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We present a Hellenic database of intensity measures from uniformly processed strong ground motion recordings, together with metadata on earthquake source attributes and recording site conditions. The database consists of information from 471 earthquakes between 1973 and 2015 that produced 2993 usable recordings from 333 sites. A key element of this work is a unified presentation of data from two major data providers that operate in Greece (Institute of Engineering Seismology and Earthquake Engineering and the Institute of Geodynamics, National Observatory of Athens) along with a university-operated local urban array (University of Patras). Consistent procedures were applied to develop source parameters that include hypocenter locations, moment magnitudes (directly estimated or derived using a conversion procedure), fault-plane solutions, and finite-fault parameters (generally, for events with M>6.0). The time-averaged shear-wave velocity in the upper 30 m parameter is provided for all 333 recording sites based on geophysical measurements where available (102) and proxy-based estimates otherwise. Most events are in the magnitude range of 3.8–7, occurred at shallow hypocentral depths (

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 each network and across networks. Moreover, the minimum ambient noise level expected for strong-motion installations is defined. Sensor orientation is estimated using surface-wave polarization methods to detect stations with misalignment on particular epochs. A single data center that hosts the complete seismic data archives with their respective metadata from networks covering similar geographical areas allows coordination between network operators and facilitates the adhesion to widely used best practices regarding station installation, data curation, and metadata definition. The overall achievement is harmonization among all contributing networks and a wider usage of all data archives, ultimately strengthening seismological research efforts in the region.

Using a recently completed database of uniformly processed strong-motion data recorded in Greece, we derive a ground-motion prediction model (GMPM) for horizontal-component peak ground velocity, peak ground acceleration, and 5% damped pseudoacceleration response spectra, at 105 periods ranging from 0.01 to 10 s. The equations were developed by modifying a global GMPM, to account for more rapid attenuation and weaker magnitude scaling in the Greek ground motions than in the global GMPM. Our GMPM is calibrated using the Greek data for distances up to 300 km, magnitudes from 4.0 to 7.0, and time-averaged 30 m shear-wave velocities from 150 to 1200 m/s. The GMPM has important attributes for hazard applications including magnitude scaling that extends the range of applicability to M 8.0 and nonlinear site response. These features are possible because they are well constrained by data in the global GMPM from which our model is derived. An interesting feature of the Greek data, also observed previously in studies of mid-magnitude events (6.1–6.5) in Italy, is that they are substantially overpredicted by the global GMPM, which may be a repeatable regional feature, but may also be influenced by soil–structure interaction. This bias is an important source of epistemic uncertainty that should be considered in hazard analysis.

This paper is one of a series of papers dealing with the investigation of the Lower ionospheric variation on the occasion of an intense tectonic activity.In the present paper, we investigate the TEC variations during the intense seismic activity in Arkalochori of Crete on December 2021 over Europe. The Total Electron Content (TEC) data are been provided by the Hermes GNSS Network managed by GNSS_QC, AUTH Greece, the HxGN/SmartNet-Greece of Metrica S.A, and the EUREF Network. These data were analysed using Discrete Fourier Analysis in order to investigate the TEC turbulence band content. The results of this investigation indicate that the High-Frequency limit fo of the ionospheric turbulence content, increases as aproaching the occurrence time of the earthquake, pointing to the earthquake epicenter, in accordane to our previous investigations. We conclude that the Lithosphere Atmosphere Ionosphere Coupling, LAIC, mechanism through acoustic or gravity waves could explain this phenomenology. Keywords: Seismicity, Lower Ionosphere, Ionospheric Turbulence, Brownian Walk, Aegean area.

On 3 March 2021, the Mw6.3 Tyrnavos earthquake shook much of the Thessalia region, leading to extensive damage in many small towns and villages in the activated area. The first main shock was followed in the next day, on 4th of March 2021, by an “equivalent” main shock with Mw6.0 in the adjacent fault segment. These are the largest earthquakes to strike the northeastern part of Thessalia since the M6.3, 1941 Larissa earthquake. The main shocks triggered extensive liquefaction mainly along the banks of the Titarisios tributary where alluvial flood deposits most probably amplified the ground motions. Our seismic monitoring efforts, with the use of recordings of the regional seismological network along with a dense local network that was installed three days after the seismic excitation initiation, led to the improved understanding the geometry and kinematics of the activated faults. The aftershocks form a north–northwest–trending, east–northeast–dipping, ~40 km long distribution, encompassing the two main ruptures along with minor activated structures, consistent with the rupture length estimated from analysis of regional waveform data and InSAR modeling. The first rupture was expanded bilaterally, the second main shock nucleated at its northern tip, where from this second rupture propagated unilaterally to the north–northwest. The focal mechanisms of the two main shocks support an almost pure normal faulting, similar to the aftershocks fault plane solution determined in this study. The strong ground motion of the March 3 main shock was computed with a stochastic simulation of finite fault model. Coseismic displacements that were detected using a dense GPS / GNSS network of five permanent stations located the Thessaly region, have shown an NNE–SSW extension as expected from the nature and location of the causative fault. Coulomb stress changes due to the coseismic slip of the first main shock, revealed that the hypocentral region of the second main shock was brought closer to failure by more than 10 bars.

There are several national and international online earthquake catalogs publishing the focal parameters of earthquakes in Turkey and surroundings. While international seismological centers provide global earthquake catalogs with data from around the world, as well as their own solutions, local and regional seismic centers are confined to publish regional catalogs with solutions derived exclusively from their own data. In this study, we investigate the consistency of the focal parameters provided by national and international agencies for a large number of earthquakes which occurred in and around Turkey during the period 2000–2017. Agencies that analyze earthquakes in this region on a regular basis and whose data are used in this study are the Bogazici University–Kandilli Observatory and Earthquake Research Institution (BOUN–KOERI; “KOERI” from now on) and the Disaster and Emergency Management Authority, Earthquake Research Directorate (AFAD–ERD; “AFAD” from now on) as well as one of the leading international seismological agencies, the International Seismological Centre (ISC). The study area covers the region bounded by the coordinates 35–42° N and 26–45° E. Estimations of origin times, epicentral coordinates, focal depths, and magnitudes, as well as their uncertainties, provided by AFAD, KOERI, and ISC, are examined. The magnitude values of these three centers are homogenized and checked against each other. Furthermore, the completeness (with regard to magnitude) of each of the tested catalogs is defined, as well as its variation in space and with time. Finally, it is shown that the locations provided by KOERI and AFAD are similar to each other, while ISC solutions are closer to those of KOERI.

In this paper we investigate the ionospheric turbulence from TEC observations before and during the intense seismic activity of October of 2018 at Zakynthos area (λ = 20.51°E, φ = 37°34'N), (Main shock: ML 6.6, 60.6 km SW of Zakynthos). The Total Electron Content (TEC) data of 5 Global Positioning System (GPS) stations of the EUREF network, which are being provided by IONOLAB (Turkey), were analyzed using Discrete Fourier Analysis in order to investigate the TEC variations. The results of this investigation indicate that the High-Frequency limit fo, of the ionospheric turbulence band content, increases as the site and the moment of the earthquake occurrence are approaching, pointing to the earthquake locus. We conclude that the LAIC mechanism through acoustic or gravity wave could explain this phenomenology.

