There is increasing demand on cost effective Structural Health Monitoring systems for buildings a... more There is increasing demand on cost effective Structural Health Monitoring systems for buildings as well a important and/or critical constructions. The front end for all these systems is the accelerometer. We present comparative study of two low cost MEMS accelaration sensors against a very sensitive, high dynamic rang strong motion accelerometer of force balance type but much more expensive. A real experiment was realized b deploying the three sesnors in a reinforced concrete building of the premises of TEI of Crete at Chania Crete, a earthquake prone region. The analysis of the collected accelararion data from many seismic events indicates tha all sensors are able to efficiently reveal the seismic response of the construction in terms of PSD. Furthermore, i is shown that coherence diagrams between excitation and response of the building under study, depict structura characteristics but also the seismic energy distribution.
The National Observatory of Athens data center for the European Integrated Data Archive (EIDA@NOA... more The National Observatory of Athens data center for the European Integrated Data Archive (EIDA@NOA) is the national and regional node that supports International Federation of Digital Seismograph Networks and related webservices for seismic waveform data coming from the southeastern Mediterranean and the Balkans. At present, it serves data from eight permanent broadband and strong-motion networks from Greece and Cyprus, individual stations from the Balkans, temporary networks and aftershock deployments, and earthquake engineering experimental facilities. EIDA@NOA provides open and unlimited access from redundant node end points, intended mainly for research purposes (see Data and Resources). Analysis and quality control of the complete seismic data archive is performed initially by calculating waveform metrics and data availability. Seismic ambient noise metrics are estimated based on power spectral densities, and an assessment of each station’s statistical mode is achieved within ea...
Strong motion sensor networks deployed in metropolitan areas are able to provide valuable informa... more Strong motion sensor networks deployed in metropolitan areas are able to provide valuable information for civil protection Decision Support Systems (DSSs) aiming to mitigate seismic risk and earthquake social-economic impact. To this direction, such a network is installed and real-time operated in Chania (Crete Island, Greece), city located in the vicinity of the seismically active south front of the Hellenic Subduction Zone. A blend of both traditional and advanced analysis techniques and interpretation methods of strong ground motion data are presented, studying indicative cases of Chania shaking due to earthquakes in the last couple years. The orientation independent spectral acceleration as well as the spatial distribution of the strong ground motion parameters such as the Peak Ground Acceleration (PGA), Peak Ground Velocity (PGV), Peak Ground Displacement (PGD) and Arias Ιntensity observed at the urban area of Chania are presented with the use of a Geographic Information System...
Results of the European collaborative project SUPRE (Study of the ULF electromagnetic Phenomena R... more Results of the European collaborative project SUPRE (Study of the ULF electromagnetic Phenomena Related to Earthquakes) executed recently by Russian, Greek, Italian, Ukrainian and Georgian teams are presented and discussed in relation to development of methodology for seismic-electromagnetic testing of the earthquake preparation zone and seismic hazard assessment. Principal aspects of the following topics are introduced: measuring technique being useful in particular seismic active zones, methods of data processing promising for extraction of the earthquake precursory signatures, and modelling the earthquake preparation processes. On that basis, strategy of the newly proposed project SHARP (Study of Seismic Hazard Anomalies Recognition Possibilities) is reviewed as a next step in development of collaborative seismic-electromagnetic research. Its preliminary results are presented. Introduction It is now evident that the earthquake preparation dynamics involves both seismo-tectonic an...
In recent years, there is a growing interest concerning the development of a multi-parametric sys... more In recent years, there is a growing interest concerning the development of a multi-parametric system for earthquakes’ short term forecast identifying those parameters whose anomalous variations can be associated to the complex process of such events. In this context, the Robust Satellite Technique (RST) has been adopted herein with the aim to detect and map thermal anomalies probably related with the strong earthquake of M6.3 occurred near the city of Larissa, Thessaly on March 3rd 2021 10:16:07 UTC. For this purpose, 10 years (2012-2021) of daily Night-time Land Surface Temperature (LST) remotely sensed data from Moderate Resolution Imaging Spectroradiometer (MODIS), were analyzed. Pixels characterized by statistically significant LST variations on a daily scale were interpreted as an indicator of variations in seismic activity. Quite intense (Signal/Noise ratio > 2.5) and rare, spatially extensive and time persistent, TIR signal transients were identified, appearing twenty five...
