Electromagnetic sounding experiments in the Schwarzwald central gneiss massif

Abstract

Geomagnetic and telluric pulsations were observed at nine stations, partially at the same time, and at two sites with additional recordings of variations. They occupied a 20 x 30 km² area of high-grade metamorphism. There is a nearly perfect spatial uniformity of the magnetic variation field except for a small local anomaly attributable to the Rheingraben. The telluric field is highly polarized in a N47 ± 7W direction but with local differences in amplitude. In contrast, telluric phases are spatially uniform and, as a function of period, distinctly different for the N47W orientation of the telluric field (= "B-polarisation") and the N43E orientation (= "E-polarisation"). Telluric and magnetic observations are not explainable by one-dimensional (1-D) models for the Schwarzwald alone. Therefore a 2-D model is derived, comprising Schwarzwald and Rheingraben, which can account for the graben Z anomaly and the phase curves in both polarisations. An unscaled 1-D model is obtained from the telluric phases in E-polarisation and then a 2-D model for Schwarzwald and Rheingraben in E- and B-polarisation. This latter model allows the scaling of the 1-D Schwarzwald model and shows a thin conductive layer under the gneiss massif at a depth of 12 km with a conductance of 650 S.

          ARK: https://n2t.net/ark:/88439/y056011

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