The Fourier spectra of ground motion \(A(f)\) can be expressed as the multiplication of source \(S(f)\), path \(P(f)\), and site \(H(f)\) terms in the frequency domain:  
\[A(f)=S(f)\times P(f)\times H(f) \tag{1}\]  
where \(f\) is the frequency. In the SSR technique, the reference site is required to have the most homogeneous geological conditions as it is assumed to be free of anomalous amplifications. The two sites should be close to each other in comparison with the distance to the source. Considering that the analysis is performed for stations which register the same earthquake:  
\[SSR(f)=\frac{|A_{i}(f)|}{|A_{j}(f)|}=\frac{|H_{i}(f)|}{|H_{j}(f)|}. \tag{2}\]  
However, it is not always possible to find records of the same event with a good signal-to-noise (S/R) ratio in two stations that meet these conditions. Thus, the Horizontal-to-Vertical Spectral Ratio (HVSR) technique [2] is used as an alternative to studying the site response. In this method, the ratio between the mean of the horizontal components \(A_{Hi}(f)\) and the vertical component \(A_{Vi}(f)\), recorded in a single station, is calculated:  
\[HVSR(f)=\frac{|A_{Hi}(f)|}{|A_{Vi}(f)|}. \tag{3}\]  
This technique can be used to estimate the fundamental resonant frequency (\(f_{0}\)) of a site, but is unreliable for determining its transfer function [3]. In the literature, several studies can be found in which the site response is analyzed in areas around the world, based on these empirical techniques and numerical models [4; 5; 6; 7; 8]. The study of this phenomenon remains current and it is an important issue to be considered in the estimation of seismic risk and damage prevention, even in areas of low seismicity [9]. The Trans-Mexican Volcanic Belt (TMVB), located in central Mexico (Figure 1), is an example of those areas where the site response might represent a potential risk despite the low frequency of earthquakes. It is a volcanic arc that covers Cretaceous and Cenozoic magmatic provinces [10]. Seismicity in this region is related to extensional faults in the crust and normal faults in the subducted Cocos plate. This zone is located between 18\({}^{\circ}\)30\({}^{\prime}\) and 21\({}^{\circ}\)30\({}^{\prime}\), and extends from the coast of the Pacific Ocean to the Gulf of Mexico. It has an approximate length of 1000 km and a variable width of 90-230 km. Figure 1: Location of the Trans-Mexican Volcanic Belt and interaction of tectonic plates in Mexico. This area presents low seismicity, compared to the Pacific Ocean coast, where the Cocos plate subducts under the North American plate. Nevertheless, there are important recent and historical occurrences of destructive events [11; 12]. Examples of these is the earthquake that occurred in Acambay on 12 November 1912 (Mw 6.9, H = 33 km) [13], and more recently in Puebla on 19 September 2017 (Mw 7.1, H = 51.2 km) [14]. This aspect is particularly important, in view that the TMVB comprises some of the largest cities in Mexico with significant industrial development and population growth in the last years. It may be difficult to find a zone in the TMVB with negligible site effects, due to the variability in geological properties [10]. Several articles have been published on this topic related to Mexico, mainly focused on the behavior of site effects in Mexico City. [PERSON] et al. [15] found that stations located in the hill zone in the Valley of Mexico present amplifications that are 10 times higher than those predicted from ground motion attenuation equations. In a later study, [PERSON] et al. [16] compared amplification responses at some of the stations analyzed by [15]. The records analyzed corresponded to inslab earthquakes with an epicenter outside the TMVB, and they observed similar behavior despite the source type and location. [PERSON] et al. [17] briefly discuss HVSR curves for 2 stations crossing the TMVB, obtained from records of 9 shallow coastal earthquakes on the Pacific Ocean coast. Likewise, [PERSON] et al.