In this paper we investigate the Lower ionospheric variations from TEC observations during the intense seismic activity of October 2020 in the area of Greece (35 o £ j £ 42o N, 19 o £ l £ 29o E). The Total Electron Content (TEC) data are been provided by the Hermes GNSS Network managed by GNSS_QC, AUTH Greece, the HxGN/SmartNet-Greece of Metrica S.A, and the EUREF Network. These data were analysed using both, statistical analysis of TEC variations in order to detect uneven gross variations and Discrete Fourier Analysis in order to investigate the TEC turbulence. The results of this investigation indicate that the High- Frequency limit fo of the ionospheric turbulence content, increases as aproaching the occurrence time of the earthquake, pointing to the earthquake epicenter, in accordane to our previous investigations (Contadakis et al., 2009; Contadakis et al., 2012; Contadakis et al., 2015; Scordilis et al., 2020). We conclude that the LAIC mechanism through acoustic or gravity waves could explain this phenomenology. Thus, observing the frequency content of the ionospheric turbidity we observe a decrease of the higher limit of the turbitity frequency band, as a result of the differential frequency attenuation of the propagating wave. In addition, the statistical analysis shows an excess greater than 3σ from the mean TEC values one and seven days before the earthquake. Since no major disturbance of the geomagnetic field occured during these days, we conclude that we probably observed precursory Ionospheric variations in accordance to analogous findings from the variation of VH/VHF electromagnetic wave propagrations over strong earthquake areas (e.g. Biagi et al. 2019) References Biagi and 11 co authors, The INFREP Network: Present Situation andRecent Results. Open Journal of Earthquake Research, vol.8, p. 101-115, 2019.Contadakis, M.E., Arabelos, D.N., Asteriadis, G., Spatalas, S.D., Pikridas, C., TEC variations over the Mediterranean during the seismic activity period of the last quarter of 2005 in the area of Greece, Nat. Hazards and Earth Syst. Sci., 8, 1267-1276, 2008.Contadakis, M.E., Arabelos, D.N., Asteriadis, G., Spatalas, S.D., Pikridas, C. TEC variations over Southern Europe before and during the M6.3 Abruzzo earthquake of 6th April 2009, Annals of Geophysics, vol. 55, iss. 1, p. 83-93, 2012.Contadakis, M. E., Arabelos, D.N., Vergos, G., Spatalas, S. D., Scordilis, E.M., 2015,TEC variations over the Mediterranean before and during the strong earthquake (M = 6.5) of 12th October 2013 in Crete, Greece, Physics and Chemistry of the Earth, Volume 85, p. 9-16., 2015.Scordilis E.M., Contadakis M.E, Vallianatos F., Spatalas S., Lower Ionospheric turbulence variations during the intense tectonic activity in Eastern Aegean area, Annals of Geophysics, 63, 5, PA544, 2020

In this paper we investigate the ionospheric turbulence from observations of TEC variations as well as from VLF/LF transmitter signal observations before and during the disastrous seismic activity of August and October 2016 in Central Italy. The Total Electron Content (TEC) data of 8 Global Positioning System (GPS) stations of the EUREF network, which are being provided by IONOLAB (Turkey), were analysed using Discrete Fourier Analysis in order to investigate the TEC variations. The data acquired for VLF/LF signal observations are from the receiver of Thessaloniki (40.59N, 22,78E), Greece, which monitor the VLF/LF transmitters of the International Network for Frontier Research on Earthquake Precursors (INFREP). A method of normalization according to the distance between the receiver and the transmitter is applied on the above data and then they are processed by the Hilbert Huang Transform (HHT) to produce the corresponding spectra for visual analysis. The results of both methods indicate that the High- Frequency limit fo, of the ionospheric turbulence content, increases as the site and the moment of the earthquake occurrence is approaching, pointing to the earthquake locus.

This paper may be considered as an additional approval of the way the tectonic activity affects the lower Ionosphere. The results of our investigation, on the occasion of the recent East Aegean tectonic activity, indicate that the High - Frequency limit, fo, of the ionospheric turbulence content, increases as the site and the time of the earthquake occurrence is approaching, pointing to the earthquake location.We conclude that the Lithosphere Atmosphere Ionosphere Coupling (LAIC) mechanism through acoustic or gravity wave could explain this phenomenology, as a result of a the frequency differential damping of the propagating turbulent in the ionosphere. Proper use of this result may lead to a method of earthquake hazard mitigation using the byproducts of the Global Positioning Network (actually Total Electron Contain, TEC, estimations) which are available freely.

In this paper, we investigate the ionospheric turbulence from TEC observations, before and during the intense seismic activity of September 2019 at Albania (main shock at l=19.445oE, j=41.372o N, Mw=5.6) and at Marmara sea (main shock at l=28.19 oE, j=40.872oN, Mw=5.7), as well as of November 2019 at Albania (main shock at l=19.470oE, j=41.381oN, Mw=6.4), and at Bosnia-Herzegovina (main shock at l=17.961oE, j=43.196oN, Mw=5.4).The Total Electron Content (TEC) data of 6 Global Positioning System (GPS) stations of the EUREF network, which are being provided by IONOLAB (Turkey), were analysed using Discrete Fourier Analysis in order to investigate the TEC variations. The results of this investigation indicate that the High- Frequency limit fo, of the ionospheric turbulence content, increases by aproaching the site and the time of the earthquake occurrence, pointing to the earthquake location (epicenter). We conclude that the LAIC mechanism, through acoustic or gravity wave, could explain this phenomenology. In addition the proximity of the tectonic active areas to the GPS stations offer us an opportunity to discriminate the origin of the disturbances

In this paper we investigate the ionospheric turbulence from TEC observations before and during the tectonic activity of the last quarter of 2019 in the Hellenic Arc, Greece (main shock at l=23.26oE, j=35.69oN, Mw=6.1). The Total Electron Content (TEC) data of 6 Global Positioning System (GPS) stations of the EUREF network, which are being provided by IONOLAB (Turkey), were analysed using Discrete Fourier Analysis in order to investigate the TEC variations. The results of this investigation indicate that the High- Frequency limit fo, of the ionospheric turbulence content, increases by aproaching the site and the time of the earthquake occurrence, pointing to the earthquake location (epicenter). We conclude that the LAIC mechanism through acoustic or gravity wave could explain this phenomenology.

We examine the active stress field of the Southern Aegean Sea subduction area from fault plane solution data, focusing on the variability resulting from the application of different stress inversion methods. The study area is characterized by a high seismicity level and has been struck repeatedly by large destructive shallow and intermediate-depth earthquakes (up to M∼8.0). A larger number of previously published Fault Plane Solutions (FPS), as well as additional FPS computed in the framework of this study, provide the basis for the detailed study of the Southern Aegean active stress field. The active stress field is examined using three well-established algorithms, as well as an adapted method proposed in this study, based on the statistical processing of solutions provided by the Gephart and Forsyth (1984) method. The results obtained from all methods show a systematic consistency, with the Gephart and Forsyth method exhibiting the largest discrepancy, in comparison to other approaches. The determined active stress field reveals several domains with similar seismotectonic characteristics. Along the Southern Aegean (Hellenic) volcanic arc, the roughly North-South extension field shows an excellent correlation with the local arc geometry (arc-normal extension). The outer arc is characterized by compression, as a result of the active subduction, with an almost constant NE-SW direction. Between these two regions, a narrow zone with approximately East-West extension develops along the whole Hellenic Arc with subtle spatial differences, while in the eastern Hellenic Arc a well-developed strike-slip faulting pattern is recognized along the broader area of the Pliny and Strabo trenches. Finally, all intermediate-depth events show the same transpressional pattern, with a characteristic down-dip extension along the subduction direction and an arc-parallel compression, which follows the local arc orientation.

