Deformation of the Kenai Peninsula, Alaska

Steven C. Cohen
Geodynamics Branch, Goddard Space Flight Center
Greenbelt, MD 20771

Jeffrey T. Freymueller
Geophysical Institute, University of Alaska
Fairbanks, AK 99775

Crustal deformation on the Kenai Peninsula in southern Alaska has been studied using data obtained from GPS (Global Positioning System) measurements in 1993 and 1995 and leveling observations in 1964, immediately after the Prince William Sound earthquake. This analysis shows that the Kenai Peninsula has experienced as much as ~ 900 mm uplift during the past three decades and that the uplift forms a ~125 km wide elongate dome with its major axis trending southwest to northeast following the trend of the major tectonic features of the region. While the averaged uplift rate between 1964 and 1995 is as high as 30 mm/yr, the current rate of vertical motion may be substantially lower. The cumulative postseismic uplift deduced for Homer, Alaska, located in the southwest portion of the Kenai Peninsula, is consistent with that determined from tide gauge data at a nearby site; however, the GPS measurements cast doubt on tide gauge data indicating rapid postseismic uplift at Nikiski, located north of Homer along Cook Inlet. Examination of the three-dimensional GPS data indicates that the eastern Kenai Peninsula is cur- rently undergoing significant SSE to NNW contraction in response to North America-Pacific Plate convergence. The horizontal velocities are consistent with the predictions of an elastic half- space model for the interseismic deformation. This result, taken in combination with the small changes in uplift between 1993 and 1995, suggests that most of the present deformation is due to steady plate convergence rather than transient postseismic rebound.

Preliminary GPS velocities 1993-1996