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  • 1
    ISSN: 1420-9136
    Keywords: fault area ; seismic moment ; stress drop ; magnitude
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract A data set of nineteen, mainly shallow, moderate to large earthquakes, which occurred in the Aegean and the surrounding area, has been used to derive empirical relations for kinematic fault parameters. Thus the relations between seismic momentM 0 and magnitudeM s andm b and betweenM 0 andM s and fault dimensionsS andL have been determined. From these relations and theoretical ones it was deduced that earthquakes in the Aegean and the surrounding events, chiefly interplate, are characterized by low average stress drop values. Values of Δσ ranging from 1 to 30 bar are consistent with the data. It was also found that, in general terms, most of the data obey the geometrical similarity conditionL=2w, whereL is the fault length measured along the strike andw is its width measured along the dip. For strike-slip faults, however, the conditionL=4w seems to hold.
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  • 2
    ISSN: 1420-9136
    Keywords: fault plane solution ; seismic sequence ; active tectonics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract A shallow earthquake ofM S=6.2 occurred in the southern part of the Peloponnesus, 12 km north of the port of the city of Kalamata, which caused considerable damage. The fault plane solution of the main shock, geological data and field observations, as well as the distribution of foci of aftershocks, indicate that the seismic fault is a listric normal one trending NNE-SSW and dipping to WNW. The surface ruptures caused by the earthquake coincide with the trace of a neotectonic fault, which is located 2–3 km east of the city of Kalamata and which is related to the formation of Messiniakos gulf during the Pliocene-Quaternary tectonics. Field observations indicate that the earthquake is due to the reactivation of the same fault. A three-days aftershock study in the area, with portable seismographs, recorded many aftershocks of which 39 withM S≥1.7 were very well located. The distribution of aftershocks forms two clusters, one near the epicenter of the main shock in the northern part of the seismogenic volume, and the other near the epicenter of the largest aftershock (M S=5.4) in the southern part of this volume. The central part of the area lacks aftershocks, which probably indicates that this is the part of the fault which slipped smoothly during the earthquake.
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  • 3
    ISSN: 1420-9136
    Keywords: Moment tensor inversion ; North Aegean ; Greece
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract Average source parameters for three large North Aegean events are obtained from body wave inversion for the moment tensor. The parameters for the events are as follows: The events exhibit dextral strike-slip faulting with theT axis striking NS and nearly horizontal, implying extension in this direction. The focal mechanisms obtained are in agreement with the seismotectonic regime of the North Aegean. It is known that the region is tectonically controlled by the existence of the strike-slip Anatolian fault and its westward continuation in the Aegean, as well as the NS extension the whole Aegean area undergoes. The components of the moment tensor show that the region is dominated by compression in the EW direction which is encompassed by extension in the NS direction. All the events were found to be shallow (≤10 km) with a source time function of approximately 8 s duration and small stress drop values. The teleseismic long period verticalP-waves exhibited distortions, that could be attributed to lateral inhomogeneities in the source structure or more probably to a nonflat water-crust interface.
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  • 4
    Electronic Resource
    Electronic Resource
    Springer
    Pure and applied geophysics 140 (1993), S. 391-402 
    ISSN: 1420-9136
    Keywords: Active deformation ; Vrancea
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract Recent and historical seismicity as well as reliable fault plane solutions are used to study the active deformation caused by the occurrence of intermediate depth (60–170 km) earthquakes of the Vrancea region, Rumania. In this area, located in the southeastern part of the Carpathian arc, the westward subduction of the Carpathian trench has terminated, leaving continental lithosphere, at present, at the arc. The principalT axis of the intermediate depth events trends N159°E and has a plunge of 74°, which is the same as the dip of the subducted plate. TheP axis has a trend of 314° and a shallow plunge of 15°. The analysis of the moment tensor of six focal mechanisms showed that the dominant mode of deformation of the subducted lithosphere is a down-dip extension at a rate of about 2 cm/yr, based on seismicity data.
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  • 5
    ISSN: 1420-9136
    Keywords: Fault plane solutions ; Aegean area
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract The distribution of the focal mechanisms of the shallow and intermediate depth (h〉40 km) earthquakes of the Aegean and the surrounding area is discussed. The data consist of all events of the period 1963–1986 for the shallow, and 1961–1985 for the intermediate depth earthquakes, withM s ≥5.5. For this purpose, all published fault plane solutions for each event have been collected, reproduced, carefully checked and if possible improved accordingly. The distribution of the focal mechanisms of the earthquakes in the Aegean declares the existence of thrust faulting following the coastline of southern Yugoslavia, Albania and western Greece extending up to the island of Cephalonia. This zone of compression is due to the collision between two continental lithospheres (Apulian-Eurasian). The subduction of the African lithosphere under the Aegean results in the occurrence of thrust faulting along the convex side of the Hellenic arc. These two zones of compression are connected via strike-slip faulting observed at the area of Cephalonia island. TheP axis along the convex side of the arc keeps approximately the same strike throughout the arc (210° NNE-SSW) and plunges with a mean angle of 24° to southwest. The broad mainland of Greece as well as western Turkey are dominated by normal faulting with theT axis striking almost NS (with a trend of 174° for Greece and 180° for western Turkey). The intermediate depth seismicity is distributed into two segments of the Benioff zone. In the shallower part of the Benioff zone, which is found directly beneath the inner slope of the sedimentary arc of the Hellenic arc, earthquakes with depths in the range 40–100 km are distributed. The dip angle of the Benioff zone in this area is found equal to 23°. This part of the Benioff zone is coupled with the seismic zone of shallow earthquakes along the arc and it is here that the greatest earthquakes have been observed (M s ∼8.0). The deeper part (inner) of the Benioff zone, where the earthquakes with depths in the range 100–180 km are distributed, dips with a mean angle of 38° below the volcanic arc of southern Aegean.
