Coda waves from local earthquakes in the southern part of the Netherlands and just across the border in Belgium and Germany are used to estimate the seismic attenuation of that area. Two different models are applied, the single back-scattering model of Aki and Chouet (1975) and the multiple scattering model of Zeng (1991). The goal is to achive attenuation as a function offrequency. The results from the single scattering model show a singnificant difference in coda Q between smaller and larger epicentral distances. Therefore the results are divided into three different models, one for epicentral distances from 0 to 25 km, one for 25 to 75 km and one for distances larger than 75 km. The value of Q₀ for smaller distances is about 100 and for the larger distances about 200. The value of n is for all distances nearly the same, namely about 0.8. In the time of this research it was not possible to do the inversion of the multiple lapse time analysis, the analysis of the multiple scattering model. Therefore no exact coda Q values are obtained from this model, but only an estimation based on figures of an article of Hoshiba, Sato and Fehler (1991(. The estimated values are slightly different from those of other studies that applied this model. When the coda Q values of the single scattering model are compared with attenuation values obtained from the local magnitude, they fall within each others error bars. This is the same when the coda Q is inserted in an approximation of peak ground acceleration of McGuire and Hanks (1980) and then compared to an empirical attenuation relation of Ambraseys (1990). 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 (Q_c) 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 (Q_i) and scattering attenuation (Q_s). 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 Q_c (=Q₀ fⁿ) values for epicentral distances shorter than 25 km (Q₀ = 90) compared to larger epicentral distances (Q₀ = 190), but similar frequency dependence (~ f^-0.9). Interpretation of MLTW results provided a seismic albedo smaller then 0.5, suggesting that the intrinsic absorption dominates over scattering in this region. Both Q_i and Q_s show similar frequency dependences as Q_c. 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 Q_c corresponds to Q_t, 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.