Classification of earthquake repeaters in the central Ionian Islands area

The central Ionian Islands area accommodates remarkable seismic activity with frequent strong (M>6.0) earthquake occurrence and continuous microseismicity. The dominant seismotectonic characteristic is the Kefalonia Transform Fault Zone (KTFZ), a dextral transform active boundary between oceanic subduction and continental collision, running along the western coastlines of Kefalonia and Lefkada Islands. KTFZ comprises two main fault branches (Kefalonia and Lefkada) connected with a step over zone in between. In the past 20 years, four strong earthquakes ruptured the Lefkada (06/08/2003&#8211;M6.5 and 17/11/2015&#8211;M6.5) and the Kefalonia (20/01/2014&#8211;M6.0 and 03/02/2014&#8211;M6.1) branches. Their aftershock activity along with the continuous microseismicity and some bursts of seismicity comprising moderate earthquakes, provided the data set proper for detailing seismicity characteristics in the area.We investigate the identification of repeating earthquakes (repeaters), which are earthquakes with highly similar waveforms caused by rupture of the same fault area, through different clustering approaches, aiming to explore strategies for the discrimination of repeaters in an accurately located dataset. We compiled a catalog of ~15600 manually picked earthquakes in the period 09/2016 &#8211; 01/2020. Relocation with the Double Difference method, using cross&#8211;correlation differential times, resulted in highly accurate locations with spatial errors ranging from a few tens to a few hundreds of meters.The establishment of groups of repeaters (multiplets) is discussed based on several approaches. We identify multiplets by grouping event pairs that contain a common event, which is a widely used method, against the application of a density-based clustering algorithm, known as DBSCAN. In DBSCAN events are grouped into multiplets based on their similarity (cross-correlation coefficient), information which is provided through a distance matrix of all event pairs whose elements correspond to zero when their cross-correlation coefficient is equal to one and so forth. A multiplet is created when an event is directly connected with at least &#160;events, i.e. their distance is within the similarity upper cutoff, &#949;. We discuss differences between the two approaches and proper parameter setting for the DBSCAN algorithm for multiplet grouping and we explore geodynamic implications of the classified clusters.AcknowledgmentsThis research is co-financed by Greece and the European Union (European Social Fund- ESF) through the Operational Program &#171;Human Resources Development, Education and Lifelong Learning 2014-2020&#187; in the context of the project &#8220;Kinematic properties, active deformation and stochastic modelling of seismogenesis at the Kefalonia - Lefkada transform zone&#8221; (MIS-5047845).

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The role of fluids in the seismicity of the Western Gulf of Corinth (Greece)

10.5194/egusphere-egu2020-5996 ◽

2020 ◽

Author(s):

Georgios Michas ◽

Vasilis Kapetanidis ◽

George Kaviris ◽

Filippos Vallianatos

Keyword(s):

