Between-event and between-station variability observed in the Fourier and response spectra domains: comparison with seismological models

In this study, we analyse a regional data set composed by about 9000 waveforms from 231
earthquakes in the magnitude range from 3 to 6 and recorded in central Italy in the time period
2008–2013. We derive a seismological model whose source, attenuation and site parameters
are used to explain the ground motion variability associated with a set of ground motion
prediction equation (GMPE) calibrated ad hoc for both Fourier and acceleration response
spectra. The main results are the following: (1) the between-event residuals δBe show a clear
dependence on the stress drop for frequencies above 2 Hz; (2) the standard deviation τ of
δBe is strongly reduced (up to 80 per cent) by introducing in the functional form the stress
drop values estimated from each source spectrum; (3) the standard deviation τ depends on the
magnitude scale used to calibrate the GMPE: while the moment magnitude better describes
the source variability at low frequency, the local magnitude better capture the source-related
ground motion variability at frequencies larger than 2 Hz; (4) for frequencies higher than
10 Hz, the observed increase of τ with frequency correlate well with the attenuation parameter
ksource, computed from the high-frequency slope of the source spectra. Regarding the stationto-station
residuals δS2S, their frequency dependency is in good agreement with the site
amplifications extracted from the S-wave spectra. Finally, while the overall dependences of
the ground motion variability on seismological parameters are similar when observed either
in the Fourier or in the response spectra domains (e.g. the dependency of the between event on
stress drop), differences in the results suggest that the response spectra do not allow to fully
capture the ground motion variability, as well as the site amplifications, at high frequencies.

This article has been accepted for publication in Geophysical Journal Internationa ©: 2017 Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.