Listric versus planar normal fault geometry: an example from the Eisenstadt-Sopron Basin (E Austria) |
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Authors: | Darko Spahić Ulrike Exner Michael Behm Bernhard Grasemann Alexander Haring Herbert Pretsch |
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Affiliation: | (1) Department for Geodynamics and Sedimentology, University of Vienna, Althanstrasse 14, 1090 Vienna, Austria;(2) Institute of Geodesy and Geophysics, Vienna University of Technology, Gusshausstrasse 27-29, 1040 Vienna, Austria;(3) Christian Doppler Laboratory for “Spatial Data from Laser Scanning and Remote Sensing”, Vienna University of Technology, Gusshausstrasse 27-29, 1040 Vienna, Austria |
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Abstract: | In a gravel pit at the eastern margin of the Eisenstadt-Sopron Basin, a satellite of Vienna Basin (Austria), Neogene sediments are exposed in the hanging wall of a major normal fault. The anticlinal structure and associated conjugated secondary normal faults were previously interpreted as a rollover anticline above a listric normal fault. The spatial orientation and distribution of sedimentary horizons and crosscutting faults were mapped in detail on a laser scan of the outcrop wall. Subsequently, in order to assess the 3D distribution and geometry of this fault system, a series of parallel ground penetrating radar (GPR) profiles were recorded behind the outcrop wall. Both outcrop and GPR data were compiled in a 3D structural model, providing the basis for a kinematic reconstruction of the fault plane using balanced cross-section techniques. However, the kinematic reconstruction results in a geologically meaningless normal fault cutting down- and up-section. Additionally, no evidence for a weak layer serving as ductile detachment horizon (i.e. salt or clay horizon) can be identified in stratigraphic profiles. Instead, the observed deflection of stratigraphic horizons may be caused by a displacement gradient along a planar master fault, with a maximum displacement in the fault centre, decreasing towards the fault tips. Accordingly, the observed deflection of markers in the hanging wall—and in a nearby location in the footwall of the normal fault—is interpreted as large-scale fault drag along a planar fault that records a displacement gradient, instead of a rollover anticline related to a listric fault. |
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