Introducing inferred geomorphological sediment thickness as a new site proxy to predict ground-shaking amplification at regional scale. Application to Europe and Eastern Turkey

Abstract. To test whether a globally inferred sediment thickness value from geomorphological studies can be used as a proxy to predict earthquake site amplification, we derive site amplification models from the relation between empirical amplification for sites in Europe and Turkey, and the geomorphological sediment thickness. The new site amplification predictions are then compared to predictions from site amplification models derived using the traditional site proxies, V_S30 inferred from slope, slope itself, as well as geological era and slope combined. The ability of each proxy to capture the site amplification is evaluated based on the reduction in site-to-site variability caused by each proxy. The results show that the highest reduction is caused by geological era and slope combined, while the geomorphological sediment thickness show a slightly larger or equal reduction in site-to-site variability as inferred V_S30 and slope. We therefore argue that including geology and geomorphology in site amplification modelling on regional scale can give an important added value and that globally or regionally inferred models for soil and sediment thickness from fields beyond engineering seismology can have a great potential in regional seismic hazard and risk assessments. Furthermore, the differences between the site amplification maps derived from different proxies capture the epistemic uncertainty of site amplification modelling. While, albeit the different proxies predict similar features on a large scale, local differences can be large. This shows that using only one proxy when predicting site amplification does not capture the full epistemic uncertainty, which is demonstrated by looking into detail on the site amplification maps predicted for Eastern Turkey and Syria, where the devastating Kahramanmaras Earthquake Sequence occurred in February 2023.