Active Sites ◽

Double Difference ◽

Upper Crust ◽

The European Union ◽

Development Education ◽

Scaling Properties ◽

Seismic Sequences ◽

Gulf Of Corinth ◽

Waveform Cross Correlation ◽

Spatio Temporal

The present study focuses on the Western Gulf of Corinth (WGoC), which is one of the most seismically active sites in Europe and also the region where the Corinth Rift Laboratory (CRL) Near Fault Observatory (NFO) has been installed. The WGoC exhibits high extension rates and intense microseismicity, with frequent occurrence of clustered seismicity, as in the cases of the 2001 Agios Ioannis swarm, the seismic sequences of 2003-2004 and 2006-2007 in the central part of the Gulf and the 2013 Helike swarm. These outbreaks of seismicity, lasting a few days to months, are characterized by a high frequency and density of earthquakes, with magnitudes generally not exceeding 4.5, with the strongest ones usually occurring in the middle or towards the end of the sequence. These short-lived seismic crises often exhibit patterns of spatio-temporal migration in their hypocentral distribution, which has been associated with the effects of diffusion and circulation of fluids to the seismogenic crust of the WGoC. Fluids appear to play an important role in both triggering and evolving seismic sequences. In the framework of the present study, earthquake hypocenters, relocated with high resolution by employing waveform cross-correlation and the double difference-method, are used to perform an upper crust Shear-Wave Splitting (SWS) study at the WGoC area. The temporal variation of the SWS is investigated, in relation with the temporal evolution of seismicity, to possibly identify patterns related to changes of the stress-field due to fluid migration, or before the occurrence of moderate to strong earthquakes. In addition, the relocated catalogue is analyzed using nonlinear statistical physics for the definition of the spatio-temporal scaling properties of clustered seismicity, as well as for the quantification and modeling of seismic diffusion phenomena associated with fluid circulation at the upper crust of the WGoC.AcknowledgementsWe would like to thank the personnel of the Hellenic Unified Seismological Network and the Corinth Rift Laboratory Network (https://doi.org/10.15778/RESIF.CL) for the installation and operation of the stations used in the current article. The present work was co-funded by the European Union (ESF) and Greek national funds through the Operational Program "Human Resources Development, Education and Lifelong Learning", project title &#8220;&#932;he effect of fluids on the seismicity of the Western Gulf of Corinth&#8221; (project code MIS: 5048127).

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Processing automatic seismic event detections: an iterative sorting algorithm improving earthquake hypocentres using interevent cross-correlation

Geophysical Journal International ◽

10.1093/gji/ggz362 ◽

2019 ◽

Vol 219 (2) ◽

pp. 1268-1280

Author(s):

F Wagner ◽

A Tryggvason ◽

R Roberts ◽

Ó Gudmundsson

Keyword(s):

Cross Correlation ◽

Seismic Event ◽

Double Difference ◽

Sorting Algorithm ◽

Time Lags ◽

Time Data ◽

Data Set ◽

Manual Inspection ◽

Local Earthquake ◽

Time Information

SUMMARY We present an iterative classification scheme using interevent cross-correlation to update an existing earthquake catalogue with similar events from a list of automatic seismic event detections. The algorithm automatically produces catalogue quality events, with improved hypocentres and reliable P- and S-arrival time information. Detected events are classified into four event categories with the purpose of using the top category, with the highest assessed event quality and highest true-to-false ratio, directly for local earthquake tomography without additional manual analysis. The remaining categories have varying proportions of lower quality events, quality being defined primarily by the number of observed phase onsets, and can be viewed as different priority groups for manual inspection to reduce the time spent by a seismic analyst. A list of 3348 event detections from the geothermally active volcanic region around Hengill, southwest Iceland, produced by our migration and stack detector (Wagner et al. 2017), was processed using a reference catalogue of 1108 manually picked events from the same area. P- and S-phase onset times were automatically determined for the detected events using correlation time lags with respect to manually picked phase arrivals from different multiple reference events at the same station. A significant improvement of the initial hypocentre estimates was achieved after relocating the detected events using the computed phase onset times. The differential time data set resulting from the correlation was successfully used for a double-difference relocation of the final updated catalogue. The routine can potentially be implemented in real-time seismic monitoring environments in combination with a variety of seismic event/phase detectors.

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Detrended Multiple Cross-Correlation Coefficient applied to solar radiation, air temperature and relative humidity

Scientific Reports ◽

10.1038/s41598-019-56114-6 ◽

2019 ◽

Vol 9 (1) ◽

Cited By ~ 2

Author(s):

Andrea de Almeida Brito ◽

Heráclio Alves de Araújo ◽

Gilney Figueira Zebende

Keyword(s):

