59 research outputs found
Recent earthquake activity in Trichonis region and its tectonic significance
No full textSUMMARY. - The aftershock activity associated with the central Greece<br />(Trichonis Lake) earthquake of |une-Dec. 1975, has been studied, with emphasis<br />on the time and magnitude distribution. It has been found that the value of b,<br />in Gutenberg - R i c h t e r ' s relationship was near the same for the primary as<br />well as the secondary or second order aftershocks of the sequences, but depends<br />upon the focal depth.<br />A correlation between the calculated focal mechanisms and the associated<br />stress components to the distribution pattern of meizoseismic effects as well<br />as to the geological structure of the seismic region was found.<br />The seismic region lies at the top of an anticline which was found moving<br />downwards, apparently due to compressional stresses.<br />Within the series of three earthquakes the progress of the destruction of<br />the buildings was observed and reported. The interest is concentrated to modern<br />buildings out of reinforced concrete and infill brick walls. The relatively unexpected<br />rather bad performance of the later case of buildings was compared to that<br />of the traditional small houses out of brick or stone masonry, the behaviour of<br />which may be considered as better from what it was expected
Classical multivariate Hermite coordinate interpolation on n-dimensional grids
No full textIn this work, we study the Hermite interpolation on -dimensional
non-equally spaced, rectilinear grids over a field of characteristic
zero, given the values of the function at each point of the grid and the
partial derivatives up to a maximum degree. First, we prove the uniqueness of
the interpolating polynomial, and we further obtain a compact closed form that
uses a single summation, irrespective of the dimensionality, which is
algebraically simpler than the only alternative closed form for the
-dimensional classical Hermite interpolation [1]. We provide the remainder
of the interpolation in integral form; we derive the ideal of the interpolation
and express the interpolation remainder using only polynomial divisions, in the
case of interpolating a polynomial function. Moreover, we prove the continuity
of Hermite polynomials defined on adjacent -dimensional grids, thus
establishing spline behavior. Finally, we perform illustrative numerical
examples to showcase the applicability and high accuracy of the proposed
interpolant, in the simple case of few points, as well as hundreds of points on
3D-grids using a spline-like interpolation, which compares favorably to
state-of-the-art spline interpolation methods
Classical multivariate Hermite coordinate interpolation on n-dimensional grids
No full textIn this work, we study the Hermite interpolation on n-dimensional non-equally spaced, rectilinear grids over a field k of characteristic zero, given the values of the function at each point of the grid and the partial derivatives up to a maximum degree. Initially, we prove the uniqueness of the interpolating polynomial, followed by deriving a concise closed expression that employs a solitary summation, independent of dimensionality, which is algebraically simpler than the only alternative closed form for the n-dimensional classical Hermite interpolation (Gasca and Sauer, 2000). We also provide the remainder of the interpolation in integral form; we derive the ideal of the interpolation and express the interpolation remainder using only polynomial divisions, in the case of interpolating a polynomial function. Moreover, we prove the continuity of Hermite polynomials defined on adjacent n-dimensional grids, thus establishing spline behavior. Finally, we perform illustrative numerical examples to showcase the applicability and high accuracy of the proposed interpolant, in the simple case of few points, as well as hundreds of points on 3D-grids using a spline-like interpolation, which compares favorably to state-of-the-art spline interpolation methods. © 2024 Elsevier B.V
Οι γνώσεις μας στη νεοτεκτονική δομή και τη σεισμικότητα του ελλαδικού χώρου τα τελευταία 40 χρόνια. Περιοχές και τομείς στους οποίους πρέπει να ενταθεί η ερευνητική δραστηριότητα
No full text
Aftershock sequences of some large earthquakes in the region of Greece
No full textDeformation characteristics, magnitude and time distribution<br />of the aftershocks of the large earthquakes, occurred in the region<br />of Greece from 1926 till 1964 are investigated. An approximate relation<br />between the number of aftershocks and the magnitude and focal depth<br />of the main shock has been found. Also, an approximate relation has been<br />derived between the magnitude of the largest aftershock and the magnitude<br />and focal depth of the main sliok. The largest aftershock occurs within<br />fourteen days after the main shock. In many cases large " late aftershocks "<br />occur one or more months after the main shock. One or more foreshocks<br />of magnitude larger than 3.5 occurred in forty per cent of the cases. The probability for an earthquake to be preceded l&gt;y a large foreshoek not much<br />smaller than the main shock is 10%. It is shown that some properties of<br />the Earth's material in the aftershock region can be derived by studying the<br />magnitude distribution and deformation characteristics of the aftershocks
