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Following the Mw 7.9 earthquake we conducted a reconnaissance of the
region to investigate the geotechnical engineering features of the
event. The focus of our investigation was to characterize the spatial
extent and amplitude of ground failures and assess damage to structures.
The most noteworthy aerial observations were that geotechnical and structural damages appeared to be focused towards the eastern end of the Denali-Totschunda fault rupture area. Sparse sand vents and lateral spreads on bars of the western Tanana River, from Fairbanks to Delta, became pervasive to the east. |
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Likewise, for the four glacier-proximal rivers draining toward the
north, little or no liquefaction was observed on the western Delta and
Johnson Rivers whereas, the eastern Robertson and Tok Rivers and
especially, the Nabesna River had observable-to-abundant fissures and
sand vents. Ice on frozen lakes and ponds was shattered within about
30-40 km of the fault along the western part of the surface rupture and
to the east became more widespread. In the Northway region ice on most
lakes was broken at distances of more than 100 km. Where the fault crossed the trans-Alaska pipeline strong shaking, inertial motions, and permanent offset of the fault beneath the pipe resulted in damage to 8 horizontal support members, and 9 anchored supports near the fault crossing. The pipe is free to slide on Teflon skids and in numerous locations, especially south of the fault, the pipe collided with vertical support members(VSM). These effects were not critical to the integrity of the pipeline, which performed well during the event. |
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