IUGG 2003
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Primary Author Information
Name Ivo Oprsal
Affiliation Swiss Seismological Service, ETH Zurich, Switzerland, on leave from Faculty of Mathematics and Physics, Charles University in Prague, Czech Republic

Co-Author Information

Co-Author - 1 Name Jiri Zahradnik
Affiliation Faculty of Mathematics and Physics, Charles University in Prague, Czech Republic
Co-Author - 2 Name Anna Serpetsidaki
Affiliation Seismological Laboratory, University of Patras, Greece
Co-Author - 3 Name G-Akis Tselentis
Affiliation Seismological Laboratory, University of Patras, Greece

Abstract Information

Abstract Number 1
Abstract Title 3D HYBRID SIMULATION OF THE SOURCE AND SITE EFFECTS DURING THE 1999 ATHENS EARTHQUAKE
Presentation Style EITHER

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Submission 017983-1-030131004732.htm
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The damaging 1999 Athens earthquake of Mw=5.9 occurred at about 20km from the city center. The intensity distribution in the capital, ranging from V to IX, was quite irregular due to combination of the source, path and site effects. The 30-stations temporary network, installed in Athens by the University of Patras, recorded and located more than 400 aftershocks. The horizontal-to-vertical spectral ratios from the 20 selected aftershock recordings provided site classification. The most significant anomaly (H/V exceeding 4 in the frequency range 1-4 Hz) was found at the Ano Liosia site, belonging to the most heavily damaged zones with intensity IX. The site is situated in a shallow basin whose surface extent is about 4x4 km, and the maximum depth is of about 150 m. The basin is filled with basically 3 layers. The topmost layer includes alluvium and soft soil, the second one consists of stiff soil and alternations of conglomerates, clay and sand, while the third layer is represented by Neogene formations like marl, marly limestone and sandstone. The bedrock of the basin consists of Triassic limestone and schist. Borders of the basin, where the topmost layer directly overlies the bedrock, are locally quite steep. Based on geophysical data (Vp, Vs, Q) measured at the site, the numerical modeling of the seismic site response was carried out. The 2D and 3D finite-difference techniques were used, and significant edge effects were revealed. No recording of the mainshock is available in Ano Liosia. Nevertheless, based on the finite-extent composite source model, validated by the existing strong motion records in Athens, we found that the bedrock motion in Ano Liosia had its PGA ranging from 0.2 to 0.3 g, resulting from the relatively small epicentral distance (~ 10 km) and the forward source directivity. The source and site effects were combined with each other by a hybrid technique (Oprsal and Zahradnik, JGR 2002), allowing fast full-wave 3D calculations up to 10-20 Hz on a standard personal computer, and showing that the combined source and site effect in Ano Liosia might provide the PGA values locally exceeding 0.6 g.

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