Main purpose of the present study is to investigate the dynamic characteristics of the remainings... more Main purpose of the present study is to investigate the dynamic characteristics of the remainings at the ancient city of Aptera (Chania) and identify the main damage mechanism, in order to evaluate the risk of structure damage or collapse in case of future events using microtremor recordings. Our study focuses on the application of HVSR method (Horizontal to Vertical Spectral Ratio) to microtremor measurements carried out in specific sites. Registrations have been performed by means of a tridirectional sensor Lennartz 3D-Lite (1 natural Hz frequency), connected with a 24-bit digital acquisition unit. A set of 10 time series of 800 second each, sampled at 125 Hz was recorded in several sites. The selected time windows of each time series were corrected for the base line and for anomalous trends, tapered with a cosine function to the first and last 5% of the signal, and band pass filtered from 0.5 to 20 Hz with cut off frequencies at 0.3 and 22 Hz. The same procedure performed for all...
In Trilling L and Perkins D and Dionysios D and Perlovsky L and Davey K and Landgrebe D Sepads 09 Proceedings of the 8th Wseas International Conference on Recent Advances in Software Engineering Parallel and Distributed Systems World Scientific and Engineering Acad and Soc, Feb 21, 2009
Wavelet Transform has been successfully used for many problems of seismological research. Its tra... more Wavelet Transform has been successfully used for many problems of seismological research. Its traditional form, based on serial implementation, satisfied the vast majority of requirements. Here we examined the parallel implementation of wavelet transform for the real time azimuth estimation. The performance improvement using parallel implementation is the objective that we seek since the above estimation is a critical part of an earthquake early warning system. Out results indicate that the improvement that we gather by the parallelization of wavelet transform can make a considerable difference on the performance of the early warning system.
Egu General Assembly Conference Abstracts, Apr 1, 2009
ABSTRACT The understanding of earthquake faulting process is one of the main factors that contrib... more ABSTRACT The understanding of earthquake faulting process is one of the main factors that contribute to earthquake damage. One of the most valuable and essential tools for the understanding of faulting process in the analysis of aftershocks. The critical point for successful aftershock studies is the mobile seismological network that will deployed in order to provide the required data. The main problem that arise for these networks is how fast the recorded data are available to data centres in order to estimate the focal mechanisms, the source parameters estimation as well as to examine microseismic activity. The ideal situation is to have these data available in real time but this is limited by the different telemetry requirements for every individual installation. Based on the experience gained from several installations in Hellenic Seismological Network of Crete (HSNC) we propose a mobile network scheme (called RaDeSeis) capable of installed in a limited amount of time and provide real time seismological data. RaDeSeis is an hybrid network based on VSAT and WiFi communication links between seismological stations and data centre. The network is deployed in star topology where the central station is the communication hub at the same time. Dedicated point-to-point links between central station and border station established using WiFi links. Communication between central station and data centre is established by VSAT. With appropriate routing on central station the data centre is collecting, control and monitor all the stations from the area of interest in real time. In order to decrease the time needed for each installation a specific software (RaLiEs - Rapid Link Establishment) is originated for the quicker link establishment between border stations and central station (with an average distance of 40km LOS) as well as to data centre. By using this software each telecommunication installation needs less than half an hour to complete the necessary link adjustments. Acknowledgements This work is partially supported by SE-RISK Project (INTERREG III, STRAND B ARCHIMED)/Axis: Integrated and Sustainable Management of Cultural and Natural Resources and of Landscape and Risk Management)
SHORT TERM EARTHQUAKE PREDICTION IN GREECE BY SEISMIC ELECTRIC SIGNALS P. VAROTSOS, M. LAZARIDOU,... more SHORT TERM EARTHQUAKE PREDICTION IN GREECE BY SEISMIC ELECTRIC SIGNALS P. VAROTSOS, M. LAZARIDOU, K. EFTAXIAS, G. ANTONOPOULOS, J. MAKPJS AND J. KOPANAS Solid State Section, Department of Physics, University of Athens, Greece. More than ...
