Tilt observations in the normal mode frequency band at the Geodynamic Observatory Cueva de los Verdes, Lanzarote

We have conducted observations with the aid of a seismo-tiltmeter station, which is based on the Ostrovsky pendulum and installed at the Geodynamic Observatory Cueva de los Verdes at Lanzarote Island since 1995. In this station the signal is separated into two frequency bands – tidal tilts (from 0 to 5 mHz) and ground oscillations in the frequency range of free Earth’s normal modes (from 0.2 to 5 mHz). The later band, called accelerometer channel, has additional amplification. We analyzed the background records in the frequency range of Earth’s free oscillations from August 2000 to September 2001, as well as, Earth’s normal modes after strong earthquakes. We found several distinctive persistent peaks in the spectra of background oscillations. Both amplitudes of distinguished peaks and noises have seasonal variations. We found that spectra of background oscillations are different in the frequency interval between 1.4 and 2.5 mHz for North- South and East-West components