A seismological examination of the structure and tectonics of southernmost South America and the Antarctic Peninsula region

Three different seismological investigations of southernmost South America and the Antarctic Peninsula region are presented in this thesis. Using new data obtained from the Seismic Experiment in Patagonia and Antarctica, I invert regional waveforms, locate earthquake hypocenters, calculate focal mechanisms, and investigate Rayleigh wave phase velocities. These techniques all provide insight into the structure and tectonics of these unique regions.; The crustal and upper mantle structure of southern South America is determined using a regional waveform inversion method that incorporates a niching genetic algorithm. This technique performs a broad search of the model space and enables examination of alternative local error minima. The vertical and transverse waveforms are used, and anisotropy is identified by solving for separate SV and SH structures in the upper mantle. Results indicate crustal thickness varies from 26 to 36 km, with thicker values towards the northeast, suggesting little crustal thickening beneath the Austral Andes. The average upper mantle velocities are similar to PREM, except in the southernmost region where velocities are 5% slower than PREM. The upper mantle has up to 5% polarization anisotropy. The anisotropic signature is limited to lithospheric depths and may imply the absence of a strong mantle flow pattern in the asthenosphere.; In the Antarctic Peninsula region 150 local earthquake hypocenters are determined (mb 2–5), with locations and depths indicative of ongoing subduction. A local focal mechanism indicates shallow angle thrusting. The South Shetland trench thus represents an extreme end member of hot subduction resulting from slow convergence of young lithosphere, and the absence of intermediate depth earthquakes is consistent with thermal assimilation of the slab at shallow depths. Earthquake locations in the backarc are consistent with the propagation of spreading from northeast to southwest.; Rayleigh wave phase velocity dispersion measurements from 20 teleseismic events are used to determine the interstation velocities in the South Shetland Islands at periods between 16 and 120 seconds. Maps of the velocities indicate crust with continental properties southwest of the Hero Fracture Zone and thinner crust with backarc spreading velocities within the Bransfield Basin proper.