## 3 Results  
### Zonation Map and Estimation of Bedrock Depth  
After processing and refining all the measurements conducted, a zonation map was created in terms of the period T, recorded using the HVSR method, as shown in Figure 5. Thanks to the high density of measurement points, the map provides a significant level of detail, allowing for a more thorough assessment of geological conditions and facilitating the subsequent creation of a numerical model for evaluating the seismic response of the city. In Figure 5, it can also be observed that the T values in the study area range from 0.15 s to 0.4 s. This variability suggests a relative homogeneity in the underlying geological conditions. Figure 5: Superposition of the isoperiod map obtained for the city of Concon, Chile, adapted by the authors. Base image taken from Google Earth. Image data © 2024 Google, © 2024 TerraMetrics. One of the key challenges in regional characterization processes is the identification of the bedrock, which cannot always be detected through the usual measurements for a given project. In the specific case of Concon, the use of the measured periods along with geological information and visual inspection of exposed rock areas, complemented by the application of the method contained in the Japanese code for determining the period in a stratified condition [25], allowed for the definition of the bedrock location throughout the entire study area. From the perspective of the bedrock, [PERSON] [32] report that the Concon dune eolian sand deposit lies above a marine terrace of Paleozoic granites that extends between approximately 25 m and 80 m above sea level, following the geomorphological profile shown in Figure 6, which suggests that abrupt changes in the bedrock topography are not expected within the study area. This may explain the limited variation between the maximum and minimum periods recorded across the entire study area, where the most significant variations can be primarily attributed to the topographical conditions of the region, such as the Holocene dune area located to the west, as shown in Figure 7.  
Considering these characteristics, a survey of geophysical tests conducted in the city for various real estate projects, for which permission for use was granted, was carried out, resulting in more than 20 shear wave velocity (Vs) profiles being obtained. A characteristic vs. profile for each zone is shown for reference in Figure 8. Considering the geological model recorded in the area, and the cross-referencing of complementary geophysical information with the periods measured during the microzonation campaign, it was deemed possible to apply the equation proposed in the Japanese standards for period estimation (Equation (1)), allowing the measured T periods to be matched, thereby enabling back analysis for estimating the bedrock location at the 208 measured points. The average depth of the bedrock location was recorded as 26 m with a standard deviation of 8.2 m, which  
Figure 6: Geomorphological profile of the Concon dune deposit. Adapted from [32]. Figure 7: View of dune deposit located to the west (source: the authors). is consistent with the characteristic velocity profiles shown in Figure 8. The following equation was used for this purpose [25]:  
\[T_{E}=\sqrt{32\underset{i=1}{\overset{L}{\sum}}\frac{h_{i}\Big{(}\frac{H_{i-1}+H_{ i}}{2}\Big{)}}{V_{s-i}}^{2}} \tag{1}\]  
where \(L\) represents the number of soil layers existing between the base of the foundation and the rock soil, and \(h_{i}\), \(H_{i}\) and \(V_{s-i}\) represent respectively the thickness, depth, and shear wave propagation velocity of the \(i\)-th soil layer.