Scattering of arbitrarily polarized electromagnetic plane waves by a dielectric cylinder buried i... more Scattering of arbitrarily polarized electromagnetic plane waves by a dielectric cylinder buried in an unbounded dielectric space and enclosing an array of parallel doubly layered (pipeline-type) dielectric circular cylinders is studied, in case of oblique incidence. The objective of this work is to present an exercise suitable for an advanced course on engineering electromagnetics. Using the boundary-value approach combined with the generalized separation variables method, we formulate the problem via a linear algebraic system with unknowns the field expansion constants. Solving this system, with single-term matrix elements, results in analytical expressions for both the scattered field and the scattering cross section of the structure. Numerical results are given for several configurations along with comparisons with previously published data.
The reconstruction of gapped microtremors recordings with the aid of CLEAN algorithm, which origi... more The reconstruction of gapped microtremors recordings with the aid of CLEAN algorithm, which originally developed for spectral analysis of unevenly spaced time series, is studied. As proved in previous relative studies the algorithm has the ability to "clean" the spectrum of a discrete signal from artifacts and additionally (through an Inverse DFT) to reconstruct the signal in time domain. We studied the algorithm's effectiveness of reconstruction in microtremors recordings, which can be consider as extremely noisy time series. We saw that for continuous gap with length up to 10% of the total length of microtremor recording, the algorithm is able to reconstruct efficiently.
There is increasing demand on cost effective Structural Health Monitoring systems for buildings a... more There is increasing demand on cost effective Structural Health Monitoring systems for buildings as well a important and/or critical constructions. The front end for all these systems is the accelerometer. We present comparative study of two low cost MEMS accelaration sensors against a very sensitive, high dynamic rang strong motion accelerometer of force balance type but much more expensive. A real experiment was realized b deploying the three sesnors in a reinforced concrete building of the premises of TEI of Crete at Chania Crete, a earthquake prone region. The analysis of the collected accelararion data from many seismic events indicates tha all sensors are able to efficiently reveal the seismic response of the construction in terms of PSD. Furthermore, i is shown that coherence diagrams between excitation and response of the building under study, depict structura characteristics but also the seismic energy distribution.
The National Observatory of Athens data center for the European Integrated Data Archive (EIDA@NOA... more The National Observatory of Athens data center for the European Integrated Data Archive (EIDA@NOA) is the national and regional node that supports International Federation of Digital Seismograph Networks and related webservices for seismic waveform data coming from the southeastern Mediterranean and the Balkans. At present, it serves data from eight permanent broadband and strong-motion networks from Greece and Cyprus, individual stations from the Balkans, temporary networks and aftershock deployments, and earthquake engineering experimental facilities. EIDA@NOA provides open and unlimited access from redundant node end points, intended mainly for research purposes (see Data and Resources). Analysis and quality control of the complete seismic data archive is performed initially by calculating waveform metrics and data availability. Seismic ambient noise metrics are estimated based on power spectral densities, and an assessment of each station’s statistical mode is achieved within ea...
