Seismic Swarm S20021111.1: Analysis of Activity Near McKinley Park, Alaska

Seismic swarm S20021111.1 occurred in central Alaska, approximately 82 km east-southeast of McKinley Park. The sequence began at 10:52 on 10 November 2002 and concluded at 03:08 on 12 November 2002, encompassing a total duration of 40 hours and 16 minutes. During this interval, 49 earthquakes were recorded, with magnitudes ranging from 0.7 to 3.7 and focal depths predominantly between 0 and 16 km.

The events clustered in time, with the majority occurring on 10 and 11 November. Notable activity included a magnitude 3.7 event at 19:13 on 11 November at a depth of 0 km, alongside several magnitude 2.0–2.9 shocks distributed across shallow depths. Earlier phases featured lower-magnitude tremors, often at 1–8 km depth, transitioning to more frequent surface-near events later in the sequence. This pattern reflects typical swarm behavior, characterized by numerous small events without a dominant mainshock.

The swarm location lies within the tectonically active Denali Fault zone of interior Alaska. This region forms part of the boundary between the Pacific and North American plates, where oblique convergence drives right-lateral strike-slip motion along the Denali Fault and associated structures. Central Alaska exhibits elevated seismicity due to ongoing deformation, with the broader area influenced by the subduction of the Pacific Plate beneath the North American Plate along the Aleutian megathrust to the south.

Geological records indicate that the Denali Fault has produced large earthquakes throughout the Holocene, including the magnitude 7.9 event of 3 November 2002 located nearby. Post-event stress redistribution in such fault systems can trigger swarm-like sequences through mechanisms such as fluid migration or aseismic slip. The 2002 swarm represents the earliest documented swarm in the regional catalog since 2000, with two additional swarms recorded in subsequent years.

Analysis of event timing shows an initial increase in frequency during the evening of 10 November, peaking with multiple magnitude 2+ events on 11 November before tapering. Depths remained consistently shallow, consistent with activity along upper-crustal fault segments. Such swarms provide insight into localized stress adjustments within the Denali Fault system, which continues to accommodate several millimeters per year of dextral shear.

Overall, swarm S20021111.1 illustrates the dynamic nature of seismicity in this portion of Alaska, where small-magnitude clusters contribute to the cumulative release of tectonic strain in a high-hazard setting.

References USGS Earthquake Hazards Program Alaska Earthquake Center, University of Alaska Fairbanks Alaska Division of Geological & Geophysical Surveys