Wiens and Zhao OPP 9527366 Abstract The present day tectonics and seismological structure of the Antarctic Peninsula and Scotia plate region are among the most poorly understood of any location in the world. This region offers a unique and complex geodynamic setting, as illustrated by the recent cessation of volcanism along the South Shetland Trench and onset of volcanism and rifting in the Bransfield Strait, the possible presence of diffuse deformation and/or microplates in the Drake Passage region, and fast back-arc spreading behind the South Sandwich Arc. This award supports the US component of an international effort to study the seismotectonics and seismic structure of the Antarctic Peninsula and Scotia Sea regions using a large scale deployment of broad band seismographs beginning during the 1996- 1997 field season. The project will deploy 9 broadband PASSCAL seismographs for 2 years in the Antarctic Peninsula region, Southernmost Chile, and South Georgia Island. The following questions will be addressed: 1) Is there seismological evidence, in the form of either subduction zone earthquakes or seismic structure, for current subduction beneath the Antarctic Peninsula? 2) Is there evidence from seismic anisotropy for large scale mantle flow around South America into the South Atlantic? 3) Are regional earthquakes and focal mechanisms consistent with current kinematic models for the Scotia plate, which imply compressional deformation in the Drake Passage region? 4) What is the deep structure of the South Sandwich subduction zone? 5) What is the seismological structure of active back-arc spreading centers in the Bransfield Strait and South Sandwich regions? Answering these questions will help to constrain important tectonic questions such as the cause of plate motion changes, what processes initiate back arc spreading, and the relationship between mantle flow and surface tectonics.
