GPR DATA-PROCESSING FOR 3D FRACTURE MAPPING IN A MARBLE QUARRY (THASSOS, GREECE)

Ground Penetrating Radar (GPR) has been successfully applied to detect and map fractures in marble quarries. The aim was to distinguish quic kly intact marketable marble areas from fractured ones in order to imp rove quarry management. The GPR profiling method was chosen because it is non destructive and quickly provides a detailed image of the subsu rface. It was performed in domains corresponding to future working are as in real quarry-exploitation conditions. Field surveying and data pr ocessing were adapted to the local characteristics of the fractures: E -W orientation, sub-vertical dip, and karst features. After the GPR pr ofiles had been processed, using methods adapted from seismics (amplit ude compensation, filtering and Fourier migration), the interpreted fr actures from a 12 x 24 x 15 m zone were incorporated into a 3D model. Due to the low electrical conductivity of the marble, GPR provides pen etration depths of about 8 and 15 m, and resolutions of about 1 and 5 cm for frequencies of 900 and 300 MHz respectively. The detection powe r thus seems to be sufficient to recommend use of this method. As requ ested by the quarriers, the 3D representation can be used directly by themselves to locate high- or low-quality marble areas. Comparison bet ween the observed surface fractures and the fractures detected using G PR showed reasonable correlation.