Verification of five magnetotelluric systems in the mini‐EMSLAB experiment

Abstract

Given the degree of complexity of modern magnetotelluric (MT) instrumentation, comparison of the total performance for two or more systems is an important verification test. This paper compares the processed data from five MT systems which were designed and constructed separately, and which employ different electrode types, electrode separations, magnetometers, and methods of signal processing. The comparison shows that there is a high degree of agreement among the data from the different systems. The study also demonstrates the compatibility and reliability of the MT systems employed as part of EMSLAB Juan de Fuca (Electromagnetic Sounding of the Lithosphere and Asthenosphere Beneath the Juan de Fuca Plate). This project, proposed by a consortium of institutions, involves not only magnetotellurics studies but also studies of magnetic variation, on land and on the sea bottom. The project calls for the real‐time MT systems to occupy stations along segments of a profile in Oregon. A composite profile will be created from the segments. Prior to commencing the main MT profiling phase, one week was set aside in August, 1984, for all groups to record and process MT data sequentially at six sites in diverse geologic terrains; this experiment was called mini‐EMSLAB.

Electrical structure of the central Cascadia subduction zone: The EMSLAB Lincoln Line revisited

“…Original MT responses were available from 7 seafloor stations deployed during EMSLAB. The onshore wideband EMSLAB data were acquired by four institutions using different sets of instruments whose parity of system responses was tested and demonstrated in a field experiment prior to the main EMSLAB acquisition (Young et al, 1988). Nevertheless, the soundings from the various systems had differing frequency values due to different sample rates and processing procedures.…”

Electromagnetic Induction Studies

“…Experience in the EMSLAB project and other field experiments has educated the community on wideband instrumentation requirements for MT studies [ Young et al , 1988; Wannamaker et al., 1989 a ]. The following features are considered necessary or highly desirable in a wideband system.…”

A Method for the Forward Modelling of 3-D Electromagnetic Quasi-Static Problems

“…8,16,17 This particular model is used in geophysical surveys where artificial or natural sources induce currents in conducting bodies. A specific example is a magnetotelluric experiment 26 where electric and magnetic fields induced by the sun are measured at the surface of the earth. A major obstacle in modelling such phenomena is that the conductivity in the air essentially vanishes.…”