Late Quaternary offsets along the Fairweather fault and crustal plate interactions in southern Alaska

Abstract

The northwest-trending Fairweather fault has undergone Cenozoic strike-slip displacement, with the most recent pulse of movement occurring in late Quaternary time. During the Lituya Bay earthquake (Ms = 7.9) of July 10, 1958, movement occurred probably along the entire 280 km onshore length of the Fairweather fault, with maximum measured displacements of 6.5 m dextral slip and 1 m dip slip near Crillon Lake. Three streams at Crillon Lake that flow on glacial till and bedrock have dextral displacements with maximum offset of roughly 55 m, and a lateral moraine of Finger Glacier southeast of Crillon Lake appears to have been offset at least 50 m in the same sense. Radiometric dating of wood from moraines near Crillon Lake and at Finger Glacier indicates that the offset stream drainages are probably not older than 940 ± 200 years BP and that the offset lateral moraine is about 1300 ± 200 years old. Data from the offset streams indicate that the minimum average displacement rate along this part of the Fairweather fault for the last millennium was at least 4.8 cm year−1 and was probably closer to 5.8 cm year−1.The deduced average offset rate is approximately equal to the full relative displacement of about 5.4 cm year−1 between the Pacific and North American plates in the Gulf of Alaska region that has been deduced from deep sea paleomagnetic data. These data indicate that the Fairweather fault is presently a transform boundary along which most, if not all, of the relative motion between the Pacific and North American plates is currently being taken up. Major valleys crossing the Fairweather fault that are probably older than Sangamon are systematically offset in a dextral sense an average of 5.5 km. These data suggest that the present high displacement rate on the Fairweather fault could not have begun more than 100 000 years ago and, together with data from other onshore faults, imply that before that time the relative motion between the plates was mainly on one or more submarine faults.

Basement and Regional Structure Along Strike of the Queen Charlotte Fault in the Context of Modern and Historical Earthquake Ruptures

“…Recent Global Positioning System (GPS) analysis of seismicity supports the latter, shorter rupture model for the 1949 event (Ding et al, 2015). Subsequent to the 1949 event, an M s 7.9 earthquake in 1958 ruptured 280 km of the Fairweather fault (Tocher, 1960;Plafker et al, 1978), and an M s 7.6 earthquake ruptured near Sitka in 1972 along the central QCF (Schell and Ruff, 1989).…”

Inference of Multiple Earthquake-Cycle Relaxation Timescales from Irregular Geodetic Sampling of Interseismic Deformation

“…Johnson and Segall (2004) also extended the Savage and Prescott (1978) model to include the localized creep on a linear viscous shear zone within the upper elastic layer. Geographic distribution of the 15 strike-slip faults considered in this study: (1) Alpine, (2) Altyn Tagh, (3) Dead Sea, (4) Elsinore, (5) Fairweather, (6) Garlock, (7) Karakoram, (8) SAF-Mojave, (9) North Anatolian, (10) Owens Valley, (11) Philippine, (12) SAF-Carrizo, (13) SAF-Indio, (14) San Jacinto, and (15) Haiyuan (Sharp, 1967(Sharp, , 1981Savage and Burford, 1973;Plafker et al, 1978;Sieh and Jahns, 1984;Lubetkin and Clark, 1988;Rockwell et al, 1990;Barrier et al, 1991;Lisowski et al, 1991;Merifield et al, 1991;McGill and Sieh, 1993;Beanland and Clark, 1994;Duquesnoy et al, 1994;Petersen and Wesnousky, 1994;Bennett et al, 1996Bennett et al, , 1997Armijo et al, 1999;Beavan et al, 1999;Lasserre et al, 1999;Bendick et al, 2000;Klinger et al, 2000;Reilinger et al, 2000;Argus and Gordon, 2001;Lee et al, 2001;Miller et al, 2001;Niemi et al, 2001;Norris and Cooper, 2001;Banerjee and Bürgmann, 2002;Brown et al, 2002;Hubert-Ferrari et al, 2002;Fletcher and Freymueller, 2003;Meghraoui et al, 2003;Lacassin et al, 2004;…”

Proceedings of conference XXXIX; directions in paleoseismology

“…One of the most significant paleoseismic studies following the 1964 event was conducted by George Plafker (Plafker and Rubin, 1978) who compared the newly created marine terraces on Middleton and Montague Islands with similar prehistoric marine terraces. Clearly several prehistoric uplifts of the same tectonic blocks had occurred at intervals of from 500 to 1,400 years.…”

“…Most Holocene marine terraces are located along tectonically active or convergent-transpressive plate margins and are related to growth of youthful anticlines (Hudson and others, 1976;Plafker and Rubin, 1978;LaJoie, 1986). In such areas, short-term crustal instability is expressed geomorphically by emergent Holocene marine terraces formed by uplift steps of 1-15 m and by crustal warps to maximum altitudes of about 70 m above sea level.…”

“…For example, as shown in figure 2, the lower three pre-1964 terraces along the windward southern end of the Middleton Island have been eroded away leaving only half the uplift record intact, due to the high erosion rate and recurrence intervals as long as 1,350 yrs (Plafker and Rubin, 1978). Rigorous interpretation of the record of coseismic uplift requires data on the amount and sense of interseismic displacement that is seldom available.…”