GNGTS 2013 - Atti del 32° Convegno Nazionale

2D GPR Survey across the Mt. Pollino Fault (Grotta Carbone site). The “Grotta Carbone” site was chosen for a first 2D-GPR survey across a sector of the Mt. Pollino Fault, due to the availability of past paleoseismological analysis (Fig. 1, Ferreli et al. , 1994; Michetti et al. , 1997), used to validate the GPR data. More than 10 high-resolution 2D GPR profiles were recorded using a Zond 12e radar system; the profiles have been recorded parallel and very close to the two original trench tracks. 300 and 500 MHz shielded antennas guaranteed an optimal imaging of the fault zone, showing the best trade-off between resolution and investigation depth. The GPR lines were recorded intercepting transversally the fault and to check the lateral extension and other possible branches. The used acquisition parameters are summarized on Tab. 1. A Topcon GR-5 GNSS receiver, connected directly to the GPR system has been employed for the positioning with a centimetric accuracy. The data processing was done using a commercial software (Tab. 1). A recovery function was applied to compensate for the attenuation losses, preserving both lateral and vertical amplitude contrasts. A frequency bandpass filter and 2D average filter were used to reduce noise components and a background removal just on the 500 MHz profiles to remove horizontal ringing. After an accurate topographic correction, a time-depth conversion was done using a constant velocity of 0.08 m/ ns, estimated by diffraction hyperbola analysis and tying the radar units with the stratigraphic logs. Finally, we calculated the “Envelope” attribute (Chopra and Marfurt, 2005; Forte et al. , 2012), then plotted over the same processed radargram, to provides additional information for data analysis and interpretation, enhancing the high-resolution imaging of the fault zone and sedimentary structures. Fig. 2 – a) Envelope attribute calculated for the Grotta Carbone profile and plotted under the processed profile after the time-depth conversion. The discontinuities are enhanced by the combination of different amplitudes and layers bedding, simplifying and improving the overall accuracy in the radargram interpretation. b) log of the trench T2 (from Michetti et al. , 1997) is here re-proposed for direct comparison with the radar data. 171 GNGTS 2013 S essione 1.2