Aeromagnetic 3D subsurface imaging with effective source volume minimisation and its application to data from the Otoge cauldron, Shitara, Central Japan

Abstract

Three-dimensional (3D) imaging techniques using the conjugate gradient solution are discussed for magnetic anomaly source reconstruction, especially for areas of rugged terrain, such as those of volcanoes. The analysis model configuration permits surface undulation and variable depth slicing. First, primitive source model data are put into the analysis to confirm the characteristic behaviour of the regularisation methods and parameter scaling. The compact regularisation method is then applied to synthetic geologic models to understand the resolving power of the method given the problem of the inherent weakness of a non-unique solution. Finally, the field data of a helicopter-borne magnetic survey of the Otoge cauldron are put into the 3D imaging analysis with the method. The analysis reveals a quite reasonable subsurface image of the magma reservoir and the Otoge cone sheets and Otoge stocks of post-cauldron activity, as inferred from geological studies.