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Oristà seismic station (CORI)

Code: CA.CORI Name: Oristà 

Latitude: 41.9724 N Longitude: 2.0487 E Height: 621 m

Local depth: - m

Owner: Institut Cartogràfic i Geològic de Catalunya

Subsoil features

Lithology

Period

Vs30 (m/s)

Classe EC8

F0 (Hz)

Shales, sandstones and conglomerates

Paleogene

1320

A

-

Instrumentation by channels and periods

Channels

Start date

Sensor type

Digitizer type

Instrumental response

HHZ, HHN, HHE

01/02/2006

Broadband velocimeter

24 bits

[StationXML]

Geophysical characterisation

H/V Spectral ratio from seismic noise

H/V Spectral ratio from seismic noise records of Oristà seismic station. An almost flat curve is observed, without any significant peak that could be related to the soil fundamental frequency, typical of the sites located on bedrock.

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

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

P-waves velocity  model

The P-waves velocity model, obtained by seismic tomography technique, provides information of the subsoil up to 10 meters depth. The fact of not having information of deeper layers is related to an important change in the velocity profile, which does not allow the propagation of seismic waves to the deepest zones. Usually this behavior is due to a velocity inversion within the subsoil. In the area of the seismic station Vp values higher than 3000 m/s are observed at the near-surface, which are related to non-rippable non-weathered rock.

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

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

S-waves velocity model

From the surface waves analysis (MASW) a vertical shear waves velocity profile (Vs) is retrieved. Two layers are identified related to the velocity inversion: (1) the first layer is about 5 meters thick with Vs of 1550 m/s, (2) and the velocity of the second layer is 1150 m/s. Both values are associated with unaltered rock.

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

S-Waves velocity model of Oristà 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 structure of three layers that can be related to changes observed in the velocity models: (1) a near-surface moderate resistive layer of 3 m thickness correlates with the high velocity layer. This level is associated with altered sandstone and sand. (2) Below we find a conductive level of about 4 meters thickness that corresponds to the low velocity layer and that is related to a layer of lutites. (3) Finally, a resistive layer associated with a level of sandstone is observed. The seismic velocity of this layer was not determined due to insufficient investigation depth. 

Surface electrical resistivity model with the location of Oristà's seismic vault

Surface electrical resistivity model with the location of Oristà's seismic vault