Relative Humidity ◽

Solar Radiation ◽

Solar Energy ◽

Correlation Coefficient ◽

Air Temperature ◽

Cross Correlation ◽

Global Solar Radiation ◽

Meteorological Variables ◽

Hourly Data ◽

Cross Correlations

AbstractDue to the importance of generating energy sustainably, with the Sun being a large solar power plant for the Earth, we study the cross-correlations between the main meteorological variables (global solar radiation, air temperature, and relative air humidity) from a global cross-correlation perspective to efficiently capture solar energy. This is done initially between pairs of these variables, with the Detrended Cross-Correlation Coefficient, ρDCCA, and subsequently with the recently developed Multiple Detrended Cross-Correlation Coefficient, $${\boldsymbol{DM}}{{\boldsymbol{C}}}_{{\bf{x}}}^{{\bf{2}}}$$DMCx2. We use the hourly data from three meteorological stations of the Brazilian Institute of Meteorology located in the state of Bahia (Brazil). Initially, with the original data, we set up a color map for each variable to show the time dynamics. After, ρDCCA was calculated, thus obtaining a positive value between the global solar radiation and air temperature, and a negative value between the global solar radiation and air relative humidity, for all time scales. Finally, for the first time, was applied $${\boldsymbol{DM}}{{\boldsymbol{C}}}_{{\bf{x}}}^{{\bf{2}}}$$DMCx2 to analyze cross-correlations between three meteorological variables at the same time. On taking the global radiation as the dependent variable, and assuming that $${\boldsymbol{DM}}{{\boldsymbol{C}}}_{{\bf{x}}}^{{\bf{2}}}={\bf{1}}$$DMCx2=1 (which varies from 0 to 1) is the ideal value for the capture of solar energy, our analysis finds some patterns (differences) involving these meteorological stations with a high intensity of annual solar radiation.

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An approach for document retrieval using cluster-based inverted indexing

Journal of Information Science ◽

10.1177/01655515211018401 ◽

2021 ◽

pp. 016555152110184

Author(s):

Gunjan Chandwani ◽

Anil Ahlawat ◽

Gaurav Dubey

Keyword(s):

High Performance ◽

Clustering Algorithm ◽

Pearson Correlation ◽

Relevant Information ◽

Document Retrieval ◽

Bhattacharyya Distance ◽

Data Set ◽

Query Matching ◽

Inverted Indexing ◽

Query Optimisation

Document retrieval plays an important role in knowledge management as it facilitates us to discover the relevant information from the existing data. This article proposes a cluster-based inverted indexing algorithm for document retrieval. First, the pre-processing is done to remove the unnecessary and redundant words from the documents. Then, the indexing of documents is done by the cluster-based inverted indexing algorithm, which is developed by integrating the piecewise fuzzy C-means (piFCM) clustering algorithm and inverted indexing. After providing the index to the documents, the query matching is performed for the user queries using the Bhattacharyya distance. Finally, the query optimisation is done by the Pearson correlation coefficient, and the relevant documents are retrieved. The performance of the proposed algorithm is analysed by the WebKB data set and Twenty Newsgroups data set. The analysis exposes that the proposed algorithm offers high performance with a precision of 1, recall of 0.70 and F-measure of 0.8235. The proposed document retrieval system retrieves the most relevant documents and speeds up the storing and retrieval of information.

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The profile of vulnerable students using the university psychosocial and medical care services

European Journal of Public Health ◽

10.1093/eurpub/ckaa166.457 ◽

2020 ◽

Vol 30 (Supplement_5) ◽

Author(s):

M Papadakaki ◽

F Sarakatsianou ◽

V Tsismeli ◽

G Lapidakis ◽

M Karapiperaki

Keyword(s):

