COMMENTS

Based on the analysis of the subsurface data provided by the oil industry (Cassano et 
al., 1986) and on geomorphological observations provided by several investigators 
(e.g. Castaldini et al., 1979; Veggiani, 1985), we propose the existence of a major blind 
thrust (Mirandola Source) having the following geometrical characteristics:
- the strike is chosen according with the general orientation of mapped tectonic 
structures;
- the fault dips 30 towards the SW, in agreement with subsurface evidence and based 
on the characteristic distance between the synclinal and anticlinal axes;
- the rake is assumed to be 90 (pure thrusting) based on strike and on general 
geodynamic considerations;
- the down-dip width (10 km) is based on the characteristic distance between the 
synclinal and anticlinal axes and on the assumptions made concerning the minimum 
and maximum faulting depth;
- the minimum and maximum depth (3 and 8 km respectively) are constrained by 
subsurface geology, by the symmetry of the anticline and by the general aspect-ratio of 
the anticline-syncline couple;
- the length (12 km) is based on scaling with width and constrained by 
geomorphological observations.

This source belongs to the outermost propagation of the Apennines compressional 
wedge and is similar to other nearby structures, particularly those located to the 
southeast.

According to Castaldini et al. (1979), after the VIII century B.C. the Po and Secchia 
rivers suffered major diversions that are in agreement with the expected pattern of 
vertical deformation associated with repeated motion on the underlying fault.

Given the estimated width and length, the fault is capable of generating a M 6+ 
earthquake that would have its strongest effects in a broad region between the Po 
river and the Apennines piedmont. Current catalogues (CPTI, 1999) report a large 
event in 1346 (Me 6.8) that falls very close to the Mirandola Source. However, both 
the location and the magnitude of this event are highly uncertain due to the very 
limited number of data available.

The Mirandola, Concordia and Canalazzo di Finale Emilia surface faults described by 
Castaldini et al. (1979) follow the trend of the anticline and fall on its northern flank 
near the hinge of the fold. These faults could be interpreted as extensional features 
associated with bending at the top of the rising structure.

In spite of the limited geomorphic expression, the Mirandola Source is very well 
developed in the subsurface. The frequent and substantial diversions and shifts of the 
rivers flowing around it suggest that this is a rather fast structure. Substantial tectonic 
rates are also suggested by the observation that the tectonic signal is enough to 
compensate the accumulation of sediments by the Secchia and Panaro rivers. 


OPEN QUESTIONS

1) There exists a fundamental question concerning the seismogenic potential of this 
source. Does it rupture in large M 6+ rather infrequent events? Or in smaller more 
frequent earthquakes in the M range 5-5.5? Or is it totally aseismic?

