Josep Vila
The broadband seismic station CAD (Tunel del Cadi, Eastern Pyrenees); site characteristics and background noise
Bulletin of the Seismological Society of America (February 1998), 88(1):297-303

Abstract:
This article presents the main characteristics of the broadband (BB) seismic station of Tunel del Cadi (CAD) along with an analysis of seismic noise and its correlation with regional meteorological conditions. The quality of the sensor site (in a closed cave, 80 m below surface) provides ideal conditions for the location of a BB station with the ability to detect small events. Through the analysis of noise series 30 min in length during a period of 15 months, a characterization of the level of detectability has been performed. Using one estimate of noise per day, the seasonal variation of the amplitude of the noise has been analyzed, and using four samples per day, short-period variations have been studied and compared with external meteorological conditions. Results show that the characteristics of the station are similar to a typical station placed in a hard basement rock and that there are no differences between the behavior of the three components. The analysis of several spectral components shows the relative excitation of microseisms and atmospheric disturbances that may differ more than one order of magnitude. There is a clear anticorrelation between the noise amplitude spectra and the atmospheric pressure in short-period variations, and the high-frequency noise is directly related to the external wind velocity, although there is not a direct impact to the sensor site. No correlation of the shape of the spectra (general or for specific frequencies) with any meteorological parameter is observed.