1,721,162 research outputs found
Time variation of spectral and wavefield features of volcanic tremor at Mt. Etna (January-June 1999)
No full textMulti-disciplinary Approach to the Study of the Pernicana Fault System, Mt. Etna, Sicily: Integration of Structural, Geodetic and Seismological Data
No full textThis contribution investigates the Pernicana Fault System (PFS), a seismogenic structure that dissects Mt. Etna (Sicily). The study was carried out through a multidisciplinary approach based on integration of structural, geodetic and seismological data, with the aim to
produce a consistent model for this complex sector of the volcano edifice. The PFS is a W-E trending fault array, organized into
segments arranged en-échelon, and displays a dominantly left lateral component of strike-slip. From West to East it joins the NE-Rift (1900 m a.s.l.), crossing Piano Provenzana and Piano Pernicana, and reaches Rocca Pignatello (1050 m a.s.l.) and Rocca Campana (900 m a.s.l.) where the fault branches out SE-wards into two fault segments. The former shows a roughly N105°E orientation from Rocca Pignatello to Rocca Campana, where the fault rotates to N090°E and terminates without morphological evidence; the latter propagates downhill from Rocca Campana with a roughly N120°E orientation. During the 2002-03 Mt. Etna eruption, an intense ground-fracturing phenomenon affected the entire NE flank, allowing to identify the development of the N120°E fault segment and to trace it down to the Ionian coast. The work has been carried out with different approaches: structural analysis, to identify the kinematics and geometry of the fault system through the study of well-recognized structural marker; seismology, based on the analysis of focal mechanisms in order to unravel the dynamics of the system, and space geodesy, in order to infer the recent ground motions due to slip along the PFS. Three main segments are recognised within the PFS: a western, a central and an eastern segment. The western and eastern segments indicate dominantly transtensional kinematics, with both important normal and strike-slip displacements, whereas the central segment best illustrates the effects of the strike-slip component. This segment was monitored with local networks based on GPS techniques since early 1997. GPS data indicate daily displacement vectors up to 50 cm as recorded during the first days of the 2002-03 eruptive event of the Mt. Etna volcano. These data collectively indicate a sliding towards SE of the southern block identified by the PFS.
The analysis of focal mechanisms is in general agreement with data inferred from structural analysis and GPS techniques, indicating a good kinematic and dynamic consistency. The eastern segment of the PFS is characterised by a low seismic activity and by the lack of
recent earthquakes, therefore outlining that this part of the PFS is dominated by aseismic creep
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe 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
Volcanic tremor at Mt. Etna: Inferences on magma dynamics during effusive and explosive activity
No full textDuring 1999, the volcanic activity at Mt. Etna was both explosive and effusive at the summit craters:
Strombolian activity, lava fountains and lava flows affected different areas of the volcano, involving three of
the four summit craters. Results from analysis of the 1999 volcanic tremor features are shown at two
different time scales. First, the long-term time variation of the features of the volcanic tremor (including
spectral and polarization parameters), during the entire year, was compared with the evolution of the
eruptive activity. This approach demonstrated the good agreement between tremor data and observed
eruptive activity; the activation of different tremor sources was suggested. Then, a more refined analysis of
the volcanic tremor, recorded during 14 lava fountain eruptions, was performed. In particular, a shift of the
dominant frequencies towards lower values was noted which corresponds with increasing explosive activity.
Similar behaviour in the frequency content has already been observed in other explosive eruptions at Mt.
Etna as well as on other volcanoes. This behaviour has been explained in terms of either an increase in the
tremor source dimension or a decrease in the sound speed in the magma within the conduit. These results
confirm that the volcanic tremor is a powerful tool for better understanding the physical processes
controlling explosive eruptions at Mt. Etna volcano.Published19-311.4. TTC - Sorveglianza sismologica delle aree vulcaniche attiveJCR Journalreserve
Variations on the Author
Full text link“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
Full text linkWe 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
High precision locations of multiplets on south-eastern flank of Mt. Etna (Italy): reconstruction of fault plane geometry
No full textOn 9, January 2001 a seismic swarm, located on the south-eastern flank of Mt. Etna and with nearly identical waveforms, caused some damage to Zafferana Etnea village, 3 km from the epicentral area.
An analysis of the seismicity occurring in the last 8 years in this area has revealed other earthquakes with the same characteristics; some pre-empted and followed (up to a few months) the 2001 January swarm, others were recorded more than five years beforehand.
Using similarity of waveforms, these earthquakes were classified into three families.
The use of a multiplet-technique has allowed to obtain the spatial distribution of the events with higher precision (mean error of 10-20 meters) with respect to traditional localization techniques.
Mt. Etna earthquakes relocation clearly describes the geometry of the seismogenic tectonic structure; the hypocenters lie on a NE-SW oriented plane that is coincident with one of the focal planes obtained by first-arrival polarities. This alignment is also coherent with one of the main regional tectonic trends cutting the Mt. Etna area, and can be interpreted as a right-lateral strike seismic source on the south-eastern flank of Mt. Etna, distant from eruptive centres, which repeats from time to time and is able to produce strong energy releases.Published281-2893.6. Fisica del vulcanismoJCR Journalreserve
High precision locations of multiplets on south-eastern flank of Mt. Etna (Italy): reconstruction of fault plane geometry
No full textOn 9, January 2001 a seismic swarm, located on the south-eastern flank of Mt. Etna and with nearly identical waveforms, caused some damage to Zafferana Etnea village, 3 km from the epicentral area.
An analysis of the seismicity occurring in the last 8 years in this area has revealed other earthquakes with the same characteristics; some pre-empted and followed (up to a few months) the 2001 January swarm, others were recorded more than five years beforehand.
Using similarity of waveforms, these earthquakes were classified into three families.
The use of a multiplet-technique has allowed to obtain the spatial distribution of the events with higher precision (mean error of 10-20 meters) with respect to traditional localization techniques.
Mt. Etna earthquakes relocation clearly describes the geometry of the seismogenic tectonic structure; the hypocenters lie on a NE-SW oriented plane that is coincident with one of the focal planes obtained by first-arrival polarities. This alignment is also coherent with one of the main regional tectonic trends cutting the Mt. Etna area, and can be interpreted as a right-lateral strike seismic source on the south-eastern flank of Mt. Etna, distant from eruptive centres, which repeats from time to time and is able to produce strong energy releases.Published281-2893.6. Fisica del vulcanismoJCR Journalreserve
Low frequency events at Mt. Etna: some problems and open questions
No full textA short period seismic array setting at Mt. Etna symmetrically in regard to the fracture of the 1991-1993 eruption allowed an analysis of low frequency events which occurred in the first phase of the mentioned eruption. We recorded about 50 events, 19 of them belong to a family. They show very low amplitude values and spectral peaks ranging 0.5-4.5 Hz. The evidence of this family of events shows how the process driving the dynamics of the fluid in the volcano is often the same.JCR Journalope
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