Robust relations correlating 10 different magnitudes of intermediate‐depth and deep‐focus earthquakes to moment magnitude are proposed, in order to be efficiently incorporated into the compilation process of homogeneous (with respect to magnitude) earthquake catalogs. By using global data available from International Seismological Centre (ISC), National Earthquake Information Center (NEIC), Comprehensive Nuclear‐Test‐Ban Treaty Organization’s International Data Centre (IDC), Institute of Physics of the Earth in Moscow, Russia, and China Earthquake Networks Center in Beijing, the performance of several widely used magnitude scales, such as body wave ( m b , m B ) and surface wave ( M s ), is examined with respect to the moment magnitude scale ( M w ). Similarly, appropriate M w ‐calibrated relations are also provided for regional magnitude scales such as the M JMA magnitude calculated by the Japan Meteorological Agency. The analysis also involves the integration of focal depth as an additional variable to some of the above magnitude‐conversion relations. This depth effect proved to be important for ISC/NEIC’s body‐wave ( m b IN) and surface‐wave ( M s IN) magnitudes, leading to significant corrections for the estimated magnitudes. More specifically, a major change in the magnitude residual variation around the depth of 230 km was identified for the case of m b IN. Furthermore, the obtained results provide important observations on the behavior of certain magnitude scales. A typical case is the m b scale reported by IDC, which shows a systematic and large bias, with respect to the published M w data values.

In the present work we propose a new seismic zonation model of area type sources for the broader Aegean area, which can be readily used for seismic hazard assessment. The definition of this model is based not only on seismicity information but incorporates all available seismotectonic and neotectonic information for the study area, in an attempt to define zones which show not only a rather homogeneous seismicity release but also exhibit similar active faulting characteristics. For this reason, all available seismological information such as fault plane solutions and the corresponding kinematic axes have been incorporated in the analysis, as well as information about active tectonics, such as seismic and active faults. Moreover, various morphotectonic features (e.g. relief, coastline) were also considered. Finally, a revised seismic catalogue is employed and earthquake epicentres since historical times (550 BC–2008) are employed, in order to define areas of common seismotectonic characteristics, that could constitute a discrete seismic zone. A new revised model of 113 earthquake seismic zones of shallow earthquakes for the broader Aegean area is finally proposed. Using the proposed zonation model, a detailed study is performed for the catalogue completeness for the recent instrumental period.Using the defined completeness information, seismicity parameters (such as G–R values) for the 113 new seismic zones have been calculated, and their spatial distribution was also examined. The spatial variation of the obtained b values shows an excellent correlation with the geotectonic setting in the area, in good agreement with previous studies. Moreover, a quantitative estimation of seismicity is performed in terms of the mean return period, Tm, of large (M ≥ 6.0) earthquakes, as well as the most frequent maximum magnitude, Mt, for a typical time period (T = 50 yr), revealing significant spatial variations of seismicity levels within the study area. The new proposed seismic zonation model and its parameters can be readily employed for seismic hazard assessment for the broader Aegean area.

We present an historical overview of the main earthquake-prediction models developed throughout the history of seismology, based exclusively on spatiotemporal changes of seismicity (rates, patterns, etc.). We discuss the main model assumptions and performance, as well as their historical evolution. We focus on those approaches that have attempted to address issues related to time-dependent seismic hazard assessment (SHA) schemes. We also discuss how recent time-dependent models and their uncertainties have been efficiently used in time-dependent SHA analysis. Finally, in order to examine the possible impact of such models in SHA, we employ a parametric analysis of uncertainties related to a generic prediction model. More specifically, we examine the effect of uncertainties of a generic prediction model on SHA (e.g., prediction failures, false alarms, etc.), in an attempt to examine whether fuzzy and approximate predictions, even prone to large errors, can have a significant effect on time-dependent SHA, in comparison to standard, time-independent probabilistic SHA models.

A new relation is proposed for accurate determination of local magnitudes in Greece. This relation is based on a large number of synthetic Wood-Anderson (SWA) seismograms corresponding to 782 regional shallow earthquakes which occurred during the period 2007–2013 and recorded by 98 digital broad-band stations. These stations are installed and operated by the following: (a) the National Observatory of Athens (HL), (b) the Department of Geophysics of the Aristotle University of Thessaloniki (HT), (c) the Seismological Laboratory of the University of Athens (HA), and (d) the Seismological Laboratory of the Patras University (HP). The seismological networks of the above institutions constitute the recently (2004) established Hellenic Unified Seismic Network (HUSN). These records are used to calculate a refined geometrical spreading factor and an anelastic attenuation coefficient, representative for Greece and surrounding areas, proper for accurate calculation of local magnitudes in this region. Individual station corrections depending on the crustal structure variations in their vicinity and possible inconsistencies in instruments responses are also considered in order to further ameliorate magnitude estimation accuracy. Comparison of such calculated local magnitudes with corresponding original moment magnitudes, based on an independent dataset, revealed that these magnitude scales are equivalent for a wide range of values.

Central Asia and its surroundings constitute a geodynamically complicated region, where almost all types of tectonic patterns can be observed. A triple junction, collision, and subduction zones, as well as extended fault systems of all types prevail in different parts of this region and compose one of the most interesting and complex geotectonic environments on Earth. This complicated setting is also associated with intense deformation, resulting in a large number of high seismicity zones, where numerous strong earthquakes occur, also extending, in some cases, to intermediate depths. Several previous studies have focused on specific seismotectonic zones in order to assess the active tectonic setting and the associated stress regime. We attempt to provide a unified but detailed picture of the stress field variability for the entire central Asia region, using the well-known inversion method proposed by Gephart and Forsyth (1984), modified in the present work on the basis of Fisher statistics. For this application, we employ a large number of focal mechanisms, spatially separated in 138 data groups. Τhe proposed modified algorithm (FD-BSM) examines the Fisher distribution of all possible stress principal axes solutions and select the one that: (a) shows the smallest angle variation from the Fisher mean in all three principal distributions and (b) minimizes the difference between the theoretical and observed slip vectors of the employed fault plane solution data. Synthetic tests and comparison of the corresponding results with real data show that, in cases where the stress regime is not clearly uniform or the number of available data is rather small, the models selected by the modified approach (FD-BSM) are more robust and show better spatial coherence compared to the initial Gephart and Forsyth (1984) method or alternative techniques such as the method of Michael (1984, 1987) as adapted by Vavrycuk (2014).

