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1.
Natural Hazards - Strong earthquakes in the proximity of densely inhabited urban areas pose one ofthe most complicated disaster management situations faced by societies today. Herethe experience... 相似文献
2.
A first-order one-way wave system has been created based on characteristic analysis of the acoustic wave system and optimization of the dispersion relation. We demonstrate that this system is equivalent to a third-order scalar partial-differential equation which, for a homogeneous medium, reduces to a form similar to the 45° paraxial wave equation. This system describes accurately waves propagating in a 2D heterogeneous medium at angles up to 75°. The one-way wave system representing downgoing waves is used for a modified reverse time migration method. As a wavefield extrapolator in migration, the downgoing wave system propagates the reflection events backwards to their reflectors without scattering at the discontinuities in the velocity model. Hence, images with amplitudes proportional to reflectivity can be obtained from this migration technique. We present examples of the application of the new migration method to synthetic seismic data where P-P reflections P-SV converted waves are present. Absorbing boundaries, useful in the generation of synthetic seismograms, have been constructed by using the one-way wave system. These boundaries absorb effectively waves impinging over a wide range of angles of incidence. 相似文献
3.
Yanis Bouchenak-Khelladi Jean-Dominique Durand Antonios Magoulas Philippe Borsa 《Journal of Sea Research》2008,59(4):269-278
Atlantic–Mediterranean anchovies were genetically characterized at two polymorphic nuclear loci (intron 6 of two creatine-kinase genes) and compared to reference Engraulis albidus and E. encrasicolus samples from the northern Western Mediterranean to provide new insights into their geographic structure. Northeastern Atlantic anchovy, represented by one sample from the Canary archipelago and one sample from the Alboran Sea, were genetically distinct from Mediterranean E. encrasicolus (Weir and Cockerham's ^θ = 0.027–0.311), indicating geographic isolation from either side of the Almería–Oran oceanographic front. Generally smaller genetic differences were evident among anchovy populations from different sub-basins in the Mediterranean (^θ = − 0.019–0.116), the genetic differences between Black Sea and Ionian Sea/Aegean Sea anchovies being the strongest (^θ = 0.002–0.116). There was no evidence of the presence of E. albidus in our samples outside Camargue (northern shore of the Western Mediterranean). However, a sample from the southern Western Mediterranean appeared to be genetically intermediate between E. albidus and Mediterranean E. encrasicolus, indicating possible hybridization. Anchovy from the Benguela current system off southern Africa possessed allele frequencies characteristic of E. albidus at one locus and Northeastern Atlantic anchovy at the other locus, suggesting past introgression. 相似文献
4.
Vassilios C. Kelessidis Cassiani Papanicolaou Antonios Foscolos 《International Journal of Coal Geology》2009,77(3-4):394-400
This review paper presents the results of an extensive study investigating whether addition of 3% w/w Greek lignite to 6.42% w/w water–bentonite suspensions, after being exposed to high temperatures, can prevent gelation and control filtration characteristics. Two different bentonites and eight lignites from different Greek basins have been used while a commercial lignite product has been used as standard. The lignite-free bentonite suspensions heated to 177 °C for 16 h (thermal aging) thicken considerably, increasing the yield stress and the yield point. Fluid consistency and flow behavior indices also change while no significant change is observed for plastic viscosity. Thermal aging of the suspensions results in unacceptably high fluid loss values.Addition of Greek lignite to water–bentonite suspensions, followed by thermal aging, provided the rheological stability of the suspensions by maintaining the low yield stress/point regardless of the type of bentonite. Some of the lignites performed as well as their commercial counterpart. No specific trends for rheological improvement have been identified with respect to various characteristics of lignites such as contents of humic, fulvic acids, humins and other parameters such as specific surface area and cation exchange capacity.Furthermore, addition of lignite in most cases provided very good filtration control of the water–bentonite suspensions after exposure to 177 °C, with some Greek lignites being superior to the commercial product. The same lignite parameters examined for rheological control, were also examined to determine their effect on fluid loss of these suspensions for both bentonites. The content of humic and fulvic acids of two groups of lignites showed weak inverse correlations with the fluid loss volumes for both bentonites, while all other parameters did not seem to directly correlate with the effectiveness of the lignites. 相似文献
5.
