During processing of magnetotelluric (MT) data, acquired in a survey carried out in southern Italy, a problem was encountered, connected with the so-called ‘dead band’ of the MT signal (around 1 Hz). In the apparent resistivity curves of some MT soundings, a V-shaped minimum appeared, centred on the dead-band frequency. This phenomenon turned out to originate from a strong artificial source and was not due to a downward bias of the robust processing techniques adopted. The source distance from the MT sounding locations was such that the V-shaped minimum fell precisely in the dead-band frequency range. Theoretical considerations about fields generated by an electric dipole led us to the probable identification of the source as the d.c.-powered railway between Naples and Bari.
On the interference of man-made EM fields in the magnetotelluric 'dead band'
SANTARATO, Giovanni
1999
Abstract
During processing of magnetotelluric (MT) data, acquired in a survey carried out in southern Italy, a problem was encountered, connected with the so-called ‘dead band’ of the MT signal (around 1 Hz). In the apparent resistivity curves of some MT soundings, a V-shaped minimum appeared, centred on the dead-band frequency. This phenomenon turned out to originate from a strong artificial source and was not due to a downward bias of the robust processing techniques adopted. The source distance from the MT sounding locations was such that the V-shaped minimum fell precisely in the dead-band frequency range. Theoretical considerations about fields generated by an electric dipole led us to the probable identification of the source as the d.c.-powered railway between Naples and Bari.I documenti in SFERA sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
