Deterministic Earthquake Scenarios For The Basel Area, Switzerland; Ground Motion Simulation of Combined Source And Site Effects

I. Oprsal (1,2), D. Faeh (1), M. Mai (1), D. Giardini (1)

Presented at European Seismological Commission, XXIX General Assembly, Potsdam, Germany, September 12-17, 2004.

Swiss Seismological Service,
ETH-Hoenggerberg/HPP, CH-8093 Zuerich, Switzerland.
FAX: +41-1-6331065,
Phone: +41-1-6332602,

Department of Geophysics, Charles University, Prague

Seismological Laboratory, University of Patras, Greece

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The Basel earthquake of October 18, 1356 is considered to be one of the most serious earthquakes in Europe (I0=IX, M ≈ 6.5-6.9). The ground motion is modeled for the area of the city of Basel and it’s vicinity. The numerical modeling consists of the finite-extent source combined with the complex local structure in a two-step hybrid 3D finite-difference (FD) method. The synthetic seismograms are accurate in the frequency band 0-2.2 Hz. The 3D FD is linear explicit displacement formulation using an irregular rectangular grid including the topography.
The finite-extent source is adjacent to the free surface, because the fault has been recognized through trenching on the Reinach fault. For the 1356 Basel earthquake (Mw = 6.5), two rupture histories are computed by a pseudo-dynamic approach. Another source is a hypothetical earthquake with the characteristics of the 1999 Athens earthquake (Mw = 5.9), modeled by kinematic approach. The scenario includes the sources located to the East, South and West from the city. The local structure computational model is determined from the recently established P and S-wave velocity structure of the Basel area, including the topography. The results are compared to recently established 2D simulations. The amplifications with respect to a bedrock site are given for the various earthquake scenarios. The 3D modeling gives, in some areas, reasonably different behavior from the 2D computations. The existence of the edge effect proved to be strongly dependent on the position of the source.

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