Shear wave velocity and crustal thickness in the Pannonian Basin from receiver function inversions at four permanent stations in Hungary

Abstract

Receiver functions of teleseismic waveforms recorded at four Hungarian permanent broadband stations have been analyzed using semilinearized and stochastic inversion methods to estimate the crustal thickness and S wave velocity structure in the Pannonian Basin. The results of both inversion methods agree well with the crustal thicknesses obtained by previous seismic refraction and reflection studies in the regions which are densely covered with seismic lines (28 and 27 km in westernmost and southern Hungary, respectively) and suggest a thicker crust compared to what was known before beneath the Transdanubian and Northern Ranges (34 and 33 km, respectively). The comparison of the one-dimensional shear wave velocity models derived by the different inversion methods shows that, in case of simple, smoothly varying structures, the results do not differ significantly and can be regarded as absolute velocities. Otherwise, the recovered velocity gradients agree, but there are differences in the absolute velocity values. The back-azimuthal variations of both radial and tangential receiver functions are interpreted as dipping structure and as waves sampling different geological areas. The signature of the deep structure on low-frequency receiver functions suggests a strong velocity contrast at the 670-km discontinuity. The vanishing 410-km boundary may be attributed to the remnant of a subducted oceanic slab with increased Poisson’s ratio in the transition zone.