Abstract - A fault array in South Australia, interpreted from
a 3-D onshore seismic survey, shows fault traces on the lowermost mapped
horizon of a shale dominated sequence which outline polygonal cells averaging
1.4km in diameter. The cell boundaries coincide approximately with the
downward terminations and near convergence of conjugate pairs of normal
faults. The pattern becomes less spatially ordered on higher horizons where
faults still show a near isotropic strike distribution. Maximum throws,
c. 70m, occur c. 400m above the downward terminations of the faults. The
faults have a systematic geometric relationship with folds, with anticlines
in the mutual hangingwalls of fault pairs and broader footwall synclines
which define the shallow dish forms of the polygons. Polygon boundaries
coincide with anticlinal ridges on the interface between the faulted sequence
and an underlying 35m thick low velocity, low density, overpressured layer.
Although the pattern of ridges defining the polygon boundaries is strikingly
similar to experimental spoke and hub patterns formed at the boundaries
between viscous materials with density inversion, the data do not exclude
the possibility of lateral extension.
Journal of the Geological Society London,
157, 151-161, 2000.