排序方式： 共有20条查询结果，搜索用时 15 毫秒
1.
The April 2006 earthquake sequence near Zakynthos (Western Greece) is analysed to identify the fault plane(-s). The sequence (33 events) was relocated to assess physical insight into the hypocenter uncertainty. Moment tensor solution of three major events was performed, simultaneously with the determination of the centroid position. Joint analysis of the hypocenter position, centroid position and nodal planes indicated sub-horizontal fault planes. Moment tensor solutions of 15 smaller events were performed under assumption that the source positions are those of the hypocenters (without seeking centroids). Their focal mechanisms are highly similar and agree with the analysis of the three major events. The preferable seismotectonic interpretation is that the whole sequence activated a single sub-horizontal fault zone at a depth of about 13 km, corresponding to the interplate subduction boundary. Considering that the Ionian Sea is a high-seismicity area, the identification of the seismic fault is significant for the seismic hazard investigation of the region. 相似文献
2.
Extreme Earthquake and Earthquake Perceptibility Study in Greece and its Surrounding Area 总被引：3，自引：0，他引：3
The sample interval for the selection of extreme magnitudes plays an important part in the quality of Gumbel model fitting. A short sample interval can produce many observations, which is helpful in obtaining a reliably fitting model. However a short sample interval can bring many dummy ``observations', a condition which adversely biases the fitting. The short sample interval also increases the chance to introduce non-independent observations as well, which violates a basic requirement of the Gumbel model. On the other hand, a large time interval not only reduces the number of observations, but also enlarges the observation error. Thus, for Greece, the most suitable parameters of the third Gumbel extreme model are obtained by using a sample interval which produces minimum error. In consideration of the reliability of the seismic data, earthquakes with magnitude M 5.5 in Greece and its surrounding region after 1900 are used mainly in the present paper. In order to obtain well resolved contour maps with smooth changes a 2°× 2° cell with half-degree overlap strategy was used to scan the region. The most expected largest earthquake for the next fifty, one hundred and two hundred years are estimated for each cell. Likewise, the events with magnitude at a probability of 90\% of non-exceedance over the next fifty, one hundred and two hundred years are estimated for each cell. In parallel to this procedure we also analyze the 67 shallow seismic zones outlined by Papazachos and his colleagues and detail individual zone results where these are obtained. The most perceptible earthquake magnitude for the range of intensities I = {VI}, VII and VIII are also calculated. All results show that the areas around the Hellenic Arc and the Cephalonia Transform Fault for Greece have comparatively high frequency of destructive earthquakes accompanied by a high occurrence probability of moderate earthquakes (M 5.5). 相似文献
3.
A. Kiratzi E. Sokos A. Ganas A. Tselentis C. Benetatos Z. Roumelioti A. Serpetsidaki G. Andriopoulos O. Galanis P. Petrou 《Tectonophysics》2008,452(1-4):51-65
We investigate the properties of the April 2007 earthquake swarm (Mw 5.2) which occurred at the vicinity of Lake Trichonis (western Greece). First we relocated the earthquakes, using P- and S-wave arrivals to the stations of the Hellenic Unified Seismic Network (HUSN), and then we applied moment tensor inversion to regional broad-band waveforms to obtain the focal mechanisms of the strongest events of the 2007 swarm. The relocated epicentres, cluster along the eastern banks of the lake, and follow a distinct NNW–ESE trend. The previous strong sequence close to Lake Trichonis occurred in June–December 1975. We applied teleseismic body waveform inversion, to obtain the focal mechanism solution of the strongest earthquake of this sequence, i.e. the 31 December 1975 (Mw 6.0) event. Our results indicate that: a) the 31 December 1975 Mw 6.0 event was produced by a NW–SE normal fault, dipping to the NE, with considerable sinistral strike-slip component; we relocated its epicentre: i) using phase data reported to ISC and its coordinates are 38.486°N, 21.661°E; ii) using the available macroseismic data, and the coordinates of the macroseismic epicentre are 38.49°N, 21.63°E, close to the strongly affected village of Kato Makrinou; b) the earthquakes of the 2007 swarm indicate a NNW–SSE strike for the activated main structure, parallel to the eastern banks of Lake Trichonis, dipping to the NE and characterized by mainly normal faulting, occasionally combined with sinistral strike-slip component. The 2007 earthquake swarm did not rupture the well documented E–W striking Trichonis normal fault that bounds the southern flank of the lake, but on the contrary it is due to rupture of a NW–SE normal fault that strikes at a 45° angle to the Trichonis fault. The left-lateral component of faulting is mapped for the first time to the north of the Gulf of Patras which was previously regarded as the boundary for strike-slip motions in western Greece. This result signifies the importance of further investigations to unravel in detail the tectonics of this region. 相似文献
4.
