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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.

We use teleseismic data to calculate the source model of the 24 May 2014 earthquake and regional catalogues to examine the spatial-temporal characteristics of the sequence. The sequence started in Saros Basin but almost simultaneously aftershocks spread along a ∼200 km zone, activating the entire North Aegean Trough. The aftershock sequence was rich in moderate (M 19 Nm (Mw6.8). This earthquake highlighted the fact that strike-slip faulting in the North Aegean Sea, can attain large lengths and activate very wide zones, reaching densely populated regions.

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.

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.

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.

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).

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.

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.

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

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.

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.

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.

— The time variation of two parameters related to accelerating seismic deformation before strong earthquakes in the Aegean area is examined. The first is the b parameter of the Gutenberg-Richter relation and the second is the curvature parameter C, which is a measure of deviation of the accelerating preshock deformation from a linear time variation of this deformation. Following two different procedures, it was found that the b value exhibits a decreasing trend prior to the oncoming earthquake, in agreement with the results of laboratory experiments and other independent observations. C values also show a decreasing trend before main shocks. These results indicate that such time variations of these parameters can be considered as precursory phenomena of ensuing strong earthquakes.

SUMMARY The large Izmit (NW Turkey) mainshock (1999 August 17, Mw= 7.6), followed by another large earthquake on 1999 November 12 (Mw= 7.2), caused extensive damage and loss of life in a zone approximately 170 km long along the coastal area of the Gulf of Izmit and further east to Adapazari and Duzce. On the basis of the critical earthquake concept and by applying a recently developed optimization algorithm, an elliptical area surrounding the 1999 August 17 mainshock epicentre was identified, in which accelerating moderate magnitude seismic activity started in 1981 and culminated in the generation of the mainshock. On the other hand, the space and time distribution of the aftershocks of the first mainshock (1999 August 17) and the time variations of the b value of the Gutenberg–Richter recurrence law and the mean aftershock magnitude, suggest that the second mainshock (1999 November 12) might have been anticipated.

We present the results of a systematic search for the identification of accelerating seismic crustal deformation in the broader northern Aegean area and in northwestern Turkey. We found that accelerating seismic deformation release, expressed by the generation of intermediate magnitude earthquakes, is currently observed in NW Turkey. On the basis of the critical earthquake model and by applying certain constraints which hold between the basic quantities involved in this phenomenon, it can be expected that this accelerating seismic activity may culminate in the generation of two strong earthquakes in this area during the next few years. The estimated epicenter coordinates of the larger of these probably impending earthquakes are 39.7°N–28.8°E, its magnitude is 7.0 and its occurrence time tc=2003.5. The second strong event is expected to occur at tc=2002.5 with a magnitude equal to 6.4 and epicenter coordinates 40.0°N–27.4°E. The uncertainties in the calculated focal parameters for these expected events are of the order of 100 km for the epicenter, ±0.5 for their magnitude and ±1.5 years for their occurrence time.

A region of intense accelerating seismic crustal deformation has been identified in the southwestern part of the Hellenic arc (broader area of Cythera island). The identification is performed using a detailed parametric grid search of the broader southern Aegean area for accelerating energy release behavior. The identified region has similar properties with past preshock (critical) regions, which have been identified for strong mainshocks in the Aegean area. Based on such observations, which suggest that this region is at a critical state that can lead to a critical point, that is, to the generation of a mainshock, an estimation is made of the possible epicenter coordinates, magnitude, and origin time of this oncoming large (M ∼7.0) earthquake. The estimation procedure is validated on the basis of retrospective analysis of strong events in the Aegean area, as well as by appropriate application on synthetic random catalogs. These results, the existence of similar observations of accelerating seismic deformation in eastern part of southern Aegean and independent information on the time distribution of large earthquakes (M ≥6.8) for the whole southern Aegean indicate that the generation of strong earthquakes in this area in the next few years must be considered as very probable.

Summary A recently developed algorithm has been applied to define regions of the northern Aegean in which accelerating seismic crustal deformation is currently occurring. An elliptical such region has been found in the western part of the North Aegean. Accelerating deformation, which started three decades ago and has been released by the generation of intermediate-magnitude earthquakes (M ≥ 4.5), is still occurring. Based on these observations we can assume that this region is now in a state (pre-shock deformation) that will lead to a critical point (main shock). The estimated basic parameters of this impending main shock are ϕ=39.7°N, λ=23.7°E for the epicentre, M=6.0 for the moment magnitude, and tc = 2001.1 for the origin time. The corresponding uncertainties are less than 100 km for the epicentre, ± 0.4 for the magnitude, and ±1.5 yr for the origin time.