Strong motion sensor networks deployed in metropolitan areas are able to provide valuable informa... more Strong motion sensor networks deployed in metropolitan areas are able to provide valuable information for civil protection Decision Support Systems (DSSs) aiming to mitigate seismic risk and earthquake social-economic impact. To this direction, such a network is installed and real-time operated in Chania (Crete Island, Greece), city located in the vicinity of the seismically active south front of the Hellenic Subduction Zone. A blend of both traditional and advanced analysis techniques and interpretation methods of strong ground motion data are presented, studying indicative cases of Chania shaking due to earthquakes in the last couple years. The orientation independent spectral acceleration as well as the spatial distribution of the strong ground motion parameters such as the Peak Ground Acceleration (PGA), Peak Ground Velocity (PGV), Peak Ground Displacement (PGD) and Arias Ιntensity observed at the urban area of Chania are presented with the use of a Geographic Information System...
Results of the European collaborative project SUPRE (Study of the ULF electromagnetic Phenomena R... more Results of the European collaborative project SUPRE (Study of the ULF electromagnetic Phenomena Related to Earthquakes) executed recently by Russian, Greek, Italian, Ukrainian and Georgian teams are presented and discussed in relation to development of methodology for seismic-electromagnetic testing of the earthquake preparation zone and seismic hazard assessment. Principal aspects of the following topics are introduced: measuring technique being useful in particular seismic active zones, methods of data processing promising for extraction of the earthquake precursory signatures, and modelling the earthquake preparation processes. On that basis, strategy of the newly proposed project SHARP (Study of Seismic Hazard Anomalies Recognition Possibilities) is reviewed as a next step in development of collaborative seismic-electromagnetic research. Its preliminary results are presented. Introduction It is now evident that the earthquake preparation dynamics involves both seismo-tectonic an...
In recent years, there is a growing interest concerning the development of a multi-parametric sys... more In recent years, there is a growing interest concerning the development of a multi-parametric system for earthquakes’ short term forecast identifying those parameters whose anomalous variations can be associated to the complex process of such events. In this context, the Robust Satellite Technique (RST) has been adopted herein with the aim to detect and map thermal anomalies probably related with the strong earthquake of M6.3 occurred near the city of Larissa, Thessaly on March 3rd 2021 10:16:07 UTC. For this purpose, 10 years (2012-2021) of daily Night-time Land Surface Temperature (LST) remotely sensed data from Moderate Resolution Imaging Spectroradiometer (MODIS), were analyzed. Pixels characterized by statistically significant LST variations on a daily scale were interpreted as an indicator of variations in seismic activity. Quite intense (Signal/Noise ratio > 2.5) and rare, spatially extensive and time persistent, TIR signal transients were identified, appearing twenty five...
Main purpose of the present study is to investigate the dynamic characteristics of the remainings... more Main purpose of the present study is to investigate the dynamic characteristics of the remainings at the ancient city of Aptera (Chania) and identify the main damage mechanism, in order to evaluate the risk of structure damage or collapse in case of future events using microtremor recordings. Our study focuses on the application of HVSR method (Horizontal to Vertical Spectral Ratio) to microtremor measurements carried out in specific sites. Registrations have been performed by means of a tridirectional sensor Lennartz 3D-Lite (1 natural Hz frequency), connected with a 24-bit digital acquisition unit. A set of 10 time series of 800 second each, sampled at 125 Hz was recorded in several sites. The selected time windows of each time series were corrected for the base line and for anomalous trends, tapered with a cosine function to the first and last 5% of the signal, and band pass filtered from 0.5 to 20 Hz with cut off frequencies at 0.3 and 22 Hz. The same procedure performed for all...
In Trilling L and Perkins D and Dionysios D and Perlovsky L and Davey K and Landgrebe D Sepads 09 Proceedings of the 8th Wseas International Conference on Recent Advances in Software Engineering Parallel and Distributed Systems World Scientific and Engineering Acad and Soc, Feb 21, 2009
Wavelet Transform has been successfully used for many problems of seismological research. Its tra... more Wavelet Transform has been successfully used for many problems of seismological research. Its traditional form, based on serial implementation, satisfied the vast majority of requirements. Here we examined the parallel implementation of wavelet transform for the real time azimuth estimation. The performance improvement using parallel implementation is the objective that we seek since the above estimation is a critical part of an earthquake early warning system. Out results indicate that the improvement that we gather by the parallelization of wavelet transform can make a considerable difference on the performance of the early warning system.