Antonios Mettos Theodora Rondoyanni Chryssanthi Ioakim 《International Journal of Earth Sciences》2009,98(8):1927-1934
The relationship between the geotectonic zones of the Hellenides orogen is important for understanding its geological evolution.
The Parnassus–Ghiona geotectonic zone in central Greece has long been interpreted as thrust over the Vardoussia subzone. On
the basis of detailed geological mapping, supported by a stratigraphic study and tectonic observations, no evidence of an
overthrust of the Ghiona limestones on the Vardoussia flysch was found. The new data show that the transition of the Ghiona
limestones to the Vardoussia flysch is a sedimentary passage and at certain places the base of the flysch is marked by a basal
conglomerate formation. The entire deformation of the Ghiona is related to a large-scale anticline of the limestone series,
presenting a highly inclined western limb, overlain by the flysch strata, which were deposited in a common basin between Ghiona
and Vardoussia mountains. Consequently, questions concerning the geotectonic position of the Vardoussia subzone and the role
of the Parnassus–Ghiona zone to the orogenic evolution of the eastern External Hellenides are raised. 相似文献
6.
Tsunami damage to coastal defences and buildings in the March 11th 2011 M
w
9.0 Great East Japan earthquake and tsunami 总被引：2，自引：0，他引：2
Stuart Fraser Alison Raby Antonios Pomonis Katsuichiro Goda Siau Chen Chian Joshua Macabuag Mark Offord Keiko Saito Peter Sammonds 《Bulletin of Earthquake Engineering》2013,11(1):205-239
On March 11th 2011 a M w 9.0 mega-thrust interface subduction earthquake, the Great East Japan Earthquake, occurred 130 km off the northeast coast of Japan in the Pacific Ocean at the Japan Trench, triggering tsunami which caused damage along 600 km of coastline. Observations of damage to buildings (including vertical evacuation facilities) and coastal defences in Tōhoku are presented following investigation by the Earthquake Engineering Field Investigation Team (EEFIT) at 10 locations in Iwate and Miyagi Prefectures. Observations are presented in the context of the coastal setting and tsunami characteristics experienced at each location. Damage surveys were carried out in Kamaishi City and Kesennuma City using a damage scale for reinforced concrete (RC), timber and steel frame buildings adapted from an earlier EEFIT tsunami damage scale. Observations show that many sea walls and breakwaters were overtopped, overturned, or broken up, but provided some degree of protection. We show the extreme variability of damage in a local area due to inundation depth, flow direction, velocity variations and sheltering. Survival of many RC shear wall structures shows their high potential to withstand local earthquake and significant tsunami inundation but further research is required into mitigation of scour, liquefaction, debris impact, and the prevention of overturning failure. Damage to steel and timber buildings are also discussed. These observations are intended to contribute to mitigation of future earthquake and tsunami damage by highlighting the key features which influence damage level and local variability of damage sustained by urban coastal infrastructure when subjected to extreme tsunami inundation depths. 相似文献
7.
Ioannis K. Georgiadis Antonios Koroneos Ananias Tsirambides Michael Stamatakis 《Central European Journal of Geosciences》2012,4(3):465-477
Modern sand samples were collected from the Vertiskos Unit of the Serbomacedonian Massif, northern Greece, and were examined for their texture and mineralogical composition. They were collected from active channels and torrents. The textural study demonstrated that these modern sands are moderately to very-poorly sorted, often polymodal in grain size distribution, texturally and mineralogically immature to submature, and consist of coarse-grained gravelly sands to slightly-gravelly muddy sands. The dominant composition is quartzofeldspathic. All samples contain detrital minerals of metamorphic origin, mainly amphibole and garnet, in addition to minor amounts of pyroxene and detrital calcite. These sediments were deposited rapidly and close to their source, the metamorphic basement of the Vertiskos Unit. The mineral constituents of the samples indicate that the Vertiskos Unit is undergoing rapid physical weathering due to the temperate and seasonal climate. The results of this study suggest that these modern sands constitute one sedimentary petrologic province comprised of primarily of amphibole-garnet. 相似文献
8.
