## 2 Data and Methods Used
### Methods Used  
There are different approaches to site characterization in urban environments. Each one has its pros and cons as well as various cost levels. There are two main categories of methods for in situ site characterization; the active and passive (non-invasive) ones. The active ones (e.g., cross-hole, down-hole, CPT, etc.) usually affect the environment and thus prove challenging to implement within cities. In contrast, non-invasive methods are based on the measurement of environmental noise, and do not affect the built environment, while also being much more cost-effective to implement. Among the non-invasive methods based on ambient noise recordings, the one based on a single station measurement per site was implemented in this study. In addition, a 1D ambient noise simulation technique was used to validate the proposed soil profiles up to the bedrock for the city of Durres. 1. Data Processing and Analyses of Single Station HVSR  
In this study, compiled ambient noise data was processed based on the SESAME project guidelines [10], and more specifically the criteria for reliability of results proposed in the Table of its 2.1 section. Their spatial distribution was investigated to divide the city  
Figure 9: Measurement points within the Durres city (**top**); An example of measurement site (**bottom**). in various categories of similar HVSR curves, that is, zones of similar dynamic properties (f\({}_{\rm o}\), A\({}_{\rm o}\)). In addition, for certain sites where an estimated V\({}_{\rm s}\)-depth profile was available (see Section 3.3). 1D synthetic ambient noise recordings were generated and their HVSRs were calculated. Comparison between experimental and synthetic HVSRs showed the degree of reliability of the latter, while any deviation from the actual HVSRs either indicated possible attenuation factor (Q) issues and/or 2D/3D imprints due to basin effects. The data set of 80 measurements was processed in a uniform way, using the Geopsy software package ([[http://www.geopsy.org](http://www.geopsy.org)]([http://www.geopsy.org](http://www.geopsy.org)), accessed on 5 November 2022). Each recording of 30 min ambient noise was automatically divided into 50 s windows, using the following set of parameters [60]:  
Short Time Average (STA) = 1 s, Long Time Average (LTA) = 30 s,  
min[STA\({}_{\rm amplitude}\)/LTA\({}_{\rm amplitude}\)] = 0.20, max[STA\({}_{\rm amplitude}\)/LTA\({}_{\rm amplitude}\)] = 2.5  
A Fourier transform was applied to each one of the selected windows, with 5% tapering, and smoothed using the approach of [61], with the b coefficient value set to 40. The mean horizontal spectra for each 50 sec time windows were derived by taking the geometric average, and then calculating the corresponding Horizontal-to-Vertical (H/V) spectral ratio. An example of the H/V processing using Geopsy is shown in Figure 10. Certain criteria for selecting H/V peaks as fundamental or higher mode frequency (ideal and/or clear peaks) were taken into account based on the SESAME guidelines ([[http://sesame.geopsy.org/SES_Reports.htm](http://sesame.geopsy.org/SES_Reports.htm)]([http://sesame.geopsy.org/SES_Reports.htm](http://sesame.geopsy.org/SES_Reports.htm)), accessed on 5 November 2022). For each site the mean \(\pm\) one standard deviation (H/V) spectral ratios were calculated. After the initial processing, 76 out of 80 measurements were considered of good quality and further processed in this study. These 76 HVSR curves are provided as a Supplementary Material of this study, in ascii format. Theoretical 1D simulation of ambient noise  
In modeling 1D synthetic ambient noise recordings for sites with heterogeneous subsurface structure, such as Durres, we used a two-step numerical code that has been de  
Figure 10: Snapshot example of the H/V processing using Geopsy. veloped in the European SESAME project. In the first step, the noise sources are represented by surface or shallow subsurface point forces randomly distributed in space, direction (vertical or horizontal), amplitude and time [62].