On October 12, 2013, an earthquake with Mw = 6.5 occurred in the southern Hellenic Arc, approximately 20 km off the west coast of Crete. The main shock, the focal depth of which is on the order of 40 km, was followed by aftershocks felt in the nearby cities and villages, although the aftershock sequence was poor. The epicentre was located at approximately 60 km from a radio receiver in Crete (CRE), which belongs to the European VLF/LF Radio Network. Several days before the earthquake, a clear disturbance occurred in one of the ten radio signals that the CRE receiver sampled. The disturbance, which can be considered an anomaly, appeared in the 216 kHz radio signal radiated by the Radio Monte Carlo (MCO) transmitter. The radio path MCO-CRE crossed directly over the epicentre area of the aforementioned earthquake. In this work, we present a detailed analysis of the MCO signal anomaly using spectral tools. We also investigate the behaviour of other radio signals sampled by the CRE receiver and consider other possible causes of disturbances on the MCO radio signal. We conclude that the disturbance in the MCO radio signal is a convincingly possible precursor of the earthquake in Crete. Emission of electromagnetic waves with a frequency band that includes 216 kHz from the focal zone of the earthquake can provide a satisfactory explanation of the radio anomaly.

In this paper, we present an investigation on the ionospheric turbulence from TEC observations before and during the recent activity of Etna’s Volcano. Mount Etna is located close to the eastern coast of Sicily. The last eruption of Etna volcano took place on 24 December 2018 while two days later (26 December, 02:19 UTC) an earthquake of M=5.0 occurred ~15 km to the ESE of the volcano, causing damage to the nearby city of Catania. The results of our investigation, on the occasion of the Etna’s Volcanic activity, indicate that the high-frequency limit fo of the ionospheric turbulence band content, is increasing with time to the volcano eruption while, at the same time, fo isdecreasing with distance from the volcano. We conclude that the LAIC mechanism through acoustic or gravity waves could explain this phenomenology, as it has happened in cases of earthquake activity. Our observations indicate that the effect of volcanic eruption on the band content of the ionospheric turbulence is insignificant at distances greater than 1000km (at the most), a fact that we must consider in our research on Ionospheric turbulence in relation to earthquake precursors research.

Hazard assessment of dangerous natural phenomena is critical because of their evident results concerning loss of human life and property, especially in dense populated areas. Earthquakes are probably the most devastating phenomenon since their immediate and long-term consequences are severe. This study is focused on the earthquake data analysis in different regions of Greece, characterised by different seismicity levels. In specific, a novel model is proposed based on evolutionary computation methods, such as symbolic regression by genetic programming and genetic algorithms in order to elucidate preliminary hidden mathematical relations and patterns found in the seismological signals under study. Furthermore, the model is calibrated using reverse engineering and closes the loop from the data collection to initial hypothesis. In this way, the model formation is achieved. The presented simulation results qualitatively and quantitatively reveal some of the fundamental characteristics of each studied geograph...

We examined the seismic activity which preceded six strong mainshocks that occurred in the Aegean (M = 6.4–6.9, 33–43° N, 19–28° E) and two strong mainshocks that occurred in California (M = 6.5–7.1, 32–41° N, 115–125° W) during 1995–2010. We find that each of these eight mainshocks has been preceded by a pronounced decelerating and an equally easily identifiable accelerating seismic sequence with the time to the mainshock. The two preshock sequences of each mainshock occurred in separate space, time, and magnitude windows. In all eight cases, very low decelerating seismicity, as well as very low accelerating seismicity, is observed around the actual epicenter of the ensuing mainshock. Statistical tests on the observed measures of decelerating, q d, and accelerating, q a, seismicity against similar measures calculated using synthetic catalogs with spatiotemporal clustering based on the ETAS model show that there is an almost zero probability for each one of the two preshock sequences which preceded each of the eight mainshocks to be random. These results support the notion that every strong shallow mainshock is preceded by a decelerating and an accelerating seismic sequence with predictive properties for the ensuing mainshock.

Βασισμένοι στα αποτελέσματα των μελετών μας επί της παλιρροϊκής συμβολής στην πρόκληση σεισμών στον Ελλαδικό χώρο, θεωρούμε το επίπεδο εμπιστοσύνης p της συσχέτισης κατανομής σεισμών παλιρροϊκών περιόδων σαν δείκτη οριακής κατάστασης τεκτονικής τάσης για την εκδήλωση σεισμού. Σε αυτή την εργασία, με την ευκαιρία του καταστροφικού σεισμού του Νεπάλ, διερευνούμε τη χρονική μεταβολή του δείκτη p για την περιοχή του Ρήγματος των Νοτίων Ιμαλαϊων. Τα πρώτα αποτελέσματα δείχνουν ισχυρή συσχέτιση αυτής της παραμέτρου συμφωνίας p και εκδήλωση σεισμικότητας, για όλες τις παλιρροϊκές περιόδους. Συμπεραίνομε λοιπόν ότι αυτή η παράμετρος συμφωνίας p μπορεί να χρησιμοποιηθεί σαν μια πρόσθετη παράμετρος στην εκτίμηση σεισμικού κινδύνου., Based on the results of our studies for the tidal triggering effect on the seismicity of the Hellenic area, we consider the confidence level of earthquake occurrence - tidal period accordance p as an index of tectonic stress criticality for earthquake occurrence. In this paper, by the occasion of the recent catastrophic earthquake of Nepal, we investigate the variation of the index p for the South Himalaia Fault area. The preliminary results indicate positive correlation of the index p with seismicity, for all the tidal periods. We suggest that this compliance parameter p may be used as an additional element for the seismic risk assessment.

Με βάση όλα τα διαθέσιμα δεδομένα ορίζονται οκτώ κυκλικές σεισμογόνες πηγές στην ευρύτερη περιοχή του Αιγαίου. Η ακριβής θέση του κέντρου κάθε πηγής βελτιώνεται με την διερεύνηση της οιωνεί-περιοδικής γένεσης ισχυρών (M≥6.0) επιφανειακών (h 100km) κύριων σεισμών που έγιναν στο διάστημα 1911-2014. Στις ίδιες σεισμογόνες πηγές έγιναν και όλοι οι κύριοι σεισμοί με μεγέθη M≥6.3 στο διάστημα 1850-2014. Οι χρόνοι επανάληψης των σεισμών και στους δύο πλήρεις καταλόγους, μετά από κατάλληλη απο-ομαδοποίηση, βρέθηκε ότι έχουν προγνωστικές ιδιότητες που εκφράζονται στο μοντέλο TIMAPR (Time and Magnitude Predictable Regional model). Παρόμοιες ιδιότητες έχουν και οι προσεισμοί πρόσφατων κύριων σεισμών, οι οποίες εκφράζονται στο μοντέλο D-AS (Decelerating-Accelerating Seismicity model). Από την αναδρομική πρόγνωση του τελευταίου κύριου σεισμού σε κάθε μια από τις οκτώ περιοχές με την εφαρμογή και των δύο μοντέλων, προκύπτουν αποδεκτές τιμές σφαλμάτων στον χρόνο γένεσης, το επίκεντρο και το μέγεθος. Επιπρόσθετα, χρησιμοποιήθηκαν δεδομένα ως το τέλος του 2014 με στόχο την πρόγνωση πιθανώς επερχόμενου κύριου σεισμού σε κάθε μία από οκτώ πηγές, καθώς και την αναγνώριση του ρήγματος στο οποίο πιθανώς αυτός θα γίνει., On the basis of all available information eight circular seismogenic sources, where shallow (h 100km) earthquakes occur, are defined in the broader Aegean area. The location of each source is further improved by optimization of the quasi-periodic properties of the strong (M≥6.0) instrumentally recorded mainshocks, identified in a complete catalogue of earthquakes (1911-2014) after declustering. Moreover, in the same seismogenic sources, all M≥6.3 mainshocks that comprise another complete catalogue (1850-2014) have also occurred. Interevent times of mainshocks generated in each source have predictive properties expressed by the TIMAPR (Time and Magnitude Predictable Regional) model whereas preshocks of recent mainshocks have also such properties expressed by the D-AS (Decelerating-Accelerating Seismicity) model. Retrospective prediction of the last mainshock in each source by the joint application of the two models resulted in reasonable uncertainties. Then, as a forward test, data up to the end of 2014 were used to predict the next expected mainshock in each of the eight sources and to identify the fault where its epicentre will probably be located.

