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.
In a first step a geological 3D-model of the sedimentary layers of
the Lower Rhine Embayment is developed. From this model virtual boreholes with a
spacing of 1x1 km can extracted.
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:
B-Weber@netcologne.de
Web:
www.seismo.uni-koeln.de
............................................................
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