S-wave velocity models in the Scotia Sea Region, Antarctica, from nonlinear inversion of Rayleigh waves dispersion

More than 60 events recorded by four recently deployed seismic broadband st ations around Scotia Sea, Antarctica, have been collected and processed to obtain a general overview of the crust and upper mantle seismic velocities. Group velocity of the fundamental mode of Rayleigh waves in the period betw een 10 s to 30-40 s is used to obtain the S-wave velocity versus depth alon g ten different paths crossing the Scotia Sea region. Data recorded by two IRIS (Incorporated Research Institutions for Seismology) stations (PMSA, EF I) and the two stations of the OGS-IAA (Osservatorio Geofisico Sperimentale -Instituto Antarctico Argentino) network (ESPZ, USHU) are used. The Frequency-Time Analysis (FTAN) technique is applied to the data set to measure the dispersion properties. A nonlinear inversion procedure, "Hedgeh og," is performed to retrieve the S-wave velocity models consistent with th e dispersion data. The average Moho depth variation on a section North to South is consistent with the topography, geological observations and Scotia Sea tectonic models . North Scotia Ridge and South Scotia Ridge models are characterised by simil ar S-wave velocities ranging between 2.0 km/s at the surface to 3.2 km/s to depths of 8 kms. In the lower crust the S-wave velocity increases slowly t o reach a value of 3.8 km/s. The average Moho depth is estimated between 17 km to 20 km and 16 km to 19 km, respectively, for the North Scotia Ridge a nd South Scotia Ridge, while the Scotia Sea, bounded by the two ridges, has a faster and thinner crust, with an average Moho depth between 9 km and 12 km. On other paths crossing from east to west the southern part of the Scotia p late and the Antarctic plate south of South Scotia Ridge, we observe an ave rage Moho depth between 14 km and 18 km and a very fast upper crust, compar ed to that of the ridge. The S-wave velocity ranges between 3.0 and 3.6 km/ s in the thin (9-13 km) and fast crust of the Drake Passage channel. In con trast the models for the tip of the Antarctic Peninsula consist of two laye rs with a large velocity gradient (2.3-3.0 km/s) in the upper crust (6-km t hick) and a small velocity gradient (3.0-4.0) in the lower crust (14-km thi ck).