Ground motion parameters of the July 22, 2002 ML 4.9 Alsdorf (Germany) earthquake

Ground motion parameters from soft rock stations of the July 22, 2002 Alsdorf, Germany earthquake with local magnitude 4.9 at epicentral distances between ca. 15 and 54 km are analyzed. Peak ground accelerations (PGAs) exceed 20 cm/s2. Empirical scaling relations given by Dost et al. (2004) describe a good upper bound to the observed PGAs of the horizontal components. The maximum acceleration response amplitudes of the geometric mean spectra are 0.213 m/s2 at 8.0 Hz and 0.205 m/s2 at 7.1 Hz for the vertical and horizontal component, respectively. At frequencies above 7 Hz, the mean response amplitudes of the vertical component are larger than those of the horizontal components. At 10 Hz the attenuation of the acceleration response is well described by the SEA99 model (Spudich et al., 1999; Pankow and Pechmann, 2004); however, at lower frequencies this model tends to overestimate the observations. While the Arias intensity shows a strong correlation with the PGA, strong motion durations do not show a clear systematic change with distance.