Regional ground-motion scaling in central Europe

Regressions of 2700 horizontal-component broadband seismograms from 213 sei smic events recorded by the German Regional Seismic Network (67 earthquakes and 146 large mining explosions and rockbursts) are carried out to study t he scaling relationships of high-frequency S-wave motion for central Europe . At a set of sampling frequencies, regressions were performed on the logar ithms of the peak amplitudes of narrow bandpass-filtered seismograms, as we ll as on the logarithms of the Fourier components of the velocity spectra. At a fixed frequency f, these values are written as AMP(f, r) = EXC(f, r(ref)) + SITE(f) + D(r, r(ref),f). EXC(f, r(ref)) is the excitation at an arbitrary reference hypocentral dist ance, r(ref) SITE(f) is a site term, and D(r, r(ref), f) describes the crus tal attenuation in the region. The crustal propagation term, empirically es timated in the (0.5-16.0 Hz) frequency band and (40-600 km) distance range, is modeled using a complex geometrical spreading function and a frequency- dependent crustal Q. We suggest [GRAPHICS] and a log-log quadrilinear geometrical spreading. A factor exp(-pi kappa(0)f) is used to fit the high-frequency roll-off of t he inverted excitation terms. Since we deal with two different kinds of sou rces (explosions-rockbursts and earthquakes), we use [GRAPHICS] The same Brune spectral model, characterized by a stress drop Delta sigma = 30 bars, is used to fit both earthquakes and explosive excitation terms. A regression on the effective duration of the ground motion following the S -wave onset is also carried out. In central Europe. duration is observed to be almost frequency-independent. This property might be explained in terms of a self-similar distribution of crustal scatterers.