The Alaska earthquake of July 10, 1958: Movement on the Fairweather fault and field investigation of southern epicentral region

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.

Strike-slip faults in Alaska

“…References: Hamilton and Myers, in press and written communication, 1966;Miller, 1953;Plafker, George, oral communication. 19&5;Stauder, I960;Tarr and Martin, 1912;Tocher, I960;Tocher and Miller, 1959-The its history suggests that it is an ancestral branch of that system.…”

The United States Geological Survey in Alaska: Accomplishments during 1978

“…Most unequivocal evidence for Holocene displacement, as manifested by seafloor displacements, is on this western trace. In most crossings of the fault trace, where seafloor offsets are well displayed, the sense of movement is northeast side down, showing the same sense of vertical displacement as occurred along the onshore Fairweather fault during the 1958 Lituya Bay earthquake (Tocher, 1960). The more sinuous or eastern trace may be an inactive or relatively less active strand of the fault system; however, several of the profiles also showed some seafloor offset along this trace.…”

“…data, 1965). On the basis of measurements made between 1910and 1960(Hicks and Shofnos, 1965, land in the Petersburg area is rising with respect to sea level at a rate of about 0.4 cm/yr.…”

“…Cox, A. W., Hopkins, D. M., and Dalrymple, G. B., 1966 The seismically active Fairweather fault (Tocher, 1960;Page, 1969;Plafker and others, 1976) has been mapped from Yakutat Bay to the shoreline of Palma Bay (Plafker, 1967), and numerous authors have speculated on the seaward extension of this major structural feature (St. Amand, 1957;Grantz, 1966;Stoneley, 1967;Plafker and others, 1978;von Huene and others, in press). Some widely spaced seismic profile lines made prior to 1978 across the shelf (1959).…”

Reconnaissance engineering geology of the Yakutat area, Alaska, with emphasis on evaluation of earthquake and other geologic hazards

“…(universal time), 6.6 m of rightlateral movement was measured along with 1 m of ver tical uplift on the southwest side of the fault. Tocher (1960) suggested that, during this earthquake, move ment occurred along much of the Fairweather fault northwestward to Yakutat Bay. George Plafker (oral commun., 1975) reported a segment of the fault located about 58 km north-northeast of Yakutat that is 5 km long with offset drainages indicative of about 1.7 m of right-lateral displacement during the earthquake.…”