Fig. 6.

Exploration studies using conventional seismological methods and a fibre-optic telecommunication line. a P- and S-waves’ travel times automatically picked along the profile: each symbol represents a P- (black star) and S- (grey dots) arrival times on the DAS records. The white squares with black dot and the white circle with black dot correspond to P- and S-wave travel times, respectively, picked on the geophone records with the same automatic picker. The continuous grey (black) lines correspond to theoretical arrival times for the inverted hypocentre using P- and S-wave picks from the cable (respectively). b Observed V_p/V_s ratio computed at all traces and compared with the results obtained from the travel time tomography (green dots) obtained from more than 2000 local earthquakes over 1.5 years⁴¹. The black line corresponds to the polynomial (Savitsky–Golay) smoothing filter of order 5 with size frame ~3 km long through the fibre-optic V_p/V_s individual values