J. Zahradník J. Janský E. Sokos A. Serpetsidaki H. Lyon-Caen P. Papadimitriou 《Journal of Seismology》2004,8(2):247-257
An earthquake sequence comprising almost 2000 events occurred in February–July 2001 on the southern coast of the Corinth Gulf.Several location methods were applied to 171 events recorded by the regional network PATNET. The unavailability of S-wave readings precluded from reliable depth determination. For the mainshock of April 8, ML= 4.7, the depth varied from 0 to 20 km. The amplitude spectra of complete waveforms at three local stations (KER,SER, DES; epicentral distances 17, 26 and 56 km) were inverted between 0.1 and 0.2 Hz for double-couple focal mechanism and also for the depth. The optimum solution (strike 220°, dip 40°, rake ‒160°, and depth of 8 km) was validated by forward waveform modeling.Additionally, the mainshock depth was further supported by the P- and S-wave arrival times from the local short-period network CRLNET (Corinth Rift Laboratory).The scalar seismic moment was 2.5e15 Nm,and the moment rate function was successfully simulated by a triangle of the 0.5 second duration. This is equivalent to a 1–1.5 km fault length, and a static stress drop 2–6 MPa. This value is important for future strong ground motion simulation of damaging earthquakes in Aegion region, whose subevents may be modeled according to the studied event. The T axis of the mainshock (azimuth 176° and plunge 67°), is consistent with the regional direction of extension N10°. However, none of the nodal planes can be associated to an active structure seen at the surface. The relationship of this earthquake sequence with deeper faults (e.g. possible detachment at about 10 km) is also unclear. 相似文献
5.
Two M6+ events occurred 15–20 km apart in central Greece on April 20 and April 27, 1894. We identify the April 27, 1894 rupture (2nd in the sequence) with the Atalanti segment of the Atalanti Fault Zone because of unequivocal surface rupturing evidence reported by Skouphos [Skouphos, T., 1894. Die swei grossen Erdbeben in Lokris am 8/20 und 15/27 April 1894. Zeitschrift Ges. Erdkunde zu Berlin, vol. 24, pp. 409–474]. Coulomb stress transfer analysis and macroseismic evidence suggest that the April 20, 1894 event (1st in the sequence) may be associated with the Martinon segment of the same fault zone. Our stress modelling suggests that this segment may have ruptured in an M = 6.4 event producing a 15-km long rupture which transferred 1.14 bar in the epicentral area of the April 27th, 1894 event, thus triggering the second M = 6.6 earthquake along the Atalanti segment and producing a 19-km long rupture. We also examined three alternative fault sources for the first event; however, all these produce smaller stress stresses for triggering the second event. The proposed slip model for the second earthquake is capable of producing coastal subsidence of the order of centimetres to decimetres, which fits the geological data. The 1894 earthquake sequence was followed by a difference in the timing of subsequent M > 5 events in each of the “relaxed” areas (stress shadows; a negative change in Coulomb failure stress > − 0.6 bar), which terminated between 22–37 years (north) and 80 years (south). 相似文献
6.
