In forced vibration testing, a vibration generator bolted to one of the top floors excites the building with a known sinusoidal force. Sweeping the frequency of the vibration generator, steady-state structural responses are recorded at each operated frequency by accelerometers deployed throughout the building. Dynamic properties of the structural system are then identified from acceleration-frequency response curves by using well-established methods in the structural dynamics area, which do not require sophisticated system identification algorithms. Its drawbacks; however, have long made ambient vibration testing an attractive alternative. This study uses the ambient vibrations recorded following the forced vibration test of a four-story reinforced concrete school building with two basement floors, which is the first permanently instrumented building in Turkey and in close proximity to the North Anatolian Fault, to determine its natural vibration frequencies, modal damping capacities, and natural vibration modes. System identification using frequency domain decomposition methods yields structural system dynamic properties that are comparable to the forced vibration test results. Ambient vibration testing will be used as an alternative when building owners do not permit forced vibration testing of their buildings. The identified structural system dynamic properties will be used in calibrating the finite element structural models of the instrumented buildings in earthquake prone areas of Europe as part of a European Union project, which ultimately aims to assess their seismic fragilities.