Seismicity observed, at Methoni seismogenic area, Greece, after the analysis of the recorded Earth_s electric field of 21/2/2008_ 22/2/2008, at PYR, ATH and HIO monitoring sites, Greece (original) (raw)
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Tectonophysics, 1993
. Periodic variations in the Earth's electric field as earthquake precursors: results from some recent experiments in Greece. In: P. Varotsos and 0. Kulhanek (Editors), Measurement and Theoretical Models of the Earth's Electric Field Variations Related to Earthquakes. Tectonophysics, 224: 103-111. The results obtained during an extensive investigation of the variations in the Earth's electric field at three tectonically active areas in Greece, and their relation to the occurrence of earthquakes are described. In all three cases, a 24 h periodic oscillation of the Earth's electric field was observed prior to large imminent earthquakes, one of which was the September 13th, 1986 (measuring M, = 6.2 R) earthquake which devastated the city of Kalamata. Finally, two physical processes, which could explain the above phenomenon are proposed.
Entropy, 2018
A strong earthquake of magnitude M w 6.8 struck Western Greece on 25 October 2018 with an epicenter at 37.515 ∘ N 20.564 ∘ E. It was preceded by an anomalous geolectric signal that was recorded on 2 October 2018 at a measuring station 70 km away from the epicenter. Upon analyzing this signal in natural time, we find that it conforms to the conditions suggested for its identification as precursory Seismic Electric Signal (SES) activity. Notably, the observed lead time of 23 days lies within the range of values that has been very recently identified as being statistically significant for the precursory variations of the electric field of the Earth. Moreover, the analysis in natural time of the seismicity subsequent to the SES activity in the area candidate to suffer this strong earthquake reveals that the criticality conditions were obeyed early in the morning of 18 October 2018, i.e., almost a week before the strong earthquake occurrence, in agreement with earlier findings. Finally, ...
Seismicity anomalies prior to 8 June 2008, Mw=6.4 earthquake in Western Greece
Natural Hazards and Earth System Science, 2009
The epicentral area of the M w =6.4, 8 June 2008 main shock in northwestern Peloponesus, Western Greece, had been forecasted as a candidate for the occurrence of a strong earthquake by independent scientific investigations. This study concerns the seismicity of a large area surrounding the epicenter of the main shock using the seismological data from the monthly bulletins of the Institute of Geodynamics of the National Observatory of Athens. This data set is the most detailed earthquake catalog available for anomalous seismicity pattern investigations in Greece. The results indicate a decrease in seismicity rate seven years prior to the 8 June main shock which constituted a two and a half year long seismic quiescence surrounding the epicentral area. This quiescence anomaly was succeeded by a period of acceleration in seismic activity for five years approximately, until the occurrence of the main shock.
In this paper we show, in terms of fracture-induced electromagnetic emissions (EME) that the Earth system around the focal areas came to critical condition a few days before the occurrence of each one of the two recent earthquakes of Kefalonia (Cephalonia), Greece. Specifically, EME were recorded two days prior to the first earthquake [(38.22o N, 20.53oE), 26 January 2014, M=6.1] & six days prior to the second one [(38.26o N, 20.39oE), 03 February 2014, M=6.0]. Specifically, the MHz EME recorded by the remote telemetric stations on the island of Kefalonia and the neighboring island of Zante came simultaneously to critical condition in both cases. The analysis was performed by means of the method of critical fluctuations (MCF) revealing critical features.
Applied Sciences
Seismicity in the Ionian Sea (W. Greece) is mainly generated along the Cephalonia–Lefkada Transform Fault Zone (CLTFZ) in the central Ionian, and on the northwestern termination of the Hellenic subduction margin in the south. Joint pre-, co- and post-seismic ground deformation and seismological analysis is performed at the broad Ionian area, aiming to homogeneously study the spatiotemporal evolution of the activity prior to and after the occurrence of strong (M > 6) earthquakes during the period of 2014–2018. The 2014 Cephalonia earthquakes (Mw6.1 and Mw5.9) were generated on a faulting system adjacent to CLTFZ, causing local ground deformation. The post-seismic sequence is coupled in space and time with the 2015 Lefkada earthquake (Mw6.4), which occurred on the Lefkada segment of the CLTFZ. Co-seismic displacement was recorded in the broader area. Seismicity was concentrated along the CLTFZ, while its temporal evolution lasted for several months. The 2018 Zakynthos earthquake (M...
Seismicity anomalies prior to the 13 December 2008, Ms=5.7 earthquake in Central Greece
Natural Hazards and Earth System Science, 2009
This investigation has applied a recent methodology to identify seismic quiescence and seismic acceleration, prior to the occurrence of the 13 December 2008, M s =5.7 earthquake in Central Greece. Anomalous seismic quiescence is observed around the epicentral area almost twelve years prior to the main shock and it lasted for a period of about four and a half years. After this period an acceleration in seismic activity began and lasted until the main shock. Modeling this seismic sequence with the time-tofailure equation and with a fixed value of the exponent "m" equal to 0.32, shows a successful estimation of the occurrence time of the main event within a few days. The physical meaning of this particular choice of the "m" value is discussed.
