Seismic activity in the Lower Rhine Embayment between Cologne, Bonn, Düren, Jülich and Aachen belongs to the highest in Europe north of the Alps. In the flat sediment basin site-effects are very important for the seismic hazard analysis.
Goal of this PhD-project of the Department for Earthquake Geology at the University of Cologne is to examine the influence of the local geology on amplitude, duration and frequency content of the earthquake ground motion. Of particular interest is the nonlinear absorption behavior of the unconsolidated sediments.

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Fig 1: Topography of the Lower Rhine Embayment with faults
& Sediment thickness .

Shear wave velocity, density and damping parameters are assigned to the lithological units. These data are used for calculation of 1D S-wave amplification with the code SHAKE91. The program computes the response in a horizontally layered soil rock system subjected to transient, vertically traveling shear waves. The method is based on Kanai's solution of the wave equation. The motion used as basis for the analysis can be applied to any layer in the system. Systems with elastic base and with variable damping in each layer can be analyzed. Equivalent linear soil properties are used with an iterative procedure to obtain soil properties compatible with the strains developed in each layer.

The results will be verified with the actually measured data of the magnitude 5 earthquake from 22.07.2002 near Aachen. From the results maps of fundamental frequency dependent amplification for appropriate levels of groundmotion for the Lower Rhine Embayment will be created. Results will be incorporated in ongoing research of seismic hazard of the region. Part of the study is financed by Munich Re.

Bernd Weber, Dipl. Geol. 

Erdbebenstation Bensberg
Vinzenz-Pallotti-Str. 26
D-51429 Bergisch Gladbach

Tel:       0049 (0)2204 98 52 12
E-mail:
Web:     www.seismo.uni-koeln.de

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