Decelerating generation of intermediate magnitude earthquakes (preshocks) in a narrow region (seismogenic region) and accelerating generation of relatively larger such earthquakes in a broader region (critical region) has been proposed as an appropriate model for intermediate-term earthquake prediction. We examined the seismic activity which preceded the Mw=7.7 (October 28, 2012) thrust event that occurred off the west coast of Haida Gwaii, Canada (formerly the Queen Charlotte islands), by applying the decelerating-accelerating seismic strain model. We found that this mainshock was preceded by a pronounced accelerating seismic sequence with the time to the mainshock, as well as by an equally easily identifiable decelerating seismic sequence. Both precursory seismic sequences occurred in different space, time and magnitude windows. The behavior of previous mainshocks that occurred close to the 2012 earthquake was also examined by the time and magnitude predictable regional model. An attempt was also made to identify such seismic strain patterns, which may also be related to the generation of strong mainshocks along the western coast of Canada.

The proposed cellular automata driven potential-basedmodel for earthquake simulation is a dynamic system constituted of cells-charges. It is assumed that the system balances through the exercitation of electrostatic Coulomb-forces among charges, without the existence of any other form of interconnection in-between. Such kinds of forces are also responsible for this level to be bonded with a rigid but moving plane below.

This paper presents an extensive simulation tool based on a Cellular Automata (CA) system that models fundamental seismic characteristics of a region. The CA-based dynamic model consists of cells-charges and it is used for the simulation of the earthquake process. The simulation tool has remarkably accelerated the response of the model by incorporating principles of the High Performance Computing (HPC). Extensive programming features of parallel computing have been applied, thus improving its processing effectiveness. The tool implements an enhanced (or hyper-) 2-dimensional version of the proposed CA model. Regional characteristics that depend on the seismic background of the area under study are assigned to the model with the application of a user-friendly software environment. The model is evaluated with real data that correspond to a circular region around Skyros Island, Greece, for different time periods, as for example one of 45 years (1901–1945). The enhanced 2-dimensional version of the model incorporates all principal characteristics of the 2-dimensional one, also including groups of CA cells that interact with others, located to a considerable distance in an attempt to simulate long-range interaction. The advanced simulation tool has been thoroughly evaluated. Several measurements have been made for different critical states, as well as for various cascade (earthquake) sizes, cell activities and different neighbourhood sizes. Simulation results qualitatively approach the Gutenberg–Richter (GR) scaling law and reveal fundamental characteristics of the system.

A two-dimensional (2-D) cellular automata (CA) dynamic system constituted of cells-charges has been proposed for the simulation of the earthquake process. In this paper, the study is focused on the optimal parameterisation of the model introducing the use of genetic algorithm (GA). The optimisation of the CA model parameterisation, by applying a standard GA, extends its ability to study various hypotheses concerning the seismicity of the region under consideration. The GA evolves an initially random population of candidate solutions of model parameters, such that in time appropriate solutions to emerge. The quality criterion is realised by taking into account the extent that the simulation results match the Gutenberg-Richter (GR) law derived from recorded data of the area under test. The simulation results presented here regard regions of Greece with different seismic and geophysical characteristics. The results found are in good quantitative and qualitative agreement with the GR scaling relations.

Decelerating generation of preshocks in a narrow (seismogenic) region and accelerating generation of other preshocks in a broader (crit- ical) region, called decelerating-accelerating seis- mic strain (D-AS) model has been proposed as appropriate for intermediate-term earthquake prediction. An attempt is made in the present work to identify such seismic strain patterns and estimate the corresponding probably ensuing large mainshocks (M ≥ 7.0) in south Japan (30- 38 ◦ N, 130-138 ◦ E). Two such patterns have been identified and the origin time, magnitude, and epicenter coordinates for each of the two corre- sponding probably ensuing mainshocks have been estimated. Model uncertainties of predicted quan- tities are also given to allow an objective for

A two-dimensional (2-D) Cellular Automata (CA) dynamic system constituted of cells-charges has been proposed for the simulation of the earthquake process. The CA model has been calibrated with the use of real data. The calibration incorporates major seismic characteristics of the area under test. The simulation results are found in good quantitative and qualitative agreement with the recorded Gutenberg–Richter (GR) scaling relations. The model is enriched with a powerful multi-parameter interface that enables the user to load real data from different regions. This paper examines the on-chip realisation of the model and its instrumentation. The CA model hardware implementation is based on Field Programmable Gate Array (FPGA) logic. It utilises an array of 32 × 32 cells. Parameters that construct the local CA rule constitute the input data. The initial seed, which to some extent corresponds to the seismic features of the area under test, is loaded in a semi-parallel way and the process is completed in a certain number of time steps. The automatic response of the processor provides the corresponding GR scaling law of the area under study. The hardware implementation of the CA-based earthquake simulation model is advantageous in terms of low-cost, high-speed, compactness and portability features. It can operate as a preliminary data-acquisition filter that accelerates the evaluation of recorded data as far as its origin time, spatial and magnitude completeness and quality are concerned. Software that performs reliable automatic phase picking, as well as data elaboration, can be assembled next to the earthquake recording instruments (the whole network) output to assure a quick and reliable iteration of the focal parameters of a recorded earthquake (epicentre coordinates, focal depth and magnitude). The dedicated processor can be accommodated right after this stage (before any manual elaboration) focusing on the near real-time development of a reliable qualitative dynamical seismic record and a mapping of the seismic characteristics of the area.

Global observations show that strong mainshocks are preceded by decelerating preshocks which occur in the focal (seismogenic) region of the ensuing mainshock and by accelerating preshocks which occur in a broader (critical) region of the mainshock. Predictive properties of these preshocks have been expressed by empirical relations supported by theory and form the Decelerating–Accelerating Seismic Strain (D–AS) model. A respective algorithm has been developed which is used to identify the critical and seismogenic region and estimate (predict) the corresponding ensuing mainshock. In the present work a forward test of this model is performed by attempting intermediate-term prediction of future big ( M ≥ 7.7) mainshocks along the western coast of south and central America. Three regions of decelerating shocks and three corresponding regions of accelerating shocks have been identified. The parameters (origin time, magnitude, epicenter coordinates) as well as their uncertainties have been estimated (predicted) for the corresponding probably ensuing three mainshocks. This forward test allows an objective evaluation of the model's ability for an intermediate-term prediction of strong shallow mainshocks.

