Data collected by seismic networks operated by the Geophysical Institute of the University of Alaska-Fairbanks are used to study the seismicity and tectonics of northern Alaska. Microearthquake activity (less than 4.7 M_L) is seen as a diffuse band trending north-northeast from Fairbanks to Barter Island and as an easterly trend roughly parallel to, but south of, the crest of the Brooks Range. Depths of the events range from 10 to 25 km. Some clustering occurs, with the most clearly defined feature being a line of epicenters at 157°30^prime that trends north between 66° and 67°N.

A crustal velocity structure of the eastern Brooks Range is constrained using refracted phases from earthquakes local to the Barter Island, Fort Yukon, and Fairbank networks, respectively. Focal mechanism solutions from the Brooks Range show normal, thrust, and strike-slip faulting. Common to all of them, however, is an east-striking nodal plane that parallels the regional structural grain, suggesting that the fault planes are on reactivated faults. This is in contrast to the earthquakes in interior Alaska, which show mainly strike-slip focal mechanisms. The orientation of the pressure axes in both areas is consistent with the convergence of the Pacific and North American plates.

End_of_Article - Last_Page 664------------