## 4 Results
### Near-Surface Seismic Surveys  
Near-surface seismic techniques respond to the steady shear modulus of subsurface materials, expressing seismic shear-wave velocity (VS) [L T\({}^{-1}\)], in which the Rayleigh wave fundamental mode dispersion curve and higher modes (if present) are extracted from a shot record and then inverted to generate 1D VS models [57; 58; 59; 60; 61; 62]. A succession of geophones records ambient microtremor to generate the Rayleigh waves from which a 2D VS model is obtained [61; 62]. REMI was the near-surface seismic technique used to acquire VS data and map 2D VS models in four surveys designed to support geotechnical research in civil works (Table 2). The total prospecting length was 22.2 km, the prospecting depth was 40-120 m, and VS varied in the 95-1050 m s\({}^{-1}\) range (Table 2). This paper reinterpreted the 2D VS models for the shallow geological definition following the interpretative criteria reported by [PERSON] et al. [63] and [PERSON] et al. [64]. These authors propose that subsurface VS propagation is a site-specific steady property determined by effective compaction and therefore is dependent on the age and depth of each geological material piled vertically [65; 66; 67; 68]. The different relationships between VS and age and depth in different lithologies described in the scientific literature [63; 64; 65; 66; 67; 68; 69; 70; 71] were used to reinterpret the VS models. The VS increased in depth according to the increasing age and compaction of geological materials, from less than 200 m s\({}^{-1}\) in recent anthropogenic fillings and lacustrine formations, 200-550 m s\({}^{-1}\) in Holocene sedimentary and volcano-sedimentary formations, and more than 550 m s\({}^{-1}\) in Pleistocene volcano-sedimentary formations. As in other near-surface seismic techniques, REMI cannot disambiguate boundaries of different geological formations with similar VS [63; 64; 70; 71]. This limitation to make inner divisions was solved by using external validation data, such as regional [24; 25] and local [26; 33; 34] geological information, geotechnical soundings logs, and other prospecting techniques [63; 64]. The REMI surveys labelled 12 and 14 in Figure 1b and Table 2 were selected (Figure 3). They were performed in November 2011 as part of the Quito Subway geotechnical research, which included 201 REMI profiles grouped into three REMI surveys with prospecting lengths of 8.6 (southern Quito), 3.2 (central Quito), and 10.3 km (northern Quito) [44]. Since these prospecting lengths are too long to be drawn in detail, two 2.5-km sections from the southern- and northern-Quito REMI surveys exploring the most representative geological formations were selected (Figure 3b). The VS data were acquired using the DAQlink-4 24-channels Compact Seismograph and the 4.5 Hz Geo-Space geophones by Seismic Source Co., Ponca city, OK, USA. The following configuration was applied: a recording array of 24 vertical component geophones, 4-m geophone spacing for a prospecting depth of around 40 m, 10-m displacement between readings, and a sampling rate of 0.25 m s\({}^{-1}\). See [PERSON] [44] for further details about the data processing and mathematical inversion. Figure 3b shows the location of the two selected REMI surveys sections, here called REMI1 from survey 12 and REMI2 from survey 14. The section features comprised an imposed prospecting length of 2.5 km, a prospecting depth of 40 m, VS in the range of 120-580 (REMI1) and 190-610 m s\({}^{-1}\) (REMI2), and average RMSEs of 10.83 (REMI1) and 9.42 (REMI2) (Figure 3c). The VS values were typical of sedimentary [63,64] and volcano-sedimentary [72] rocks. Figure 3: (**a**) General location of the selected southern- and northern-Quito REMI surveys labelled 12 and 14 in Figure 1b and Table 2, updated and reinterpreted from [PERSON] [44]. (**b**) Detailed location of two selected 2.5-km sections from REMI surveys 12 and 14, here called REMI1 and REMI2. (**c**) REMI1 and REMI2 profiles’ sections.