The inclusion of site-specific conditions is essential to adequately represent the seismic hazard and the seismic risk for a region. We acquired, gathered and organized a near surface shear-wave velocity database for Portugal, and applied a three-step methodological approach for developing a V S30 site-conditions map using extrapolation based on surface geology. The methodology includes: 1) defining a preliminary set of geologically defined units; 2) calculating the probability distribution of log V S30 for each unit; and 3) merging the units according to the results of statistical tests. The final model comprises three geologically defined units characterized by log V S30 distributions that are statistically significantly different from each other: F1-Igneous, metamorphic and old sedimentary rocks; F2-Neogene and Pleistocene formations; and F3-Holocene formations. The site conditions for F3 unit may be further refined using correlations with topographic slope based on the SRTM3 dataset. We analysed the performance site-conditions models based on correlations with exogenous data (topographic slope and surface geology analogues). The results show that the residual distributions between log V S30 values measured and estimated from those proxies are strongly biased for some geological units, emphasizing the need for acquiring regional V S data.

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This paper focuses on the susceptibility evaluation to bank gullies on earthen embankments through the application of SIMWE (SIMulated Water Erosion) model, using a high resolution digital elevation model (1 meter spatial resolution). The results provided by the model are compared with the hydrologic characteristics, soil texture and soil structure of the agricultural terraces. This approach demonstrates an association between the spatial distribution of erosive forms with high values of water depth and reduced water discharge that are consistent with the lower values of electrical resistivity. The areas with the highest percentage of erosive forms, related to sediment flux, transport capacity and sediment concentration susceptibility, assume medium values. These figures, combined with a low hydraulic conductivity and soil infiltration capacity, are consistent with the fine texture of soils, allowing increased runoff and the development of linear erosion.

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