## 3 Results
### Development of the Three-Dimensional Finite Element Model, 3D FEM  
Based on the mapping of all recorded soil periods, along with the collection of background information on the study area--specifically regarding shear wave velocity and areas with rock outcrops--a potential model of the spatial distribution of bedrock in the explored area of Concon was generated. This information, combined with the topographic survey and bathymetry of the area, enabled the creation of a three-dimensional model of the explored area, encompassing the urban limits of the municipality of Concon. The model was created with an area larger than the urban zone to establish boundary conditions, resulting in dimensions of 4150 m by 4600 m.  
For subsequent modeling of the seismic response, the 3D FEM was developed using Plaxis 3D V2023, specialized software for geotechnical simulations [42]. In order to consider a more comprehensive soil response for this case study, the soil behavior was represented using the Hardening Soil with Small Strain (HSSS) constitutive model [43]. This model allows for the incorporation of the nonlinear stiffness degradation that occurs in the soil as strain amplitude increases. The model parameters were derived from field tests, including shear wave velocity (Vs) profiles obtained from geophysical tests conducted in various zones across the study area, as well as laboratory data. These parameters were further supplemented by information collected from previous projects carried out in the sector, ensuring an accurate representation of the local geotechnical conditions. Based on all the background information about the dune soil deposit, which exhibits a relatively homogeneous profile throughout the study area, the HSSS parameters for the Concon dune soil were obtained and are shown in Table 1. For the marine terrace composed of granite, on which the eolian deposit primarily rests, a bedrock with stiffness was considered, with a velocity recorded through geophysical tests, resulting in an average value of 1200 m/s. This information is of great importance, as it allowed for the inclusion of impedance contrast effects between the soil and the rock. In addition to the bedrock input, the 3D FEM employed specific boundary conditions to ensure the proper simulation of seismic wave propagation. The lateral boundaries of the model were assigned \"free-field\" conditions, which allow for the simulation of seismic wave propagation as if the model were part of a larger region, reducing reflections at the edges. For the bottom boundary, a \"compliant base\" condition was applied, designed to absorb upward-propagating seismic waves and minimize wave reflection at the base of the model. This condition allows for the direct application, i.e., upward propagation, of an input accelerogram without interference caused by waves reflected from the upper layers [42]. Figure 9: Relationship between measured and estimated periods using Equation (1) for estimation of bedrock depth. For the FEM's meshing, 10-node tetrahedral elements were used, with an average size of 33 m across the entire area, which is a notable magnitude given the model's dimensions and allows for the adequate recording of wave propagation throughout the domain. The mesh used, which is shown referentially superimposed on the city map in Figure 10, was constructed with a total of 673,000 elements. To evaluate the regional seismic response, the acceleration record of the 2010 Maule earthquake in Chile, Mw = 8.8, measured on bedrock at the Rapel seismological station, was used as the signal [44]. The characteristics of the signal used are shown in Table 2 and Figure 11. This record was applied at the base of the model beneath the bedrock, using a time step equal to the sampling period of the signal; that is, 0.005 s per step.