Higher Education ◽

Family Income ◽

Psychosocial Support ◽

Academic Progress ◽

Health Examination ◽

The European Union ◽

Psychosocial Needs ◽

Development Education ◽

Medical Unit ◽

Set Up

Abstract Background Increasing the capacity of higher education institutes to address students' vulnerabilities has been deemed necessary due to the financial crisis. Multilevel interventions have thus been initiated at the Hellenic Mediterranean University of Crete, as part of a project co-financed by Greece and the European Union (European Social Fund-ESF) through the Operational Programme <<Human Resources Development, Education and Lifelong Learning 2014- 2020 >> (MIS 5045937). The project aims to offer support to students with low family income or a certified disability, monitor their bio-psychosocial needs, increase their accessibility to health and psychosocial care, and improve their academic outcomes. Methods As part of the project, a primary health care unit has been set up to offer medical and nursing care (medical unit) as well as psychosocial support (counseling centre) to students in need. An observatory has also been set up to monitor their health and psychosocial needs and their academic progress. Results A total of 228 eligible students used the services in the second half of 2019 (counseling centre 37; medical unit 191). Out of the 37 individuals who used the counseling centre, 30 (81.0%) were female and 16 (43.2%) were at the first 2 years of their studies. A total of 36 (97.3%) requested psychological support, 6 (16.2%) warranted social welfare services and 1 (2.7%) support for learning disabilities. As for the 191 individuals who used the medical services, 101 (52.8%) were male and 88 (46.0%) were at first 2 years of their studies. Most of them had a health examination to receive a health certificate (74.8%) followed by those who received emergency care (e.g. respiratory infection, allergic reaction, injury, etc), chronic disease management and medicine subscription, as well as vaccination. Conclusions Complex bio-psychosocial needs have been identified, recorded and analyzed to explain the academic progress of socially vulnerable students. Key messages The students’ journey through medical and counseling services is being mapped to offer important information for educational policy. Assessment and monitoring of students’ complex needs are important to achieve quality in higher education.

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Changes in Energy Consumption in Agriculture in the EU Countries

Energies ◽

10.3390/en14061570 ◽

2021 ◽

Vol 14 (6) ◽

pp. 1570

Author(s):

Tomasz Rokicki ◽

Aleksandra Perkowska ◽

Bogdan Klepacki ◽

Piotr Bórawski ◽

Aneta Bełdycka-Bórawska ◽

...

Keyword(s):

European Union ◽

Renewable Energy ◽

Energy Consumption ◽

Correlation Coefficient ◽

Renewable Energy Sources ◽

Energy Sources ◽

The European Union ◽

Eu Countries ◽

Research Hypothesis ◽

The Eu

The paper’s main purpose was to identify and present the current situation and changes in energy consumption in agriculture in the European Union (EU) countries. The specific objectives were the determination of the degree of concentration of energy consumption in agriculture in the EU countries, showing the directions of their changes, types of energy used, and changes in this respect, establishing the correlation between energy consumption and changes in the economic and agricultural situation in the EU countries. All member states of the European Union were deliberately selected for research on 31 December 2018 (28 countries). The research period covered the years 2005–2018. The sources of materials were the literature on the subject, and data from Eurostat. Descriptive, tabular, and graphical methods were used to analyze and present materials, dynamics indicators with a stable base, Gini concentration coefficient, concentration analysis using the Lorenz curve, coefficient of variation, Kendall’s tau correlation coefficient, and Spearman’s rank correlation coefficient. A high concentration of energy consumption in agriculture was found in several EU countries, the largest in countries with the largest agricultural sector, i.e., France and Poland. There were practically no changes in the concentration level. Only in the case of renewable energy, a gradual decrease in concentration was visible. More and more countries developed technologies that allow the use of this type of energy. However, the EU countries differed in terms of the structure of the energy sources used. The majority of the basis was liquid fuels, while stable and gaseous fuels were abandoned in favor of electricity and renewable sources—according to which, in the EU countries, the research hypothesis was confirmed: a gradual diversification of energy sources used in agriculture, with a systematic increase in the importance of renewable energy sources. The second research hypothesis was also confirmed, according to which the increase in the consumption of renewable energy in agriculture is closely related to the economy’s parameters. The use of renewable energy is necessary and results from concern for the natural environment. Therefore, economic factors may have a smaller impact.

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Variations of the earthquake diffusion rates in the Western Gulf of Corinth (Greece)

10.5194/egusphere-egu21-5282 ◽

2021 ◽

Author(s):

Georgios Michas ◽

Vasilis Kapetanidis ◽

George Kaviris ◽

Filippos Vallianatos

Keyword(s):

