Minimum Norm Inversion of Magnetic Anomalies with Application to Aeromagnetic Data in the Tanna Area, Central Japan.

Abstract

An improved method of magnetization intensity mapping is proposed to interpret magnetic anomalies in terms of subsurface structure, where the side effect of source bodies surrounding the observational area is taken into account. The problem, which usually becomes underdetermined, can be solved iteratively by the conjugate gradient method. The asymptotic iteration gives the minimum Euclidean norm solution, to be suitable for subsurface modeling. This scheme was tested against synthetic data to evaluate its performance and applied to actual aeromagnetic data. From the analysis of aeromagnetic anomalies in the Tama area, a model of the distribution of magnetization intensity was derived, which revealed good correlation with active faults. Lower magnetization intensities appeared to the west of the southernpart and to the east of the northernpart of the Tanna fault, and in a narrow zone between the Ukihashi central and west faults. They were well correlated to highly fractured zones, and the quadrant pattern around the Tanna fault was interpreted as the effect of the compressional stress field brought about by strike-slip faulting.