Magnitude 6.0 earthquake rocks 26 miles from Willow Alaska
A magnitude 6.0 earthquake struck southcentral Alaska on Wednesday, Nov. 27 at 8:11 a.m. Alaska Standard Time, occurring 26 miles southwest of Willow. The tremor registered at a depth of 42.8 miles, placing it in the intermediate-depth category that characterizes much of the region’s seismic activity.
The Alaska Earthquake Center confirmed the event has been reviewed by a seismologist, verifying the initial readings and location data. The quake’s epicenter was positioned at coordinates 61.5700°N and 150.75°W, placing it in a seismically active zone where the subducting Pacific Plate descends beneath the North American Plate.
Understanding this earthquake’s context within Alaska’s complex tectonic setting helps residents and officials assess potential impacts and prepare for future seismic events in the region.
Proximity to major population centers
The earthquake occurred relatively close to several populated areas in southcentral Alaska. The epicenter sat 37 miles northwest of Anchorage, Alaska’s largest city, and the same distance north of Tyonek. Elmendorf Air Force Base and Fort Richardson both lie approximately 39 and 41 miles from the epicenter respectively.
Eagle River residents experienced shaking from a quake 43 miles away, while Wasilla and Chugiak both sit 43 and 44 miles from the earthquake’s origin point. The tremor occurred 30 miles southeast of Skwentna and 54 miles west of Palmer.
Further afield, the quake struck 245 miles southwest of Fairbanks and 268 miles north of Kodiak. Mount Spurr, an active volcano, lies 53 miles east of the epicenter, though volcanic activity was not associated with this seismic event.
Depth indicates intermediate seismicity
The 42.8-mile depth places this earthquake in the intermediate-depth category, which occurs within the Wadati-Benioff Zone. This zone marks the area where the subducting Pacific Plate descends toward the mantle beneath the overriding North American Plate.
Intermediate-depth earthquakes in Alaska typically occur below 20 miles and can extend to approximately 140 miles deep in southern and central Alaska. This depth range reflects the down-dip extension of the Pacific Plate as it plunges beneath the continent.
The Wadati-Benioff Zone extends along the Aleutian Arc, Alaska Peninsula and Cook Inlet before terminating beneath the northern foothills of the Alaska Range. Seismicity in this zone represents one of three major earthquake sources in southcentral Alaska.
Understanding Alaska’s tectonic complexity
Southcentral Alaska earthquakes originate from multiple tectonic features, creating a complex seismic landscape. The strongest earthquakes in the region are generated by the megathrust fault marking the contact zone between the subducting Pacific and overriding North American plates.
The 1964 M9.2 Great Alaska Earthquake, which originated under Prince William Sound, remains the second largest earthquake ever recorded worldwide. This megathrust event set the standard for understanding Alaska’s most powerful seismic potential.
Beyond the megathrust and intermediate-depth events, crustal seismicity in southcentral Alaska stems from three major sources. These include the faults and folds of the Cook Inlet basin, the Castle Mountain Fault and a wide band of diffuse seismicity extending from northern Cook Inlet to the Denali Fault.
Recent notable intermediate-depth events
The 2016 M7.1 Iniskin earthquake and the 2018 M7.1 Anchorage earthquake represent the most recent significant intermediate-depth events in the region. Both produced substantial ground shaking throughout southcentral Alaska and resulted in structural damage to buildings and infrastructure.
These precedents demonstrate that intermediate-depth earthquakes, despite occurring tens of miles below the surface, can generate powerful shaking at ground level. The depth can actually cause seismic waves to spread across wider areas, affecting multiple communities simultaneously.
The magnitude 6.0 event on Nov. 27 falls below these recent major quakes but still represents a significant seismic event capable of producing noticeable shaking across the region.
Crustal earthquake sources threaten region
Mapped geological structures in upper Cook Inlet are capable of generating strong earthquakes independent of subduction zone activity. The April 1933 M6.9 earthquake, which caused considerable damage in Anchorage, appears to have occurred on such a structure.
The Castle Mountain Fault passes 25 miles north of Anchorage and exhibits geological evidence of Holocene offsets. This fault generated the 1984 M5.6 Sutton Earthquake, demonstrating its continued activity and threat potential.
A diffuse zone of seismicity between Cook Inlet and the Denali Fault may mark a deformation zone between the Bering microplate to the west and the southern Alaska block to the east. This broad zone includes a series of predominantly thrust faults, and a 1943 M7.0 earthquake may have originated in this band.
Assessing earthquake impacts
The Alaska Earthquake Center maintains a “Did You Feel It?” reporting system that allows residents to submit their experiences of ground shaking. These crowdsourced reports help seismologists understand how earthquakes affect different areas and inform future hazard assessments.
The magnitude 6.0 classification indicates this earthquake released significant energy, though its intermediate depth likely moderated ground shaking intensity at the surface. Depth acts as a natural dampener, reducing the violence of shaking compared to shallow earthquakes of similar magnitude.
Buildings and infrastructure in southcentral Alaska are generally constructed to withstand seismic activity given the region’s earthquake frequency. Modern building codes account for Alaska’s position along one of Earth’s most active plate boundaries.
Ongoing seismic monitoring continues
The Alaska Earthquake Center operates an extensive network of seismic monitoring stations throughout the state. These instruments continuously record ground motion, allowing rapid detection and characterization of earthquakes as they occur.
Seismologists review significant events to refine initial automated determinations of magnitude, depth and location. This quality control process ensures accurate information reaches emergency managers, infrastructure operators and the public.
The center maintains detailed historical records of Alaska seismicity, providing context for current events and supporting research into the state’s complex tectonic processes. Understanding past earthquake patterns helps scientists assess future hazards and guide preparedness efforts.
Alaska’s earthquake preparedness imperative
Living in one of North America’s most seismically active regions requires residents and institutions to maintain constant earthquake preparedness. The potential for large, damaging earthquakes exists across multiple fault systems and tectonic settings in southcentral Alaska.
Emergency kits, structural retrofitting, earthquake drills and family communication plans represent essential preparedness measures for Alaska residents. The combination of megathrust, intermediate-depth and crustal earthquake sources means significant shaking can occur with little or no warning.
While this magnitude 6.0 earthquake represents routine seismic activity for Alaska’s standards, it serves as a reminder of the ongoing tectonic forces shaping the region and the importance of maintaining vigilance regarding earthquake hazards.
Source: Alaska Earthquake Center
