Stress map for Alaska from earthquake focal mechanisms

Tectonics of Alaska is dominated by subduction of the Pacific plate beneath the North American plate. Additional complications are imposed by the ongoing collision of the Yakutat block into Alaska's southern margin. A number of tectonic models have been proposed for southcentral Alaska in the past. Information on the regional stress orientations complements these models and helps to verify or reject them. A comprehensive set of the earthquake focal mechanisms has been assembled for southern and central Alaska. This dataset includes P-wave first motion focal mechanisms (1986-present), regional seismic moment tensors (2002-present), and Harvard CMT solutions (1976-present). Stress maps were calculated for the crust and subducting slab using ZMAP package. The crustal stresses indicate that strike-slip is the predominant type of faulting in the region with the exception of the area of the Yakutat block collision and upper Cook Inlet (thrust faulting) and a region at the eastern end of the Castle Mountain fault system (normal faulting). The stress directions are radiating outward from the collision zone and consistent with previous findings. Major deviation from this pattern are the stress directions between the Denali and Castle Mountain fault where maximum principal stresses are oriented in E-W direction. Results for the subducting slab show difference in terms of the type of faulting and orientations of the stresses between the McKinley block to the northeast and Kenai block to the southwest.