1,721,274 research outputs found
THE SEISMIC SIGNATURES OF THE VOLCANIC CRISES: A REVIEW
No full textVolcano seismology is considered a good proxy of the internal conditions of the
volcanic systems. In particular, the volcanic crises are anticipated by a loading process
triggered by an overall upward magma migration inducing gas exsolution and
stress build up within the feeding system and the hosting rocks. This process activates
brittle failures within the volcanic edifice and pressurized magmatic fluids flowing
through magma-filled cavities, generating the two end-members of the volcano
seismicity: Volcano-Tectonic and Long-Period events, respectively. Volcano seismicity
follows the disequilibrium conditions within the plumbing system preceding and
accompanying the volcanic crises, exhibiting modifications of the source process in
respect to the inter-eruptive phase in terms of wavefield properties and statistics of the
earthquake occurrence. Although some common correlations between seismic activity
and magma dynamics during the eruptive crises have been identified, a wide variability
of behaviors appears as well, with a sharp dependence on the volcano and on the
eruptive episode.
Here I critically review the characteristics of the volcano seismicity before and
during the volcanic crises, describing the source process of the volcanic earthquakes
in terms of both the seismologic parameters and the statistical properties of the point
process ruling their occurrence times and magnitude
Wavefield analysis of the background seismic signal recorded at Volcàn de Colima, Mexico
No full text
Wavefield decomposition and phase space dynamics of the seismic noise at Volcan de Colima, Mexico: evidence of a two-state source process
No full textWe analyse the seismic noise recorded at the Colima
Volcano (Mexico) in the period December 2005–May
2006 by four broadband three-component seismic stations.
Specifically, we characterize the spectral content of the signal and follow its time evolution along all the data set. Moreover, we infer the properties of the attractor in the phase space by false nearest neighbours analysis and Grassberger–Procaccia algorithm, and adopt a time-domain decomposition method (independent component analysis) to find the basic constituents (independent components) of the system.
Constraints on the seismic wavefield are inferred by the polarization analysis.We find two states of the background seismicity visible in different time-intervals that are Phase A and Phase B. Phase A has a spectrum with two peaks at 0.15 Hz
and 0.3 Hz, with the latter dominating, an attractor of correlation dimension close to 3, three quasi-monochromatic independent components, and a relevant fraction of craterpointing
polarization solutions in the near-field. In Phase B,
the spectrum is preserved but with the highest peak at
0.15 Hz, the attractor has a correlation dimension close to
2, two independent components are extracted, and the polarization solutions are dominated by Rayleigh waves incoming from the southwest direction. We depict two sources acting on the background seismicity that are the microseismic noise
loading on the Pacific coastline and a low-energy volcanic tremor. A change in the amplitude of the microseismic noise
can induce the switching from a state of the system to the
other
Backprojection of the high-frequency radiation released during the Pisagua (Chile) earthquake (01/04/2014, Mw 8.1) and the Iquique aftershock (03/04/2014, Mw 7.6)
No full textNorthern Chile has recently been struck by the Mw 8.1 Pisagua earthquake, which occurred
on 01/04/2014 and partially filled the Iquique seismic gap. The Pisagua earthquake has been
preceded by intense foreshock activity which started in July 2013 and culminated in a cluster
of events in March 2014. We have inferred the rupture dynamics of the mainshock and of its
largest (Iquique) aftershock (03/04/2014, Mw 7.6) by backprojecting the high-frequency
seismic radiation released during the events and recorded by 310 stations of USArray.
The time-evolution of the high-frequency (1-4 Hz) energy radiated during the
mainshock shows that the rupture lasted about 80 s, with most of the energy released
between 25 s and 50 s from the onset. The cumulative energy emitted during the whole
rupture process mainly originated downdip the epicenter just off the coast line, approximately
in the latitude range 19.5°-20°S. This region falls at the down-dip side of the co-seismic slip
area, similarly to the case of the Maule earthquake (South Chile, 27/02/2010, Mw 8.8) and of
other large earthquakes. Differently from the Maule case, most aftershocks not located in the
area of large seismic radiation. The time-evolution of the coherent seismic radiation displays
an initial low-energy phase (lasting about 20s) during which the source starts to migrate from
the nucleation point at the epicenter towards the south-east, activating deeper parts of the
subduction interface. After reaching points close to the coast line (after ~30s from the onset),
the source moves back towards the epicenter mainly activating in sequence two patches of
the interface located around 20°S,70.5°W (F1) and 19.7°S,70.2°W (F2), shortly followed by
the activation of points close to the area of the largest co-seismic slip (F3). In the last ~15s of
the fracturing (F4), the re-activation of the area releasing energy during F2 is observed. Thus,
despite the simple bullseye co-seismic slip pattern, the history of energy radiation is quite
scattered, suggesting peculiar and sharply site-dependent frictional properties along this
segment of the Chilean subduction interface.
The Mw7.6 aftershock displays a similar time-evolution of the radiating source, with an
initial low-energy stage, during which the rupture front migrates from the epicenter towards
deeper zones. Most energy is released about 25s from the onset, when the rupture front
reaches points around 20.5°S,70.0°W
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
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
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