## 4 Applications to Field Data
### Estimation of Equivalent Shear-Wave Velocity  
As an important dynamic parameter in seismic safety evaluation, the shear-wave velocity of soil layer can best reflect the dynamic characteristics of site soil. The shear-wave velocity Vs30 may be a weak proxy in order to assess soil dynamic characteristics [31], according to the American code _Minimum Design Loads for Buildings and Other Structures_ (ASCE/SEI 7-10), the European code _Design of Structures for Earthquake Resistance. Part 1: General Rules, Seismic Action and Rules for Buildings_ (Eurocode 8), etc. According to the Chinese _Code for Seismic Design of Buildings_ (GB50011-2010), the site category is determined according to the equivalent shear-wave velocity within 20 m below the ground surface (_Vs_20) and overburden thickness. The overburden thickness in the study area has been analyzed above, and the equivalent shear wave calculation is follows:  
\[V_{se}=d_{0}/t \tag{4}\]  
\[t=\sum_{i=1}^{n}\frac{d_{i}}{V_{si}} \tag{5}\]  
where the calculated depth \(d_{0}\) is the smaller of the overburden thickness and 20 m. Based on the borehole-measured wave velocity and microtremor inversion velocity model, the statistics of the calculated equivalent shear-wave velocity are shown in Table 1. \begin{table}
\begin{tabular}{c c c c c c c c c c} \hline \hline \multirow{3}{*}{**Study Area**} & \multirow{2}{*}{\begin{tabular}{c} **Bore-** \\ **Hole** \\ **No.** \\ \end{tabular} } & \multirow{2}{*}{\
\begin{tabular}{c} **Overburden** \\ **Hole** \\ **In****(m)** \\ \end{tabular} } & \multirow{2}{*}{
\begin{tabular}{c} **Size** \\ **S-Wave Velocity** \\ **Vs20 (m/s)** \\ \end{tabular} } & \multicolumn{4}{c}{**Microtremor Inversion Velocity Model**} \\  & & & & **Equivalent** & **Size** & **Covburden** & **Equivalent S-Wave** & **Site** & **Overburden** & **Selectity** \\  & & & & **S-Wave Velocity** & **Point No.** & **Thickness** & **Velocity** & **Category** & **Error** \(\epsilon_{h}\) & **Error** \\  & & & & **Vs20 (m/s)** & & **_h_ (**m/s)** & & **_v_20 (m/s)_ & & **_e_** \\ \hline \hline
1 He/an & zk43 & 51.8 & 173.9 & III & H32 & 55.8 & 181.1 & III & 7.7\% & 4.1\% \\ Line & zk47 & 55.0 & 178.3 & III & H110 & 57.2 & 175.7 & III & 4.0\% & 1.5\% \\ \hline
1I & zk10 & \textgreater{}90.0 & 211.7 & III & S33 & 93.7 & 195.8 & III & - & 7.5\% \\ Sha & zk11 & \textgreater{}90.0 & 214.7 & III & S95 & 101.0 & 192.8 & III & - & 10.2\% \\ masoLine & zk12 & \textgreater{}90.0 & 215.3 & III & S151 & 107.6 & 204.5 & III & - & 5.0\% \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Equivalent S-wave velocity, overburden thickness and engineering site category of each borehole and exploration point. Figure 7: Partial core sample photos of borehole zk10. The errors between the equivalent shear-wave velocity estimated by the microtremor model of exploration points H32 and H110 of the He'an Line and the borehole-measured estimate are 4.1% and 1.5%, respectively, and those of exploration points S33, S95, and S151 of the Shamao Line are 7.5%, 10.2%, and 5.0%, respectively. For overburden thickness, the errors of the two exploration points of the He'an Line are 7.7% and 4.0%, respectively. The errors of the Shamao Line are counted temporarily, as the moderately-weathered bedrock roof is not exposed in the borehole. Although there is an error between the microtremor inversion model and borehole-measured data, it is small. Besides, the site classification in relevant specifications is relatively rough. So, the result of the microtremor survey is decided to be consistent with the borehole-measured one, both being site III. The calculation formula of the error \(e\) between the two defined in the table is follows:  
\[e=\frac{measured\ data-\text{\it inversion\ data}}{measured\ data}\times 100\% \tag{6}\]  
With increasing requirements for earthquake prevention and disaster reduction, to predict seismic hazards in key areas, it is necessary to consider a wide range of regional site conditions.