Group Velocity Tomography in the Subantarctic Scotia Sea Region

Abstract

—More than 150 events, recently recorded by seven seismic broadband stations (OGS-IAA, IRIS, GSETT3-IDC), have been collected and processed to obtain an overview of the crust and upper mantle shear wave velocities.¶Group velocities of the fundamental mode Rayleigh and Love waves, in the period range from 15 s to 50 s, are used to obtain tomographic maps of the Scotia Sea region, the tip of Antarctic Peninsula, and the tip of South America. Errors in the measurements, estimated on clusters, are larger for Love waves than for Rayleigh waves and their averages are 0.060–0.080 km/s and 0.030–0.040 km/s, respectively.¶From the regionalisation of the dispersion measurements, we obtain smoothed local dispersion curves in correspondence with the main geological and tectonic features, and from their nonlinear inversion, the shear wave velocity versus depth profiles.¶The correlation length of the heterogeneity, which can be resolved by Rayleigh waves, varies between 200 and 400 km in most parts of the studied area, but becomes greater near the periphery of the maps. The spatial resolution of Love waves (400–600 km) is poorer than that of Rayleigh waves, due to the deteriorated path coverage and to the larger errors in the group velocity measurements.¶Models of the shear wave velocity in the crust and upper mantle for the tip of South America, the Falkland Plateau, the Scotia Sea, the South Sandwich oceanic spreading ridge, the South Sandwich trench, the South Scotia ridge, the tip of Antarctic Peninsula, the Bransfield Strait and the Drake Passage are presented.¶Our regional models and the existing large-scale models (e.g., CRUST5.1), help to define a 3-D velocity model of the Scotia Sea region to be further investigated by waveform inversion.