WORKING GROUP 9 
MARCHESINI, PISTOLESI, BOLOGNINI 
531 
of long, curved fractures, which tend to organize in a pattern, roughly half 
elliptical, centred in the highly mineralized area South of Monterotonde, and 
encircling the outcrop of the oldest formations (fig. 6). This pattern is also 
extremely close to the pattern of the Pliocene iso-uplift contours. This fracture 
pattern could, with high probability, be related with the shape and location 
of the intrusive body which has been postulated as the source of the thermic 
energy of the steam-field. 
43*20'l 
Fig. 6. Total fracture field (producing areas shaded) 
Conclusion 
The photo interpretation of fracture patterns appears a significant addition 
to the knowledge of the geologic conditions of the area including the steam- 
fields. The information sought with this technique has a direct bearing on 
conditions essential or important for steam productivity, such as the shape and 
location of the buried body source of heat, and the trend and location of frac 
tured belts affecting reservoir permeability. As to the first, the photo inter 
pretation has shown a peculiar subelliptical pattern, of curved concentric 
fractures, closely coincident with local Bouguer gravity contours, and with 
contours picturing the Pliocene uplift. This pattern appears strongly suggestive 
of the shape and location of the buried heat source. As to the role of fractures, 
the statistical processing of the photo interpretation data suggests a prominent 
influence of certain fracture sets on productivity. The hypothesis that shear and