Using the transit pulse method, we have determined compressional wave
velocities of rocks from various geological units belonging to the
Penninic zone along the NFP20-West profiles of the Swiss western Alps.
The velocities have been measured at confining pressures up to 400 MPa,
along three orthogonal axes defined by the macrostructure of the rocks.
The samples analysed show a degree of metamorphism ranging from
greenschist to eclogite facies. This collection includes schists,
dolomites, gneisses and ophiolitic rocks. The mean velocities range from
5.9 km/s for a quartzitic calcschist to 7.9 km/s for an eclogitic
metagabbro. The velocity anisotropy is as high as 20 %. The range of
acoustic impedance is wide, from 15 to 27 10(6) kg/m2s. From these
measurements, normal incident reflection coefficients for likely rock
assemblages within and between geological units were estimated in order
to interpret zone of the strong reflections recorded along the seismic
profiles. Reflection coefficients as high as 0.17 could be determined.