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Seismotectonic implications of the 2020 Samos, Greece, Mw 7.0 mainshock based on high resolution aftershock relocation and source slip model

Karakostas V., Tan O., Kostoglou A., Papadimitriou E., Bonatis P.

Acta Geophysica

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2021

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Vol. 69, no. 3

979--996

EN

The 30 October 2020, Mw 7.0 Samos mainshock took place in the ofshore north of Samos Island in eastern Aegean area, previously struck in 1904 with a comparable magnitude earthquake ofshore the southern coastline. The investigation of the aftershock seismicity evolution and the properties of the activated fault network was accomplished with aftershock relocation performed with the double-diference and cross-correlation techniques. The highly accurate relocated seismicity illustrates a well-defned E–W activated structure located deeper than 5 km with an average depth of~12 km. Moment tensor solutions indicate mostly normal faulting with an average T-axis~ 185ο . Strong-motion waveform modeling revealed a N-dipping fault plane with a coseismic slip patch of 36 km × 22 km and a maximum slip equal to 1 m at 12 km depth. The slip is mainly concentrated in a single asperity implying a rupture mode of asperities breaking in isolated earthquakes rather than to cooperate to produce a larger rupture. Coulomb stress calculations unveil increased positive static stress changes values at the locations of the majority of the aftershocks and activation of minor fault segments by stress transfer.

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Relocation of the 2018 Zakynthos, Greece, aftershock sequence: spatiotemporal analysis deciphering mechanism diversity and aftershock statistics

Karakostas V., Kostoglou A., Chorozoglou D., Papadimitriou E.

Acta Geophysica

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2020

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Vol. 68, no. 5

1263--1294

EN

An Mw 6.8 earthquake occurred on October 25, 2018, 35 km ofshore from the southwest coastlines of Zakynthos Island. The aftershock sequence appeared remarkably productive with six aftershocks of M≥5.0 in the frst month and tens of aftershocks with M≥4.0 during the study period. The GCMT solution for the main shock suggests a very low angle plane (dip=24°) for a dextral strike–slip faulting (rake=165°). A similar solution is suggested for the largest aftershock (Mw 5.9) that occurred 5 days afterward. The proximity of the main shock location with the dextral active boundary of Kefalonia Transform Fault Zone (KTFZ) along with the Hellenic Subduction front supports this oblique faulting. The aftershock activity is comprised mostly in depths 5–12 km and forms eight distinctive clusters that accommodate regional strain and evidence strain partitioning. The role of stress transfer and statistical analysis are combined for detailing the highly productive aftershock sequence. Earthquake networks analysis reveals their random structure soon after the main shock, which became small-world structure after the frst 200 days. Time series analysis constructed from the aftershock frequency and seismic moment release and manifested signifcant correlation among the eight seismicity clusters.

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Application of a linked stress release model in Corinth Gulf and Central Ionian Islands (Greece)

Mangira O., Vasiliadis G., Papadimitriou E.

Acta Geophysica

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2017

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Vol. 65, no. 3

517--531

EN

Spatio-temporal stress changes and interactions between adjacent fault segments consist of the most important component in seismic hazard assessment, as they can alter the occurrence probability of strong earthquake onto these segments. The investigation of the interactions between adjacent areas by means of the linked stress release model is attempted for moderate earthquakes (M ≥ 5.2) in the Corinth Gulf and the Central Ionian Islands (Greece). The study areas were divided in two subareas, based on seismotectonic criteria. The seismicity of each subarea is investigated by means of a stochastic point process and its behavior is determined by the conditional intensity function, which usually gets an exponential form. A conditional intensity function of Weibull form is used for identifying the most appropriate among the models (simple, independent and linked stress release model) for the interpretation of the earthquake generation process. The appropriateness of the models was decided after evaluation via the Akaike information criterion. Despite the fact that the curves of the conditional intensity functions exhibit similar behavior, the use of the exponential-type conditional intensity function seems to fit better the data.

4

Analysis of damage processes in nanopillar arrays with hierarchical load transfer

Derda T.

Journal of Applied Mathematics and Computational Mechanics

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2016

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Vol. 15, nr 3

27--36

EN

A computational model for the damage analysis in the axially loaded nanopillar arrays was developed on the basis of the Fibre Bundle Model and hierarchical load sharing protocol. The nanopillars are characterised by random strength-thresholds drawn according to the nanoscale Weibull statistics. We study the influence of the coordination number and the number of hierarchy levels on the system strength, size of the catastrophic avalanche and probability of breakdown.