Egu General Assembly Conference Abstracts, Apr 1, 2009
ABSTRACT The understanding of earthquake faulting process is one of the main factors that contrib... more ABSTRACT The understanding of earthquake faulting process is one of the main factors that contribute to earthquake damage. One of the most valuable and essential tools for the understanding of faulting process in the analysis of aftershocks. The critical point for successful aftershock studies is the mobile seismological network that will deployed in order to provide the required data. The main problem that arise for these networks is how fast the recorded data are available to data centres in order to estimate the focal mechanisms, the source parameters estimation as well as to examine microseismic activity. The ideal situation is to have these data available in real time but this is limited by the different telemetry requirements for every individual installation. Based on the experience gained from several installations in Hellenic Seismological Network of Crete (HSNC) we propose a mobile network scheme (called RaDeSeis) capable of installed in a limited amount of time and provide real time seismological data. RaDeSeis is an hybrid network based on VSAT and WiFi communication links between seismological stations and data centre. The network is deployed in star topology where the central station is the communication hub at the same time. Dedicated point-to-point links between central station and border station established using WiFi links. Communication between central station and data centre is established by VSAT. With appropriate routing on central station the data centre is collecting, control and monitor all the stations from the area of interest in real time. In order to decrease the time needed for each installation a specific software (RaLiEs - Rapid Link Establishment) is originated for the quicker link establishment between border stations and central station (with an average distance of 40km LOS) as well as to data centre. By using this software each telecommunication installation needs less than half an hour to complete the necessary link adjustments. Acknowledgements This work is partially supported by SE-RISK Project (INTERREG III, STRAND B ARCHIMED)/Axis: Integrated and Sustainable Management of Cultural and Natural Resources and of Landscape and Risk Management)
SHORT TERM EARTHQUAKE PREDICTION IN GREECE BY SEISMIC ELECTRIC SIGNALS P. VAROTSOS, M. LAZARIDOU,... more SHORT TERM EARTHQUAKE PREDICTION IN GREECE BY SEISMIC ELECTRIC SIGNALS P. VAROTSOS, M. LAZARIDOU, K. EFTAXIAS, G. ANTONOPOULOS, J. MAKPJS AND J. KOPANAS Solid State Section, Department of Physics, University of Athens, Greece. More than ...
Scattering of arbitrarily polarized electromagnetic plane waves by a dielectric cylinder buried i... more Scattering of arbitrarily polarized electromagnetic plane waves by a dielectric cylinder buried in an unbounded dielectric space and enclosing an array of parallel doubly layered (pipeline-type) dielectric circular cylinders is studied, in case of oblique incidence. The objective of this work is to present an exercise suitable for an advanced course on engineering electromagnetics. Using the boundary-value approach combined with the generalized separation variables method, we formulate the problem via a linear algebraic system with unknowns the field expansion constants. Solving this system, with single-term matrix elements, results in analytical expressions for both the scattered field and the scattering cross section of the structure. Numerical results are given for several configurations along with comparisons with previously published data.
The reconstruction of gapped microtremors recordings with the aid of CLEAN algorithm, which origi... more The reconstruction of gapped microtremors recordings with the aid of CLEAN algorithm, which originally developed for spectral analysis of unevenly spaced time series, is studied. As proved in previous relative studies the algorithm has the ability to "clean" the spectrum of a discrete signal from artifacts and additionally (through an Inverse DFT) to reconstruct the signal in time domain. We studied the algorithm's effectiveness of reconstruction in microtremors recordings, which can be consider as extremely noisy time series. We saw that for continuous gap with length up to 10% of the total length of microtremor recording, the algorithm is able to reconstruct efficiently.
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