This paster was presented at AGU 2002 Fall Meeting, December 6-10,
2002, San Francisco, USA.
THREE DIMENSIONAL MODELING OF STRONG GROUND-MOTION
SITE EFFECTS IN THE UPPER
I. Oprsal (1,2), D. Faeh (1), D. Giardini (1), M. Mai
RHINE GRABEN DUE TO THE FINITE-EXTENT SOURCE - 1356 BASEL EARTHQUAKE
Swiss Seismological Service,
ETH-Hoenggerberg/HPP, CH-8093 Zuerich, Switzerland.
Department of Geophysics, Charles University,
Ke Karlovu 3, 121 16, Prague, Czech Republic,
The Basel earthquake of October 18, 1356, is
considered to be one of the most serious earthquakes in Europe of the
last centuries (I0=IX, M ~
6.9). Combined effects of the finite-extent source and complex local
structure are modelled to supply the strong motion estimates for today
seismically moderate region. To model the ground motion, 3D finite
differences (FD) were applied.
The 3D explicit FD method for topography models on irregular
rectangular grid is an approximation to the hyperbolic partial
differential equation (PDE). Elastodynamic PDE is solved in the time
domain. The Hooke’s isotropic inhomogeneous medium contains
discontinuities and a topographic free surface. The boundary conditions
are satisfied via the treatment of the effective parameters. A
particle-velocity dependent term is added to the PDE to approximate
viscoelastic behavior of the medium.
The 3D FD modeling is computed for the recently established P and
S-wave velocities structure of the Basel area (Kind, 2002), including
the topography. The first attempts for a double-couple point source and
relatively simple source function are now upgraded to kinematic
finite-extent source simulation. The finite-extent source is adjacent
to the free surface, because the fault has been recognized through
trenching on the Reinach fault. The 1356 Basel earthquake source
features cannot be determined and therefore several rupture histories
are tested. The results are compared to the macroseismic information of
the Basel area and to recently established 2D simulations.
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