Slip-rates of blind thrusts in slow deforming areas: examples from the Po Plain (Italy)

We calculate Plio-Pleistocene slip rates on the blind thrusts of the outer Northern Apennines fronts,
that are the potential sources of highly damaging earthquakes, as shown by the MW 6.1-6.0, 2012
Emilia-Romagna seismic sequence. Slip rates are a key parameter for understanding the
seismogenic potential of active fault systems and assessing the seismic hazard they pose, however,
they are difficult to calculate in slow deforming areas like the Po Plain where faulting and folding is
mostly blind. To overcome this, we developed a workflow which included the preparation of a
homogeneous regional dataset of geological and geophysical subsurface information, rich in Plio-
Pleistocene data. We then constructed 3D geological models around selected individual structures
to decompact the clastic units and restore the slip on the fault planes. The back-stripping of the
differential compaction eliminates unwanted overestimation of the slip rates due to compactioninduced
differential subsidence. Finally, to restore the displacement we used different methods
according to the deformation style, i.e. Fault Parallel Flow for faulted horizons, trishear and elastic
dislocation modeling for fault-propagation folds. The result of our study is the compilation of a slip
rate database integrating former published values with 28 new values covering a time interval from
the Pliocene to the present. It contains data on 14 individual blind thrusts including the Mirandola
thrust, seismogenic source of the 29 May 2012, MW 6.0 earthquake. Our study highlights that the
investigated thrusts were active with rates ranging between 0.1-1.0 mm/yr during the last 1.81 Myr.
The Mirandola thrust slipped at 0.86±0.38 mm/yr during the last 0.4 Myr. These rates calculated
with an homogeneous methodology through the entire Po Plain can be charged entirely to the thrust
activity and not to secondary effects like the differential compaction of sediments across the
structures.