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Styk między betonami układanymi w różnym czasie – parametry i nośność według fib Model Code 2010

Halicka A., Jabłoński Ł.

Inżynieria i Budownictwo

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2015

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R. 71, nr 7

346--350

PL

Zestawiono dane dotyczące obliczania nośności granicznej styku między betonami według zaleceń fib Model Code 2010. Zamieszczono przykład obliczeniowy i porównano uzyskane wyniki z obliczeniami według EC 2-1-1.

EN

In the paper the data concerning the calculations of limit capacity of interface between two concrete members given in fib Model Code 2010 are compiled. The exemplary calculations are presented. The results are compared with calculations executed in accordance with EC 2-1-1.

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Badania przyczepności stali w betonie zbrojonym

Siempu R., Kumar R. P.

Cement Wapno Beton

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2015

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R. 20/82, nr 6

341--358

PL

Przydatność betonu zbrojonego jako materiału kompozytowego zależy od przyczepności zbrojenia stalowego do otuliny betonowej. Połączenie to pełni ważną rolę przy przenoszeniu naprężeń ścinających, które powstają na powierzchni rozdziału stal – beton podczas obciążenia. Zaburzenie przenoszenia naprężeń w tej strefie będzie powodowało zakłócenia procesu przenoszenia obciążenia i właściwości kompozytu. Na zachowanie się strefy przejściowej stal – beton wpływa szereg czynników, a przede wszystkim wytrzymałość na ściskanie betonu, grubość otuliny, średnica i długość zakotwienia stali zbrojeniowej, kształt elementów zbrojeniowych, zbrojenie poprzeczne, itp. W pracy przyjęto program doświadczalny zmierzający do określenia wpływu wytrzymałości betonu, średnicy prętów zbrojeniowych (12 mm i 16 mm), długości zakotwienia prętów zbrojeniowych (wielokrotności określanej współczynnikami odpowiednio 2.5; 5 i 8.3 w przypadku prętów o średnicy 12 mm oraz 9.4 w przypadku prętów o średnicy 16 mm) na kształtowanie przyczepności stal – beton. Zaprojektowano trzy klasy betonu w oparciu o mieszanki spoiwowe zawierające dodatki mineralne. Wytrzymałość przyczepności betonu do stali zmierzono metodą wyrywania („pull out”). Na podstawie wyników uzyskanych tą metodą określono wartości naprężenia niszczącego powierzchni rozdziału stal – beton, wielkość przemieszczenia, jak również energię pękania. Stwierdzono, że ze wzrostem wytrzymałości na ściskanie betonu wzrastała również wytrzymałość wiązania betonu ze stalą. Zaobserwowano, że przemieszczenie pręta w strefie przejściowej oraz energia pękania wzrastały nie tylko ze wzrostem wytrzymałości na ściskanie betonu, ale też ze średnicą i długością prętów zbrojeniowych. Na podstawie uzyskanych wyników zaproponowano wzór określający przyczepność betonu do prętów stalowych.

EN

Effectiveness of reinforced concrete as a composite element depends on the bond between reinforcing steel and encapsulating concrete. Bond plays an important role in the transfer of shear stress that develops along the steel-concrete interface upon loading. Failure of this transfer of stress will result in the failure of strain compatibility and composite action. Several factors such as compressive strength of concrete, cover to concrete, diameter of bar, embedment length of bar, type of bar, confinement of concrete etc., influence the bond performance. In the present study, a rigorous experimental program is undertaken to check the effect of concrete strength, diameter of bar (12 mm and 16 mm), embedment length of bar (2.5 times, 5 times and 8.3 times [in case of 12 mm bar], 9.4 times [in case of 16 mm bar] on the bond behavior. Three concrete classes were designed with binary addition of supplementary cementitious materials. Pull out test was chosen to evaluate the bond strength and the ultimate bond stress, ultimate slip as well as fracture energy are the parameters determined from the experiments. Based on the results obtained, it was noted that with the increase in compressive strength of concrete, there is an increase in the bond strength. It was also observed that the slip and fracture energy increased with the concrete strength, diameter and embedment length of the bar. An equation to predict the bond strength is proposed based on the experimental results.