Harilaos Kontoyiannis Alexander Theocharis Efstathios Balopoulos Soterios Kioroglou Vassilios Papadopoulos Michael Collins Antonios F. Velegrakis Athanasia Iona 《Progress in Oceanography》1999,44(4):58
Five research cruises were undertaken incorporating ADCP sections along the Cretan Arc Straits and CTD surveys covering the entire area of the Straits and the Cretan Sea. In addition, six moorings (with 15 current meters) were deployed within the Straits, which monitored flows in the surface (50 m), intermediate (250 m), and deep (50 m from the bottom) layers. The ADCP, CM, and CTD datasets enable the derivation of water transports through the Cretan Arc Straits to be assessed. Flow structure through the Cretan Arc Straits is not the typical flow regime with a surface inflow and deep outflow, instead there is a persistent deep outflow of Cretan Deep Water (CDW) (σθ>29.2) with an annual mean of ˜0.6 Sv, through the Antikithira and Kassos Straits at depths below 400 m and 500 m, respectively. CDW outflowing transports are higher (˜0.8 Sv) in April–June, and lower (˜0.3 Sv) in October–December. Within the upper water layer (0–˜400 m), the transport and the water exchanges through the Straits are controlled by local circulation features, which weaken substantially below 200 m. The Asia Minor Current (AMC) influences the Rhodes and the Karpathos Straits, resulting in a net inflow of water. In contrast, the Mirtoan/West Cretan Cyclone influences the Antikithira and Kithira Straits, where there is a net outflow. In the Kassos Strait, there is a complex interaction between the East Cretan Cyclone, the Ierapetra Anticyclone and the westward extension of the Rhodes Gyre, which results in a variable flow regime. There is a net inflow in autumn and early winter, and a switch to a net outflow in early spring and summer. The total inflow and outflow, throughout all of the Straits, ranged from ˜2 to ˜3.5 Sv, with higher values in autumn and early winter and lower in summer. The AMC carries ˜2 Sv of inflow through the Rhodes and Karpathos Straits, and this accounts for 60–80% of the total inflow. About 10–15% of the total outflow is of CDW, and a further 45–70% occurs through the upper 400 m of the Kithira and Antikithira Straits. The Kassos Strait exhibits a net inflow of ˜0.7 Sv in autumn and early winter, with a net outflow of ˜0.5 Sv in early spring and summer. 相似文献
9.
Recent studies have provided theoretical and empirical evidence about the importance of hatchling production for sea turtle population dynamics. Therefore, understanding the effect of nesting habitat loss as a factor leading to hatchling reduction is essential in order to establish conservation plans for the recovery of sea turtle populations. In the present study, we developed a method to quantify habitat loss and link it with hatchling production. We used data for loggerhead sea turtles (Caretta caretta) collected at Sekania nesting beach, western Greece, to describe biological and behavioral attributes of nesting individuals. Spatial characteristics of the nesting site were analyzed and alternative scenarios of habitat loss were examined. We then used circle-packing technique to evaluate the impact of an increasingly reduced available nesting area on the spatial distribution of nests. An increased number of nests within the study site resulted in density-dependent processes regulating hatchling production. Under the different scenarios, we evaluated the risk of the laying nests exceeding the estimated carrying capacity of the nesting beach. Our results clearly demonstrated the need to apply direct and efficient conservation measures at Sekania nesting site to minimize further habitat loss from human-related processes and a rising sea level. The approach developed evaluates the effect of habitat loss upon nesting by linking it with quantifiable processes (density dependence), providing a conservation tool to guide planning decisions towards the conservation of the sea turtle population. 相似文献
10.
Earthquake damage data is of vital importance both as an indicator of the likely performance of buildings in future earthquakes,
as well as for the calibration of existing theoretical-analytical models regarding building vulnerability. The analysis of
damage data collected shortly after the August 14, 2003 Lefkada Island, Greece earthquake revealed the higher vulnerability
of masonry buildings vis-à-vis all other building typologies on the island. However, promising means in strengthening the
existing masonry stock emerge, when considering the improved performance of buildings of a dual-system of stone-masonry and
timber frame – a construction practice uniquely adopted in the island. Based on the parameterless seismic intensity scale
(psi) proposed by Spence et al. (1991) a set of preliminary vulnerability curves for the typologies of the island’s buildings are proposed. 相似文献