Seismicity is an extended geophysical characteristic of the Greek dominion. There are certain areas of high seismic activity, as well as, regions of low seismicity where strong earthquakes are rather rare events. Consequently, it is of great interest to present a methodology concerning the earthquake process in Greece even for areas considered to be of low seismicity. In this paper, a study of the earthquake activity of an area in Northeastern Greece, centred at Xanthi, Thrace, extending over a region of radius R=80km, during a certain time period is presented. A two-dimensional cellular automaton (CA) dynamic system consisting of cells representing charges is used for the simulation of the earthquake process. The model has been tested as well as calibrated using the recorded events of the above-mentioned region as initial conditions. The simulation results are found in good quantitative and qualitative agreement with the Gutenberg-Richter (GR) scaling relations. Finally, the CA model has a user-friendly interface and enables the user to change several of its parameters, in order to study various hypotheses concerning the seismicity of the region under consideration.

During the past few decades the critical earthquake model, which is based on observations concerning accelerating seismic deformation and concepts of the critical point dynamics, has been proposed by various seismologists as a useful tool for intermediate-term earthquake prediction. A refined approach of this model has been previously applied to search for preshock (critical) regions in the southern Aegean, using all available data until the middle of 2002. A critical region corre- sponding to a large mainshock had been identified (Papazachos et al., 2002a,b) in the southwestern part of the Aegean, near the Cythera island. The predicted (in 2002) parameters for this ensuing earthquake are u 36.5� N, k 22.7� E for the epicental geographic coordinates (with a model uncertainty of 120 km), focal depth 100 km, moment magnitude M 6.9 0.5, and origin time tc 2006.4 2.0. The generation of the strong Cythera earthquake on 8 January 2006 with M 6.9, epicenter coordinates u 36.2� N and k 23.4� E and a focal depth of h 65 km satisfies this intermediate-term prediction. The region where significant macroseismic effects were anticipated from the predicted mainshock (Cythera, south Peloponnesus, west Crete, and west Cyclades) corresponds to the area where damage by the 8 January 2006 strong earthquake has been observed. The verification of this prediction is strong evidence that the intermediate-term prediction of strong earthquakes is potentially feasible, but additional forward testing of the model is needed to validate this result.

Recent reliable data are used to study the behavior of seismic activity before 46 strong shallow earthquakes (M ≥6.0), which correspond to five complete samples of mainshocks. These samples include 6 mainshocks (M=6.0–7.1) that occurred in western Mediterranean since 1980, 17 mainshocks (M=6.0–7.2) which occurred in the Aegean (Greece and surrounding area) since 1980, 5 mainshocks (M=6.4–7.5) that occurred in Anatolia since 1980, 12 mainshocks (M=6.0–7.3) that occurred in California since 1980 and 6 mainshocks (M=7.0–8.3) that occurred in Japan since 1990. In all 46 cases, a similar precursory seismicity pattern is observed. Specifically, it is observed that accelerating Benioff strain (square root of seismic energy) release caused by preshocks occurs in a broad circular region (critical region), with a radius about eight times larger than the fault length of the mainshock, in agreement with results obtained by various research groups during the last two decades. However, in a much smaller circular region (seismogenic region), with a radius about four times the fault length, the corresponding preshock strain decelerates with the time to the mainshock. The time variation of the strain follows in both cases a power law but the exponent power is smaller than unit (m¯=0.3) in the case of the accelerating preshock strain and larger than unit (m¯=3.0) in the case of the decelerating preshock strain. Predictive properties of this “Decelerating In–Accelerating Out Strain” model are expressed by empirical relations. The possibility of using this model for intermediate-term earthquake prediction is discussed and the relative model uncertainties are estimated.

In the present work a detailed seismotectonic study of the broader area of the Mygdonia basin (N. Greece) is performed. Digital data for earthquakes which occurred in the broader Mygdonia basin and were recorded by the permanent telemetric network of the Geophysical Laboratory of the Aristotle University of Thessaloniki during the period 1989–1999 were collected and fault plane solutions for 50 earthquakes which occurred in the study area were calculated with a modified first motions approach which incorporates amplitude and radiation pattern information. Fault plane solutions for the 3 main shocks of Volvi (23/05/78, M W = 5.8 and 20/06/78, M W = 6.5) and Arnaia (04/05/95, M W = 5.8) events and the 1978 aftershock sequence were additionally used. Moreover, data from two local networks established in the Mygdonia basin were also incorporated in the final dataset. Determination of the stress field was realized by the use of the method of Gephart and Forsyth [Gephart, J.W., Forsyth, D.W., 1984. An improved method for determining the regional stress tensor using earthquake focal mechanism data: application to the San Fernando earthquake sequence: Jour. Geophys. Res., v.89, no. B11, p. 9305–9320] for the stress tensor inversion and the results were compared with independent estimates based on the calculation of the average moment tensor [Papazachos, C.B.,Kiratzi, A.A., 1992. A formulation for reliable estimation of active crustal deformation and its application to central Greece. Geophys. J. Int. 111, 424–432]. The obtained stress results show a relatively good agreement between the two approaches, with differences in the azimuth of the dominant extension axis of the order of 10°. Furthermore, comparison with independent information for the mean stress axes provided by the study of kinematics on neotectonic faults [Mountrakis, D., Kilias, A., Tranos, M., Thomaidou, E., Papazachos, C., Karakaisis, G., Scordilis, E., Chatzidimitriou, P., Papadimitriou, E., Vargemezis, G., Aidona, E., Karagianni, E., Vamvakaris, D. Skarlatoudis, A. 2003. Determination of the settings and the seismotectonic behavior of the main seismic-active faults of Northern Greece area using neotectonic and seismological data. Earthquake Planning and Protection Organisation (OASP) (in Greek)] shows a similar agreement with typical misfit of the order 10°. The stress inversion method was modified in order to select one or both nodal planes of the focal mechanism which corresponds to the “true” fault plane of the occurred earthquakes and was able to select a single fault plane in the majority of examined cases. Using this approach, the obtained fault plane rose diagrams are in agreement with results from various neotectonic studies. Moreover, several secondary active fault branches were identified, which are still not clearly observed in the field.

The existence of several magnitude scales used by seismological centers all over the world and the compilation of earthquake catalogs by many authors have rendered globally valid relations connecting magnitude scales a necessity. This would allow the creation of a homogeneous global earthquake catalog, a useful tool for earthquake research. Of special interest is the definition of global relations converting different magnitude scales to the most reliable and useful scale of magnitude, the moment magnitude, MW. In order to accomplish this, a very large sample of data from international seismological sources (ISC, NEIC, HRVD, etc.) has been collected and processed. The magnitude scales tested against MW are the surface wave magnitude, MS, the body wave magnitude, mb, and the local magnitude, ML. The moment magnitudes adopted have been taken from the CMT solutions of HRVD and USGS. The data set used in this study contains 20,407 earthquakes, which occurred all over the world during the time period 1.1.1976–31.5.2003, for which moment magnitudes are available. It is shown that well-defined relations hold between MW and mb and MS and that these relations can be reliably used for compiling homogeneous, with respect to magnitude, earthquake catalogs.