Machine learning and features for the prediction of thermal sensation and comfort using data from field surveys in Cyprus
No full textPerception can influence individuals’ behaviour and attitude affecting responses and compliance to precautionary measures. This study aims to investigate the performance of methods for thermal sensation and comfort prediction. Four machine learning algorithms (MLA), artificial neural networks, random forest (RF), support vector machines, and linear discriminant analysis were examined and compared to the physiologically equivalent temperature (PET). Data were collected in field surveys conducted in outdoor sites in Cyprus. The seven- and nine-point assessment scales of thermal sensation and a two-point scale of thermal comfort were considered. The models of MLA included meteorological and physiological features. The results indicate RF as the best MLA applied to the data. All MLA outperformed PET. For thermal sensation, the lowest prediction error (1.32 points) and the highest accuracy (30%) were found in the seven-point scale for the feature vector consisting of air temperature, relative humidity, wind speed, grey globe temperature, clothing insulation, activity, age, sex, and body mass index. The accuracy increased to 63.8% when considering prediction with at most one-point difference from the correct thermal sensation category. The best performed feature vector for thermal sensation also produced one of the best models for thermal comfort yielding an accuracy of 71% and an F-score of 0.81. © 2022, The Author(s) under exclusive licence to International Society of Biometeorology
Silhouette labeling and tracking in calibrated omnidirectional video sequences
No full textIn this paper, we present a methodology for labeling and tracking human silhouettes in indoor videos acquired by omnidirectional (fish-eye) cameras. The proposed methodology is based on a fisheye camera model that employs a spherical optical element and central projection, which has been calibrated to allow extraction of 3D geometry clues as described in [11]. The proposed algorithm requires input from a video segmentation algorithm, generating segmented human silhouettes. The history of a person's real position, as well as his appearance in the form of R, G, B color values are utilized in the described methodology. According to initial experimentation, the proposed algorithm is able to track efficiently multiple silhouettes with prolonged partial or full occlusions and it can calculate the trajectory of each silhouette. The algorithm can operate in the presence of imperfect segmentation, with the persons moving in any direction with respect to the camera, thus producing radically different shapes and color appearances. Copyright 2016 is held by the owner/author(s)
The Mw = 6.0, 7 September 1999 Athens earthquake
No full textOn 7 September 1999 at 11:56 GMT a destructive earthquake (Mw = 6.0) occured close to Athens (Greece). The rupture process is examined using data from the Cornet local permanent network, as well as teleseismic recordings. Data recorded by a temporary seismological network were analyzed to study the aftershock sequence. The mainshock was relocated at 38.105°N, 23.565°E, about 20 km northwest of Athens. Four foreshocks were also relocated close to the mainshock. The modeling of teleseismic P and SH waves provides a well-constrained focal mechanism of the mainshock (strike = 105°, dip = 55° and rake = -80°) at a depth of 8 km and a seismic moment Mo = 1.01025 dyn·cm. The obtained fault plane solution represents normal faulting indicating an almost north-south extension. More than 3500 aftershocks were located. 1813 of which present RMS &lt;0.1 s and ERH, ERZ &lt; 1.0 km. Two main clusters were distinguished, while the depth distribution is concentrated between 2 and 11 km. Over 1000 fault plane solutions of aftershocks were constrained, the majority of which also correspond to N-S extension. No surface breaks were observed but the fault plane solution of the mainshock is in agreement with the tectonics of the area and with the focal mechanisms obtained by aftershocks. The hypocenter of the mainshock is located on the deep western edge of the fault plane. The relocated epicenter coincides with the fringe that represents the highest deformation observed on the differential interferometric image. The calculated source duration is 5 sec, while the estimated dimensions of the fault are 15 km length and 10 km width. The source process is characterized by unilateral eastward rupture propagation, towards the city of Athens. An evident stop phase observed in the recordings of the Cornet local stations is interpreted as a barrier caused by the Aegaleo Mountain
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