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The major earthquake-induced tsunamis reliable known to have occurred in and near Greece since antiquity are considered in the light of the recently obtained reliable data on the mechanisms and focal depths of the earthquakes occurring here. (The earthquake data concern the major shocks of the period 1962–1986.) First, concise information is given on the most devastating tsunamis. Then the relation between the (estimated) maximum tsunami intensity and the earthquake parameters (mechanism and focal depth) is examined. It is revealed that the most devastating tsunamis took place in areas (such as the western part of the Corinthiakos Gulf, the Maliakos Gulf, and the southern Aegean Sea) where earthquakes are due to shallow normal faulting. Other major tsunamis were nucleated along the convex side of the Hellenic arc, characterized by shallow thrust earthquakes. It is probably somewhere there (most likely south of Crete) that the region's largest known tsunami occurred in AD 365, claiming many lives and causing extensive devastation in the entire eastern Mediterranean. Such big tsunamis seem to have a return period of well over 1000 years and can be generated by large shallow earthquakes associated with thrust faulting beneath the Hellenic trench, where the African plate subduces under the Euroasian plate. Lesser tsunamis are known in the northernmost part of the Aegean Sea and in the Sea of Marmara, where strike-slip faulting is observed. Finally, an attempt is made to combine the tsunami and earthquake data into a map of the region's main tsunamigenic zones (areas of the sea bed believed responsible for past tsunamis and expected to nucleate tsunamis in the future). 相似文献
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Deamplification of strong motion and the increase of the effective period of soil deposits are typical nonlinear effects; we seek them in SMART1-array data by applying the horizontal-to-vertical spectral ratio (HVSR) technique. The recordings, from four soil and one rock stations, represent 23 earthquakes (ML 4.9–7.0); PGA varies between 20–260 cm/s2. For each station, mean HVSR curves are calculated for two PGA ranges: <75 cm/s2 and >100 cm/s2 (weak and strong motion). At the soil stations, the “weak” (linear) and “strong” (nonlinear) responses are significantly different. Below 1–1.8 Hz, the nonlinear response exceeds the linear one. Above 2 Hz, the nonlinear response drops below the linear one and above 4–6 Hz below unity (deamplification). From 10 to 16 Hz, the two responses converge. One soil site shows significant negative correlation between resonance frequency and ground acceleration. Such behaviour agrees with other empirical studies and theoretical predictions. Our results imply that the HVSR technique is sensitive to ground-motion intensity and can be used to detect and study nonlinear site response. 相似文献
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N. Theodulidis V. Lekidis B. Margaris C. Papazachos Ch. Papaioannou P. Dimitriu 《Journal of Geodynamics》1998,26(2-4)
The Kozani-Grevena (Greece) destructive earthquake occurred in a region of low seismicity. A considerable amount of strong-motion data was acquired from the permanent strong motion network of the Institute of Engineering Scismology and Earthquake Engineering (ITSAK) as well as from a temporary one installed after the earthquake. On the basis of this data set as well as on the observed macroseismic intensities, local attenuation relations for peak ground acceleration and velocity are proposed. A posteriori seismic hazard analysis is attempted for the affected and surrounding areas in terms of peak ground acceleration, velocity, bracketed duration and spectral acceleration. The analysis shows that the event of May 13, 1995 can be characterized as one with a mean return period of 500 to 1000 years. Relying on the observed spectral-acceleration amplification factors and the expected peak ground acceleration for mean return period of 500 years, region-specific elastic design spectra for the buildings of the Kozani and Grevena prefectures are proposed. 相似文献
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Nikolaos Theodulidis Zafeiria Roumelioti Areti Panou Alexandros Savvaidis Anastasia Kiratzi Vassilios Grigoriadis Petros Dimitriu Theodoros Chatzigogos 《Bulletin of Earthquake Engineering》2006,4(2):101-130
