The Pannonian basin is a continental back-arc basin in Central Europe, surrounded
by the Alpine, Carpathian, and Dinaric mountain ranges. To better understand this
area's tectonic affinity and evolution, a high-resolution model of the crust, the
mantle lithosphere, and the asthenosphere is essential. The region's crustal structures
are well documented, e.g., classical active seismic, receiver functions, and ambient
noise surface wave studies, but consistent imaging of the entire lithosphere remains
a challenge. Here we present a new high-resolution 3D shear wave velocity model of
the crust and upper mantle of the broader Pannonian region using joint tomographic
inversion of ambient noise and earthquake data.For this purpose, we collected continuous
waveform data from more than 1280 seismic stations for ambient noise cross-correlation
measurements from a region centered to the Pannonian Basin and encompassing the rimming
orogenic chains. This dataset embraces all the permanent and temporary stations operated
in the time period from 2005 to 2018. We calculated Rayleigh wave ambient noise phase
velocity dispersion curves using the phase of the noise cross-correlation functions
of the vertical components in the period range from 5 to 80 s. Then we combined this
dataset with existing measurements from earthquake data in the period range of 8-300
s.At lower periods (< 50 s) and shorter interstation distances, there is a well-documented
systematic discrepancy between the dispersion measurements collected by the two methods.
The phase-velocity curves measured by the noise-based method are slower on average
than the dispersion curves extracted by the earthquake-based method. A correction
term is defined by comparing phase velocity curves from both data sets for the same
station pairs. Phase velocity maps are then calculated from 5 s to 250 s periods using
ambient noise and earthquake measurements.Local dispersion curves extracted along
each grid node of the 2D phase velocity maps are inverted for depth velocity models
using a newly implemented Particle Swarm Optimization (PSO) algorithm to obtain the
3D distribution of the shear-wave velocities. The shear wave velocity structure reveals
pronounced variations of the lithospheric thickness and physical properties related
to deep tectonic mechanisms operated in the region.