Accelerating strain energy released by the generation of intermediate magnitude preshocks in a broad (critical) region, and decelerating energy released in a narrower (seismogenic) region, is considered as a distinct premonitory pattern useful in research for intermediate-term earthquake prediction. Accelerating seismicity in the broad region is satisfactorily interpreted by the critical earthquake model and decelerating seismicity in the narrower region is attributed to stress relaxation due to pre-seismic sliding. To facilitate the identification of such patterns an algorithm has been developed on the basis of data concerning accelerating and decelerating preshock sequences of globally distributed already occurred strong mainshocks. This algorithm is applied in the present work to identify regions, which are currently in a state of accelerating seismic deformation and are associated with corresponding narrower regions, which are in a state of decelerating seismic deformation in California. It has been observed that a region which includes known faults in central California is in a state of decelerating seismic strain release, while the surrounding region (south and north California, etc.) is in a state of accelerating seismic strain release. This pattern corresponds to a big probably oncoming mainshock in central California. The epicenter, magnitude and origin time, as well as the corresponding model uncertainties of this probably ensuing big mainshock have been estimated, allowing a forward testing of the model's efficiency for intermediate-term earthquake prediction.

The preshock (critical) regions of 20 mainshocks with magnitudes between 6.4 and 8.3, which occurred recently (since 1980) in a variety of seismotectonic regimes (Greece, Anatolia, Himalayas, Japan, California), were identified and investigated. All these strong earthquakes were preceded by accelerating time-to-mainshock seismic crustal deformation (Benioff strain). The time variation of the cumulative Benioff strain follows a power law with a power value ( m = 0.3) in very good agreement with theoretical considerations. We observed that the dimension of the critical region increased with increasing mainshock magnitude and with decreasing long-term seismicity rate of the region. An increase of the duration of this critical (preshock) phenomenon with decreasing long-term seismicity rate was also observed. This spatial and temporal scaling expresses characteristics of the critical earthquake model, which are of importance for earthquake prediction research. We also showed that the critical region of an oncoming mainshock coincides with the preparing region of this shock, where other precursory phenomena can be observed.

SUMMARY Properties of the accelerating seismic crustal deformation pattern and of the intermediateterm seismic quiescence pattern have been combined to identify faults in the Aegean area (34 ◦ N‐43 ◦ N, 19 ◦ E‐30 ◦ E) that have a considerable probability of generating strong earthquakes (M ≥ 6.4) during the next 5-yr period. Eight groups of such faults have been identified, and the probability of each fault being activated during this time period has been estimated. Three of these groups are located in southern Greece (Hellenic Arc), two in central Greece (East Central Greece, Ionian Islands), two in northwestern Turkey and one in the area of the borders of Albania, Greece and the Former Yugoslav Republic of Macedonia. The importance of these results for intermediate-term seismic hazard assessment is discussed.

According to previous observations [Geophys. Res. Lett. 27 (2000) 3957], the generation of large (Mz7.0) earthquakes in the western part of the north Anatolian fault system (Marmara Sea) is followed by strong earthquakes along the Northern Boundary of the Aegean microplate (NAB: northwestermost Anatolia–northern Aegean–central Greece–Ionian islands). Therefore, it can be hypothesized that a seismic excitation along this boundary should be expected after the occurrence of the Izmit 1999 earthquake (M=7.6). We have applied the method of accelerating seismic crustal deformation, which is based on concepts of critical point dynamics in an attempt to locate more precisely those regions along the NAB where seismic excitation is more likely to occur. For this reason, a detailed parametric grid search of the broader NAB area was performed for the identification of accelerating energy release behavior. Three such elliptical critical regions have been identified with centers along this boundary. The first region, (A), is centered in theeasternpartofthisboundary(40.2jN,27.2jE:southwestofMarmara),thesecondregion,(B),hasacenterinthemiddlepartof the boundary (38.8jN, 23.4jE: East Central Greece) and the third region, (C), in the westernmost part of the boundary (38.2jN, 20.9jE: Ionian Islands). The study of the time variation of the cumulative Benioff strain in two of the three identified regions (A and B) revealed that intense accelerating seismicity is observed especially after the occurrence of the 1999 Izmit mainshock. Therefore, it can be suggested that the seismic excitation, at least in these two regions, has been triggered by the Izmit mainshock. Estimations of the magnitudes and origin times of the expected mainshocks in these three critical regions have also been performed, assuming that the accelerating seismicity in these regions will lead to a critical point, that is, to the generation of mainshocks.

Time accelerating Benioff strain releasebefore the mainshock has been observed inall five cases of strong (M > 6.0) shallowmainshocks, which have occurred during thelast four decades in the area surroundingthe Adriatic Sea. This observation supportsthe idea that strong mainshocks arepreceded by accelerating seismic crustaldeformation due to the generation ofintermediate magnitude shocks (preshocks).It is further shown that the values ofparameters calculated from these datafollow appropriately modified relations,which have previously been proposed asadditional constraints to the criticalearthquake model and to the correspondingmethod of intermediate term earthquakeprediction. Thus, these results show thatthe identification of regions wheretime-accelerating Benioff strain followssuch constraints may lead to usefulinformation concerning the epicenter,magnitude and origin time of oncomingstrong mainshocks in this area. Theprocedure for identification of thetime-acceleration is validated byappropriate application on synthetic butrealistic random catalogues. Largerdimension of critical regions in Adriaticcompared to such regions in the Aegean isattributed to an order of magnitude smallerseismic deformation of the crust in theformer in comparison to the latter.

In the present article new predictive relations are proposed for the peak values of the horizontal components of ground acceleration, velocity, and displace- ment, using 619 strong motion recordings from shallow earthquakes in the broader Aegean area, which are processed using the same procedure in order to obtain a homogeneous strong motion database. The data set is derived from 225 earthquakes, mainly of normal and strike-slip focal mechanisms with magnitudes 4.5 M 7.0 and epicentral distances in the range 1 km R 160 km that have been relocated using an appropriate technique. About 1000 values of peak ground acceleration (PGA), velocity (PGV), and displacement (PGD) from horizontal components were used to derive the empirical predictive relations proposed in this study. A term ac- counting for the effect of faulting mechanisms in the predictive relations is intro- duced, and the UBC (1997) site classification is adopted for the quantification of the site effects. The new relations are compared to previous ones proposed for Greece or other regions with comparable seismotectonic environments. The regression anal- ysis showed a noticeable (up to 30%) variance reduction of the proposed relations for predicting PGA, PGV, and PGD values compared to previous ones for the Aegean area, suggesting a significant improvement of predictive relations due to the use of a homogeneous strong motion database and improved earthquake parameter infor- mation.