On the basis of growing evidence thatstrong earthquakes are preceded by a periodof accelerating seismicity of moderatemagnitude earthquakes, an attempt is madeto search for such seismicity pattern in NWAegean area. Accelerating seismic crustaldeformation has been identified in the areaof southern Albanides mountain range(border region between Greece, formerYugoslavia and Albania). Based on certainproperties of this activity and on itssimilarity with accelerating seismicdeformation observed before a strongearthquake which occurred in the sameregion on 26 May 1960 (M = 6.5), we canconclude that a similar earthquake may begenerated in the same region during thenext few years. This conclusion is inagreement with independent results whichhave been derived on the basis of the timepredictable model.

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.

Precise zonation of the territory of China has been performed based on the active known faults, type of faulting and seismicity level. One hundred and forty seven seismogenic regions were defined, forming 10 larger seismic areas, and the seismotectonic characteristics in each one of them were investigated in detail. After checking for data accuracy and completeness of the shallow earthquakes (h # 60 km), the regional time and magnitude predictable model was applied and the model parameters were estimated. Based on the model applicability in the studied area, probabilities for the occurrence of strong (M $ 6.0) earthquakes during the next 10 years were calculated for each seismogenic region. Statistical tests have been used proving the superiority of the model in comparison with the time independent one, as well as in comparison with the actual earthquake occurrence. q 2001 Elsevier Science Ltd. All rights reserved.

Historical and instrumental data of the last five centuries show that major earthquakes in the Marmara Sea area are followed by high strong-earthquake seismicity in the Aegean area. During the first phase of this excitation period, which lasts about 3 years, strong shallow earthquakes concentrate almost exclusively along the Northern Boundary of the Aegean plate. Within 1–5 years after the first strong earthquake along this boundary, strong-earthquake seismicity also increases in the Eastern Aegean Boundary. On the basis of current ideas on active tectonics and the previous observations, we expect the generation of several mainshocks with a mean magnitude of M=6.5 along the Northern Aegean Boundary during the next 3 years, following the recent large Izmit (NW Turkey) earthquake (1999.8.17, M=7.4).

—The seismicity in the territory of China, a seismotectonically complicated region, has been examined by using three complete samples of earthquakes which occurred during the last two centuries (1800–1995). The b value of the Gutenberg-Richter relation was estimated by using this data sample. Taking into account the fact that the b value is spatially more stable than the a value, the b values were calculated at the nodes of a normal grid superposing on the entire area studied, and their distribution was examined. The results showed that the b value increases smoothly from 0.4 in inner-Mongolia to 0.8 in the east, south and southwest of China with higher values (b>0.8) in the Taiwan region. Furthermore, keeping fixed the obtained b values, the a value distribution was also examined. In order to display more detailed information about the seismicity, smaller cell surface (10,000 km2) for the calculation of the a values was chosen. The mean return periods for different cutoff magnitudes were also calculated for each of these small cells. It was observed that the mean return periods are the shortest ones in China, which are 10 and 50 years for the magnitude larger than or equal to 6.0 and 7.0, respectively.

The seismicity of western Macedonia is examined in the present paper. On the basis of historical information as well as on instrumental data it is found that this area is characterized by low seismicity. The focal region of the Grevena-Kozani 1995 earthquake exhibits the highest seismicity in terms of probabilities for the generation of strong (M s ≥ 6.0) earthquakes in a period of fifty years. Two other regions with relatively high seismicity were also distinguished (west of Edessa and around Prespes lakes). Accurate determination of focal parameters of all earthquakes occurred in the area during October 1975-April 1995, by the use of a 3-D crustal model shows that the seismic activity is related to the graben structures of the studied area. Finally, evidence is presented that the triggering of the 1995 earthquake may be related to the impoundment of the Polyfytos artificial lake.

The regional time and magnitude predictable model has been introduced, and has been shown to be appropriate to describe the behaviour in the occurrence of mainshocks. The model implies that the magnitude of the preceding mainshock in a seismogenic region, that is the largest earthquake during a seismic excitation, governs the time of occurrence and the magnitude of the expected mainshock in this region. This model has been applied in 149 seismogenic regions of the Alpine-Himalayan seismic belt. The model probability for the occurrence of the next very strong main shock (Ms ≥ 6.5 during the decade 1993–2002, as well as the magnitude of this shock in each of these regions have been calculated. Furthermore, two tests have been performed to check the validity of this model. These tests have shown the reliability of the model and its superiority compared to the classical time-independent model.

