Site response study in Abruzzo (Central Italy): underground array versus surface stations

In this site response study we examined local earthquakes recorded at surfa ce stations of a local seismic network and at a temporary underground seism ic array installed in a tunnel underneath the Gran Sasso Massif in Abruzzo (central Italy). This allowed us to compare the seismic site response benea th the mountain and on the surface in similar geological environment (soft rock sites). We applied spectral ratios method on different segments of the seismograms and used different reference spectra in the 1-20 Hz frequency band. We found little or no amplification effects at most of the surface stations whereas site transfer functions evaluated with respect to underground site s show an amplification factor up to 6 in the 1-8 Hz frequency range. Coda spectral ratios estimated at soft rock sites are confirmed as good estimate s of shear wave transfer function.