110
where k
AM MB AN NB=− −+
−
211111
π is the geomet-
ric factor.
Electrical Resistivity Tomography (ERT) measurements
were undertaken with a multi-electrode 2D device (ABEM
TERRAMETER SAS 4000), using 64 electrodes with spac-
ing depending on the desired resolution and depth. We used
a spacing of 0.5 m above the outcrops (high resolution but
low depth) and a spacing of 5 m for the prospective lines. We
usually used a gradient array to obtain both high resolution
and satisfactory depth (1252 points of measure, 45 m depth)
and occasionally pole-dipole array in order to increase the
investigation depth (588 points, 70 m depth). Each prospec-
tive line was acquired using several 315 m ERT sections,
according to a roll-along procedure, with a half-covering.
Prior to the acquisition, a check-up of the electrodes has been
realized consisting in an injection of 20 mA (ABEM
Instrument 2006 ).Fig. 6.4 Synthetic map of the
geological and geophysical
data on the Pavin proximal
and intermediate volcanic
deposits
H. Leyrit et al.