Investigation of the time-dependent seismicity in 274 seismogenic regions of the entire continental fracture system indicates that strong shallow earthquakes in each region exhibit short as well as intermediate term time clustering (duration extending to several years) which follow a power-law time distribution. Mainshocks, however (interevent times of the order of decades), show a quasiperiodic behaviour and follow the ‘regional time and magnitude predictable seismicity model’. This model is expressed by the following formulas $$\begin{gathered} \log T_t = 0.19 M_{\min } + 0.33 M_p - 0.39 \log m_0 + q \hfill \\ M_f = 0.73 M_{\min } - 0.28 M_p + 0.40 \log m_0 + m \hfill \\ \end{gathered} $$ which relate the interevent time,Tt (in years), and the surface wave magnitude,Mf, of the following mainshock: with the magnitude,Mmin, of the smallest mainshock considered, the magnitude,Mp, of the preceded mainshock and the moment rate,m0 (in dyn.cm.yr−1), in a seismogenic region. The values of the parametersq andm vary from area to area. The basic properties of this model are described and problems related to its physical significance are discussed.

A seismic source is defined, in the present work, as the part of the seismogenic layer of theearth’s crust with a circular horizontal dimension (E, R), where E is the epicenter of the largestearthquake (mainshock) ever occurred in this seismic source and radius equal to the half faultlength of this largest earthquake (R=L/2). In addition to foreshocks and aftershocks othersmaller mainshocks occur in other smaller faults of this source or in parts of the main fault.All available historical and instrumental data concerning strong (M³6.0) shallow (h≤60 km) andintermediate depth (60km

Two models, which contribute to the knowledge on intermediate term earthquake prediction are further examined, improved and applied. The first of these models, called Time and Magnitude Predictable (TIMAP) regional model is based on repeat times of mainshocks generated by tectonic loading on a network of faults which are located in a certain seismic region (faults’ region). The second model, called Decelerating-Accelerating Strain (D-AS) model, is based on triggering of a mainshock by its preshocks. Parameters of the TIMAP model have been specified for the Aegean area and applied by a backward test in 86 circular faults’ regions of this area. The test shows the validity of this time dependent model with 29% false alarms. Data concerning decelerating and accelerating seismic (Benioff) strain, which preceded 46 strong (M≥6.3) recent mainshocks in a variety of global seismotectonic regimes, show that the generation of a mainshock is triggered by quasi-static stress changes due to accelerating preshocks which occur in a broad (critical) region and by static stress changes due to the large number (frequency of occurrence) of small preshocks generated in a narrow (seismogenic) region. Retrospective predictions (postdictions) of these 46 mainshocks by the D–AS model confirms previous results concerning the prediction uncertainties (2σ) of the model in the origin time (± 2.5 years), epicenter location (≤ 150 km) and magnitude (± 0.4) of an ensuing mainshock with a probability ~ 80%. Information is also given on the successful prediction by the D-AS model of: 1) the Cythera strong (M = 6.9) earthquake which occurred on 8 January 2006 in the southwestern part of the Hellenic Arc and 2) of the Rhodes strong (M = 6.4) earthquake which occurred on 15 July 2008 in the Eastern part of this Arc. A backward combined application of both models in the Aegean area shows an uncertainty ≤120km in the epicenter location of an ensuing mainshock.

