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Ambient seismic noise as an interesting indirect cue for the Cerithidea decollata migrations
Get PDFPresence or absence of water, food availability, capability of avoiding predation, and body temperature are con- stantly changing according to the tidal excursion. In fact, more than the diurnal light-dark variation, tide is shaping the whole intertidal animal life. Therefore, physiological and behavioural systems exist to reduce the stress that the intertidal fauna may face during the unsuitable tidal phase. Cerithidea decollata is a common western Indian Ocean mangrove gastropod. It feeds on the ground at low tide, and climbs the trees two/three hours before the water arrival to avoid submersion. In spite of the irregular East African tidal pattern, it also regularly settles on trunks roughly 40 cm above the maximum level of the incoming tide. Migrations usually take place about twice a day unless at Neap Tide, when snails may remain on the dry ground. Past experiments showed that a biological clock cannot account for water level foreseeing, nor direct visual cues or chemical information from the water itself or from previous migrations have been detected. On the other hand, tidal gravity variations can be felt by the snails. Moreover, other indirect cues could be hypothesize related to a) the oceanic waves reaching the coast and the barrier reef (seismic noise), or b) the changes in ground resistivity (self potential) caused by the sea water moving close. To verify these hypotheses, an integrated geophysical survey (single-station seismic noise and self potential survey) was carried out at Mida Creek (Kenya) to characterize the local seismic wavefield in terms of its amplitude and to measure the temporal variations of the electric potential field. Final goal was to verify whether a correlation exists between the time evolution of these phenomena and the snail movements. Here we present the first results of the seismic noise measurements. Data were acquired by means of a single station all-in-one 3-directional 24-bit digital tromometer equipped with 4.5 Hz geophones. The acquisition run for 11 days (29th June, 2013 - 9th July, 2013). We assumed that the tide transgressions/regressions generate pressure fluctuations on the ground, that are locally transformed into microseismic waves at seafloor propagating inland. Therefore, we evaluated a possible correlation, in terms of decision to climb up or not, between the seismic signals amplitude fluctuations and the snails’ movements. To do so we performed: a) the analysis of the trend of the LF (0.1-2 Hz) and HF (2-60 Hz) seismic noise amplitudes, and b) the comparison of the seismic signals with the height of tide, the number of animals that climbed to the safety level, and the height that they reached during each tide cycle. The study showed an interesting similarity between the time evolution (mean value) of the LF amplitude trend and the animals’ movements. Even thought additional data should be collected to improve the results, it is the first time that a consistent physical cue other than the obvious but discarded ones (visual and chemical), has been identified that could potentially be detected by the snails as well as by other intertidal organisms
Could Ambient Vibrations Be Related to <i>Cerithidea decollate</i> Migration?
No full textPhysiological and behavioral systems exist to reduce the stress that the inter- tidal fauna may face during the unsuitable tidal phase. Cerithidea decollata is a common western Indian Ocean mangrove gastropod. It feeds on the ground at low tide, and climbs the trees two-three hours before the water arrival to avoid submersion. Moreover, it regularly settles on the trunk roughly 40 cen- timeters above the level that the water will reach, in spite of the irregular East African tidal pattern. Migration usually takes place about twice a day unless at Neap Tide, when snails may remain on the dry ground. Biological clock can- not account for water level foreseeing while direct visual cues or chemical in- formation from the water itself or from previous migrations have already been experimentally discarded. Indirect cues could be hypothesize related to the ef- fect of the oceanic wave reaching the coast and the barrier reef (seismic noise), or alternatively related to changes in ground resistivity (self potential) caused by the sea water moving close. To verify these hypotheses a seismic noise and self potential survey was carried out at Mida Creek (Kenya). This paper presents the first results of the seismic noise measurements. A significant cor- relation between the time evolution (mean value) of the low frequency seismic signal, tides, and snails movements has been identified
Seismic monitoring of a rockslide: the Torgiovannetto Quarry (Central Apennines, Italy)
No full textA small-scale seismic network was deployed in the Torgiovannetto quarry (Central Apennines, Italy) from December 2012 to July 2013 to evaluate the possibility of improving the early-warning monitoring network of a rockslide by means of seismic observations. Four seismometers, acquiring data in continuous mode, were set up inside and at the edge of the quarry, with an average inter-station distance of about 100 m. The entire data set (7 months of recording) was analyzed through three different procedures: an STA/LTA (short-time-average /long-time-average) trigger, HVSR (Horizontal to Vertical Spectral Ratio and NCF (Noise-Correlation Function). The data analysis is still in progress. The preliminary data processing related to the identification and classification of recorded signals shows promising results but further refinements of the adopted algorithms are necessary in order to make this technique an helpful early warning tool. Extensive comparison and cross-analysis with parameters independently recorded by the other instruments of the monitoring network are necessary to reach the goals of the study
Seismic response monitoring of the Arno river masonry embankment during the conservation works after the Lungarno Torrigiani riverbank landslide (Florence - May 25, 2016)
Get PDFGeohazards are the most relevant processes that can damage or increase the risk of human beings, properties, critical and transport infrastructures, and environment itself. They also could involve the interruption of human activities. The concepts of disaster risk reduction and disaster risk management involve the development, improvement, and application of policies, strategies, and practices to minimize disaster risks throughout society. Since 1972 (UNESCO Convention) the identification, protection, and preservation of cultural and natural heritage has been recognized to be of outstanding value to humanity, and a key resource to build resilient societies. Nevertheless, world architectural wealth is accumulating damages and heavy losses because of both materials deterioration and exceptional natural or man-made events. The "health" of buildings/structures/infrastructures may be evaluate by its deterioration or damage level. Thus, structure dynamic characterization and microtremor analysis are considered powerful techniques, even thought seismic noise techniques in densely populated area are hardly to carry out because of the background noise due to the human activities. A wide bibliography about buildings/structures/infrastructures seismic dynamic characterization is counterposed to a missing one about their seismic response during conservation/safety works, even thought the seismic vibration monitoring (SVM) is widely used. On May 25, 2016 a riverbank landslide seriously damaged a portion roughly 100 m long of the Lungarno Torrigiani historical masonry embankment wall (left river bank of the Florence urban stretch of the Arno river, between Ponte alle Grazie e Ponte Vecchio). The street next to the embankment wall collapsed, and the earth fill material was fully retained by the embankment wall that did not collapse but seriously deformed towards the Arno river, fracturing itself in three main areas (a cusp roughly in the middle of the damaged wall, where is also concentrated the maximum landslide pressure, and two hinges). In this work we present the results of the SVM carried out during the conservation works. The SVM (sampling frequency 200 Hz) was carried out from August 14 to October 10, 2016 by means of three high gain triaxle velocimeters SS45 (own frequency 4.5 Hz), each one coupled with a SL06 24-bit digitiser, located onto the masonry embankment wall, in the three main fractured areas. The H/V results of the traces acquired to evaluate the resonance frequency of the masonry embankment wall showed that its main resonance frequency was between 4 Hz and 15 Hz, in agreement with the frequency range of roughly 10-meters-high, squat and monolithic structure. Moreover, the maximum peak component particle velocities substantially increased during the roto-percussion piling works, and clearly showed the works advancement. The spectra analysis showed that the NS component, perpendicular to the wall, was the most stressed until the end of the piling works. The SMV indicated that the piling works stressed more the embankment wall section between Ponte alle Grazie hinge and the cusp. Finally, the hinge zones seem to be more sensitive to the vibrations characterized by low-frequency content, while the cusp section (the most damaged one) was more sensitive to vibrations associated with on site works
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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