Attenuation models inferred from intraplate earthquake recordings

Strong‐motion recordings at 87 sites from 56 different intraplate earthquakes from North America, Europe, China and Australia have been used through a two‐step regression analysis to develop new attenuation models for peak ground acceleration, and for pseudo‐relative velocity for frequencies of 0.25, 0.5, 1.0, 2.0, 5.0 and 10.0 Hz, all for 5 per cent of critical damping. The estimates are obtained along with an analysis of residuals and scatter. A similar regression analysis has been performed also for Fourier spectra of acceleration, in which case the coefficient for the anelastic term has been interpreted in terms of a frequency dependent quality factor Q. The resulting Q‐model shows a strong frequency sensitivity with values around 600–700 at 1 Hz, around 2000 at 10 Hz and around 5200 at 25 Hz. These PGA, PSV and Q results depend, however, on the underlying assumption for geometrical spreading, in particular for low frequencies.