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.

P-wave velocity structure beneath the northern Antarctic Peninsula: evidence of a steeply subducting slab and a deep-rooted low-velocity anomaly beneath the central Bransfield Basin

“…Green et al 1991;Ritsema et al 1998;Nyblade et al 2000;Achauer & Masson 2002;Park & Nyblade 2006). The low-velocity anomaly in the central Bransfield Basin produced in this study supports the hypothesis that crustal thinning was associated with a hot upper mantle and soft lid velocity models (Vuan et al 2000(Vuan et al , 2005a.…”

“…Johnson 1999;Yegorova et al 2011) and regional surface wave dispersions and receiver function studies (e.g. Vuan et al 1999Vuan et al , 2000Vuan et al , 2001Vuan et al , 2005a. The deeper structure of the area, however, has not yet been studied.…”

Back-arc spreading and mantle flow in the East Scotia Sea

“…This may be improved by recording events from a number of depths beneath the recording station, or by use of surface waves (e.g. Vuan et al 2000). Depth information is critical in subduction zones, where arrivals may have sampled the mantle above, beneath and within the subducting slab, and where stress and strain may vary over relatively small distances.…”

The age and origin of the central Scotia Sea

“…7; Barker et al 1991; Livermore et al 2007). Surface wave tomographic models are of limited resolution in the region, but along with seismic refraction and reflection data they show no sign of a subducted slab beneath the eastern parts of the trough (Ludwig & Rabinowitz 1982; Vuan et al 2000). Nearer the surface, the only evidence for convergence comes in the form of minor reverse faults and folds seen in seismic reflection and sidescan sonar data north of Shag Rocks, and there is no such evidence at all for Cenozoic convergence north of South Georgia (Ludwig & Rabinowitz 1982; Cunningham et al 1998).…”