Migration and inversion of magnetic and magnetic gradiometry data

A new method of rapid interpretation of magnetic field and magnetic tensor field data is introduced. It is based on ideas of potential field migration, which extend to the case of the potential field the general principles of seismic and electromagnetic migration. Potential field migration represents a direct integral transformation of the observed magnetic fields into a subsurface susceptibility distribution, which can be used for interpretation or as an a priori model for subsequent 2-D or 3-D regularized inversion. Potential field migration is very stable with respect to noise in the observed data because the transform is reduced to the downward continuation of a function analytical everywhere in the lower half-plane. Following recent advances in SQUID technology, full tensor magnetic gradiometry (FTMG) is emerging as a practical exploration method. We indroduce 3-D regularized focusing inversion for FTMG data. Our model studies show that inversion of magnetic tensor data can significantly improve resolution compared to inversion of magnetic vector data for the same model. In this thesis, we present case studies for the imaging of GETMAG magnetic tensor data acquired over a magnetite skarn at Tallawang, Australia using potential field migration technique, 3-D regularized smooth inversion and 3-D regularized focusing inversion. Our results fit very well with the known geology. Three dimensional regularized focusing inversion produces much more compact image than 3-D regularized smooth inversion. Two dimensional migration shows the advantage of faster image than both 3-D regularized smooth inversion and 3-D regularized focusing inversion.