The convergent motion of the Pacific and North American Plates in Alaska has produced geologic features associated with subduction zones and has transported displaced terranes along the Queen Charlotte-Fairweather fault system that forms the northeastern boundary of the Pacific Plate. These subduction features stop abruptly at the edge of the Yakutat Block displaced terrane, approximately 300 km from the Queen Charlotte-Fairweather fault. The purpose of this study was to determine the type and geometry of the boundary between the Yakutat Block and North American as well as the cause of the offset volcanic arc and missing Wadati-Benioff zone.
I calculated P and S-wave receiver functions for 57 broadband seismic stations located in southeast Alaska. S-wave data was migrated using a Common Conversion Point procedure. P-wave data was imaged via a three-dimensional, pre-stack migration using plane-wave decomposition weighted by an inverse generalized Radon transform to calculate the scattering potential for each event. I also calculated the temperatures at the top of the Yakutat slab and mantle wedge using three different analytical thermal models.
The 3-D images and animations I produced show that the Yakutat Block is being subducted, continuous with the Pacific slab, and extends to the Queen Charlotte-Fairweather strike-slip fault systems. The subducted slab extends north to the Wrangell Volcanic Field with a dip than increases gradually from 10° in the west to 15° in the east, stripping approximately 15 km of overlying sediments. The location of the Wrangell Volcanic Field and lack of Wadati-Benioff zone are consistent with the temperatures I calculated for the top of slab and mantle wedge after stripping 15 km of sediment.
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|Advisor:||Pavlis, Gary L.|
|Commitee:||Douglas, Bruce, Hamburger, Michael W., Johnson, Kaj, Robeson, Scott|
|School Location:||United States -- Indiana|
|Source:||DAI-B 75/05(E), Dissertation Abstracts International|
|Keywords:||Alaska, Seismology, Subduction, Tectonics, Thermal modeling, Yakutat Block|
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