Μία βασική διεργασία κατά τη σύνταξη ομογενών και πλήρων καταλόγων σεισμικότητας είναι η διεξοδική διερεύνηση των δυνητικά εύρωστων σχέσεων που συνδέουν μεταξύ τους κλίμακες διαφορετικών μεγεθών. Η συντριπτική πλειονότητα των ήδη δημοσιευμένων σχέσεων αφορά ως επί το πλείστον δεδομένα επιφανειακών σεισμών με εστιακά βάθη μέχρι και τα 60-70 χιλιόμετρα. Στην παρούσα εργασία, διαφορετικές κλίμακες μεγέθους προερχόμενες από 66 κέντρα σε παγκόσμια κλίμακα, σε συνδυασμό με ήδη δημοσιευμένους καταλόγους, εξετάζονται για σεισμούς με εστιακά βάθη 61-700 χιλιομέτρων. Εφαρμόζοντας ανάλυση ελαχίστων τετραγώνων προέκυψαν 12 νέες αξιόπιστες σχέσεις βαθμονόμησης που συνδέουν τις αντίστοιχες κλίμακες μεγεθών με το μέγεθος σεισμικής ροπής. Μεταξύ άλλω ελέγχθηκαν οι κλίμακες χωρικού (mb) και επιφανειακού μεγέθους (Ms) που ανακοινώνονται από Διεθνή (ISC, NEIC και IDC) και εθνικά κέντρα ( MOS από Μόσχα, BJI από Πεκίνο, DJA από Τζακάρτα) καθώς και το μέγεθος που υπολογίζεται από το JMA (Ιαπωνία). Από τα παραπάνω αποτελέσματα προκύπτουν σημαντικές παρατηρήσεις σχετικά με την συμπεριφορά ορισμένων από τις κλίμακες μεγέθους. Αξιοσημείωτη είναι η διαφοροποίηση που παρατηρείται ως προς τους ενδιαμέσου και τους μεγάλου βάθους σεισμούς για το χωρικό μέγεθος mb του IDC. Επιπλέον, η σύγκριση του μεγέθους σεισμικής ροπής του NIED με τα αντίστοιχα μεγέθη από GCMT και NEIC αναδεικνύει ένα εμφανώς κατώτερο επίπεδο "κορεσμού" προσδιοριζόμενο περίπου στη τιμή 5.0, An essential step in the compilation of homogeneous and complete earthquake catalogs is the thorough investigation of potentially robust relations between different magnitude scales. The vast majority of already published relations usually concerns shallow-focus earthquake data with depths up to 60-70 km. In the present study, several magnitude scales reported by 66 world-wide data providers in conjunction with published catalogs are examined within the depth range of 61-700 km, by applying least-squares regression analysis. Among other widely used scales, as body wave (mb, mB) and surface wave (Ms) magnitudes cited by International Centers (i.e. ISC, NEIC and IDC), the behavior of relevant magnitude scales determined by MOS (Moscow, Russia), BJI (Beijing, China), DJA (Djakarta, Indonesia) and the Japanese magnitude calculated by JMA, is also examined. By this way, robust calibrating relationships of 12 magnitude scales to the moment magnitudes provided by GCMT, NEIC and JMA are defined. From the obtained results important observations on the behavior of certain magnitude scales were made. Thus, a remarkable variation of mb scale cited by IDC could be noted for intermediate and deep focus events. Furthermore, a comparison with the Mw of NIED revealed an apparent lower “saturation” level around 5.0 below which the moment magnitude values published by GCMT and NEIC, are systematically overestimated.

H παρακολούθηση και eκτίμηση της eξέλιξης σeισμικών eξάρσeων σe σχeδόν πραγματικό χρόνο έχeι μeγάλη πρακτική σημασία, καθώς μπορeί να παρέχeι χρήσιμeς πληροφορίeς αξιοποιήσιμeς για την αντισeισμική προστασία. Eπί πλέον παρέχeι eνδeίξeις για την πιθανή eξέλιξη της διέγeρσης κάτι eξαιρeτικά σημαντικό τόσο για τους πολίτeς όσο και για τις αρχές. Για την eξυπηρέτηση αυτού του σκοπού, υλοποιήθηκe ένα ημι-αυτοματοποιημένο λογισμικό το οποίο απαρτίζeται από ένα πλήθος eπιμέρους υποπρογραμμάτων. Κύριος στόχος του λογισμικού αυτού eίναι η σe σχeδόν πραγματικό χρόνο αυτοματοποιημένη παρακολούθηση μιας σeισμικής διέγeρσης που eίναι σe eξέλιξη. Έτσι, μέσω διαδοχικών υπολογισμών των παραμέτρων της διέγeρσης και κατασκeυής των αντίστοιχων διαγραμμάτων eπιτυγχάνeται η eξαγωγή συμπeρασμάτων σχeτικά μe την eξέλιξή της. Συγκeκριμένα, το λογισμικό παράγeι ανά τακτά χρονικά διαστήματα (οριζόμeνα από το χρήστη) γραφήματα που πeριγράφουν την κατά μέγeθος, χωρική, χρονική, και χωρο-χρονική κατανομή καθώς και τη μeταβολή του μέσου μeγέθους των σeισμών-μeλών της διέγeρσης, δίνοντας κατ’ αυτόν τον τρόπο τη δυνατότητα διαμόρφωσης τeκμηριωμένης eκτίμησης σχeτικά μe την ομαλή ή μη eξέλιξη της διέγeρσης. Eφαρμογή του λογισμικού eπιχeιρήθηκe κατά τη διάρκeια της σeισμικής ακολουθίας η οποία eκδηλώθηκe στις 8/1/2013 ΝΑ της Λήμνου μe κύριο σeισμό μeγέθους Μ=5.9 (14:16 GMT). Τα διαδοχικά γραφήματα που προέκυψαν από την eφαρμογή του παραπάνω λογισμικού κατά τις πρώτeς eπτά μέρeς, που αποτέλeσαν την κύρια φάση αυτής της διέγeρσης, έδeιξαν «ομαλή» eξέλιξη της διέγeρσης μe χαρακτηριστικά τυπικής μeτασeισμικής ακολουθίας.

