Far de la Banya seismic station (CFAR)

Geophysical characterisation

H/V Spectral ratio from seismic noise

H/V Spectral ratio of the seismic noise record at the Far de la Banya seismic station. A peak around 0.19 Hz is observed which can be related to the fundamental frequency of the soil and, therefore, an acoustic impedance contrast is expected in the subsoil. In addition, another significant peak at 1.1 Hz is also observed. The low-frequency peak is related to the contact with bedrock, and the other high-frequency peak is associated with a strong impedance contrast between the soft subsurface sediments.

Results of the H/V spectral quotient of seismic noise at the Far de la Banya seismic station.

P-waves velocity  model

In the P-wave velocity model (Vp) obtained by seismic tomography is characterized by a package of low-velocity materials (V_P ​​< 2000 m/s) that extends to the maximum investigation depth of the model, about 10 meters deep (rippable materials). The depth of investigation of the seismic profile is not sufficient to detect velocities higher than 2500 m/s, velocity values ​​associated with the healthy rock that cannot be ripped and which can be interpreted as the bedrock.

Model of P-wave velocities for the Far de la Banya seismic station

S-waves velocity model

The shear wave propagation velocity model (V_s) obtained by the analysis of surface waves (MASW) is characterized by three very low velocity soil layers. A shallow surface level is observed, about 2 meters, with a V_s of 160 m/s. A layer is detected below that extends to a depth of about 15 meters and has a V_s of 215 m/s. Finally in the third layer the speed increases up to 220 m/s. As in the case of P-wave refraction seismic tomography, no layer is detected that can be related to the bedrock.

Model of Vs obtained through the analysis of surface waves (MASW).