Natural Hazards and Earth System Science, 2008
In this paper the Total Electron Content (TEC) data of eight Global Positioning System (GPS) stations of the EUREF network (AUT1, Thessaloniki, TUC2, Crete in Greece, MATE, Matera, LAMP, Lampedusa in Italy, GAIA, in Portugal, RABT, Rabat, EVPA, Evpatoria in Ukrain and TRAB, Trabson in Turkey) were analysed using wavelet analysis in order to detect any frequency dependence of the correlation between TEC over different stations. In the same time frequency dependence of Dst (Global geomagnetic field disturbances) and TEC variations over each GPS station are searched in order to detect any correlation between them. The main conclusion of this analysis is that the components of TEC variation with periods <3 h are more suitable in searching for earthquake precursors. On the base of this conclusion the analyzed TEC series are searched for possible precursory phenomena on the occasion of the seismic activity of the last quarter of 2005 in the area of Greece. An exalting (i.e. an increase in the amplitude) of variations with periods up to the tidal ones (period of 6 h,8 h,12 h) may be observed a month before and during the seismic activity over the stations TUC2 and AUT1 and may be attributed to this tectonic activity. Statistical properties of the 1.5 h component of the Total Vertical Electron Content (TVEC) over the nearest GPS stations (TUC2 and AUT1) of the areas of the seismic activity indicate that this component present characteristic exalting in the time period of 15 days before the shock.
A STATISTICAL REAPPRAISAL IN THE RELATIONSHIP BETWEEN GLOBAL AND GREEK SEISMIC ACTIVITY
Greek seismic activity exhibits a very significant positive correlation to the preceding global activity with a time-lag of 15 years. It seems that all Greece and the two characteristic areas in which we have separated it (Greece without Arc, and the area of the Greek seismic Arc), follow the global seismic activity but with a time-shift of 15 years. Moreover, it seems to exist an intrinsic interaction mechanism between the Greek seismic arc and the rest of Greece, which may be deduced by their different behavior exhibited when they are correlated with the global activity, as well as from the correlation between themselves, where a very significant positive correlation has been found with a time-lag of 3 years, for Greece without arc preceding. A quasi-periodic term of 30-yrs is also observed in these detailed four seismic time-series. The cross-correlation analysis of seismic time-series, as shown, is served as a powerful tool to clarify the complicated space-time pattern of the world wide mosaic of tectonic plate motions. The implications of spring-block model of tectonic plates interaction is invoked, considering the earth's rotation rate changes as their triggering agent. Particular emphasis is given to the potential of such studies in earthquake prediction efforts from local or regional scales to a global scale and vice-versa. EaEWEAER T p ~rt
A catalogue of seismicity in Greece and adjacent areas
Geophysical Journal International, 1981
A new earthquake catalogue for Greece has been formed to cover the instrumental period 1901-78, in particular 605 earthquakes for the period 1917-63 inclusive are relocated using first arrival data from the International Seismological Summary. These relocations incorporate macroseismically and other well-controlled master events into an ensuing joint epicentre determination technique. The largest annual average shift is 165 km for 78 earthquakes during the decade after 1917, decreasing to 17 km for the later years 1957-63. Magnitudes are redetermined mainly using readings from the Swedish network and Uppsala since as early as 1908. Catalogue completeness exists for magnitudes around 5.5 for at least the last 60 years, but magnitudes of about 4.7 are completely reported only during the most recent 15 years. The new epicentral positions lead to a better delineation of the seismic zones than has previously been achieved. The majority of shallow earthquakes are contained in a belt parallel to the Hellenic Arc which extends north into Albania, in the southeast the epicentral locations give a more diffuse extension of this zone into the west coast of Turkey. Depths of intermediate earthquakes along the Hellenic Arc tend to relocate to shallower depths, in the southwest part of Crete no earthquake focus deeper than 100 km is found, although in the southeastern section of the arc a tendency to increased depths is observed. A second zone starts at Leukas Island in the west and extends through central Greece to near Volos on the east coast, where it divides into two branches, which are less well defined, but which eventually join the seismicity of western Turkey. A third zone follows the Saronikos and Corinth gulfs.
2023
The Nor ther n Thessaly Basin in central Greece ranks amongst the most well pronounced extensional (graben) basins in the backarc Aegean Sea region, with well-mapped faults having an ∼E-W orientation, compatible with the ongoing predominant ∼N-S extension. The southern margin of the basin is bounded by major faults associated with strong (M 6 to M 7) earthquakes, whereas along its nor ther n margin, strong events are more scarce, in the documented catalogues. Along this nor ther n margin, a weak, albeit persisting foreshock activity, culminated within 3 d, to an M w 6.3 earthquake on 3 March 2021 associated with a 15-km-long NE dipping fault segment. It was followed the next day, by the second M w 6.0 main shock associated with a 13-km-long NE dipping fault segment and 9 d later by an M w 5.5 earthquake associated with an 8-km-long SW dipping fault segment, with its aligned epicentres, showcasing the cascade type acti v ation of adjacent fault segments. The sequence, evolved to be very productiv e, with aftershocks e xtending ∼50 km along a ∼NW-SE trending narrow seismic zone. All events indicate pure normal faulting, with an NNE-SSW oriented extensional axis, oblique to our previous consensus of the pre v alence of ∼N-S extension. This observ ation documents that inherited fault fabric can be reacti v ated within the modern tectonic stress field. We use high-quality seismological data, alongside Interferometric Synthetic Aperture Radar (InSAR) methodology and Global Navigation Satellite System (GNSS) data, to study the temporal and spatial evolution of the sequence, and to provide inferred kinematic models that describe the complexity of the seismic process, in terms of heterogeneous slip distribution, activated fault planes, fault geometry and displacement field. Cross-sections show that the activity defines the crustal seismogenic layer at depths between 5 and 10 km, associated with low-angle fault segments dipping to the NE. Other faults, both antithetic and secondary ones, appear active and accommodated aftershocks clusters. Using our preferred finite fault source model, we calculated the changes of Coulomb failure stress on the neighbouring faults.