The densely populated city of Thessaloniki (Northern Greece) is situated in~the vicinity of active seismic faults, capable of producing moderate to strong earthquakes. The city has been severely affected by such events several times during the last 15 centuries. The most recent event occurred on 20 June 1978 (M6.5) in the Mygdonian graben, with an epicentral distance of about 30 km, causing extended damage in the city, with macroseismic intensities between MSK V+ and VIII+. The majority of buildings affected by the earthquake were of reinforced-concrete typology, typical to many southern European metropolitan areas. The source properties of the normal-faulting causative event and the source-to-city propagation path are well known from previous studies. The soil structure under the metropolitan area of Thessaloniki is assigned NEHRP categories B, C, D on the basis of geotechnical and geologic information and single-station ambient-noise measurements. A finite source model and various rupture scenarios of the June 1978 earthquake are used to perform forward stochastic modeling of strong ground motion in terms of peak ground and spectral acceleration. Rock motion is assessed under the city and it is transferred to the surface in accordance with the respective soil category. A GIS tool is employed to compare the estimated strong-motion parameters with the observed detailed damage pattern induced by the 1978 earthquake. For selected natural periods, a satisfactory correlation is established between macroseismic intensity and peak ground and spectral acceleration, thus encouraging the application of stochastic modeling for generating realistic ground-shaking scenarios in metropolitan areas. 相似文献
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V. Starostenko V. Buryanov I. Makarenko O. Rusakov R. Stephenson A. Nikishin G. Georgiev M. Gerasimov R. Dimitriu O. Legostaeva V. Pchelarov C. Sava 《Tectonophysics》2004,381(1-4):211
A map of Moho depth for the Black Sea and its immediate surroundings has been inferred from 3-D gravity modelling, and crustal structure has been clarified. Beneath the basin centre, the thickness of the crystalline layer is similar to that of the oceanic crust. In the Western and Eastern Black Sea basins, the Moho shallows to 19 and 22 km, respectively. Below the Tuapse Trough (northeastern margin, adjacent to the Caucasus orogen), the base of the crust is at 28 km, whereas in the Sorokin Trough, it is as deep as 34 km. The base of the crust lies at 29 and 33 km depths respectively below the southern and northern parts of the Mid-Black Sea Ridge. For the Shatsky Ridge (between the Tuapse Trough and the Eastern Black Sea Basin), the Moho plunges from the northwest (33 km) to the southeast (40 km). The Arkhangelsky Ridge (south of the Eastern Black Sea Basin) is characterised by a Moho depth of 32 km. The crust beneath these ridges is of continental type. 相似文献
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P. Dimitriu N. Theodulidis P. Hatzidimitriou A. Anastasiadis 《Soil Dynamics and Earthquake Engineering》2001,21(1)
We investigate the dependence of the S-wave high-frequency spectral-decay parameter, κ (“kappa”) — a measure of wave attenuation — on ground-motion amplitude. 21 three-component accelerograms from two adjacent sediment sites in the town of Lefkas, western Greece, are used, representing 17 earthquakes with magnitudes Mw 4.7–7.0 and hypocentral distances 12–93 km. Recorded peak horizontal ground accelerations (PGA) and velocities (PGV) are 22–540 cm/s2 and 1.3–54.5 cm/s.Fourier amplitude spectra are computed for S-wave windows, and the frequency range is visually determined where the high-frequency spectral decay can be approximated by a straight line on the linear-log plot; its slope (and hence κ) is computed by linear regression. κ is found to depend on hypocentral distance as κ=0.108+0.058R (r=0.518).As PGV increases from 1.3 to 54.5 cm/s, κ0 (κ at 0 km, characterising inelastic attenuation in the site's subsurface geology) varies between 0.060 and 0.160 s. κ0 is found to correlate very strongly with log MGA (r=0.645) (MGA — mean horizontal acceleration in the S-wave window) but also with log PGA (r=0.447) and log PGV (r=0.627). We attribute this behaviour to sediment non-linearity (shear-modulus degradation), resulting in the decrease of the site's dominant-resonance frequency (from about 3.5 to 2.4 Hz) and leading to the increase of κ0. Our results imply that at sediment sites, an important contribution to κ comes from wave attenuation (damping) in the softest sediments and show that κ0 is amplitude dependent, thus being a measure of sediment non-linearity. 相似文献
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The issue is addressed as to whether the horizontal-to-vertical spectral ratio (HVSR) method is sensitive to the amplitude of ground motion from near-field earthquakes. Twenty-one three-component accelerograms from two closely located similar soil sites in the town of Lefkas are used. The recordings represent 17 earthquakes covering a wide range of magnitudes, epicentral distances and azimuths. Peak horizontal accelerations (PGA) and velocities (PGV) lie in the ranges 20–540 cm/s2 and 1.4–55.2 cm/s. For each HVS ratio, the site's fundamental-resonance frequency, fres, is determined visually. Linear correlation analysis shows that fres is strongly (negatively) correlated to PGA and PGV (r between −0.7 and −0.8); no correlation is found with resonance amplitude or epicentral distance. We show that the observed correlation is attributable to soil nonlinearity and indicate how weak-motion estimates of fres can be corrected for use in assessing site response during strong shaking. 相似文献
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