Paper No. 99-2
Presentation Time: 8:15 AM
UPPER MANTLE SHEAR WAVE VELOCITY STRUCTURE BENEATH THE TRANSANTARCTIC MOUNTAINS AND EASTERN WILKES SUBGLACIAL BASIN
The Transantarctic Mountains (TAMS) are the largest non-compressional mountain chain on earth. They extend along strike 4000 km, reach elevations of ~4500 m, and separate low-lying west Antarctica from topographically high east Antarctica. The Wilkes Subglacial Basin (WSB) lies inland, east of the TAMS, extending from the Oates Coast to Southern Victoria Land. The origin of both the TAMS and WSB is unknown, and investigation into the area will provide insight towards an uplift and subsidence mechanism for each area. Data used to study the area are recorded using the Transantarctic Mountains Northern Network (TAMNNET) broadband seismic array. Rayleigh wave phase velocities are sampled at 25 periods, ranging from 18 to 182 s, and are used to create phase velocity maps of the area. Phase velocities are calculated using a two-plane wave method, and the resultant dispersion curves are inverted for shear wave velocity structure. Shear wave velocity is smoothed across the entire study area using a Gaussian weighted smoothing parameter creating a pseudo-3-D shear velocity model. Results show slow shear velocities (<4.5 km s-1) along the coast and slightly inland with fast velocities (>4.55 km s-1) towards the eastern WSB. The boundary from slow to fast shear wave velocity is detected underneath the TAMS as opposed to previous studies positioning this transition zone below the coast, and the transition to faster velocities under the eastern WSB is abrupt. The slow shear wave velocity zone underneath the TAMS extends to a depth of ~250 km and appears to extend both north and south of the TAMNNET study area, indicating a continuous zone of slow upper mantle shear velocities along strike. The discovery of a continuous slow velocity body underneath the TAMS could indicate a plausible uplift mechanism for the mountain chain. The abrupt transition zone from slow to fast velocities could also better define and characterize the eastern WSB. Analyses are ongoing to improve resolution and interpretation of the area, and preliminary results will be shown.