Fluid Pressure ◽

Stress Transfer ◽

The European Union ◽

Triggering Mechanism ◽

Development Education ◽

Seismic Sequences ◽

Gulf Of Corinth ◽

Aftershock Sequences ◽

Triggering Mechanisms ◽

Diffusion Rates

Earthquake diffusion is frequently observed in the spatiotemporal evolution of seismic clusters and regional seismicity, a characteristic that is attributed to a triggering mechanism, such as fluid flow, aseismic creep and/or stress transfer effects. In this work, we study the earthquake diffusion properties in the Western Gulf of Corinth (central Greece), an area that presents high extension rates, moderate to large magnitude earthquakes, intense microseismicity and frequent seismic swarms. We focus on the period 2013&#8211;2014 that is characterized by intense background microseismic activity along with significant seismic sequences. More specifically, the latter include the 2013 Helike swarm, the 2014 seismic sequence between Nafpaktos and Psathopyrgos, which culminated with an Mw 4.9 event on 21 September 2014, as well as moderate magnitude events that were followed by aftershock sequences. In the herein analysis, we employ a relocated earthquake catalogue of ~9000 events which delineates the activated areas during the study period in high-resolution. We consider the most significant seismic sequences and calculate their respective spatial correlation histograms and the evolution of the mean squared distance of the hypocenters with time, in order to study the earthquake diffusion rates and possible variations that might be related to the triggering mechanisms of seismicity. Our results demonstrate a weak earthquake diffusion process, analogous to subdiffusion within a stochastic framework, for the seismic sequences under consideration, providing further evidence for slow earthquake diffusion in regional and global seismicity. In addition, the earthquake diffusion rates exhibit variations that can be associated with the triggering mechanism. In particular, seismic sequences which are related with pore-fluid pressure diffusion present considerably higher diffusion rates than mainshock/aftershock sequences or the background activity. Such results may provide novel constraints on the triggering mechanisms of clustered seismic activity based on the study of the earthquake diffusion rates.&#160;AcknowledgementsWe would like to thank the personnel of the Hellenic Unified Seismological Network (http://eida.gein.noa.gr/) and the Corinth Rift Laboratory Network (https://doi.org/10.15778/RESIF.CL) for the installation and operation of the stations used in the current article. The present research is co-financed by Greece and the European Union (European Social Fund- ESF) through the Operational Programme &#171;Human Resources Development, Education and Lifelong Learning 2014-2020&#187; in the context of the project &#8220;The role of fluids in the seismicity of the Western Gulf of Corinth (Greece)&#8221; (MIS 5048127).

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Empirical Evaluation of Genetic Clustering Methods Using Multilocus Genotypes From 20 Chicken Breeds

Genetics ◽

10.1093/genetics/159.2.699 ◽

2001 ◽

Vol 159 (2) ◽

pp. 699-713

Author(s):

Noah A Rosenberg ◽

Terry Burke ◽

Kari Elo ◽

Marcus W Feldman ◽

Paul J Freidlin ◽

...

Keyword(s):

Cluster Analysis ◽

Population Structure ◽

Clustering Algorithm ◽

Empirical Evaluation ◽

Unknown Origin ◽

Clustering Methods ◽

Genetic Cluster ◽

Data Set ◽

Multilocus Genotypes ◽

Chicken Breeds

Abstract We tested the utility of genetic cluster analysis in ascertaining population structure of a large data set for which population structure was previously known. Each of 600 individuals representing 20 distinct chicken breeds was genotyped for 27 microsatellite loci, and individual multilocus genotypes were used to infer genetic clusters. Individuals from each breed were inferred to belong mostly to the same cluster. The clustering success rate, measuring the fraction of individuals that were properly inferred to belong to their correct breeds, was consistently ~98%. When markers of highest expected heterozygosity were used, genotypes that included at least 8–10 highly variable markers from among the 27 markers genotyped also achieved >95% clustering success. When 12–15 highly variable markers and only 15–20 of the 30 individuals per breed were used, clustering success was at least 90%. We suggest that in species for which population structure is of interest, databases of multilocus genotypes at highly variable markers should be compiled. These genotypes could then be used as training samples for genetic cluster analysis and to facilitate assignments of individuals of unknown origin to populations. The clustering algorithm has potential applications in defining the within-species genetic units that are useful in problems of conservation.

