Spatial Variation in Present Day Deformation, Southcentral Alaska, Revealed by GPS Measurements

Southcentral Alaska is a region of complex tectonics. The plate boundary between the Pacific and North-American plates changes from being convergent to transform with the additional complication of the Yakutat block colliding into and accreting onto the North-American plate. In 1964 an M_W9.2 earthquake occurred on the very shallow dipping plate interface between the subducting Pacific plate and the overriding North-American plate. Recent studies of deformation have revealed postseismic deformation continuing to the present, in addition to variation in coupling along the plate interface. Here we present a spatially and temporally improved dataset that allows for more detailed study of deformation processes affecting the region. GPS velocities from more than 150 sites reveal considerable spatial variation in deformation, caused by multiple deformation processes. In general points on the eastern part of the Kenai Peninsula and Prince William Sound show rapid NNW movement, as expected from the plate convergence direction. On the western Kenai Peninsula, however, sites move in opposite direction, trenchward, resultng from postseismic deformation. East of the Kenai Peninsula, velocity vectors are more westerly, showing the effect of the colliding Yakutat block. We use three dimensional models to estimate the contributions of these deformation sources, as well as permanent deformation, translation and rotation of the overriding North American plate.