The extensional Pannonian Basin is set within the convergent arc of the Alpine-Carpathian mountain system in central Europe. Various models have been proposed as mechanisms to drive extension within this collisional setting. As part of the Carpathian Basins Project(CBP), a temporary network of 56 broadband seismometers was deployed. With a further 44 permanent broadband seismometers, tomographic inversion of P and S-wave relative
arrival-time residuals from teleseismic earthquakes, reveal the velocity structure of the mantle to a depth of 850 km throughout the Carpathian-Pannonian region.
The tomographic models reduce the P-wave rms residual by 71% from 0.446 s to 0.130 s, and the S-wave rms residual by 59% from 1.513 s to 0.624 s. The effect of applying a deterministic crustal correction on the relative arrival-time residuals is tested using a crustal velocity model derived from previous crustal seismic experiments, but I show that the use of a station term parameter in the inversion provides a robust method of correcting for near-surface velocity variations in this experiment.
At shallow sub-lithospheric depths several localised slower regions are imaged, which correlate with extensional depocentres and regional volcanics, and are interpreted as upwelling asthenosphere. Beneath the Eastern Alps, I image a high velocity structure, which continues east beneath the Pannonian Basin with depth and into the mantle transition
zone (MTZ). The fast anomaly in the MTZ is distributed laterally as far as the Carpathians, the Dinarides and the Eastern Alps.
The high velocity mantle material linking the structure beneath the Pannonian Basin with the Eastern Alps indicates a once continuous continental collision zone. Eastward
extrusion from the Adria collision and detachment of the continental lithosphere beneath the Carpathians resulted in asthenospheric upwelling, which may have provided the driving force for extension of the Pannonian Basin.
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