ABSTRACT

The Fairweather fault is recognizable as a geologic and geomorphic feature from Palma Bay on the southeast at least as far northwest as Nunatak Fiord east of Yakutat Bay, a distance of 200 kilometers along the surface trace. The earthquake of July 10, 1958, was caused by movement on much or all of that segment of the fault: a 10-foot or larger right-lateral offset occurred at Palma Bay where the surface trace trends southeastward under the ocean, and fresh scarps were formed on the south shore of Nunatak Fiord. A displacement in which the southwest side moved relatively northwest 21 1/2 feet and up 3 1/2 feet was measured at one point on the fault just east of the north end of Crillon Lake. Continuity of breakage between Palma Bay and Nunatak Fiord cannot be demonstrated positively because ice and water conceal the ground surface in the fault zone along about 80 per cent of that distance.

Extensive minor faulting in bedrock east of the center of Crillon Lake was observed on flat areas on both sides of the Fairweather fault. These systems of minor faults were similar in general appearance to those formed on the Nunatak at Nunatak Fiord both in this earthquake and in the Yakutat Bay earthquakes of 1899.

A wide variety of geological effects other than faulting was observed throughout a broad area along the Pacific coast from Cape Spencer to Mount St. Elias. Among these were earth and rock avalanches, snow and ice avalanches, earth slumps, earth lurches, and sandblows from craterlets and fissures.

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