124,687 research outputs found
Precursory accelerated Benioff strain in the Aegean area
No full textAccelerating seismic crustal deformation due to the occurrence of intermediate magnitude earthquakes leading to the generation of a mainshock has recently been considered a critical phenomenon. This hypothesis is tested by the use of a large data sample concerning the Aegean area. Elliptical critical regions for fifty-two strong mainshocks, which have occurred in the Aegean area since 1930, have been identified by applying a power-law relation between the cumulative Benioff strain and the time to the main rupture. Empirical relations between the parameters of this model have been further improved by the use of a large data sample. The spatial distribution of preshocks with respect to the mainshock is examined and its tectonic significance is pointed out. The possibility of using the results of this work to predict the epicentre, magnitude and time of ensuing mainshocks are discussed and further work towards this goal is suggested.JCR Journalope
Large seismic faults in the Hellenic arc
No full textUsing information concerning reliable fault plane solutions, spatial distribution of strong earthquakes (Ms³ 6.0) as well as sea bottom and coastal topography, properties of the seismic faults (orientation, dimension, type of faulting) were determined in seven shallow (h < 40 km) seismogenic regions along the convex part of thc Hellenic arc (Hellenic trench) and in four seismogenic regions of intermediate depth earthquakes (h = 40-100 km) along the concave part of this arc. Except for the northwesternmost part of the Hellenic trench, where the strike-slip Cephalonia transform fault dominates, all other faults along this trench are low angle thrust faults. III thc western part of the trench (Zante-west Crete) faults strike NW-SE and dip NE, while in its eastern part (east Crete-Rhodos) faults strike WNW-ESE and dip NNE. Such system of faulting can be attributed to an overthrust of the Aegean lithosphere on the eastern Mediterranean lithosphere. The longest of these faults (L = 300 km) is that which produced the largest known shallow earthquake in the Mediterranean area (21 July 365, Ms = 8.3) which is located near the southwestern coast of Crete. The second longest such fault (L = l 70 km) is that which produced a large earthquake (December 1303, Ms = 8.0) in the easternmost part of the trench (east of Rhodos island). Both earthquakes were associated with gigantic tsunamis which caused extensive damage in the coast of many Eastern Mediterranean countries. Seismic faults of the intermediate depth earthquakes in the shallow part of the Benioff zone (h = 40- 100 km) are of strike-slip type, with a thrust component. The orientations of these faults vary along the concave part of the arc in accordance with a subduction of remnants of all old lithospheric slab from the convex side (Mediterranean) to the concave side (Aegean) of thc Hellenic arc. The longest of these faults (L = 220 km) is that which produced the largest known intermediate depth earthquake in the whole Mediterranean area (12 October 1856, M = 8.2) north of Crete. The second longest such fault (L = 160 km) produced a large earthquake (26 June 1926, M = 8.0) in the easternmost part of the concave part of the arc (near Rhodos). Both earthquakes caused very serious damage in several Eastern Mediterranean countries but were not associated with tsunamis.JCR Journalope
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
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
A deterministic seismic hazard analysis for shallow earthquake in Greece
No full textThe maximum expected ground motion in Greece is estimated for shallow earthquakes using a deterministic seismic hazard
analysis (DSHA). In order to accomplish this analysis the input data include an homogeneous catalogue of earthquakes for the
period 426 BC–2003, a seismogenic source model with representative focal mechanisms and a set of velocity models. Because of
the discrete character of the earthquake catalogue and of errors in location of single seismic events, a smoothing algorithm is
applied to the catalogue of the main shocks to get a spatially smoothed distribution of magnitude. Based on the selected input
parameters synthetic seismograms for an upper frequency content of 1 Hz are computed on a grid of 0.2°×0.2°. The resultant
horizontal components for displacement, velocity, acceleration and DGA (Design Ground Acceleration) are mapped. The maps
which depict these results cannot be compared with previously published maps based on probabilistic methodologies as the latter
were compiled for a mean return period of 476 years. Therefore, in order to validate our deterministic analysis, the final results are
compared with PGA estimated from the maximum observed macroseismic intensity in Greece during the period 426 BC–2003.
Since the results are obtained for point sources, with the frequency content scaled with moment magnitude, some sensitivity
tests are performed to assess the influence of the finite extent of fault related to large events. Sensitivity tests are also performed to
investigate the changes in the peak ground motion quantities when varying the crustal velocity models in some seismogenic areas.
The ratios and the relative differences between the results obtained using different models are mapped and their mean value
computed. The results highlight the importance in the deterministic approach of using good and reliable velocity models.
