Site response estimation in alpine valleys - the case of Tagliamento river valley
Risposta sismica delle vallate alpine: applicazione alla media Val Tagliamento
This thesis consists of a site effect study in an alpine valley, where seismic action is amplified by 2D basin effects. The study area was a stretch of the Tagliamento river valley, in an area between the Tolmezzo and Cavazzo Carnico municipalities, in the north-western part of the Friuli Venezia Giulia Region (NE Italy). The valley is densely inhabited and large industrial factories are situated on the quaternary alluvial deposits, where big amplifications are expected. All the available geophysical and geotechnical data on the area has been collected and new data has been acquired. An array of six stations for earthquake recording was deployed throughout the valley for 18 months . 250 noise measurements have been recorded in the plain, with more intensive detail in the two villages of Tolmezzo and Cavazzo Carnico. Conventional methods, such as spectral ratio techniques were applied to the new earthquake recordings to infer the amplification of the valley. The horizontal to vertical component ratio of noise data (H/V) indicates the crucial period of vibration of the valley. The bedrock morphology was inspected using the joint inversion of H/V ratios and the residual gravity anomaly carried out in a former study. The lack of geological information does not allow verification of the model, but the strong convergence of the two distinct methodologies makes the structural model realistic. The great success of joint techniques, although some corrections have to be made in the calculation of Quaternary sedimentary cover, gives encouraging prospects for economical, wide-ranging surveys.