Geomagnetic depth sounding and magneto-telluric survey of the Southern Alps

Abstract

Measurements of the natural geomagnetic variations caused by ionospheric current systems, and their induced counterparts within the earth, are used to investigate electrical conductivity anomalies within the crust of the Southern Alps region. Single-station recording along three survey lines perpendicular to the Alpine fault provide Parkinson vector maps that reveal many anomalous zones of conductivity. A possible correlation between the location of these zones and surface expressions of crustal movement, such as fault lines and fold axes, is discussed. Estimates of apparent resistivity from magneto-telluric measurements at selected sites are used to suggest models for the conductivity structure. Tensor conductivities calculated by rotating the measuring axes of these telluric stations, show a preferred axis of conductivity aligned parallel with the magnetic North-South axis.