Ultrasound monitoring of applied forcing, material ageing, and catastrophic yield of crustal structures

Abstract

Abstract.A new kind of data analysis is discussed -and a few case histories of actual application are presentedconcerning the physical information attainable by acoustic emission (AE) records in geodynamically active or volcanic areas. The previous analyses of such same kind of observations were reported in several papers appeared in the last few years, and here briefly recalled. They are concerned with the inference of the forcing ("F ") acting on the physical system, and on the ageing ("T ") or fatigue of its "solid" structures. The new analysis here discussed deals with the distinction between a state of applied stress ("hammer regime"), compared to state of "recovery regime" of the system while it seeks a new equilibrium state after having been perturbed. For instance, in the case of a seismic event -and according to some kind of almost intuitive argument -the "hammer regime" is the phenomenon leading to the main shock, while the "recovery regime" deals with the well known aftershocks. Such same intuitive inference, however, can be investigated by a much more formal algorithm, aimed at envisaging the minor changes of the behaviour of the system, during its history and during its present dynamic evolution. As a demonstrative application, detailed consideration is given of AE records -each one lasting for a few years -collected on the Italian peninsula vs. records collected on the Kefallinìa Island (western Greece). Such two areas are well known being characterised by some great comparative difference in their respective tectonic setting. When considering planetary scale phenomena, they appear comparatively very close to each other. Hence, they are likely being presumably affected by similar large-scale external actions, although they ought to be expected to respond in some completely different way. Such facts are clearly manifested by some substantially different AE responses of the local crustal structures. However, a full understanding of such entire set of geodynamic Correspondence to: M. Poscolieri (maurizio.poscolieri@idac.rm.cnr.it) and tectonic details ought to require several year data series of AE records, and/or (maybe) also simultaneous AE records collected within some suitable array of AE stations. Such understanding ought to permit the inference of the spatial features of the crustal stress propagation -including its diagnosis and "forecasting" -in addition to the temporal diagnosis and "prevision" that can be attained by isolated point-like AE recording stations. Additional analyses are in progress.

Structural Ageing of a Cable-Stayed Bridge During Load-Test: The Overall Effect Monitored by Acoustic Emission

“…According to the so-called "hammer effect" (see Gregori et al, 2007), we found that, in the present AE records, the AE release almost always occurs only during the "recovery stage", rather than during the "hammer stage". That is, no AE release occurs while the material is subjected, on an instant basis, to an externally applied stress.…”

“…The criterion used for the definition of the aforementioned threshold began by choosing ten trial values for the threshold, everyone arbitrarily defined as [σ/k] (with k=1, 2,..., 10). The fractal dimension D t (k) was computed on the entire aforementioned subset "S", and for every given k.…”

“…In addition, the "perturbation" by external causes, which may eventually simulate a false behavior, is much better evidenced by means of HF AE compared to LF AE. 10 One additional relevant concern, related to the role of the external trigger, deals with a technological problem, i.e. with the time required by the whole AE recording device to reach its operative regime.…”

“…As far as the methods are concerned, refer toPaparo et al (2002Paparo et al ( , 2006,Gregori et al (2002Gregori et al ( , 2005Gregori et al ( , 2007Gregori et al ( , 2012,Paparo and Gregori (2003),Gregori and Paparo (2004), andPoscolieri et al(2006Poscolieri et al( , 2006a, where several applications are discussed in detail. Other applications are here mentioned passim.…”

Resilience, Vulnerability and Prevention Policies of Territorial Systems in Areas at High Seismic Risk

“…These waves can be detected and recorded by transducers applied to the surface of the structural elements. AE monitoring is performed by means of piezoelectric sensors that give out signals when subjected to a mechanical stress (Gregori et al 2007(Gregori et al , 2012Poscolieri et al 2012). In this way, the AE technique makes it possible to estimate the amount of energy released during the fracture process, to obtain information on the criticality of the process underway and to localize the damage source locations.…”