ALBERT

Description: We present the first systematic study of attenuation derived from the S-wave coda in the frequency range 1-32 Hz for the southern part of the Netherlands and its surroundings. For this we used two methods, the coda Q (Qc) method and the Multiple Lapse Time Window (MLTW) method. In the interpretation of the results both single and multiple scattering in a half space are considered. Our aim is to validate these interpretations in our region and to try to identify the effects of attenuation due to intrinsic absorption (Qi) and scattering attenuation (Qs). For this we analyzed more than 100 3-component high-quality digital seismograms from 43 crustal events and 23 stations in the Netherlands, Germany and Belgium. Coda Q results show smaller Qc (= Qofn) values for epicentral distances shorter than 25 km (Qo = 90) compared to larger epicentral distances (Qo = 190), but similar frequency dependence (∝ f-0.9). Interpretation of MLTW results provided a seismic albedo smaller than 0.5, suggesting that the intrinsic absorption dominates overscattering in this region. Both Qi and Qs show similar frequency dependences as Qc. These results are comparable to those obtained in other areas, but we also show that more sophisticated models are required to remove ambiguities in the interpretation. For short lapse times and short event-station distances we find for the simple half space model a corresponding interpretation of both methodologies, where Qc corresponds to Qt, suggesting that a model with single scattering in a half space is appropriate. For long lapse times and long-event station distances, however, we find that the S-wave coda is, most probably, too much influenced by crust-mantel heterogenities. More sophisticated Q inversion models using larger data sets are required for more reliable attenuation estimates.