Acoustic emission and released seismic energy

International audienceIntense crises of crustal stress appear to cross large regions, and to precede by several months the eventual occurrence of some strong earthquake within them. The phenomenon is not linear, and the stress control reflects some wide scale-size rather than local effects. The stress propagation through the crust can be effectively monitored by means of acoustic emission (AE) techniques (ultrasounds). The correlation is here investigated between crustal stress crises and the total release of seismic energy within some space domain around the AE recording site. Some clear inferences can be envisaged, although a significant diagnosis of the state of the crust within a given region ought to request arrays of simultaneously operated AE recorders. Some case histories are described dealing with the Italian peninsula and with the Cephallonia Island

Dinâmica espaço-temporal de Rhopalosiphum padi e disseminação de BYDV-PAV - calibração do modelo ABISM utilizando microparcelas.

Orientador: José Maurício Cunha Fernandes

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

International audienceA new kind of data analysis is discussed ? and a few case histories of actual application are presented ? concerning 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 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

Dinâmica espaço-temporal de Rhopalosiphum padi e disseminação de BYDV-PAV.

Orientador: Douglas Lau

Crustal deformation and <i>AE</i> monitoring: annual variation and stress-soliton propagation

International audienceThe stress propagation through the crust can be effectively monitored by means of acoustic mission (AE) techniques (ultrasounds). The \textit{AE} intensity is indicative of the amount of stress that affects some lithospheric and/or crustal slab of some (ultimately unknown) scale size. In principle, such scale size can be different in different areas, as it depends on their respective tectonic setting, by which a variety of prime causes ought to be considered: every cause can eventually prevail over others. Two basic phenomena are here reported. If the crust behaves like a comparatively ideal elastic body, an annual variation is observed, which appears in-phase and correlated, when comparing AE records collected at the Italian site and on the Cephallonia Island. It seems being astronomically modulated, hence it should display a planetary scale. One likely explanation is in terms of the loading tide. Such interpretation can be confirmed by some additional modelling and analysis upon considering the motion of the Sun and of the Moon. A second observed effect refers to the case in which the crust feels the effect of the fatigue that reduces its elastic performance. The phenomenon can be described in terms of stress solitons that cross the area being monitored. They can be unambiguously recognised, and the possibility is therefore envisaged of eventually using them for measuring the propagation speed of stress through the crust over continental or planetary scales. The residuals, with respect to such regularly recognisable effects, of the recorded AE signals are to be investigated in a few subsequent analyses (in progress), as they appear to contain additional relevant physical information, still being much different from any simple random noise. A final recommendation ought therefore to be stressed, for setting up some array of at least a few AE recording stations to be simultaneously operated over some continental scale area and for a few years at least. Their potential applications still appear much promising and to be still focused in their complete, specific, operative and physical details and interpretation

A new experimental snow avalanche test site at Seehore peak in Aosta Valley (NW Italian Alps) - Part II: Engineering aspects

The estimate of the effects produced by the impact of a snow avalanche against an obstacle is of the utmost importance in designing safe mountain constructions. For this purpose, an ad-hoc instrumented obstacle was designed and built in order to measure impact forces of small and medium snow avalanches at Seehore peak (NW Italian Alps). The structural design had to consider several specific and unusual demands dictated by the difficult environment. In this article, the new test facility is described from the engineering point of view, discussing the most important aspects of the analyzed problems which were solved before and after the construction. The performance of the instrumented obstacle in the first two operating seasons, and some proposals for future upgrading are eventually illustrate

Search for strange quark matter and Q-balls with the SLIM experiment

We report on the search for Strange Quark Matter (SQM) and charged Q-balls with the SLIM experiment at the Chacaltaya High Altitude Laboratory (5230 m a.s.l.) from 2001 to 2005. The SLIM experiment was a 427 m$^{2}$ array of Nuclear Track Detectors (NTDs) arranged in modules of $24 \times 24$ cm$^{2}$ area. SLIM NTDs were exposed to the cosmic radiation for 4.22 years after which they were brought back to the Bologna Laboratory where they were etched and analyzed. We estimate the properties and energy losses in matter of nuclearites (large SQM nuggets), strangelets (small charged SQM nuggets) and Q-balls; and discuss their detection with the SLIM experiment. The flux upper limits in the CR of such downgoing particles are at the level of $1.3 10^{-15}$/cm$^{2}$/s/sr (90% CL).Comment: 4 pages, 7 eps figures. Talk given at the 24th International Conference on Nuclear Tracks in Solids, Bologna, Italy, 1-5 September 200