## 4 Application: Building Measurements and Structural Monitoring in Thessaloniki, Greece  
As shown within the framework of the Strategies and Tools for Real Time EArthquake Risk ReducTion (REAKT; [[http://www.reaktproject.eu/](http://www.reaktproject.eu/)]([http://www.reaktproject.eu/](http://www.reaktproject.eu/))) project, the combination of systems like the MPwise with permanent accelerometric arrays, like that which operates (since May 2012) in the reinforced concrete AHEPA hospital building in Thessaloniki, Greece (this hospital includes two 7-storey blocks, which are joined, but not strongly mechanically coupled, leading to each block responding almost independently of each other to ground motion), as well as temporary networks, makes it possible to evaluate the risk to structures under various earthquake scenarios. For example, measurements of ambient noise data made over even short periods of time may be used to evaluate the dynamic characteristics of a building, namely the natural frequencies (see Figure 5) and mode shapes, making use of such methods as system identification and Operational Modal Analysis, which may be performed by applying both nonparametric and parametric methodologies (e.g., frequency domain decomposition [22], stochastic subspace identification [23]).  
Long-term seismic noise measurements (from both natural and anthropogenic sources) and earthquakes recorded within buildings may be used to develop structural health monitoring techniques to identify a building's structural conditions and fragility using both waveform and vibrational approaches [22]. This can provide, for example, a building's mode shapes, which may be updated and better constrained over time as more observations become available, or when changes in the building's structural behavior becomes apparent as a result of, for example, aging or minor damage arising from seismic events. It also allows predictions of how a building will respond (in terms of potential damage) given a level of ground shaking. The making of such recordings are one of the specific roles that the MPwise units have been designed for.  
Figure 4: Example of output from the Seiscomp3 system implemented within the EEW software module of the MPwise, based on the GFZ-Sentry software developed at the GFZ [5; 6; 7] for the case of the Kyrgyz Republic. Note that this processing and associated images may be produced by a data center computer connected to the recording network, or on the touchscreen embedded in or connected to one of the units themselves (see Figure 1).  
Furthermore, a network made up of MPwise units may be used to develop an operational framework for EEW and rapid post-earthquake damage assessment. For example, Figure 6 shows earthquake data from the 11. October 2013 M4.5 Volvi event ([[http://geofon.gfz-potsdam.de/eqinfo/event.php?id=gfz2013](http://geofon.gfz-potsdam.de/eqinfo/event.php?id=gfz2013) tblu]([http://geofon.gfz-potsdam.de/eqinfo/event.php?id=gfz2013](http://geofon.gfz-potsdam.de/eqinfo/event.php?id=gfz2013) tblu)), recorded by the strong motion sensors deployed in the AHEPA hospital on the 4 th floor and the roof. Such recordings, while potentially useful for structural measurements and EEW purposes, may also be used to investigate other earthquake-engineering issues, such as soil-building interactions (see [24]).