. The nearest mapped fault system is the Cascadia Subduction Zone. View all earthquakes in Washington.
Learn more: Cascadia Subduction Zone · 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 467 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
-122.6448°E
Technical Information
Nearby Earthquakes (Last 7 Days)
Common Questions
How strong was the magnitude 3.9 earthquake near Castle Rock, Washington?
The magnitude 3.9 earthquake that struck 20 km E of Castle Rock, Washington on September 5, 2026 at 11:09 UTC had a depth of 17.2 km. It was felt by 467 people with maximum shaking intensity of MMI 3.6 (light). For context, this was a minor earthquake typically detected only by instruments.
Where did the earthquake occur?
The earthquake epicenter was located at 46.2450°, -122.6448°, which is 20 km E of Castle Rock, Washington. View all earthquakes in Washington.
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.
Has Washington had earthquakes this big before?
The largest recorded earthquake in Washington was the M7.4 offshore earthquake of April 13, 1949. Today's magnitude 3.9 event is significantly smaller than that historical record.
Authoritative source: USGS event page (event ID: uw714095342). All scientific values on this page are sourced verbatim from the USGS feed.
Cite this page: EarthquakeTracker.org. (2026, September 5, 2026). M3.9 Earthquake 20 km E of Castle Rock, Washington — September 5, 2026. Retrieved September 5, 2026 from https://www.earthquaketracker.org/earthquakes/event/uw714095342/