Instrumental magnitudes in Greece have been reported as: a) M magnitudes based on the records of the Wiechert or Mainka seismographs, b) MLGR magnitudes based on the records of the Wood-Anderson (WA) seismographs (To = 0.8 sec, Veffective ∼ 1000) or other short period seismographs calibrated against WA records and, c) MLSM magnitudes based on strong motion records (accelerograms). Comparison of such magnitudes with moment magnitudes, Mw, for 329 earthquakes, with epicenters in the broader Aegean area, performed in this study, showed that M, MLGR+0.5 and MLSM are practically equal to Mw, with a small overall standard error (σ = 0.23). Therefore, equivalent moment magnitudes, Mw ∗ , estimated from these magnitudes and reported in the catalogues of the Geophysical Laboratory of the University of Thessaloniki are equal to moment magnitudes for all practical purposes with reasonable uncertainties. It has been further shown that surface wave magnitudes, Ms ,f or M s

Ένας ομογeνής ως προς το μέγeθος, παγκόσμιος κατάλογος σeισμικότητας, που βασίζeται αποκλeιστικά σe δeδομένα σeισμών eνδιάμeσου-μeγάλου βάθους, που καλύπτουν χρονικά πeρίοδο μισού αιώνα, παρουσιάζeται στη παρούσα eργασία. Πeριγράφουμe τις διeργασίeς ομογeνοποίησης του μeγέθους σe δύο βασικά στάδια, κάνοντας χρήση 10 αξιόπιστων σχέσeων μeτατροπής μeγeθών, όπως προέκυψαν αποκλeιστικά από δeδομένα σeισμών eνδιάμeσου-μeγάλου βάθους (Tsampas et al., 2016). Αρχικά πραγματοποιeίται μeτατροπή όλων των διαθέσιμων, διαφορeτικής προέλeυσης μeγeθών, σe ένα ισοδύναμο ως προς τη κλίμακα σeισμικής ροπής μέγeθος (Mw*~Mw), eνώ στη συνέχeια γίνeται υπολογισμός της σταθμισμένης μέσης τιμής μeγέθους για όλα τα έμμeσα υπολογισμένα, Mw*. Μe αυτό τον τρόπο προκύπτeι μία ομογeνής κλίμακα μeγέθους (M), ως αποτέλeσμα των eπιμέρους συσχeτίσeων μeγeθών μe τη κλίμακα αναφοράς, το μέγeθος σeισμικής ροπής (Mw). Eπιπλέον,πραγματοποιeίται βeλτιστοποίηση της παραμέτρου του βάθους, μe σύνθeση δeδομένων βαθών υπολογισμένων από διαφορeτικές πηγές. Τέλος, και αφού διαπιστώνeται η αξιοπιστία του eνιαίου, ομογeνούς μeγέθους για το κατάλογο που προέκυψe, eφαρμόζeται μια συνοπτική μeθοδολογία χώρο χρονικής ανάλυσης του καταλόγου, που αναδeικνύeι τις δυνατότητeς πeραιτέρω αξιοποίησής του σe μeγάλης κλίμακας μeλέτeς eκτίμησης της σeισμικής eπικινδυνότητας ή μeλέτeς άλλου τύπου σe παγκόσμια κλίμακα.

Η μeσο-Ατλαντική ράχη (Μ-ΑR), η οποία διατρέχeι το μέσο του Ατλαντικού Ωκeανού, αποτeλeί ένα από τα πιο γνωστά συστήματα αποκλινόντων λιθοσφαιρικών ορίων. Οι σeισμικές έρeυνeς συνeτέλeσαν σημαντικά στην αποκρυπτογράφηση της δομής του ωκeάνιου φλοιού. Για την πραγματοποίησή τους απαραίτητη προϋπόθeση eίναι η ύπαρξη eνός αξιόπιστου καταλόγου σeισμών την eυρύτeρης πeριοχής. Στην παρούσα eργασία έγινe μια προσπάθeια για την δημιουργία eνός καταλόγου σeισμών της Μ-ΑR που θα μπορούσe να χρησιμοποιηθeί ως «eργαλeίο» για eυρeίας κλίμακας σeισμολογικές μeλέτeς της πeριοχής. Αυτό eπιτeύχθηκe μέσω της συλλογής και eπeξeργασίας eνός μeγάλου όγκου δeδομένων από διeθνή σeισμολογικά κέντρα και δημοσιeυμένους καταλόγους ισχυρών σeισμών του παρeλθόντος. Ως κύρια πηγή αναφοράς χρησιμοποιήθηκe το ISC, eνώ η κλίμακα μeγέθους που υιοθeτήθηκe eίναι αυτή του μeγέθους σeισμικής ροπής (MW). Κύριος στόχος ήταν ο eντοπισμός και η οργάνωση, βάσeι κριτηρίων, των καλύτeρων και πιο πρόσφατων διαθέσιμων πληροφοριών για τους σeισμούς που eντάσσονται μέσα στα όρια συντeταγμένων των ~81 (Β) έως -51 (Ν) και 10 (Α) έως ~ -50 (Δ) και έγιναν κατά το χρονικό διάστημα 1900-2014. Μeτά από την ομογeνοποίηση των μeγeθών, τον έλeγχο αξιοπιστίας eστιακών βαθών και του καθορισμού μeγέθους πληρότητας, δημιουργήθηκe ένας ομοιογeνής κατάλογος σeισμών της Μ-ΑR που αποτeλeίται από 14.211 σeισμούς που έγιναν κατά το χρονικό διάστημα 1900-2014.

Στην παρούσα eργασία eπαναξιολογeίται η σeισμική eπικινδυνότητα στην eυρύτeρη πeριοχή του Αιγαίου, μe τη χρήση eνός τροποποιημένου μοντέλου χρονικά ανeξάρτητης σeισμικότητας. Μια διαδικασία Monte-Carlo χρησιμοποιeίται για τη δημιουργία συνθeτικών καταλόγων που παρουσιάζουν συγκeκριμένα χαρακτηριστικά αναφορικά μe τη χωροχρονική κατανομή των σeισμών, αλλά και την κατανομή των μeγeθών τους. Eπιπλέον, eιδικότeρα γeωμeτρικά χαρακτηριστικά, όπως κeκλιμένeς ζώνeς συνeκτιμούνται στη δημιουργία των συνθeτικών καταλόγων. Ένας αναθeωρημένος σeισμικός κατάλογος, όλοι οι διαθέσιμοι μηχανισμοί γένeσης, αλλά και πληροφορίeς για τα σeισμοτeκτονικά χαρακτηριστικά της πeριοχής χρησιμοποιήθηκαν από κοινού ώστe να προταθeί ένα eπικαιροποιημένο μοντέλο σeισμικών ζωνών. Υπολογίστηκαν οι παράμeτροι σeισμικότητας για το μοντέλο και δημιουργήθηκαν οι συνθeτικοί σeισμικοί κατάλογοι μe την προτeινόμeνη διαδικασία. Eκτιμήθηκe η κατανομή των αναμeνόμeνων τιμών για διάφορeς παραμέτρους της eδαφικής κίνησης (π.χ. PGA, PGV), μe τη χρήση συνθeτικών καταλόγων σe διάφορeς θέσeις, eκτeλώντας υπολογισμούς απ' eυθeίας για όλους τους σeισμούς κάθe καταλόγου. Οι υπολογισμοί πραγματοποιήθηκαν για ένα πυκνό κάναβο σημeίων και η eκτίμηση της σeισμικής eπικινδυνότητας πραγματοποιήθηκe τόσο βάσeι της κατανομής της μέγιστης αναμeνόμeνης eδαφικής κίνησης, όσο και βάσeι της κατανομής των ακραίων τιμών του Gumbel. Παράλληλα, έγιναν υπολογισμοί μe τη χρήση κλασσικών αλγορίθμων eκτίμησης της σeισμικής eπικινδυνότητας (EqRISK) μe σκοπό να αξιολογηθeί η συμβατότητα της προτeινόμeνης μeθόδου μe άλλeς συμβατικές προσeγγίσeις.