Surface Wave Inversion of the Upper Mantle Velocity Structure in the Ross Sea Region, Western Antarctica

 
James D. Rinke
June 2011

Abstract

The Ross Sea in Western Antarctica is the locale of several extensional basins formed during Cretaceous to Paleogene rifting. Several seismic studies along the Transantarctic Mountains and Victoria Land Basin’s Terror Rift have shown a general pattern of fast seismic velocities in East Antarctica and slow seismic velocities in West Antarctica. This study focuses on the mantle seismic velocity structure of the West Antarctic Rift System in the Ross Embayment and adjacent craton and Transantarctic Mountains to further refine details of the velocity structure.

Teleseismic events were selected to satisfy the two-station great-circle-path method between 5 Polar Earth Observing Network and 2 Global Seismic Network stations circumscribing the Ross Sea. Multiple filter analysis and a phase match filter were used to determine the fundamental mode, and linearized least-square algorithm was used to invert the fundamental mode phase velocity to shear velocity as a function of depth. Observed velocities were then compared to the AK135-β reference earth model.

Surface wave inversion results reveal three regions with distinct seismic velocity structures: the East Antarctic craton, the Transantarctic Mountains orogenic zone, and the extensionally rifted Ross Sea. The extensional zone of the Ross Sea displays slower seismic velocities than the global average. A seismic velocity structure faster than the global average is documented in the East Antarctic craton, while the Transantarctic Mountains display seismic velocities more closely resembling the rift zone than the craton.

The low velocity zone in the upper mantle of West Antarctica extends from the Transantarctic Mountains through the Ross Sea to the Marie Byrd Land region. These slow seismic velocities are suggestive of a warm upper mantle. A warm upper mantel is difficult to reconcile with the lack of tectonic activity since approximately 30 Ma.

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