Liquefaction was widespread throughout eastern central-Alaska, and its
pattern suggests that during the earthquake directivity of rupture
amplified motions towards the eastern region. Liquefaction and related
ground deformations, both derivative features of the event, noticeably
increased in severity and spatial extent towards the east end of the
rupture zone.
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On the north side of the Alaska range in the Tanana River valley
extensive liquefaction was observed where very young river deposits
were capped by a thin (<0.3m) frozen surface layer at source
distances of 50 to 120 km. Tanana River valley liquefaction was
widespread from Fairbanks to the west, to at least several hundred
kilometers eastward. Liquefaction damage became increasingly severe
to the east of Delta, even as the distances to the fault increased.
In the Tok region nearly every river bar deposit appear to have
failed.
 
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Further east, for many kilometers around the towns of Northway and
Slana, large continuous lowland areas of liquefaction and lateral
spread failures were observed. Two measured transects along the
Tanana river at Tetlin bridge showed 1.6% to 3.8% of lateral
extension (spreading) of sand bars across distances of 200 meters
(21 fissures) and 400 meters (48 fissures). Also, compression zones
occurred in some places where separate lateral spreads collided.
 
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In some places the lateral spreads were generally parallel with the direction of extension toward the river. However, in most places the fissures in the frozen surface were sub-linear with random orientations forming networks of polygons that in places were continuous across many acres, and in some places kilometers. In total, Tanana River bar failures covered a vast area.   |