Geological deformations in the Pannonian Basin during the neotectonic phase: New insights from the latest regional mapping in Hungary

Abstract

The present paper introduces the new 1:500 000 scale map of young geological deformations in Hungary, including all important deformation structures (faults and folds) related to the neotectonic evolutionary phase (<6–8 Ma) of the Pannonian basin.The new map is based on the interpretation of nearly 2900 2D seismic profiles and 70 3D seismic volumes, as well as on the critical evaluation of the results of published neotectonic studies. An important novelty of the map is that not only the near-surface manifestations of the neotectonic faulting, but also their roots in the underlying pre-Pannonian substratum are displayed, allowing correlation between various reactivated fault segments of longer fault zones and aiding the better understanding of the regional structural context.The new map provides a significantly more accurate definition (actual position, extension and geometry) of the neotectonic structures and provide more details compared to previous regional studies. The prevailing (E)NE–(W)SW striking neotectonic fault pattern clearly reflects the control of identically oriented pre-Pannonian fault systems during the neotectonic deformations. Markedly different orientations in the neotectonic structures indicate important differences in the overall orientation of the underlying fault systems. These observations demonstrate that neotectonic activity is predominantly due to the reactivation of pre-existing (predominantly synrift) structures all over the Pannonian basin, as also indicated by previous studies.Despite experiencing the largest Middle- to Late Miocene extension and the formation of the deepest depocenters in the whole Pannonian basin, SE Hungary practically lacks any observable neotectonic activity, which is a striking, but still poorly understood feature.Detailed 3D seismic analysis of fault segment geometries indicates a consistent regional pattern: sinistral shear along (E)NE–(W)SW oriented, and dextral shear along (W)NW–(E)SE oriented fault zones, respectively. These observations — together with the E–W trending contractional/transpressional structures (folds, reverse faults, imbricates) occurring in western and southern Hungary — indicate a dominantly strike-slip stress regime with a laterally slightly rotating (from N–S to NNE–SSW) maximum horizontal stress axis (σ1) during the neotectonic phase. Lateral displacement along major root zones amounts to a maximum of 2–3 km during the neotectonic phase.