Joint two-dimensional cross-gradient imaging of magnetotelluric and seismic traveltime data for structural and lithological classification

TLDR

Collocated magnetotelluric and seismic profiling is increasingly recognized as essential for deep and near‑surface imaging, yet the data are usually interpreted separately because joint inversion programs are lacking. The study introduces a joint 2‑D inversion method that images collocated MT and seismic refraction data using cross‑gradient structural constraints. The algorithm employs cross‑gradient constraints to jointly invert MT and seismic refraction data, first tested on synthetic models of a complex geological setting and then applied to near‑surface field data to evaluate resistivity‑velocity relationships for lithofacies discrimination and structural classification. The joint inversion produced synthetic models with superior structural similarity and more accurate resistivity and velocity estimates, matched the MT‑seismic relationship observed in field data, and demonstrated that cross‑gradient imaging enhances characterization of heterogeneous targets from near‑surface to mantle depths.

Abstract

Collocated magnetotelluric (MT) and seismic profiling is emerging as a necessary combined approach for deep and near-surface imaging but the resulting experimental data are typically interpreted separately since no production programs exist for multidimensional joint inversion of MT and seismic data. We present a joint 2-D inversion approach for imaging collocated MT and seismic refraction data with cross-gradient structural constraints. We describe the main features of the algorithm and first apply it to synthetic data generated for a hypothetical complex geological model. For the synthetic data, we find that the scheme leads to models with remarkable structural resemblance and improved estimates of electrical resistivity and seismic velocity. We apply the scheme to near-surface field data to test the consistency of a previously suggested resistivity—velocity interrelationship and its potential use for subsurface lithofacies discrimination or structural classification. The MT-seismic relationship is found to be in excellent accord with that derived previously for DC resistivity and seismic data set at the test site. Our results suggest that joint MT-seismic cross-gradient imaging leads to improved characterization of heterogeneous geological targets at near-surface to mantle depths.