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Into the Vicious Cycle of Precarity: Labour Market, Precarious Work, Social Vulnerability and Youth: The case of Greece within the EU context

Advances in Social Sciences Research Journal ◽

10.14738/assrj.712.9511 ◽

2021 ◽

Vol 7 (12) ◽

pp. 474-496

Author(s):

Nikos Papadakis ◽

Maria Drakaki ◽

Sofia Saridaki ◽

Vassilis Dafermos

Keyword(s):

European Union ◽

Young People ◽

Labour Market ◽

Social Vulnerability ◽

The State ◽

The European Union ◽

Development Education ◽

Ongoing Research ◽

Precarious Work ◽

The Impact

Ιn the last decade, there has been a widespread expansion of both precarious work and precarious forms of employment (such as temporary and low-qualified jobs, seasonal and part-time jobs etc.), in which a growing share of young people work. The impact of precarious work on young people is likely to be permanent, while it seems to affect (even over-determine) their life courses. Non-smooth and early transitions into labour market are very likely to worsen progressively their long-term life chances (Lodovici & Semenza, 2012: 7). Undoubtedly, the long-lasting global economic Crisis and the subsequent Recession, has heavily affected the state of play in the labour market worldwide, provoking severe modifications both in the field of employment and countries’ social cohesion. Based on the above mentioned, the paper deals with precarious work in general, while it emphasizes precarious work among youth. It initially captures, briefly, the state of play in terms of the impact of the Crisis on the widening of the phenomenon of precarious work and then it focuses on theoretical insights and critical conceptual definitions concerning precariousness in the labour market. Further, based on secondary quantitative -data analysis, it analyses the key- parameters and facets of precarious work (focusing on youth) in the European Union and, mainly, in Greece. Additionally, it briefly presents parameters of the impact of the COVID-19 pandemic on precariousness in Greece. Finally, the paper explores the correlation between precarious work and social vulnerability, especially among young people. The present paper is based on an ongoing Research Project. More specifically, this research is co-financed by Greece and the European Union (European Social Fund- ESF) through the Operational Programme «Human Resources Development, Education and Lifelong Learning 2014-2020» in the context of the project “Precarious Work and Youth in today’s Greece: secondary quantitative analysis, qualitative filed research and research-based policy proposals” (MIS 5048510).

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Cause-and-effect relations between cosmic rays, electric field, aerosols and clouds

10.5194/egusphere-egu21-544 ◽

2021 ◽

Author(s):

Stavros Stathopoulos ◽

Stergios Misios ◽

Konstantinos Kourtidis

Keyword(s):

Cosmic Rays ◽

Electric Field ◽

Causal Effect ◽

Atmospheric Electricity ◽

Potential Gradient ◽

Galactic Cosmic Rays ◽

The European Union ◽

Development Education ◽

Cause And Effect ◽

Global Coordination

Here we examine the cause-and-effect relations between galactic cosmic rays, electric field, aerosols and clouds over a region of Atlantic Ocean, during a Forbush Decrease (FD) event on 07/12/2015, using Convergent Cross Mapping (CCM) method. For this purpose, we used FD data from the Neuron Monitor Database (NMDB), Potential Gradient data (PG) from Global Coordination of Atmospheric Electricity Measurements (GLOCAEM) and remote sensing data from MODIS/Aqua, namely Aerosol Optical Depth at 550nm (AOD), Cloud Fraction (CF), Cloud Optical Thickness (COT), Cloud Top Pressure (CTP), Cirrus Reflectance (CR) and Cloud Effective Radius-Liquid (CERL). A cause-and-effect relation was found between FD and AOD, CERL, CF and PG, over the region. On the other hand, no causal effect was found between FD and COT, CTP and CR. This research is funded in the context of the project "Cosmic and electric effects on aerosols and clouds&#8221; (MIS: 5049552) under the call for proposals &#8220;Support for researchers with emphasis on young researchers - Cycle B&#8221; (EDULL 103). The project is co-financed by Greece and the European Union (European Social Fund - ESF) by the Operational Programme Human Resources Development, Education and Lifelong Learning 2014-2020.

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