Applications of Controlled Source and Natural Source Audio‐Frequency Magnetotellurics to Groundwater Exploration

Abstract

Audio‐frequency magnetotellurics (AMT), using either a controlled source (CSAMT) or natural source (NSAMT), has become an efficient, cost‐effective tool for groundwater exploration. Advancements in field equipment have improved data quality and increased data acquisition speed, and the availability of 2D inversion modeling has significantly improved data interpretation. Since depth of investigation is not related to the receiver electric field dipole size, AMT can be used as either a high‐resolution tool (using short dipoles) or as a reconnaissance tool (using large dipoles). Several recent field examples are presented, including fractured bedrock targets, in which lateral resolution is important, as well as reconnaissance‐style basin mapping, in which speed and economic efficiency is critical. In one project, located in Tule Desert, Nevada, CSAMT was used successfully to map an undeveloped basin, and was instrumental in subsequent court hearings to support water right applications to develop groundwater resources from this basin.