Seismic velocities and geotechnical data applied to the soil microzoning of western Algarve, Portugal

The Algarve province of Portugal is located near the E–W Eurasia–Africa plate boundary. It is characterized by a moderate seismicity with some important historical and instrumental earthquakes causing important loss of lives, serious damage and economical problems. It has therefore been a target of several risk assessment projects. This paper focuses the evaluation of the most interesting and useful geotechnical near-surface parameters, through the acquisition, processing and interpretation of P and S-waves refraction profiles and the use of SPT parameters. VP/VS ratios and the Poisson's ratio were estimated and a subsoil classification based on geophysical and geotechnical parameters is presented. The classification based upon the European Code 8 for civil engineering and SPT bedrock data, was carried out for land use planning and design of critical facilities. Other parameters were computed to provide information for future site effect studies. The quality and volume of the data gathered here using established approaches can be quite useful to estimate soil microzoning in the absence of local earthquake records. The results also show that the lithology is the most influent parameter on the values of seismic velocities and SPT data. Therefore, surficial geology is inappropriate for this kind of studies and lithological maps should be used instead.