Title of research project: Expression of fracturing and faulting zones traits using electric potential and resistivity variation
Reference number of the grant: INTAS-94-3951
Period of performance: 1995 to 1997
Project Coordinator: Prof. S. Pride (Institut de Physique du Globe de Paris, France)
Principal Investigator: Dr. P.N. Shebalin
The goal of the project was to 1) analyse the large volume of electric potential data that had been collected on the walls of an underground limestone quarry near Paris, and 2) determine whether the recorded potentials correlate to the presence of either active or passive fractures. Central to these goals was the creation of a user-friendly data base that allows the simple retrieval, visualisation and processing of over six years of recorded electric-potential data. A variety of physical mechanisms can be proposed as to how a growing fracture might generate an electric signal. The initial objective was to determine from the data which mechanism(s) are responsible for electric-potential variations in the quarry. The scientific work separated naturally into three general categories: -- numerical processing and data display; -- laboratory measurements; -- theoretical modelling. The results obtained were: -- The creation of a user-friendly numerical database that allows for all pertinent information of a given data set to be easily stored, cheaked and corrected for possible inconsistencies, accessed, visualised, and processed. -- Laboratory results determining the uniaxial compressive and tensive yield (fracture) strengths of a multitude of limstone samples, the conductivity and dielectric properties of the limestone samples as a function of frequency, fluid salinity and applied stress, and the stability of different electrodes as a function of time when they are used as electric-potential monitors in a partially-satirated rock mass. -- The creation of a computer code that models how the fluids inside the quarry redistribute as a function of variation in air pressure and the associated electric potentials induced through electrofiltration. Unfortunately, despite the creation of the fully-operational database software, no definitive conclusion has yet been reached as to the correlation between fractures, fracturing and the recorded electric signals.