A Szentendrei-sziget környéki folyóvízi szeizmikus szelvényezések földtani eredményei

Abstract

the region of the Visegrád and Börzsöny Mountains and the and the east side of the Danube region is uncertain. In recent years several seismic surveys were carried out by the geophysicists of the Eötvös University, Geomega Ltd. and the
Technological University of Delft on that section of the River Danube between Budapest and Esztergom. Multi-channel seismic surveys were carried out in both branches of the river around the Szentendre Island, and in two selected areas of
the main Danube branch; single-channel data acquisition was performed over a dense network. This led to a good correlation of the data and tectonic features and, furthermore proper projection of well-data became available in the vicinity
of the river. On the two test areas, a pseudo-3D interpretation was performed.
Integrated interpretation shows that the Triassic basement is unconformably overlain by Oligocene strata (Hárshegy Sandstone, Kiscell Clay, Törökbálint Sandstone Formations) to the north of Budapest. In front of the Börzsöny Mountains,
Middle Miocene volcanic rocks, are situated just bellow the fluvial sediments, while in the Pilismarót Basin Middle Miocene marls are present. These formations were deformed by well-identifiable faults, which generally have a NW-SE strike
direction. According to our interpretation, most of them were activated in the stress field of the late Early to Middle Miocene (ca. 15–18 Ma), due to NW–SE extension. E–W trending dextral strike-slip faults belong to this phase, while the stress field was, locally, of a strike-slip type, with the same NE–SW extensional axis. Neotectonic reactivation of some faults is possible although this can not be proved unequivocally. The interpretation of the present study suggests a higher level of deformation in the region than previously thought, indicating that the subsurface of the Szentendre Island is densely faulted. The water seismic measurements offer a more detailed image about the structure of the area than the surface observations.