Time series analysis of acoustic emissions in the Asinelli Tower during local seismic activity

The existence of ongoing damage processes in a masonry wall of the Asinelli Tower in Bologna have been investigated by the acoustic emission (AE) technique. A time correlation between the AE activity in the monitored structural element and the nearby earthquakes has been observed. In particular, the largest cluster of AE signals has been recorded within a few hours after the main shock (4.1 magnitude) occurrence. The presented findings suggest that aging and deterioration of the monitored structural element significantly depend on the action of light earthquakes, even at considerable distance. Trends of two evolutionary parameters, the b-value and the natural time variance k1, have been derived from the AE time series in order to identify the approach of the monitored structural element to a “critical state” in relation to the earthquake occurrence.