## 1 Introduction  
Geophysical techniques used to study the subsoil properties have been widely applied due to their relative low cost compared to direct in-situ tests (e.g., boreholes). Additionally, these methods are less invasive and able to reach great depths. Therefore, they are specially adapted for urban environments where it is not possible to carry out deep invasive exploration or deploy heavy machinery. Among the great variety of geophysical methodologies, gravity and ambient noise horizontal-to-vertical spectral ratio (H/V) are two of the most used because they are relatively easy to perform and they do not require very complex logistics in the field. Even though their physics are very different, they describe complementary variables. The gravimetric method measures the variations in the gravity field caused by the density contrast within the soil domain and with respect to the bedrock underneath [1]. Following this simple principle, gravimetric surveys have been used in many fields such as hydrogeology, e.g., [2; 3; 4], mining exploration, e.g., [5; 6], or geometric characterization of sedimentary basins, e.g., [7; 8], among others. On the other hand, among the seismic methods, the H/V method, introduced by [PERSON] and [PERSON] [9] and widespread by [PERSON] [10], consists in determining the ratio between the Fourier spectra amplitudes of the horizontal and vertical components of microtremors [11]. According to these authors, the frequency peak of the H/V curve correlates with the predominant frequency of vibration at the site. Following this idea, many publications have used the H/V method to study the dynamic properties of the subsoil, e.g., [11; 12; 13; 14; 15; 16]. In addition, the ellipticity from the Rayleigh waves obtained from the H/V curve, e.g., [17; 18], can be used in a combined inversion with other seismic constrains (e.g., shear wave dispersion, autocorrelation curves) to improve the resolution of the deeper layers in the shear wave velocity profile [19]. In the study of sedimentary basins, many authors have combined both methods with others geophysical measurements, to conduct an integrated interpretation of their geometry and dynamic properties, and to estimate their seismic response, e.g., [7; 8; 20; 21; 22; 23; 24]. In this context, the parameter in common between both methods is the inference of the depth to rocky basement. However, the definition of basement given by each technique is different and it is very important to understand this distinction. The gravity methods, in the study of sedimentary basins, result in the depth of the basement, as compared to the negative anomaly produced by the low-density infill sediments versus bedrock. On the other hand, the H/V information can also be used directly as an infilling sediment thickness estimator under certain conditions assuming 1-D wave propagation and using the shear-wave velocity information [25]. Nevertheless, this method defines a mechanical or seismic bedrock in terms of a predominant impedance contrast, which does not necessarily imply rock. Thus, the location of both basements is not always the same, which can lead to wrong interpretations. Consequently, it is very important to understand the connection between both methodologies and to define conditions in which both results can be correlated. A correlation between the methods could be beneficial in terms of the geophysical survey. Firstly, each gravity measurement requires less time than the H/V, so this possible correspondence could lead to better spatial coverage in less time. Secondly, the H/V results can help to discern between zones with different density contrast through the form of the curve. Finally, in cases when both methodologies are available, they can be complementary. However, a correlation between both methods, if it exists, has not been thoroughly studied, and thus very little information is available on whether one method could be an estimator of the other.