The region of Iran has been divided into 21 seismogenic source areas on the basis of certain seismological and geomorphological criteria. In each of these source areas, the inter-event times between successive main shocks with magnitudes equal to or larger than certain cut-off magnitudes were considered. These inter-event times as well as the magnitudes of the main shocks have been used to determine the following relationships by a multilinear regression technique: log T t = 0.10M min + 0.36M p – 0.33 log M 0 + 6.97 M f = 0.66M min – 0.29M p + 0.61 log M 0 – 10.69 where Tt is the calculated inter-event time measured in years, Mmin is the magnitude of the smallest main shock considered, Mp and Mf are the magnitudes of the preceding and following main shocks and M 0 is the annual seismic moment release in each source area. These relationships express the basic idea of the time- and magnitude-predictable model from which given the time of occurrence and the magnitude of the last main shock in a certain seismogenic source area, one can calculate the time of occurrence and the magnitude of the next main shock in that area by using the first and second of the equations respectively. However, as there is considerable scatter in the observations, conditional probabilities for the occurrence of a main shock during the next 10 years (1993–2002), as well as the magnitude of the expected main shock in each seismogenic source area were determined.

SUMMARY The North and East Anatolian Fault Zones have been separated into 10 seismogenic sources on the basis of certain seismological and geomorphological criteria. In each of these sources, the interevent times between successive main shocks with magnitudes equal to or larger than a certain magnitude threshold were considered. These times and the magnitudes of the main shocks have been used to determine the following empirical relations: log Tt= 0.27 Mmin+ 0.19 Mp+a, Mf= 0.76 Mmin - 0.48Mp+m where Tt is the interevent time measured in years, M,min the surface wave magnitude of the smallest main shock considered, Mp is the magnitude of the preceding main shock, and Mf is the magnitude of the following main shock. Multiple correlation coefficients equal to 0.83 and 0.70 and standard deviations equal to 0.16 and 0.34 were calculated for the first and second of these relations, respectively. On the basis of these relations and taking into account the time of occurrence of the last main shock, the probabilities of occurrence of main shocks in each seismogenic source during the next decade were determined.

The New Guinea-Bismarck Sea region has been divided into 17 seismogenic sources on the basis of certain seismological and geomorphological criteria. In each of these sources the interevent times between successive main shocks with magnitudes equal to or larger than certain cut-off magnitudes were considered. These interevent times as well as the magnitudes of the main shocks have been used to determine the following relations: log Tt = 0.36Mmin + 0.28Mp - 0.49 logMo + 9.58, ME = 0.74Mmin-0.31Mp+0.49logMo-8.53, where Tt is the calculated interevent time measured in years, Mmin is the magnitude of the smallest main shock considered, Mp and ME are the magnitudes of the preceding and the expected main shocks and Mo is the yearly released seismic moment in each source. On the basis of these relations and considering the date and the magnitude of the last main shock, conditional probabilities for the next 10 years (1993-2002) and the magnitude of the expected main shock in each source were determined.

Recent observations of strong earthquakes that occurred in the Aegean and surrounding areas during the last several years indicate rather low stress drop values. An interesting example is the 1978 Thessaloniki earthquake (northern Greece), with Ms = 6.5. Values between 6.6 and 12 bars have been determined for this earthquake by assuming unilateral or bilateral rupture propagation and circular or rectangular fault models. These values are considerably lower than the average values calculated not only for intraplate earthquakes (about 60 bars) but also for interplate earthquakes (about 30 bars). In this paper an attempt is made to investigate the cause of this fact by studying the dynamic rupture process of this earthquake. A three-dimensional, spontaneous, shear crack model on a dipping fault in a layered medium was assumed, and a finite-difference approach has been adopted for numerically solving the wave equations in a three-dimensional space. It was found that such a low stress drop may be obtained in cases of small differences between ambient stress and fault strength, and between tectonic shear stress and dynamic frictional stress. Such physical conditions in the focal region may result in an average fault displacement which is close to the observed one for this earthquake.

