Current Research Status and Future of Electromagnetic Survey Methods towards Integrated Analysis with Seismic Methods

Abstract

Electromagnetic （EM） methods have been developed for estimating the apparent resistivity or conductivity of material composing subsurface structure depending on survey objectives, while seismic methods are applied mainly to understand geological structure or stratigraphy. Magne-totelluric subsurface sounding （MT） methods are proven tools detect high-conductivity anoma-lies in the Earth's interior; controlled source EM （CSEM） methods detect high-conductivity anomalies; and, nuclear magnetic resonance （NMR） methods estimate " the mean free path " of hydrogen atoms in various molecules composing underground materials. Regarding methodolo-gies, EM methods frequently applied in practice are: （1） natural source MT methods, （2） artifi-cial source MT or EM methods, and （3） borehole EM methods. The fundamental principles of these methods can be summarized as measuring the induction effects of a survey target using a natural or artificial electromagnetic source. Finally, we investigate examples of recent EM ap-proaches in connection with seismic methods and discuss the integration of survey data from both methods as a key to exploring underground structures not only in terms of stratigraphic in-terpretation but also for estimating material physical properties.