GNGTS 2022 - Atti del 40° Convegno Nazionale

GNGTS 2022 Sessione 2.1 235 INTRODUCING INFERRED GEOMORPHOLOGICAL SEDIMENT THICKNESS AS A NEW SITE PROXY TO PREDICT GROUND-SHAKING AMPLIFICATION K. Loviknes 1,2 , F. Cotton 1,2 , G. Weatherill 1 1 GFZ German Research Centre for Geosciences, Potsdam, Germany 2 Institute for Geosciences, University of Potsdam, Potsdam, Germany Local geological features can have a strong impact on earthquake ground shaking. Sites with mainly loose sediments have been observed to amplify the recorded ground motion. In many, non-site-specific, applications where seismic hazard and risk assessments must be computed on large regions, this site amplification is commonly characterized using the average shear-wave velocity of the upper 30 meters of the soil column (V S30 ). For a single site the velocity profile and V S30 can be measured directly, for larger areas and regions, however, the V S30 must be inferred from other parameters. A much-used method to calculate V S30 is the model by Wald and Allen (2007) based on topographic slope from digital elevation models (DEMs). However, inferring V S30 based on topographic slope has several limitations, especially for basins and particular geological conditions (Lemoine et al., 2012). Furthermore, the measured V S30 values should not be used interchangeably with inferred V S30 values without properly accounting for the additional uncertainty related to the V S30 calculations (Lemoine et al., 2012, Weatherill et al., 2020). In this study we propose a geomorphological model for inferred sediment depth by Pelletier et al. (2016), as an alternative site proxy to predict ground motion site-amplification on a regional or global scale. The Pelletier et al. (2016) model uses DEM and geological maps to distinguish between landforms, lowlands, uplands, hillslopes and valley bottoms. The thickness of sediments, soil and intact regolith is then inferred for each landform using several global and regional values including geological maps, water table depth and climate data. The final model provides a global map of inferred regolith, soil and sediment thickness up to 50 meters. In this study we focus on the average soil and sediment thickness, from hereon called geomorphological sedimentary thickness, as shown in Fig. 1 for Europe. To test whether the model can be used to predict ground-motion site amplification, we compare the geomorphological sedimentary thickness to inferred V S30 , topographic slope and empirical site amplification as shown in Fig. 2 for frequency f = 1.062 Hz. The empirical site Fig. 1 - The inferred geomorphological sedimentary thickness for Europe from the Pelletier et al. (2016) model.