During the cruise of the Soviet research vessel RIFT in April 1987 in the southern Aegean Sea, an array of five ocean bottom seismographs was deployed. During its operation (19–27 April), more than 400 events with magnitudes, M L , varying between −0.5 and 4.4 were recorded. Their spatial distribution reconfirms the typical characteristics of a subducting slab (Mediterranean lithosphere) under the Aegean lithosphere. The thickness of the seismogenic layer in the southern Aegean sea is of the order of 30 km.

[1] Accelerating preshock seismic strain in a broad (critical) region and decelerating preshock seismic strain in a narrower (seismogenic) region constitute a model for intermediate-term prediction of strong main shocks. An effort is made in the present work for a forward test of the Decelerating-Accelerating Seismic Strain (D-AS) model by identifying such patterns and estimating the corresponding, probably ensuing, strong main shocks (M ≥ 7.0) in central Asia (20°N–45°N, 42°E–105°E). Five such patterns have been identified, and the origin time, magnitude, and epicentral geographic coordinates of each of the corresponding main shocks have been estimated (predicted). Model uncertainties of the estimated time, magnitude, and space parameters of these probably ensuing main shocks, as well as appropriate statistical tests against a standard Gutenberg-Richter seismicity distribution, are also presented to allow a future objective evaluation of the model's efficiency for intermediate-term earthquake prediction.

The results of the study of seismic sequences of all the mainshocks with M>5.6 during 1911-1965 and M>5.0 during 1966-1985 which occurred in the Aegean and surrounding area are presented. As regards the foreshocks, two relations have been proposed that can be used to determine (1) the probability that at least one foreshock, with magnitude Mf or larger, will precede a strong (M>6.0) earthquake, and (2) the probability for the largest foreshock to occur during t days before the mainshock. It was also found that the rate of foreshock occurrence, N(TS), increases as the time of the mainshock approaches and is described by a power-law function. The time and magnitude distribution of several foreshock sequences were also studied. The study of aftershock sequences concerned properties of their largest aftershock, the dependence of the duration and number of the aftershocks on the magnitude of the mainshock and the time and magnitude distribution of several aftershock sequences. The conclusion is that the study of a seismic excitation which is based on continuous monitoring and fast determination of the basic focal parameters of the earthquakes can contribute to clarify whether this activity evolves normally or not.

Evia Island (Greece) lies in a transition zone from strike-slip faulting in the east, due to the strands of the North Anatolian Fault (NAF) that enter to the Aegean Sea, to normal faulting in the west along central Greece. In June 2003 a series of moderate events occurred in central Evia whose source parameters are investigated. These earthquakes caused serious damage to almost 20 residencies mainly in the town of Psachna. The sequence could be identified as an earthquake swarm with earthquake magnitudes in the range of 3 < M < 4.9. We used the Ρ and S arrivals at the stations of the National Seismic Network to relocate the events using the double-difference algorithm. All Ρ and S phase pickings were made by us using the broad band records from the network operated by the Geodynamic Institute of Athens. The relocated epicenters define a pronounced ENE- WSW zone, parallel to the high topography of the area. All depths are shallow from 1 to 8 Km. Regional waveform modeling was applied to determine the focal mechanisms of the larger events and FPFIT for the focal mechanisms of the smaller magnitude events. The majority of the focal mechanisms indicate normal faulting along almost E-W striking planes suggesting that deformation is mainly taken by normal faulting with a minor dextral horizontal motion. Normal faults with a N-S strike have been also observed showing that the E-W extension is present as it is observed in other parts of the Aegean region. Evia Island and its pattern of deformation is very interesting from the seismotectonic point of view. The fact that no large magnitude earthquake has occurred in Evia Island during instrumental times, makes the study of this earthquake swarm important. Previous work (Kiratzi, 2002) has shown that the deformation in northern Evia Island is taken up mainly by strike-slip faulting. Moreover, depending on the orientation of the activated faults in respect to the present state stress field, dextral or sinistral horizontal motion is observed. The Psachna earthquakes showed that an almost N-S extensional field prevails in central Evia Island with a few strikeslip focal mechanisms, suggesting that this part is mostly affected by the normal faulting system of central Greece.