SURFACE-WAVE DISPERSION AND UPPER-MANTLE STRUCTURE BENEATH SOUTHERN GERMANY FROM JOINT INVERSION OF NETWORK RECORDED TELESEISMIC EVENTS

We have determined the dispersion of fundamental mode Rayleigh waves in Southern Germany in the frequency range 4-50 mHz by simultaneously inverting data from 66 teleseismic events recorded at a network of up to 9 broadband stations. Three different inversion experiments were performed: determination of (1) isotropic phase velocity, of (2) azimuthally anisotropic phase velocity assuming a plane wave traveling across the network, and (3) isotropic phase velocity but now allowing for non-plane properties of the wavefield. In experiments (1) and (2), for each event amplitude, phase and deviation from the great circle azimuth were estimated as well. We have obtained remarkably stable results for phase velocity over the whole frequency range. Between 7 and 25 mHz azimuthal anisotropy is definitely below 0.5 percent. Below 7 and above 25 mHz we found up to 3 percent anisotropy but with negligible variance reduction compared to the isotropic inversion experiment (1). Admitting non-plane wavefields in the inversion still yields nearly identical phase velocities. On inversion of the phase velocity curve in terms of shear-wave velocity we obtained a rather shallow asthenosphere with minimum vs of 4.28 km/s at about 130 km depth covered by a thin lid with vs of 4.63 km/s.