S -wave Velocity Models in the Scotia Sea Region, Antarctica, from Nonlinear Inversion of Rayleigh Waves Dispersion

Abstract

More than 60 events recorded by four recently deployed seismic broadband stations 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 between 10 s to 30 -40 s is used to obtain the S-wave velocity versus depth along ten different paths crossing the Scotia Sea region. Data recorded by two IRIS (Incorporated Research Institutions for Seismology) stations (PMSA, EFI) 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, ''Hedgehog,'' is performed to retrieve the S-wave velocity models consistent with the 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 similar S-wave velocities ranging between 2.0 km/s at the surface to 3.2 km/s to depths of 8 km/s. In the lower crust the S-wave velocity increases slowly to 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 and 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 plate and the Antarctic plate south of South Scotia Ridge, we observe an average Moho depth between 14 km and 18 km and a very fast upper crust, compared 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 contrast the models for the tip of the Antarctic Peninsula consist of two layers with a large velocity gradient (2.3 -3.0 km/s) in the upper crust (6-km thick) and a small velocity gradient (3.0 -4.0) in the lower crust (14-km thick).

A geological and geophysical crustal section across the Magallanes–Fagnano fault in Tierra del Fuego

“…A 30 Ma age has been proposed (Barker and Burrell, 1977), coincident with the early stages of the development of the western Scotia Sea, but others claim an older regime of transcurrent motion between southern South America and the Antarctic Peninsula was active at approximately 100 Ma (de Witt, 1977;Grunow et al, 1991Grunow et al, , 1992. Recent studies of the seismicity along the transform boundary (Wiens et al, 1998;Vuan et al, 1999) report low, shallow seismicity (!3.5 magnitude), consistent (Fig. 7), and simplified geologic map (Fig.…”

Holocene mass-wasting events in Lago Fagnano, Tierra del Fuego (54°S): implications for paleoseismicity of the Magallanes-Fagnano transform fault

“…1a). Seismicity along this transform boundary has been high ( M w >7) and shallow (<40 km) during the last couple of centuries (Vuan et al , 1999; Febrer et al , 2000). Historically recorded seismic events are limited due to population scarcity in Tierra del Fuego during this period.…”

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

“…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.…”