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  • 6
    ISSN: 1420-9136
    Keywords: Crustal deformation ; North Aegean trough ; North Anatolia
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract The rates and configuration of seismic deformation in the North Aegean trough-North Anatolian fault are determined from the moment tensor mechanisms of the earthquakes that occurred within this region. The analysis is based onKostrov's (1974) formulation. The fault plane solutions of the earthquakes of the period 1913–1983 withM s ≥6.0 are used. The focal mechanism of some of the past events (before 1960) is assumed, based on the present knowledge of the seismotectonics as well as on the macroseismic records of the area studied. The analysis showed that the deformation of the northern Aegean is dominated by EW contraction (at a rate of about 15 mm/yr) which is relieved by NS extension (at a rate of about 9 mm/yr). It was also shown that the northern part of North Anatolia (north of 39.7°N parallel) undergoes contraction in the EW direction (at a rate of about 9 mm/yr) and NS extension as the dominant mode of deformation (at a rate of about 5 mm/yr). It may be stated therefore, that the pattern of deformation of the northern Aegean and the northern part of North Anatolian fault is controlled by the NS extension the Aegean is undergoing as a whole, and the dextral strike-slip motion of the North Anatolian fault. The southern part of North Anatolia is undergoing crustal thinning at a rate of 2.3 mm/yr, NS extension (at a rate of 5 mm/yr) as well as EW extension (at a rate of 4 mm/yr), which are consistent with the occurrence of major normal faulting and justify the separation of North Anatolia into two separate subareas.
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  • 7
    ISSN: 1420-9136
    Keywords: Probabilistic earthquake prediction ; Aegean area
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract Repeat times of large shocks are obtained for 17 seismic fracture zones of the Aegean and surrounding area, from times of historic and present century earthquakes. The mean standard deviation of the repeat times is approximately 50% of any one observation. A probabilistic approach is then used to forecast the likelihood of large future earthquakes in each fracture zone, using as input the time of the last large shock, the average repeat time and its standard deviation. Shallow and intermediate depth earthquakes are examined separately. The calculated probabilities are high for the entire Hellenic arc, both for shallow and intermediate depth seismicity, for the area of Leucas island (Ionian), of Lesbos island (Aegean), for Patraikos-west Corinthiakos Gulfs, for Evoikos Gulf as well as for southern Bulgaria. The probability estimates based on the most recent large earthquakes, involve a number of basic physical assumptions and we would think that they provide a semi-stochastic approach to the problem of earthquake prediction in Greece.
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  • 8
    ISSN: 1365-246X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: The source parameters of the recent 1983 January 17 Ionian island event are obtained by the inversion of body waves. An optimum source depth of 8 km is determined and the source parameters of the major double couple are: strike = 60°, dip = 47°, rake = 174° and seismic moment M0= 7.3 × 1025 dyne cm. This mechanism implies a strike-slip dextral fault with a small thrust component. This solution ascertains the existence of a transform fault connecting the northwestern edge of the Hellenic are with the compressional zone which is produced by the collision of the Apulian plate with the Eurasian plate along the Adriatic-north Ionian coast. This right lateral strike-slip fault probably terminates the Hellenic subduction zone.
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  • 9
    ISSN: 1365-246X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: A procedure for the analysis of data, concerning seismic moment release and fault-plane solutions, for the estimation of active crustal deformation is proposed. The formulation takes advantage of all the available historical and instrumental data for the calculation of the ‘size’ of the deformation in a seismic zone and of all the reliable fault-plane solutions which are available for a broader seismic belt for the determination of the ‘shape’ of the deformation. A detailed analysis of the errors involved in each parameter, based on a Monte Carlo numerical method, is suggested. The proposed procedure is applied to a region of extensional tectonics in central Greece. The resulting seismic strain rates show that the dominant mode of deformation in the area is extension at a rate of the order of 6 mm yr-1 and a mean azimuth of N25°W. A vertical contraction rate of about 1 mm yr-1 has also been calculated. The results from geodetic measurements performed by Billiris et al. (1991) declare that the calculated seismic deformation represents about 60 per cent of the total strain of this area.
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  • 10
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    In:  J. Geodynamics, Beijing, Pergamon, vol. 37, no. 2, pp. 253-296, pp. 1246
    Publication Date: 2004
    Keywords: Seismology ; Greece ; Subduction zone ; Fault plane solution, focal mechanism ; Hypocentral depth ; Seismicity ; JGD
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