Strong 6.9 Earthquake Near Chignik, United States
A strong magnitude 6.9 earthquake struck 112 km E of Chignik, United States on Monday, October 11, 2021 at 09:10:25 AM UTC. This shallow crustal event (51.6 km depth) released energy equivalent to approximately 338 kt of TNT. Here is the verified AK telemetry, live epicenter map, and ground shaking assessment.
(112 km E of)Seismic Telemetry Specifications
6.9MWW
Strong Seismic Class
51.6km
Crustal Layer
56.295° N, 156.581° W
GPS Coordinates
338 kt
TNT Equivalent Power
AK
USGS Real-time Feed
Epicenter Location & Tectonic Fault Map
Is This Earthquake Dangerous?
A magnitude 6.9 event is classified as a strong earthquake. Can be destructive in populated areas up to ~160 km from the epicenter. Well-built structures withstand shaking, but unreinforced masonry may suffer serious damage.
Estimated Shaking Across Nearby Communities
Difficult to stand. Damage negligible in good buildings; slight to moderate in ordinary structures.
Did You Feel This Earthquake?
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What Does Magnitude 6.9 Mean?
Earthquake strength is measured on a logarithmic scale. Compare this event with the full seismic scale:
Logarithmic Energy Multiplier
Because seismic scales are logarithmic, each whole integer increase represents:
Why Did This Earthquake Happen?
United States's seismicity is fundamentally governed by its tectonic setting: Pacific Plate sliding past North American Plate along San Andreas; Juan de Fuca subducting along Cascadia; Pacific subduction along the Aleutian Trench. Major regional fault structures include San Andreas Fault System, Cascadia Subduction Zone, Aleutian Megathrust, Hayward Fault, New Madrid Seismic Zone.
Originating at a depth of 51.6 km (Earth's Crust (0–70 km)), this rupture occurred occurred within the brittle upper crust. shallow earthquakes produce the highest peak ground acceleration and the sharpest surface shaking.
Aftershock Outlook & Secondary Tremors
Following an earthquake of magnitude 6.9, an active aftershock sequence is expected over the coming days and weeks. In accordance with Omori's Law and Båth's Law of seismology, secondary tremors decrease in frequency over time, with the largest expected aftershock historically averaging approximately 1.0 to 1.2 magnitude units below the mainshock. Local residents should remain vigilant for secondary shaking, particularly when inspecting older structures or unreinforced masonry.
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Earthquake Safety Action Plan
Complete Safety Guide →- •Drop, Cover, and Hold On: Take cover beneath a sturdy table or desk.
- •Stay indoors away from exterior glass windows and heavy unanchored fixtures.
- •If outdoors, move into an open area away from power lines and building facades.
- •Inspect utilities for damaged gas lines, water leaks, or electrical hazards.
- •Expect Aftershocks: Secondary tremors frequently strike after significant events.
- •Avoid damaged structures and listen to official emergency broadcasts.
- •Maintain a 72-hour emergency go-bag with water, food, and first aid.
- •Anchor heavy furniture, water heaters, and appliances to structural studs.
- •Establish a family emergency communication protocol and meeting point.
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