Seismic record during the “Encores” part of the Bruce Springsteen rock concert at FCB stadium (14/05/2016). (a) North-South component of the horizontal seismic acceleration Trace has been band-pass filtered between 1 and 10 Hz. (b) Corresponding spectrogram. Each song has a specific frequency content showing a fundamental frequency and harmonics. Titles of the songs are included for reference. (c) Particle motion of the horizontal components rotated to N50E/N140E during one of the Encores songs (marked by an arrow in the spectrogram). Each frame corresponds to 4 s. Some seconds after the beginning of the signal the phase shift between the fundamental and 1st harmonic mode results in a PPM following a Lissajous curve.