Resistivity and induced polarisation sounding for location of saline water pockets

Abstract

Combined and interactive inversion of D.C. resistivity and time domain induced polarisation sounding data (i) appears to be an effective approach for quantitative interpretation of induced polarisation sounding data, (ii) shows better resolution of the subsurface for a certain class of earth models, (iii) provides more information about the subsurface, (iv) is one of the approaches for studying saline water and fresh water problems. Field observations, taken in a sedimentary terrain near Federicton Junction, New Brunswick, Canada, were analysed. Weighted and non weighted ridge regression estiamtors were used to solve the inverse problems. Two tier inversion algorithm is chosen where resistivities and thicknesses are modified in the first stage. Apparent chargeability sounding curves with negative values for certain elecrode spreads, in between, revealed the presence of negligibly polarisable layers. These zones, which also show low resistivities, are demarcated as saline water pockets. Induced polarisation forward model curves are resistivity model dependent. Vertical resolution in an IP sounding curve is the best in Q type and worst in A type resistivity models for K type (m1 < m2 > ma) layer chargeabilities.