Time Series Analysis of Acoustic Emissions in the Asinelli Tower during Local Seismic Activity

Abstract

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 κ 1 , 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.

Analysis of Acoustic Emission Activity during Progressive Failure in Heterogeneous Materials: Experimental and Numerical Investigation

“…The behavior indicated through the b-value is coherent with the natural time (NT) results, Figures 5f and 6f, which also present the following auxiliary horizontal lines: κ 1 = 0.070 (dashed red), < D > limit = 10 −2 (dashed green), and entropy limit S u ≈ 0.0966 (dashed blue). The corresponding analysis was performed according to the same methods given in [49], taking the energy component (Q k ) as equal to A max 1.5 , where A max is the maximum amplitude of the signal (in µV), an approach also commonly found in seismology studies [50]. The calculation of the term A max 1.5 was performed hit-by-hit, i.e., every time a new signal was identified, it was included in the NT analysis, leading to the rescaling of the (χ k ,Q k ) time series and the recalculation of κ 1 , S, S rev and < D >.…”

Long-Range Correlations and Natural Time Series Analyses from Acoustic Emission Signals

“…The evolution of natural-time parameters versus normalized time is plotted in Fig- ure 7d. For this analysis, we follow the same reasoning as [47] and [62], taking the energy component (Q k ) as equal to A max,k 1.5 , where A max,k is the maximum amplitude of the signal, an approach commonly found also in seismology studies [63]. Calculation of A max 1.5 (t) (with t denoting the conventional time) was performed hit by hit, i.e., every time a new signal comes up, a new signal is included in the NT analysis, leading to the rescaling of the (χ k , Q k ) time series and the recalculation of κ 1 , S, S rev and D .…”

Long-Range Correlations and Natural Time Series Analyses from Acoustic Emission Signals

“…The evolution of natural-time parameters versus normalized time is plotted in Figure 7d. For this analysis, we follow the same reasoning as [50] and [65], taking the energy component ( A is the maximum amplitude of the signal, an approach commonly found also in seismology studies [66]. Calculation of Results are shown in normalized time for easier identification of the possible entry point to a critical state, that is, the instant when criticality conditions described in section 2.2 [67 -68] are fulfilled.…”