# The Contribution of Near-Surface Geophysics for the Site Characterization of Seismological Stations
## 3 Application of the Geophysical Surveys and Processing Results
### Seismological Station at Villa, Attica (VILL)  
Station _VILL_ (Figure 6) is situated at the children's camps of Aspropyrgos municipality, near Villa town in western Attica, established on 12 October 2009. The station is currently equipped with a _Nanometrics Centaur CTR3-3S_ datalogger and a _Trillium Horizon/120s_ broadband seismometer, deployed in collaboration with the Ruhr-University Bochum as part of the AdriaArray project ([[https://orfeus.readthedocs.io/en/latest/adria_array_main.html#](https://orfeus.readthedocs.io/en/latest/adria_array_main.html#)]([https://orfeus.readthedocs.io/en/latest/adria_array_main.html#](https://orfeus.readthedocs.io/en/latest/adria_array_main.html#)), accessed on 25 March 2023). The station's proximity to the eastern Gulf of Corinth [69,70], where a sequence of three major (M \(\geq\) 6.0) earthquakes occurred in 1981, makes this site crucial for the monitoring of seismicity. The carbonate bedrock, where the station is based (Figure 6), comprises dolostones, dolomitic limestones, and limestones of the Upper Triassic (_TRm_) of the Sub-Pelagonian Unit [68], i.e., the same formation as the _MDRA_ seismological station. Figure 5: SRT and MASW (**top**) and ERT (**bottom**) sections at the site of the seismological station _MDRA_. Figure 6: Location of the seismological station VILL and the geophysical measurements along with the geology of the area. The HVSR curves for station _VILL_ (Figure 7) present two types of behavior, due to a replacement in the instrumentation that took place on 7 October 2022. The previous seismometer was a _CMG-40T/30s_ sensor; the new instrument is a _Trillium Horizon/120s_, considered of higher quality and more reliable. For the recordings before 7 October 2022 (old sensor), at higher frequencies (_f_ > 5 Hz) the HVSR seems to gradually drop, with the amplification factor reaching values below unity above 10.0 Hz. This does not occur with the new sensor, which presents a base level of amplification almost at 1.5 up to 12.0 Hz. In the latter case, a high-frequency peak can be distinguished in the HVSR, at \(f\) = 10.4 Hz, with \(A\) = 1.9 \(\pm\) 0.3. We investigated whether this high peak could be an artifact of the specific instrument type, which is also installed on other sites, but there was no evidence that it is a systematic issue. Therefore, it is considered likely that the peak at \(f\) = 10.4 Hz is real and simply could not be identified with the old sensor, which had problems at frequencies above 5.0 Hz. In Figure 8, the results of the geophysical measurements at the site of the VILL seismological station are presented. Concerning the SRT technique, the seismic data processing revealed three seismic layers with velocities \(V_{P1}\) = 900 m/s, \(V_{P2}\) = 1300 m/s, and \(V_{P3}\) > 1700 m/s, with average thickness of 1.0 m and 0.5 m for the first and the second layer, respectively. As mentioned above, the solid bedrock of the seismological station is the Triassic dolostones, which have also been found at the _MDRA_ station. The relatively smaller depth of penetration and the lower value of P-wave velocity in this location is assumed to be caused by the possible karstification of the carbonate rocks present in the area. The  
Figure 7: Average HVSR curves (solid lines) determined for station _VILL_ on different days, from 60 s long windows selected after the application of STA/LTA anti-triggering on 6 h long records. Circles denote the global frequency on each curve, while diamond symbols mark the average of the frequency band denoting the range of peak frequencies of the HVSR lines from the individually selected windows (light/dark gray band in Figure 2b). Squares mark the prominent global and secondary peak frequencies recognized from the HVSR spectra, with error bars indicating the uncertainty of the amplification factor (Table A1).