Studio Microstrutturale di rocce di faglia in calcescisti (Corsica alpina, Francia).

We are not able to investigate most of the complex phenomena occurring during earthquake propagation by means of seismological methods, mainly because of source, path and attenuation effects that result in loss of information transported by seismic waves. At present, this limitation forces us to a complementary approach which involves field geology (e.g., investigation of ancient now exhumed seismogenic structures), microstructural (e.g., investigation of natural fault rocks) and laboratory (e.g., experiments reproducing seismic deformation conditions) studies. In this preliminary study, we propose that, because of the eastward migration of the lithospheric extension starting from the Oligocene, the normal faults now outcropping in Alpine Corsica are the exhumed analogs of the seismogenic structures now active at depth in the Apennines. Microstructural (EDS equipped scanning electron and optical microscopes) and X-Ray powder diffraction studies conducted on fault rocks from the Corsican normal faults, evidenced a sequence of seismic and inter-seismic deformation processes during exhumation: pseudotachylyte (scars of ancient seismic ruptures) produced at 8-15 km depth are overprinted by carbonate-rich veins and eventually cut by amorphous silica-rich (silica gel ?) mirror like fault surfaces. The above overprinting microstructural relationships suggests continuous seismicity aided by the ingression of pressurized CO2-rich fluids during exhumation. These relationships are consistent with those proposed between crustal-mantle degassing and CO2 fault fluid ingression that characterize the actual seismicity in the Apennines.