UNUSUAL EARTHQUAKES IN THE GULF OF ALASKA AND FRAGMENTATION OF THE PACIFIC PLATE

• Main Authors: J. C. Lahr, C. D. Stephens, D. H. Christensen
• Other Authors: The Pennsylvania State University CiteSeerX Archives
• Format: Text
• Language: English
• Subjects: Bruns; Gulf of Alaska; McCann; Pacific; Perez; Yakutat; Alaska
• Online Access: http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.554.9326; http://www.iris.edu/seismo/quakes/1987-1988gulfofalaska/Lahr_et_al_1988.pdf

Abstract. Two recent M s 7.6 strike-slip which ruptured in an M s 7.9 event in 1958. West of earthquakes in the northern Gulf of Alaska rup- longitude 144øW, motion is accommodated by under-tured a composite 250-km-long north-striking zone thrusting and subduction along the Aleutian mega-in the Pacific plate. These shocks are attributed thrust, which last slipped in the 1964 earthquake. to a combination of enhanced tensional stress in In the intervening region, which has been iden-the Pacific plate seaward of and following the tified as a seismic gap (Tobin and Sykes, 1968; great (M w 9.2) Alaska earthquake of 1964, and Kelleher, 1970; Sykes, 1971), the tectonics are compressional stress resulting from collision of complicated by the collision of the Yakutat ter-the Yakutat terrane with North America. The rane, which moves with nearly the Pacific plate occurrence of these shocks reflects fragmentation velocity (Plafker et al., 1978; Lahr and Plafker, of the northeast corner of the Pacific plate, 1980; Perez and Jacob, 1980; Bruns, 1983; Plafker, possibly the initial step in establishing a new 1987). Although no great earthquake has occurred plate boundary seaward of the current boundary. within the Yakataga seismic gap since the turn of the century (McCann et al., 1980), two sequences Introduction with low-angle thrusting have occurred there since