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

Relations between morphological settings and vegetation covers in a medium relief landscape of Central Italy

Morphometric units and vegetation classes were determined by applying two classification methods to the Soratte Mount area, a medium relief structure within the Italian Latium region. The study aims at defining the relationships between vegetation and landform types and highlighting the main morphological characteristics within examined land cover classes. These were the result of the application of a supervised classification method to the first 28 (VIS-NIR) bands of the airborne MIVIS data collected within an extensive survey campaign over Rome Province. The analysis was supported by photo-interpretation of peculiar MIVIS band combinations and by data acquired during field surveys and from a pre-existing vegetation map. The morphometric data were obtained by processing a raster DEM created from topographic maps. These data were processed by means of a new morphometric classification method based on the statistical multivariate investigation of local topographic gradients, calculated along the 8 azimuth directions of each pixel neighbourhood. Such approach quickly estimates the spatial distribution of different types of homogeneous terrain units, emphasizing the impact of erosional and tectonic processes on the overall relief. Mutual relations between morphometric units and vegetation types were assessed by performing a correspondence analysis between the results of the two classifications

Relations between morphological settings and vegetation covers in a medium relief landscape of Central Italy

Mount area, a medium relief structure within the Italian Latium region. The study aims at defining the relationships between vegetation and landform types and highlighting the main morphological characteristics within examined land cover classes. These were the result of the application of a supervised classification method to the first 28 (VISNIR) bands of the airborne MIVIS data collected within an extensive survey campaign over Rome Province. The analysis was supported by photo-interpretation of peculiar MIVIS band combinations and by data acquired during field surveys and from a pre-existing vegetation map. The morphometric data were obtained by processing a raster DEM created from topographic maps. These data were processed by means of a new morphometric classification method based on the statistical multivariate investigation of local topographic gradients, calculated along the 8 azimuth directions of each pixel neighbourhood. Such approach quickly estimates the spatial distribution of different types of homogeneous terrain units, emphasizing the impact of erosional and tectonic processes on the overall relief. Mutual relations between morphometric units and vegetation types were assessed by performing a correspondence analysis between the results of the two classifications

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

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

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

The stress propagation through the crust can be effectively monitored by means of acoustic mission (AE) techniques (ultrasounds). The extit{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

Relations between morphological settings and vegetation covers in a medium relief landscape of Central Italy

Morphometric units and vegetation classes were determined by applying two classification methods to the Soratte Mount area, a medium relief structure within the Italian Latium region. The study aims at defining the relationships between vegetation and landform types and highlighting the main morphological characteristics within examined land cover classes. These were the result of the application of a supervised classification method to the first 28 (VIS-NIR) bands of the airborne MIVIS data collected within an extensive survey campaign over Rome Province. The analysis was supported by photo-interpretation of peculiar MIVIS band combinations and by data acquired during field surveys and from a pre-existing vegetation map. The morphometric data were obtained by processing a raster DEM created from topographic maps. These data were processed by means of a new morphometric classification method based on the statistical multivariate investigation of local topographic gradients, calculated along the 8 azimuth directions of each pixel neighbourhood. Such approach quickly estimates the spatial distribution of different types of homogeneous terrain units, emphasizing the impact of erosional and tectonic processes on the overall relief. Mutual relations between morphometric units and vegetation types were assessed by performing a correspondence analysis between the results of the two classifications

Morpho-Structural Comparison of Latin American Volcanoes.

The geomorphometric classifications of local topographic gradients of two groups of Andean volcanoes situated in the Andes Cordillera are introduced and compared. Input data are eight topographic gradients obtained by processing each volcano raster Digital Elevation Models extracted from ASTER stereo-pairs. Based on these data, the pixels have been classified into 17 classes through a clustering procedure applied to coordinates resulting from Principal Component Analysis. The resulting thematic colour maps show the spatial distribution of homogeneous landform units, highlighting the impact of erosional and tectonic processes on the whole relieves. The comparison of the corresponding classes of the different volcanoes may be interpreted as similarity among the volcanoes

Comparison of three Andean volcanic complexes through Multidimensional Analyses of geomorphometric data

The geomorphometric classifications of local topographic gradients for three volcanoes situated in the Andes Cordillera, Parinacota, Socompa, and Tata Sabaya, are introduced and compared.. Input data are eight topographic l gradients obtained by processing raster Digital Elevation Models extracted from ASTER stereo-pairs. Based on these data, the pixels have been classified through a clustering procedure applied to coordinates resulting from Principal Component Analysis. The resulting thematic colour maps show the spatial distribution of homogeneous landform units, highlighting the impact of erosional and tectonic processes on the whole reliefs. Moreover, each class is described by both mean gradient values and mean topographic attributes such as elevation, slope and aspect. An unexpected result concerns the high similarity among the three volcanoes concerning the classes of pixels oriented toward SE, S, and SW: this suggests some common trigger phenomenon

Earlier appraisal of seismic and volcanic events by means of recurrence quantification analysis of AE time-series: preliminary results

Recurrence Quantification Analysis (RQA) appears one of most promising non linear time series techniques for the analysis of complex systems [1]. Recently, it has been applied to investigate acoustic emissions from both rocky samples [2] and complex seismic processes dynamics [3]. Friction induced vibrations may occur whenever two objects, once put in contact, slide with respect to each other. Typical examples are active faults inside seismogenic zones, train wheels running along tight curves with their narrow-banded noise, friction in bearings, and events at microscopic scale in molecular physics. Within this context, the application of RQA to Passive Acoustic Emission (AE) signals released, at ultrasonic frequencies, by stressed rocks in the Earth’s crust beyond a specific threshold (event) is presented. The data records are constituted by AE time-series collected nearby active tectonic and volcanic sites in Italy, Greece and Argentina. The AE data were gathered, with 30 sec of sampling rate, by piezoelectric transducers, operating at two ultrasonic frequencies (typically 25 and 150 kHz), fixed to a rock [4, 5, 6]. Usually, the data set is very huge and the AE signal amplitude changes with to the acoustic impedance, associated with local rock stress conditions and particularly sensitive to fracture density and water content. The evolution features of the quiescence and activation status of the crustal structure is examined by applying the RQA method to the AE time-series focusing on characteristic recurrence patterns, disregarding the signal amplitude. RQA is a quite simple processing method which considers few parameters describing the whole complexity of a signal. The RQA parameters are simply reckoned from the so-called “Recurrence Plot” [7] and are used to monitor quantitative changes in dynamics of temporal distribution [2], loss of synchronization of dynamic mechanism or spatial irregularities occurring along time [8]. In particular, this work aims at defining few descriptors that are able to explain the main characteristics of the AE signals and identifying anomalies to be related to crustal stress modifications or paroxysmal volcanic activities in the monitored seismic and volcanic areas [4,5]