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Parâmetros sísmicos espectrais de fonte e de propagação nas regiões do Vale do Tejo e Sul de Portugal
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Orientador(es)
Resumo(s)
The ground motion results from three distinct processes: energy release at the seismic source; seismic energy propagation through the medium, from the source to the bedrock; modification of the energy content due to local effects. Source and path spectral parameters that characterize the mentioned processes are essential for simulating intense ground motion, as they enable the calibration of finite fault stochastic models. The purpose of this work is to determine the kappa parameter and stress drop for the areas around Tagus Valley and South of Portugal, two regions with significant seismic risk in Portugal mainland. Source spectra were first obtained for the records of the Portuguese seismic network, for both horizontal components. In a first approach, kappa parameter was determined by fitting the high-frequency decay of the acceleration spectrum with a straight line, in a log-linear scale. Corner frequency was determined by the half square root of the ratio between the velocity source spectra integral and displacement source spectra integral. Stress drop was determined correlating corner frequency and seismic moment, considering the ɷ-square model. On a second alternative approach, the SourceSpec package was used to compare results. Kappa parameter was estimated to be k = (0.025±0.013) s for the Tagus Valley region and k = (0.025±0.016) s for the South of Portugal. Stress drop estimates range between 0.1 MPa and 13 MPa (mean Δσ = 2.11 ± log10 (0.8) MPa, median = 2.96 MPa) for the events in the Tagus Valley. For the South of Portugal, stress drop estimates range between 0.01 MPa and 30 MPa (mean Δσ = 1.51 ± log10 (0.7) MPa, median = 1.98 MPa). Kappa values obtained indicates low attenuation for hard rock and higher attenuation for less consolidated rock. Determined stress drop values are in agreement with the region’s interplate tectonic setting.
Descrição
Tese de Mestrado, Ciências Geofísicas, 2025, Universidade de Lisboa, Faculdade de Ciências
Palavras-chave
Ground motion Spectral parameters Seismic source Seismic wave propagation