The Hubbard cluster is named after Hubbard Glacier, north of Yakutat,
Alaska. Nearly all events lie under an icesheet. The cluster is based on
the 7.0 Mw earthquake on December 6, 2025, and it includes 53
aftershocks through January 1, 2026. The cluster spans the U.S.-Canada
border. The local distance arrival time data are best fit with a
relatively high velocity at shallow depths (6.2 and 3.55 km/s) and a
single-layer crustal model with these velocities fits the data well.
Most aftershocks of the December 6 mainshock prefer a shallow depth,
with a peak of ~5 km. The location calibration is very robust, due to
good azimuthal coverage. The arrival time data for the December 6
mainshock are not consistent with a single, simple rupture process. The
initial rupture is reported consistently by most stations within about
600 km but at greater distances, especially teleseismic, many reported
first arrival times are delayed by 2-5 seconds from that initial source,
apparently representing one or more later pulses of energy release. To
avoid location bias, only data within 6.0° epicentral distance were used
to estimate the relative location for this event. At the northwestern
end of the aftershock sequence the epicenters spread orthogonal to the
main trend over ~15 km. All events have depth control from near-source
or local-distance readings and some events have teleseismic depth phase
data in general agreement with those depths.
