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Characterization of Site Conditions for Selected Seismic Stations in Eastern Part of Romania

Grecu B., Zaharia B., Diaconescu M., Bala A., Nastase E., Constantinescu E., Tataru D.

Acta Geophysica

2018

Vol. 66, no. 2

153--165

Strong motion data are essential for seismic hazard assessment. To correctly understand and use this kind of data is necessary to have a good knowledge of local site conditions. Romania has one of the largest strong motion networks in Europe with 134 real-time stations. In this work, we aim to do a comprehensive site characterization for eight of these stations located in the eastern part of Romania. We make use of a various seismological dataset and we perform ambient noise and earthquake-based investigations to estimate the background noise level, the resonance frequencies and amplification of each site. We also derive the Vs30 parameter from the surface shear-wave velocity profiles obtained through the inversion of the Rayleigh waves recorded in active seismic measurements. Our analyses indicate similar results for seven stations: high noise levels for frequencies larger than 1 Hz, well defined fundamental resonance at low frequencies (0.15-0.29 Hz), moderate amplification levels (up to 4 units) for frequencies between 0.15 and 5-7 Hz and same soil class (type C) according to the estimated Vs30 and Eurocode 8. In contrast, the eighth station for which the soil class is evaluated of type B exhibits a very good noise level for a wide range of frequencies (0.0120 Hz), a broader fundamental resonance at high frequencies (~ 8 Hz) and a flat amplification curve between 0.1 and 3-4 Hz.

The solution to the Lamb’s problem for nonlocal thermo-visco-elastic medium

Gawinecki J. A., Rafa J., Łazuka J.

Biuletyn Wojskowej Akademii Technicznej

2017

Vol. 66, nr 4

225--234

In our work we constructed the solution of the initial-boundary value problem so-called Lamb’s problem for the half space occupied with thermo-visco-elastic medium. The visco-elastic medium was described by the Biot model, whereas thermal interactions were described by the Gurtin-Pipkin model. Using the Cagniard de Hoop method we obtained the solution of the Lamb’s problem to the considered system of integro-differential equations. Based on the constructed solution of the above mentioned problem, we described the type of waves which propagate in the thermo-visco-elastic medium and the domain of their influence. The propagation of the Rayleigh’s wave was investigated. We discovered the new Rayleigh’s wave in thermo-visco-elastic medium (second Rayleigh’s wave) and named it GRL-wave (Gawinecki-Rafa-Lazuka–wave).

W pracy skonstruowano rozwiązanie zagadnienia brzegowo-początkowego typu Lamba dla półprzestrzeni wypełnionej ośrodkiem termo-lepko-sprężystym. Ośrodek lepko-sprężysty został opisany przez model Biota, natomiast oddziaływania termiczne zostały opisane przez model Pipkina-Gurtina. Rozważano również zagadnienie brzegowo-początkowe typu Daniłowskiej. Rozważano propagacje fal typu Rayleigha w badanym ośrodku termo-lepko-sprężystym.