Talks and Poster Presentations (with Proceedings-Entry):
S. Spahic, U. Exner, M. Behm, B. Grasemann, A. Haring:
"Characterization of shallow normal fault systems in unconsolidated sediments using 3-D ground penetrating radar (SE Vienna Basin, Austria)";
Poster: EGU 2009,
- 2009-04-24; in: "Geophysical Research Abstracts",
Paper ID EGU2009-8654,
In a gravel pit at the eastern margin of the Eisenstadt Basin, a subbasin of Vienna Basin (Austria), a set of normal
faults crosscuts a Middle Miocene succession consisting of gravel layers, sandy gravels, fine-grained sands and
silts with variable thicknesses between 1 and 4 m. These mainly friable sediments are cut by a numerous N-S
striking high angle normal faults of ca. 0.5 - 10m length, offsetting, dragging and tilting the sedimentary layering.
Normal faults occur either as isolated planes, or as parallel sets of high-angle faults dipping to the West. The
outcrop is situated in the hanging wall of a major normal fault with a vertical displacement of at least 40m, which
was interpreted as listric fault associated with a rollover anticline (Decker & Peresson, 1996).
The displacement magnitude varies significantly along individual faults from cm to a few meters. The strong
displacement gradients along these short faults result in the formation of perturbation fields around them, which
deflect the initially planar sedimentary marker beds in the vicinity of the faults producing a pronounced reverse
fault drag. None of these short faults display listric geometries or are associated with low angle detachment
horizons. The spatial orientation and distribution of the faults and the associated fault drag was mapped in detail
on a 3D laser scan of the outcrop wall.
In order to assess the 3D distribution and geometry of this fault system, a series of parallel GPR (ground
penetrating radar) profiles were recorded with a low frequency antenna behind the well-studied outcrop wall. The
profile data were interpolated into a 3D GPR cube. Faults with normal offset of ca. 0.5-1,5 m can be mapped
by detailed correlation of conspicuous marker horizons. Additionally, the deflection of markers around the fault
planes can be documented from the GPR dataset.
Both outcrop and GPR data were compiled in a 3D structural model using Gocad (Paradigm). The detailed
geometry of the sedimentary horizons, the normal fault system and the associated fault drag is used to infer the
subsurface continuation of the major normal fault below. Kinematic reconstruction of the fault plane using the
Coulomb Collapse Theory predicts a bending of the fault plane into a subhorizontal orientation at ~70 m below
the outcrop level. It is important to note, that these kind of reconstruction techniques inherently assume a listric
fault geometry and therefore will always result in extensional fault, which flatten at a certain depth. However,
correlation of reconstructed detachment this level with outcrop observation in the same gravel pit strongly question
the interpretation as a listric fault. Instead, we suggest that in analogy to the smaller sized structures in the hanging
wall, the observed deflection of stratigraphic horizons could be caused by displacement gradients along the
fault, and that the deflection of markers should be interpreted as large scale fault drag instead of a rollover anticline.
Electronic version of the publication:
Created from the Publication Database of the Vienna University of Technology.