Does VS30 reflect seismic amplification? Observations from the West Bohemia Seismic Network.

The present study addresses verification of average seismic shear-wave velocity from the surface to a depth of 30 m (V_S30) as a suitable proxy for a seismic amplification. For this purpose, we used instrumentally homogeneous and spatially dense seismic network WEBNET (West Bohemia Seismic Network), designed to monitor an intraplate earthquake swarm activity in the West Bohemia/Vogtland region (Czech Republic/Germany). Using a Multichannel analysis of surface waves (MASW) shear-wave velocity models and parameters V_S30 and H₈₀₀ (depth of V_s > 800 m/s) were obtained at 17 WEBNET sites. V_S30 were compared with (i) H₈₀₀ and (ii) determined bedrock densities. To understand the relation between V_S30 and site amplification, V_S30 values were correlated with amplitudes of two earthquakes: (1) Mw 6.4 Petrinja, Croatia (12/2020) and (2) Mw 4.2 SE of Vienna, Austria (03/2021) both recorded by the WEBNET. The correlation analysis examined four categories of seismic waves in nine frequency windows and described the relation between amplification and V_S30 using newly defined regression model. The results show that for the regression model, the frequency window with the highest correlation is in the 1–3 Hz range, and this dependence is statistically best observed in the full wave record. The amplification generally decreases with increasing V_S30. However, a large scatter in amplification within Eurocode 8 category B is observed. Based on the observations a new general approach is put forward to finely indicate the relation between amplification and V_S30 and the use of other site proxies is discussed. [ABSTRACT FROM AUTHOR]