Investigating ultra-low velocity zones at the core-mantle boundary beneath the Southern Hemisphere using an Antarctic dataset

• Main Author: Carson, Sarah
• Other Authors: Hansen, Samantha E., Mahatsente, Rezene, Stowell, Harold Hilton, Garnero, Edward J.
• Format: Thesis
• Language: English
• Published: University of Alabama Libraries 2018
• Subjects: Geophysics; Geology; Antarctic; New Zealand; Pacific; Transantarctic Mountains; Weddell; Weddell Sea; Antarc*; Antarctica
• Online Access: http://ir.ua.edu/handle/123456789/5419

Electronic Thesis or Dissertation The core-mantle boundary (CMB) represents the largest absolute density contrast on our planet, and it is associated with significant heterogeneities. The CMB structure focused on in this study are ultra-low velocity zones (ULVZs), laterally-varying, 5-50 km thick isolated patches seen in some locations just above the CMB that are associated with increased density and reduced seismic wave velocities. The variable characteristics associated with ULVZs have led to many questions regarding their origins, but only about 17% of the CMB has been surveyed for the presence of ULVZs given limited seismic coverage of the lowermost mantle. Therefore, investigations that sample the CMB with new geometries are critical to further our understanding of ULVZs and their potential connection to other deep Earth processes. The Transantarctic Mountains Northern Network (TAMNNET), a 15-station seismic array that was deployed in Antarctica from 2012-2015, provides a unique dataset to further study ULVZ structure with new and unique path geometry. Core-reflected ScP phases recorded by TAMNNET well sample the CMB in the vicinity of New Zealand in the southwestern Pacific, providing coverage between an area to the northeast where ULVZ structure has been previously identified and another region to the south, where ULVZ evidence is inconclusive. This area is of particular interest because the data sample across the boundary of the Pacific Large Low Shear Velocity Province (LLSVP). The Weddell Sea region near Antarctica is also well sampled in this study, providing new information on this area that has not been previously studied. By identifying and modeling energy associated with the ScP waveform, new portions of the CMB have been explored and evidence for ULVZs in both regions has been found. A correlative scheme between 1-D synthetic seismograms and observed data demonstrate that ULVZs are required in the study regions, but modeling uncertainties limit the ability to definitively define ULVZ ...