OPP 9615147 Anandakrishnan Abstract The Antarctic crust and mantle composition and geometry are poorly known. The primary methods for studying the crust, upper mantle, and the deeper asthenosphere is interpretation of seismic data; either OactiveO through use of explosives or OpassiveO using natural sources and interpreting various earthquake phase arrival times and amplitudes. Integrating passive and active seismology can result in efficient use of resources to produce detailed images of the lithosphere. This award supports development of a passive seismic network for the Antarctic interior. The Antarctic is a gaping hole in the rapidly improving field of global seismic imaging and tomography. On this huge continent (surface area of 14 million square km) there are only eight broadband seismic observatories. Further, with the exception of South Pole, all of those stations are along the margins of the continent and none are in the West Antarctic. By contrast, there are 200 permanent stations worldwide in the FDSN (Federation of Digital Seismograph Networks) and on the order of a thousand in national networks not yet integrated into the FDSN. There have been innumerable temporary deployments (1 to 5 years) through PASSCAL (Program for Array Seismic Studies of the Continental Lithosphere), but which have rarely been attempted in the Antarctic. The obvious reason for this lack of data from the interior is the need to supply power continuously and store data on-site during the dark winter months. This project will develop and deploy eleven long term broadband seismic stations on the continent itself. Because 98% of the continent is ice covered, these stations will be installed at the surface of the ice sheet. The body-wave data thus recorded from regional and teleseismic earthquakes can be analyzed at each station for local crustal thickness, lamination, Poisson's ratio (a measure of crustal composition), crust and mantle anisotropy (a measure of current and former stress regimes), and identification of rift zones and crustal block boundaries. In addition, the data from all the stations (including the existing peripheral ones) can be used for seismic tomographic analysis to detail lateral variations in these properties. Six of the stations will be installed at existing Automated Geophysical Observatory sites (in East Antarctica) which will provide heat and power for the data loggers. The remaining five stations will be in the West Antarctic and will be powered and heated by wind turbines during the austral winter. The wind- powered stations are an experimental undertaking that will extend our capabilities for installing seismic stations anywhere in the Antarctic. The stations on the periphery of the continent (and other stations in the high southern latitudes---most notably the stations of the French GEOSCOPE network) have been used to measure surface wave dispersion functions for different paths that cross the Antarctic. These data have been successful in measuring mantle properties, but the resolution (both horizontal and vertical) achievable by this technique is limited compared to body-wave analysis. Nonetheless, this is a valuable existing tool that would be greatly enhanced by the presence of data from within the continent that will be available after successful implementation of the unattended seismometers under this project.
