SEGJ Technical Conference

Attempt of AMT survey with electric field measurements by ultra-short baseline

Abstract High-density magnetotelluric (MT) surveys, with station separation less than 100m, are rarely done in geothermal areas. It is due to less availability of enough wide-flat spaces for MT measurements. In this study, we tried audio-frequency MT (AMT) survey with electric dipole length less than 1m. We compared two AMT responses: the ultra-short-baseline AMT (USB-AMT), and the conventional AMT exploration with 15m dipoles for electric-field measurements. The results indicated a pretty good correspondence between two responses. Although the inferred errors were larger in the USB-AMT, the error levels are acceptable in the modeling of resistivity structure by inversion procedures. In addition, the degree of static shift in case of the USB-AMT was discussed. We infer that the static shift levels were less than a decade, similar to the conventional AMT explorations. In conclusion, the proposed USB-AMT is valid and can produce the MT responses with enough good quality. The USB-AMT method is available at narrow spaces: therefore, it allows us high-density AMT surveys.