Seismic Measurements in Claystone and Limestone at Tournemire (France)

In 2014 and 2015 we performed seismic experiments in the IRSN tunnel laboratory at Tournemire in the Aveyron region (France). A 1.9 km long inoperative railway tunnel gives direct access to a claystone layer and at 1.6 km from the southern tunnel end the Cernon fault is crossed which separates the claystone from limestone.

As a result of a series of seismic experiments during the previous years we had determined the elastic stiffness tensor of the transversely isotropic claystone. The seismic velocities were lower than ultrasonic velocities measured on samples from the same site. The previous measurements had focused on the area near the intersection of the tunnel with the excavated galleries where the claystone is fractured due to a crossing fault zone. The analysis of the 2014 and 2015 seismic data reveals that seismic qP, SH and qSV velocities are higher to the north of the previously investigated area which indicates that the claystone is less fractured. We observed seismic wave in transmission across the Cernon fault and determined the P and S wave velocities in the isotropic limestone.