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Morphotectonic Analysis of the Neotectonic and Active Faults of Viotia (Central Greece), using Geographic Information Systems (GIS)
No full textThe Greek Database of Seismogenic Sources: seismotectonic implications for North Greece
No full textAlthough Greece and the broader Aegean Region belong to the most tectonically and seismically active places in the world, a GIS-based database of seismogenic sources was lacking. Data and information concerning the occurrence and behaviour of numerous active faults are usually scattered or hidden in the rich literature, making their acquirement a hard and time-consuming task. On the other hand, such data and information are useful for several purposes: SHA (and especially probabilistic SHA), geodynamic models and seismotectonic interpretations are some of the disciplines for which such a database can be an irreplaceable tool.
The core of this research is the development of GreDaSS which was started from North Greece as a pilot area. The compilation procedure includes several stages. The first stage is the recognition of a seismogenic source and the collection of its respective available data and information. The synthesis, critical analysis and homogenization of the collected material follows, in order to define the principal seismotectonic parameters, to plot the source in a geographic coordinate system according to its geometric attributes and to fill in all the corresponding informational fields (comments, open questions, summaries, pictures and references). The final stage includes a processing of all informational levels in order to be linked and interactive. This procedure was followed for 38 CSSs and 58 ISSs that belong to the study area (North Greece). However, some of those steps were followed for the rest sources of the broader Aegean Region in the frame of the SHARE project.
During the parameterization process, an important issue came up: given that the majority of the seismogenic sources in Greece is not connected with recently (historically or instrumentally) recorded earthquakes – which is the more hazardous case, the only data to rely on are the ones based on cumulative effects-based investigations (or generally characterized as geological investigations). On the other hand, investigations based on single-event effects (having the seismological investigations as the most prevailing method) sometimes provide wrong information especially when it is about old events. The comparison of these two different approaches is important to define the reliability of the provided data and information. Based on four characteristic case studies which all involve a major earthquake covering a wide period of the historical and instrumental era, it is shown that i) the single-event effects-based investigations provide improved results as technology advances, and ii) the cumulative effects-based investigations steadily provide reliable results regardless if the seismogenic source is associated with recent earthquakes or not.
Another important matter that emerged during parameterization is the determination of two important SHA parameters: the maximum fault depth and the slip rate. Defining the maximum fault depth is important because the faults dimensions can be constrained and hence its maximum expected magnitude. For crustal faults, maximum depth is limited within the seismogenic layer, which can be defined by the brittle-ductile transition zone (BDT). Although it is not necessary that a fault will rupture the entire thickness of the seismogenic layer, by estimating the depth of the BDT we can set the maximum depth which a possible rupture can reach. The estimation of the BDT depth relies on the calculation of the strength profiles that reflect the mechanical behaviour of the upper lithosphere. In the current dissertation, the rheological models of three different areas are compared and calibrated based on the local seismic distribution. Since temperature is the key-factor of lithospheric strength, the geothermal gradients are also calculated. However, in the radiogenic heat productive crust, the geotherm equations depend on some thermophysical parameters. For this reason several sensitivity tests were run for various compositions of the upper and lower crust which allowed distinguishing two relative thermal conditions of the crust: the cool and warm crust. Based on these tests and on rheological modelling, the BDT depth of the three case studies is calculated and it is compared with the available seismic distributions. The results are in good match and verify the rheological models of each case study, giving confidence for further application in the surrounding areas.
The calculation of the slip rate is based on the geodetic strain rate field that derives from GPS measurements. Given that GPS measurements span only few decades, short-term slip rate is actually calculated by this method. The theoretical approach relies on the fact that the deformation between two GPS stations that move relatively to each other is not uniform, but it is concentrated within a zone around the fault plane. During a seismic event, most of the so far accumulated elastic strain is suddenly released on the fault plane and transformed into relative slip, leaving a small, practically neglectful, amount of plastic deformation. The calculation process is based on a series of strain fundamental formulas that can provide the two slip rate components: the strike-slip component and heave which provides the dip-slip component. The obtained results derive from three different datasets that provide either the principal strain axes, or dilatation and maximum shear strain. The patterns coming from the three results are quite similar, although some differences exist in their absolute values. The geodetically calculated slip rates are also compared with the ones found in the literature (wherever these are available), which are basically obtained by geological methods. The comparison suggests that the former not only show reasonable values, but they are of the same order of magnitude. The usually lower values of the geodetic slip rates can be explained by the facts that GPS stations measure velocities during a very short period of a seismic cycle, and that strain accumulation is not necessarily linear with time, so it could be wrong to infer that its rate is steady. It is important to mention that during the calculation process rake is also calculated as a collateral result.
The completeness of GreDaSS for North Greece, including all seismogenic sources that are known so far, allowed the separation of the area into five sectors, each documenting an internal uniform behaviour. Moreover, the pattern, geometry and the geodynamic setting of some regions imply the presence of low-angle normal (detachment) faults defining a seismogenic volume in which faults’ behaviour can change significantly (fault interaction, random rupture path, etc.). Nevertheless, beyond these qualitative observations, the database can offer several other applications especially for the enhancement of SHA. Two examples are given in this thesis. The first one concerns the improvement of the seismic zonation map of Greece by introducing a new seismogenic zonation map. Until now, seismic zonation of Greece was based only on seismological data. This method produces several inconsistencies with major seismotectonic features in the Aegean. The proposed seismogenic zonation map of this thesis relies on other geological criteria and especially the seismogenic sources of GreDaSS. However, the best solution would be a map that would take into account both geological and seismological criteria. The second application example involves earthquake triggering scenarios that are based on Coulomb stress transfer. The Volos and Nea Anchialos ISSs, both lying in the Pagasitikos Gulf, are selected as a case study. Each fault is responsible for one of the two strongest shocks of the 1980 Volos earthquake sequence. Coulomb stress change models based on the seismogenic sources of GreDaSS suggest that earthquake triggering between these two ISSs is a possible scenario.
