## 5 Application: Site Amplification Assessments in L'Aquila  
Seismic noise is a highly variable and irregular assemblages of seismic waves (e.g., body waves, surface waves, and their related scattered and diffracted phases). Among them, surface waves (i.e., Rayleigh and Love waves) are considered to be the dominant and most coherent component. From these recordings, consistent and reliable estimates of parameters related to site effects may be retrieved from the analysis of the horizontal-to-vertical (H/V) spectral ratio curve [25] and the Rayleigh wave dispersion curves (e.g., [26; 27]). The great interest that seismologists reserve for these waves is  
Figure 5: Example of output for short-time building measurements (note, this is the Graphical User Interface (GUI) developed for the SIBYL project for the case of the AHEPA hospital in Thessaloniki, Greece. The results may be viewed either on an embedded or external touchscreen). (**a**) Spectra computation to identify the resonance frequencies of the building. (**b**) Interferometry plot to evaluate the shear wave velocity inside the building.  
Figure 6: Earthquake data (11. October 2013 Volvi earthquake) for the east-west (EW), north-south (NS) and vertical (V) components recorded using MEMS sensors installed in a predecessor of the MPwise units (SOSEWIN, see [1]) deployed in the AHEPA hospital at the 4 th floor and the roof.  
mainly justified by the relationship existing between their velocity and the subsoil structure, and, in particular, the S-wave velocity. Hence, considering that Rayleigh waves sample portions of the subsoil at depths proportional to their wavelengths, and that their phase velocities are strongly conditioned by the S-wave velocities of the layers sampled, they are used to deduce information about the subsoil structure, and in particular the local S-wave velocity profile and the so-called V\({}_{\text{s30}}\) (average S-wave velocity in the upper-most 30 m). The local S-wave velocity profile may be found using the Single Value Decomposition (SVD) inversion technique applied to the Rayleigh wave dispersion curves [28]. The H/V curve is obtained by single-station seismic noise recordings, while the V\({}_{\text{S30}}\) is estimated by the effective Rayleigh wave phase velocity corresponding to a wavelength of 40 m.  
The MPwise system is suitable for performing real-time analyses of seismic noise data gathered during seismic array measurements for site assessments. Once the system is deployed in the field, a relatively simple operation where the nodes, equipped with geophones, are distributed across an area (50-100 m across) with varying distances between nodes (3-65 m), the MPwise units create a wireless mesh network, allowing an operator to retrieve in real-time the data from all stations of the network, and to perform the analysis already in the field during the acquisition phase (see Figure 7). Each station in addition continuously and independently stores the data in miniseed ([[http://ds.iris.edu/ds/nodes/dmc/data/formats/miniseed/](http://ds.iris.edu/ds/nodes/dmc/data/formats/miniseed/)]([http://ds.iris.edu/ds/nodes/dmc/data/formats/miniseed/](http://ds.iris.edu/ds/nodes/dmc/data/formats/miniseed/))) format on its SD card.