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Authors
Abstract(s)
Lisbon has a moderate to high seismic risk due to its seismicity, socioeconomic importance and dense urbanisation. Its complex geomorphological structure may aggravate soil amplification and cause higher structural damage.
The present work improves the soil dynamic characterisation and seismic site response assessment in Lisbon. Based on a multidisciplinary dataset composed of surface geology, a geotechnical database and a geophysical database, an integrated approach to seismic ground characterisation was performed.
A regression analysis of the shear-wave velocity values compiled in the geophysical database was done for each geological unit. The peak frequency distribution in the city was assessed from ambient vibration measurements, and it indicated a decrease from the oldest to the most recent geological formations that outcrop in the SW-NE direction. Three zones based on the peak frequency distribution were proposed.
An estimation of the impedance contrast depths was computed through two processes: (i) the shallower contrast depth was determined by a sharp variation in 𝑁𝑆𝑃𝑇 values, and (ii) the deeper contrast depth was estimated using geology data and deep borehole information. For the upper 100 m of depth, a consistent relationship between the contrasts identified through different data sources was obtained, even if uncertainty increased with depth.
The seismic bedrock position was identified, and soil classification was performed using the current version of Eurocode 8 and the draft version of new Eurocode 8 classification schemes.
The seismic site effects were evaluated through one-dimensional and two-dimensional numerical simulations using the equivalent linear method and the finite element method, with the two types of seismic action defined in the Portuguese National Annex of Eurocode 8.
The amplification factors in the city were assessed, and the estimated soil factors were compared to Eurocode 8 reference values. Overall, the estimated soil factors exceed the reference soil factors of Eurocode 8.
Description
Keywords
Seismic site effects Seismic microzonation Impedance contrast depth Soil dynamic characterisation Amplification factors Efeitos de sítio Microzonagem sísmica Profundidade do contraste de impedância Caracterização dinâmica do solo Fatores de amplificação