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Fontmartina seismic station (CFON)

Code: CA.CFON Name: Fontmartina

Latitude: 41.7611 N Longitude: 2.4345 E Height: 973 m

Local depth: - m

Owner: Institut Cartogràfic i Geològic de Catalunya

Subsoil features

Lithology

Period

Vs30 (m/s)

Classe EC8

F0 (Hz)

Shales

Cambroordovician

430

B

4.0

Instrumentation by channels and periods

Channels

Start date

Sensor type

Digitizer type

Instrumental response

HHZ, HHN, HHE

01/06/1999

Broadband velocimeter

24 bits

[StationXML]

Geophysical characterisation

H/V Spectral ratio from seismic noise

H/V Spectral ratio using seismic noise records from Fontmartina seismic station. A peak around 4Hz is observed, which can be associated with the fundamental frequency of the soil, and so, it is expected to encounter an acoustic impedance contrast in the subsoil.

H/V Spectral ratio curve using seismic noise records from Fontmartina seismic station

P-waves velocity  model

The P-waves velocity model, obtained by seismic tomography technique, provides information about the behaviour of the subsoil up to 100 metres deep. In the resulting model , Vp increases gradually distinguishing 3 layers: a recent soil layer with little compactness with Vp between 400 and 1000 m/s up to 10 metres deep, the completely to moderately altered substrate with Vp between 1500 and 2500 m/s up to 30-40 m deep and, finally, the unaltered substrate up to the bottom of the model achieving Vp values around 4400 m/s.

P-waves velocity model of Fontmartina seismic station, obtained by seismic tomography technique.

S-waves velocity model

S-waves velocity model resulting of the surface waves analisi (MASW) consist of three layers: Vs1=281 m/s for quaternary colluvial materials composed by gravels and blocks with a sandy and low compacted matrix, Vs2=536 m/s for the completely to moderately altered bedrock and, finally, Vs3=1100 m/s for the bedrock.

S-Waves velocity model of Fontmartina seismic station, obtained from the analisi of surface waves (MASW).

Electrical tomography

The geoelectrical model resulting after inverting the electrical resistivity (electrical tomography) shows a very resistive surface layer with vaules of electrical resistivity from 1500 to 10000 Ω·m. This layer is consistent and continuous along the profile but with a varying depth from 7 meters at the SW to 10 meters at the NE. This layer is related to very low waves velocities (Vp between 400 m/s and 1000 m/s, Vs=280 m/s). All these measured parameters show a very low compacted material which could be related with the quaternaty colluvial soil.

Between 10 and 40 meters deep a second intermediate layer is observed with electrical resistivity vaules from 500 to 1000 Ω·m. This layer is interpreted as the completely to moderately bedrock and it is related to the second layer of the S-waves velocity model (Vs=536 m/s) and with a slight increase in depth of the P-waves velocity until reaching 2500 m/s.

Surface electrical resistivity model with the location of Fontmartina's seismic vault, up to 30 meters deep.