© 2007 Elsevier B.V. All rights reserved
On the validity of the regional time and magnitude predictable model in China
No full textA simplified form of the "regional time and magnitude predictable model" gives the time interval, T, between two successive mainshocks in a region and the magnitude, Mf, of the following mainshock by the relations: logT=cMP+a; Mf=CMp+A, where Mp is the magnitude of the preceding mainshock, a, A are constants which depend on the minimum considered mainshock and on the region's tectonic loading (moment rate). The physical meaning of the model is that the larger the magnitude of the preceding main shock, Mp, the longer the time, T, will be till the occurrence of the next one and the smaller its magnitude, Mf. This means that parameters c and C are positive and negative, respectively, when the model has been found valid for a certain area. In order to examine if the above model is appropriate to describe the seismicity behavior in the area of China, a detailed inspection was carried out aiming to show if the estimated values of parameters c and C favor the model. The results show that c tends to the global value 0.33, obtained by Papazachos and Papadimitriou (1997), and that C tends to be within the range [-0.30, -0.23]. The results, which favored the model, greatly outnumber those that do not follow it, the latter being concentrated around the boundaries of the seismically active regions. It is concluded that the results, which favor the model, obviously dominate the whole territory of China.JCR Journalope
Rayleigh Wave Group Velocity Tomography in the Aegean Area
Get PDFData from a large-scale experiment which took place in Greece during the period January–July 1997 have been used to investigate the structure of the Aegean area using surface waves. During this experiment, 30 seismic broadband instruments were deployed throughout the whole Greek area. Additional data during the period 1996–2000 from other temporary networks have been included in the dataset. One hundred eighty-five events with magnitudes 4.0 V Mw V 5.5 recorded by these stations have been collected and processed. The individual dispersion curves of the group velocity of Rayleigh waves for each source-station path have been calculated, producing more than 700 paths covering the studied region. These curves have been used to determine Rayleigh group velocity maps using a 2D-tomography method. On the basis of a regionalization of the dispersion measurements, local averaged dispersion curves have been obtained and non-linearly inverted to obtain models of shear-wave velocity versus depth. Since the dispersion curves in the period range 5 s V T V 30 s are mostly affected by the crustal structure, the model velocities are estimated down to a depth of approximately 35–45 km. The results from the non-linear Hedhehog inversion as applied to a few local dispersion curves show a crustal thickness of approximately 32 km for the Northern Aegean Sea, and a relatively thin crust of approximately 22–24 km for the Southern Aegean Sea
Shear velocity structure in the Aegean area obtained by inversion of Rayleigh waves.
No full textThe purpose of this work is to derive a 3-D tomographic image of the shear wave velocity structure of the crust—uppermost mantle in the Aegean area using the group velocities of Rayleigh wave fundamental mode. The database consists of 185 regional earthquakes recorded at broad-band stations that were installed for a period of 6 month in the Aegean area within the framework of a large-scale experiment. In a previous work (Karagianni et al. 2002), an averaged group velocity has been determined using the method of frequency time analysis (FTAN) for each epicentre–station ray path and the data were used in order to determine the local group velocities for different periods over the area covered by the seismic ray paths. Taking into account additional resolution results obtained for the local group velocities, a grid of 0.5◦ was adopted for the Aegean area and a local dispersion curve was defined for each gridpoint. More than 80 local dispersion curves were finally inverted using a non-lin
Pragmatic Case Studies as a Source of Unity in Applied Psychology
No full textTo unify or not to unify applied psychology: that is the question. In this article we review pendulum swings in the historical efforts to answer this question—from a comprehensive, positivist, “top-down,” deductive yes between the 1930s and the early 60s, to a postmodern no since then. A rationale and proposal for a limited, “bottom-up,” inductive yes in applied psychology is then presented, employing a case-based paradigm that integrates both positivist and postmodern themes and components. This paradigm is labeled “pragmatic psychology” and, its specific use of case studies, the “Pragmatic Case Study Method” (“PCS Method”). We call for the creation of peer-reviewed journal-databases of pragmatic case studies as a foundational source of unifying applied knowledge in our discipline. As one example, the potential of the PCS Method for unifying different angles of theoretical regard is illustrated in an area of applied psychology, psychotherapy, via the case of Mrs. B. The article then turns to the broader historical and epistemological arguments for the unifying nature of the PCS Method in both applied and basic psychology.Peer reviewe
Re-examining the stress field of the broader southern Aegean subduction area using an updated focal mechanism database
Get PDFΧρησιμοποιήσαμε δεδομένα από το δίκτυο EGELADOS (Οκτώβριος 2005-Απρίλιος 2007) και υπολογίσαμε 88 νέους μηχανισμούς γένεσης στην περιοχή του Ν. Αιγαίου με τη χρήση του αλγορίθμου RAPIDINV algorithm (Cesca et al., 2010). Οι μηχανισμοί αυτοί, σε συνδυασμό με παλαιότερα στοιχεία χρησιμοποιήθηκαν για τον προσδιορισμό του ενεργού πεδίου τάσεων, όπως προτείνεται από την κατανομή των αξόνων P και T. Για τον προσδιορισμό αυτό χρησιμοποιήθηκε η μεθοδολογία των Gephart and Forsyth (1984) και ειδικότερα η μέθοδος αναζήτησης του Gephart (1990a,b), η οποία χρησιμοποιεί τους άξονες P και T των μηχανισμών γένεσης. Για την αντιστροφή, οι αρχικές λύσεις βασίστηκαν στη λύση των μέσων κινηματικών αξόνων P και T των Papazachos and Kiratzi (1992). Η διαδικασία αντιστροφής επιτρέπει τον καθορισμό των "ιδανικών" ρηγμάτων των μηχανισμών γένεσης, με βάση την προσαρμογή των παρατηρημένων και αναμενόμενων από το πεδίο τάσεων διανυσμάτων ολίσθησης τα οποία προκύπτουν με τη βοήθεια της μεθόδου αντιστροφής.We have employed the data of EGELADOS temporary network (October 2005-April 2007) to determine 88 focal mechanism solutions from Southern Aegean Sea using the RAPIDINV algorithm (Cesca et al., 2010). The new focal mechanism solutions determined, complemented with the previously available ones for Southern Aegean Seα provide the basis for a detailed examination of the stress field, using the distribution of P and T axes. To obtain the stress field we applied the method of Gephart and Forsyth (1984), namely the grid search inversion approach of Gephart (1990a,b), which incorporates the P and T axes of selected focal mechanisms. For the inversion, the initial stress solutions were computed by the “average” kinematic P and T-axis approach of Papazachos and Kiratzi (1992). The stress-inversion allows choosing the "ideal" fault plane corresponding to the minimum misfit rotation about an axis of general orientation which is needed to match an observed fault plane/slip direction with one consistent with the final stress model
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