The neotectonic habitat of the eastern part of Lake Balaton and its broader environs: inferences from highresolution seismic profiling

Abstract

High-resolution reflection seismic data acquired from Lake Balaton (mainly east of the Tihany Peninsula), provide a
solid basis for a detailed analysis of the neotectonic habitat in the region. Two types of seismic profiling — imaging the
subsurface with different resolutions and penetration — were utilised to carry out a structural investigation. Singlechannel seismic sections show the uppermost 20 to 30 metres with an unparalleled (decimetre scale) resolution. A
closely-spaced seismic grid allowed a 3D structural interpretation to be performed, as well a lateral correlation of the
tectonic features. Multi-channel seismic data have a lower (i.e. on the metre scale) resolution which is compensated by
deeper penetration down to 150–200 m. The joint interpretation of the two data sets enabled (1) the kinematic
interpretation and detailed mapping of neotectonic structural elements, (2) the analysis of the relationship between older
(Miocene) and younger (neotectonic) structures, and (3) the reactivation potential of the reconstructed faults. Several
shear zones were identified under Balaton; these were oriented mainly parallel to the lake axis. Areas of localised
deformation contain numerous smaller scale faults arranged primarily in an en-echelon manner. Geometric and
kinematic considerations suggest the presence of relatively wide, sinistral strike-slip fault zones, with most first-order
faults being rooted in the basement. Their repeated reactivation is demonstrated in the Miocene as well as post-Miocene
(neotectonic). Tectonic activity at the Berhida seismic zone east of Lake Balaton suggests that some of these faults could
still be active. Besides faulting, gentle folding of the Upper Miocene (Pannonian s.l.) sediments is also notable. 3D
mapping of key horizons and unconformities within the Pannonian strata allowed the identification of a well-defined
system of anticlines and synclines of neotectonic origin. However, interpretation of fold axis distribution is not
straightforward because features of a secondary deformation appear near the strike-slip fault zones; this has resulted in a
complex, often en-echelon folding geometry.
The neotectonic habitat at Lake Balaton was put in a more regional context by integrating the reconstructed structural
pattern into a neotectonic model of South Transdanubia. Special attention was paid to the age of deformation, and the
kinematics and morphological expression of fault geometries; this also referred to the present-day stress field and,
particularly, the recent geodynamics of the Pannonian Basin System.