Structural change detection applying long-term seismic interferometry by deconvolution method to a modern civil engineering structure (New Zealand)

Pulse-wave propagation velocity and resonance frequency measured in civil engineering structures are both related to structural design. Monitoring their variation following seismic strong shaking provides information about the immediate building capacity. Joint-interpretation of frequency and velocity variation requires a better understanding of the processes controlling seismic structural health. In this study, we analysed 8 years of earthquake data recorded by the vertical array installed in the Te Puni building in Wellington, New Zealand, as part of the GeoNet building instrumentation programme. Co-seismic variations of pulse wave velocity and fundamental frequency are analysed and interpreted through a Timoshenko beam-like building model. This study shows that even though no structural damage was visually reported over the considered time of monitoring, co- and post-seismic variation of both parameters' values are observed for almost all earthquakes, including a permanent shift following strong ground shaking. Variations of pulse-wave velocity and resonance frequency are cross-interpreted in terms of the building model. They reflect a time variant building response, correlated with the seismic loading. In addition, time delay of the pulse-wave velocity as a function of the building height provides relevant information on the location of the changes and confirms the efficient cross-interpretation of both methods for seismic Structural Health monitoring.