Simultaneous inversion of spectral IP data with frequency constraints

Abstract

Spectral-induced polarization (SIP) measures the apparent complex resistivities (CRs) of electrical current sources at frequencies of less than 10 kHz. The measured apparent CRs are usually inverted to recover the intrinsic subsurface CRs, which depend on the source frequencies. The Cole-Cole (CC) model is commonly used to describe the dispersion characteristics of the intrinsic CRs; electrical resistivity, chargeability, and the time and relaxation constants can be derived using this model. For quantitative estimation of these parameters, a reliable inversion method for multifrequency SIP datasets is required. Conventionally, SIP data at each frequency are independently and sequentially inverted. This does not consider the relationships between SIP datasets of different frequencies. To consider such relationships, here, we simultaneously invert multi-frequency SIP datasets by introducing frequency-smoothness constraints between adjacent frequencies. We numerically verified the utility of the approach in terms of both amplitude and phase recovery; the method yielded more reliable relaxation models (e.g., CC models) than conventional inversion. For field verification, the method was applied to SIP data of several frequencies obtained in South Korea.