Crustal and upper mantle velocity structure in Alaska

Abstract

The crustal and upper-mantle velocity structure of Alaska testifies to a complex tectonic framework. Much of the structure and history of this framework remains to be conclusively determined. This thesis presents the results of three independent investigations of velocity structure in Alaska in an attempt to provide some insight into its tectonic development. The first study involved the analysis of receiver functions to determine velocity structure beneath College Station (COL), located in Fairbanks, Alaska. Receiver functions from several back azimuths facilitate a fairly detailed analysis of deep crustal velocity structure beneath COL, including an indication that Moho dips to the northeast. The second study also employed receiver function methods to investigate velocity structure for four temporary three-component seismic stations placed in the Brooks Range. Due to the short deployment of these stations in the Brooks Range only a rough estimate of crustal velocities were obtained. Nevertheless, crustal thickening beneath the Brooks range is clearly indicated by an increase in the depth to Moho. The final study undertaken was a three-dimensional tomographic P-wave velocity inversion for the subduction zone region of south central Alaska. Data for the tomographic inversion consisted of local and teleseismic ray paths. The resulting velocity perturbations indicate a positive velocity anomaly associated with the subducting Pacific plate. Furthermore, the tomographic images clarify physical characteristics of the subducting plate such as structure, thickness, and depth of penetration into the mantle.