Anisotropic Seismic Structure Beneath Cratons From Interstation Surface-Wave Dispersion Measurements on GSN and Geofon Data

Seismic structure of stable continental lithosphere offers insight into the origin and evolution of the tectosphere. The structure is still poorly known, especially its anisotropic components. Measurements of interstation dispersion of Rayleigh and Love surface waves can produce accurate, radially anisotropic S-velocity profiles that average between pairs of stations. A recently proposed (Lebedev and Meier, 2005) combination of station-station cross-correlation and event-station multimode waveform inversion allows to maximize the frequency band of the measured dispersion curves and yields improved structural constraints. With a view to applying the new method to large global data sets, here we make the measurements using all pairs of GSN and Geofon stations that are situated on stable continents and separated by sufficiently short interstation distances. If the distance between the two stations exceeds about 1000 km then it is difficult to make measurements at shorter periods---below 20 s or so---and trade-offs between the crustal and mantle structure cannot be resolved: in particular, nothing can be concluded on the nature or even the presence of radial anisotropy in the mantle. Limiting the scope of the study to station pairs separated by a few hundred kilometers, we make dispersion measurements using all suitably situated events and select a few pairs---all within stable tectonic blocks in Eurasia---for which broad-band dispersion curves are constrained with large amounts of data. Inverting the curves for S-velocity profiles, we find that the magnitudes of both the isotropic high-velocity anomaly and radial anisotropy in the mantle lithosphere vary strongly from one location to another. When radial anisotropy is present, it is with SH waves being faster than SV waves. We shall discuss the anisotropic seismic structures in the context of regional tectonic settings.