We present the results of P‐to‐S
receiver function analysis to improve the 3D image of the sedimentary layer, the upper
crust, and lower crust in the Pannonian Basin area. The Pannonian Basin hosts deep
sedimentary depocentres superimposed on a complex basement structure and it is surrounded
by mountain belts. We processed waveforms from 221 three‐component broadband seismological
stations. As a result of the dense station coverage, we were able to achieve so far
unprecedented spatial resolution in determining the velocity structure of the crust.
We applied a three‐fold quality control process; the first two being applied to the
observed waveforms and the third to the calculated radial receiver functions. This
work is the first comprehensive receiver function study of the entire region. To prepare
the inversions, we performed station‐wise H‐Vp/Vs grid
search, as well as Common Conversion Point migration. Our main focus was then the
S‐wave velocity structure of the area, which we determined
by the Neighborhood Algorithm inversion method at each station, where data were sub‐divided
into back‐azimuthal bundles based on similar Ps delay times. The 1D, nonlinear inversions
provided the depth of the discontinuities, shear‐wave velocities and Vp/Vs ratios
of each layer per bundle, and we calculated uncertainty values for each of these parameters.
We then developed a 3D interpolation method based on natural neighbor interpolation
to obtain the 3D crustal structure from the local inversion results. We present the
sedimentary thickness map, the first Conrad depth map and an improved, detailed Moho
map, as well as the first upper and lower crustal thickness maps obtained from receiver
function analysis. The velocity jump across the Conrad discontinuity is estimated
at less than 0.2 km/s over most of the investigated area. We also compare the new
Moho map from our approach to simple grid search results and prior knowledge from
other techniques. Our Moho depth map presents local variations in the investigated
area: the crust‐mantle boundary is at 20–26 km beneath the sedimentary basins, while
it is situated deeper below the Apuseni Mountains, Transdanubian and North Hungarian
Ranges (28–33 km), and it is the deepest beneath the Eastern Alps and the Southern
Carpathians (40–45 km). These values reflect well the Neogene evolution of the region,
such as crustal thinning of the Pannonian Basin and orogenic thickening in the neighboring
mountain belts.
