## 4 Results
### 2D VS Models  
Figure 5 shows the 2D VS models obtained in sites 1 and 3 (Figure 1d) on 23 June 2014 (Table 2). Prospecting depth was 30 m in MASW1 (Figure 5a) and 27 m in MASW3 (Figure 5b). There is not MASW2 survey in site 2 because the operation was cancelled due to a heavy storm occurred while acquiring data, thus provoking a battery discharge that left the equipment inoperable. Both MASW1 and MASW3 were interpreted recurring to (i) reference VS values compiled from the scientific literature for equivalent lithologies [34; 59] as in Table 4, (ii) local geological information after [43; 46; 47; 48], and (iii) detailed geological data for Pliocene to Holocene formations deduced from geotechnical soundings S1 to S3 [40] as in Figure 1d.  
In both MAWS1 and MASW3, VS is in the 50-950 m s\({}^{-1}\) range. In general, VS increases in depth according to the increasing age and compaction of sediments, from less than 200 m s\({}^{-1}\) for Holocene, 200-500 m s\({}^{-1}\) for Pleistocene, to more than 500 m s\({}^{-1}\) for Pliocene formations. This vertical VS distribution correlates well with regional geological information reported by [47; 48] and geotechnical data from soundings S1 to S3 [40]. The horizontal continuity of this vertical VS distribution is frequently interrupted due to sedimentary processes (e.g., lateral facies changes, erosive channels) and action of faults, which determine the accommodation space for Holocene sedimentation, as discussed in Section 5.2.  
In MASW1, the uppermost 8 m (northern and southern valley boundaries) and 10 m (central valley) thick VS \(<\) 200 m s\({}^{-1}\) values are attributed to aquifer H, the underlying 18 m (central valley) and 20 m (valley boundaries) thick 200 \(<\) VS \(<\) 500 m s\({}^{-1}\) to Pleistocene sands and gravels, and the deeper 5 m (central valley) and 10 m (valley boundaries) thick VS \(>\) 500 m s\({}^{-1}\) to Pliocene formations (Figure 5a).  
In MASW3, VS data acquisition at distances 131-220 m was interrupted due to the impossibility of the equipment to work in the inundated Cascalheira stream bed (Figure 5b). This VS model gap does not compromise the geological interpretation because the ERT3 survey partially covered that sector, as described in next Section 4.4. In MASW3, the uppermost 9 m (northern and southern valley boundaries) and 12 m (central valley) thick VS \(<\) 200 m s\({}^{-1}\) values are attributed to aquifer H, the underlying 20 m (central valley) and 15 m (northern valley boundary) thick 200 \(<\) VS \(<\) 500 m s\({}^{-1}\) to Pleistocene sediments, and the deeper 7 m (northern valley boundary) thick VS \(>\) 500 m s\({}^{-1}\) to Pliocene formations (Figure 5b). At distances 220-310 m, the Pleistocene-Pliocene boundary is not identified because it is below the prospecting depth. As in site 1, site 3 shows contrasted VS valuesassociated to geological formations having different age and compaction. However, at the southern sector, Holocene sediments and underlying Pleistocene sand dunes show similar VS \(<\) 200 m s\({}^{-1}\), thus limiting to identify its boundary. As described in next Section 4.4, ERT enables disambiguating the boundary of these formations.  
The VS models statistics are in Table 5. Average VS lightly decreases from MASW1 to MASW3 as the influence of high VS values from Pliocene materials decreases because they were below its prospecting depth. The coefficient of variation of VS shows similar natural variability of VS in both MASW1 and MASW3 associated to a similar, predictable vertical geological structure. As deduced, VS is predictable enough to produce a confident near-surface geological definition.