Concluding, the development and the state-of-the-art of GreDaSS for North Greece are presented in this dissertation, along with the calculation of two basic parameters, the observation of some seismotectonic features and the usage of the database as a SHA tool. It is important to mention though, that the database is always updatable, which means that whenever new data and information are available these will be included in GreDaSS
The Greek database of seismogenic sources (GreDaSS): State-of-the-art for northern greece
No full textThe Greek Database of Seismogenic Sources (GreDaSS) is a repository
of geological, tectonic and active-fault data for the Greek territory and its
surroundings. In this report, we present the state-of-the-art of an on-going
project devoted to the building of the GreDaSS, which represents the results
of decades of investigations by the authors and a myriad of other researchers
working on the active tectonics of the broader Aegean Region.
The principal aim of this international project is to create a homogeneous
framework of all of the data relevant to the seismotectonics, and especially
the seismic hazard assessment, of Greece and its surroundings, as
well as to provide a common research platform for performing seismic hazard
analyses, modeling and scenarios from specific seismogenic structures.
In particular, we introduce and synthetically describe the results obtained
(and included in the database) to date in the northern sector of continental
Greece and the Aegean Sea. As a first step we collected all available
(both published and unpublished) historical and instrumental seismicity
data relevant to the determining of the causative faults. Following the experience
of recent 'surprising' earthquakes (e.g. 1995 Kozani, and 1999
Athens), we realized the deficiency of such an approach, and decided to
also include in the GreDaSS active faults (i.e. seismogenic sources) recognized
on the basis of geological, structural, morphotectonic, paleoseismological
and geophysical investigations. A second step is the critical
analysis of all of the collected data for the extraction of the necessary seismotectonic
information, enabling the recognition of as many seismogenic
sources as possible, as well as their characterization and parameterization.
The most updated version of the database consists of numerous seismogenic
sources that are categorized into three types: composite,
individual, and debated. In this report, we describe the major seismotectonic
properties of all of the composite seismogenic sources and individual
seismogenic sources in northern Greece, which imply the partitioning
of the area into five sectors that show similar internal behavior. Northern
Greece was chosen as a pilot area because the parameters and accompanied
metadata of its seismogenic sources show a high level of confidence
and completeness. The amount of information and the degree of uncertainty
is different for the three types
The Atalanti active fault: Re-evaluation using new geological data
No full textThe Northern Gulf of Evoia is a region with an intense neotectonic activity, dominated by characteristic and impressive active faults. The only fault in the region which is connected with a strong historical earthquake, is the Atalanti fault, with the well-known earthquake sequence of 1894. For an accurate mapping of the fault trace, the 1894 surface ruptures investigation and the estimation of the area’s seismic hazard, there has been made a detailed geological – neotectonic investigation of the Atalanti city area. The results of this investigation show that the Atalanti fault comprises a 20-30km long fault zone, divided in at least 4 segments: Atalanti, Kiparissi-Almyra, Tragana-Proskyna, Martino and possibly Larymna segment. The maximum earthquake magnitude is estimated in Msmax=6.8, and the recurrence interval, concerning the same magnitude, for Atalanti fault is larger than 1000 years, possibly even more than 2000 years. Paleoseismological trenching in Agios Konstantinos area excludes the connection of this fault with the earthquake sequence of 1894
Palaeoseismological study of the eastern branch of Heliki fault (Corinthian gulf)
No full textPaleoseismological analysis based on seismological data enable us to understand the recent seismic history of the Eliki fault. Along the eastern "segment (or strand)" scarp 5 trenches have been excavated (8x5x2m), their walls were mapped in scale 1:20 and further analyzed by precise tectono-stratigraphic methodology. The Kerynitis river, which crsses the Eliki fault from S to N and supplies the alluvial plain, has subsided at a rate of 1.4mm/yr. The river was running from west to east, resulting the fluvial conglomerates in the trenches, which have buried under the colluvial sediments. Based on colluvium stratigraphy, displacement of distinct horizons, deposition of sedimentary layers and C14 dating, faulting events have been identified affecting unconsolidated sediments in the trench. The penultimate 373 BC event and the two younger events with a throw of 0.93m and 1.37m respectively, the third event, with a throw of 0.44m, suggest a variable seismic history
Possible occurrence of low-angle normal faults in Central and Northern Greece
No full textDuring the elaboration of the Greek Database of Seismogenic Sources (Gre.Da.SS) (Pavlides et al., 2010; Sboras et al., 2009) many active faults of Central and Northern Greece were analysed in detail either from literature sources or new field data in order to reassess their principal seismotectonic parameters. Based on the great amount of information gathered for the database and especially on its good uniformity, in different and distinct areas of central and northern Greece it is possible to observe fault systems very similar in terms of geological setting and structural pattern. For these crustal volumes, the collected data suggest the occurrence of parallel synthetic, and sometimes antithetic, faults merging at depth on low-angle fault planes. The fault geometry, kinematics and tectonic evolution of these regions were compared with the well-known (and widely accepted) detachment fault zone characterising the Gulf of Corinth. In continental central-northern Greece, at least three other regions, from which the two have been already more or less explicitly suggested by other authors, are probably associated with low-angle faulting at depth. The occurrence of a low-angle shear zone has important consequences not only for the geodynamic processes and the crustal extension behaviour, but also for seismic hazard assessment (SHA) estimations
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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