Old?ich Novotny Efthimios Sokos Vladimír Plicka 《Studia Geophysica et Geodaetica》2012,56(4):1007-1018
The western part of the Corinth Gulf attracts attention due to its seismically active fault system and considerable seismic hazard. A moderate size earthquake occurred close to the town of Efpalio on January 18, 2010, followed by a sequence of smaller earthquakes. In the present paper we use this sequence to derive a local structural model for the region in the vicinity of Efpalio. The model is based on the minimization of traveltime residuals. In particular, we used arrival times from 51 selected events recorded on January 19 and 20 by at least 5 stations at epicentral distances less than about 25 km. A variant of the method of conjugate gradients has been used for this purpose. In comparison with several previous models, the new model is characterized by higher velocities to a depth of about 8 km. The velocity ratio in the model is vP / vS = 1.83. The hypocentres of the selected earthquakes lay at depths between about 5 and 9 km, but their distribution is rather irregular. 相似文献
7.
Deviation of earthquakes from the double‐couple mechanism is an important, but delicate tool to study their source processes. For assessing the double‐couple percentage, the paper suggests to complement the standard least‐square moment‐tensor retrieval with a hierarchic spatio‐temporal grid search, progressively closer to the true source position and time. It enables identification of the double‐couple percentage convergence, while its limit is the resulting double‐couple percentage value, or range. The so‐called double‐couple percentage (DC%) versus correlation plots are introduced and difficulties of the double‐couple percentage assessment are discussed. It is proved that even close to the true source position, where the strike‐dip‐rake angles are already stable (within a few degrees), the double‐couple percentage may still vary by dozens of per cent. Moreover, even at the optimum spatial position, the double‐couple percentage estimate is extremely sensitive (0 to 100%) to small variations of the subevent origin time. This behaviour is explained in terms of the source complexity, implying a time‐dependent moment tensor. Therefore, the double‐couple percentage of complex events depends on the studied frequency band and, in general, also on the station azimuth. This explains broad variations of the double‐couple percentage reports among seismic agencies. Three earthquakes of mutually close epicentres were investigated (Zakynthos, Western Greece, April 2006, magnitudes ～5.5) and a strong non‐double‐couple component of one of them was identified (double‐couple percentage of about 20%). Two equivalent models of this earthquake were found: a single‐event non‐ double‐couple model, and a double‐event model consisting of two double‐couple sources with highly different mechanisms. 相似文献
8.
9.
Paul W. Burton Yebang Xu G. -Akis Tselentis Ethimios Sokos Willy Aspinall 《Soil Dynamics and Earthquake Engineering》2003,23(2):159-181
In an early paper [Tectonophysics 117 (1985) 259] seismic hazard in Greece was analyzed using a relatively homogeneous earthquake catalogue spanning 1900–1978 and a strong motion attenuation relationship adapted to use in Greece. Improved seismic hazard analyses are obtained here using Gumbel's asymptotic extreme value distribution applied to peak horizontal ground acceleration occurrence, but now taking into account the increased length and quality of earthquake catalogue data spanning 1900–1999 and the burgeoning information on earthquake strong motion data and attenuation relationships appropriate for Europe and, explicitly, Greece. Seismic acceleration hazard results tabulated for six cities reveal (e.g. using arbitrarily the 50-year p.g.a. with 90% probability of not being exceeded) changes of about 10% in the new calculated values: two cities show an increase and four a decrease. These are relatively small and reassuring adjustments.Inspection of the available attenuation relationships leads to a preference for the models of Theodulidis and Papazachos, particularly with the model modification to produce a ‘stiff soil’ site relationship, as these relationships explicitly exploit the Greek strong motion database. Isoacceleration maps are produced for Greece as a whole from each attenuation relationship inspected. The final set of maps based on the Theodulidis and Papazachos models provide a foundation for comparison with the Seismic Hazard Zones adopted in the New Greek Seismic Code where scope can be found to modify zone shape and the level at which p.g.a.s are set. It should be noted that the generation of the present isoacceleration maps is based on a seismogenic zone-free methodology, independent of any Euclidean zoning assumptions. 相似文献
10.
A catalogue of seismicity in Greece and the adjacent areas for the twentieth century 总被引：2，自引：0，他引：2
Paul W. Burton Yebang Xu Changyuan Qin G-Akis Tselentis Ethimios Sokos 《Tectonophysics》2004,390(1-4):117-127