Clastic sedimentary features of beachrocks and their palaeo-environmental significance:comparison of past and modern coastal regimes   总被引：1，自引：0，他引：1  

David PSOMIADIS  Konstantinos ALBANAKIS  Nikoleta ZISI  Matthieu GHILARDI  Elissavet DOTSIKA 《国际泥沙研究》2014,29(2):260-268

Clastic sedimentary features of beachrocks and unconsolidated deposits of parent beaches were investigated along the northern Aegean coastline（Greece） to assess their suitability in palaeo-environmental reconstruction.Twelve paired datasets were collected in the Thermaikos,Toroneos,Siggitikos and lerissos gulfs of the Chalkidiki Peninsula,the adjoining Kavala Gulf and Thassos Island,comprising beachrock cores and companion beach subsurface sediments.Particle size analyses based on univariate and bivariate statistics suggest that,during the time period of beachrock formation,depositional conditions differed distinctly from those of the modern parent beaches.The results imply difference of maturity level of beach evolution from the time of cementation（coarser materials-early stage of beach formation） to modern situation（finer materials-reworked and ’mature’ beach sediments）.Furthermore,the findings indicate increasing coastal protection due to beachrock exposure in the modern swash zone.In conclusion,it is suggested that textural analysis of beachrocks in comparison with unconsolidated sediments of the parent beach might provide information regarding differences of coastal depositional regimes and future research could focus on specific-layer analysis and comparison.  相似文献   

Spectral assessment of isostatic gravity models against CHAMP,GRACE, GOCE satellite-only and combined gravity models     

Dimitrios Tsoulis  Konstantinos Patlakis 《Acta Geophysica》2014,62(4):679-698

The availability of digital elevation databases representing the topographic and bathymetric relief with global homogeneous coverage and increasing resolution permits the computation of crust-related Earth gravity models, the so-called topographic/isostatic Earth gravity models (henceforth T/I models). Although expressing the spherical harmonic content of the topographic masses, the interpretation purpose of T/I models has not been given the attention it deserves, apart from the fact that they express some degree of compensation to the observed spectrum of the topographic heights, depending on the kind of the applied compensation mechanism. The present contribution attempts to improve the interpretation aspects of T/I Earth gravity models. To this end, a rigorous spectral assessment is performed to a standard Airy/Heiskanen T/I model against different CHAllenging Minisatellite Payload (CHAMP), Gravity Recovery and Climate Experiment (GRACE), Gravity field and steadystate Ocean Circulation Explorer (GOCE) satellite-only, and combined gravity models. Different correlation bandwidths emerge for these four groups of satellite-based gravity models. The band-limited forward computation of the models using these bandwidths reproduces nicely the main features of the applied T/I model.  相似文献   

Identifying the occurrence time of an impending mainshock:a very recent case     

Panayiotis A. Varotsos  Nicholas V. Sarlis  Efthimios S. Skordas  Stavros-Richard G. Christopoulos  Mary S. Lazaridou-Varotsos 《地震科学（英文版）》2015,28(3):215-222

The procedure by means of which the occurrence time of an impending mainshock can be identified by analyzing in natural time the seismicity in the candidate area subsequent to the recording of a precursory seismic electric signals(SES) activity is reviewed. Here, we report the application of this procedure to an MW5.4 mainshock that occurred in Greece on 17 November 2014. This mainshock(which is pretty rare since it is the strongest in that area for more than half a century) was preceded by an SES activity recorded on 27 July 2014, and the results of the natural time analysis reveal that the system approached the critical point(mainshock occurrence) early in the morning on 15 November 2014.  相似文献   

Investigation of sedimentary aquifers in Denmark using the magnetic resonance sounding method (MRS)     

Konstantinos Chalikakis  Mette Ryom Nielsen  Anatoli Legchenko  Tom Feldberg Hagensen 《Comptes Rendus Geoscience》2009,341(10-11):918-927

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Damage sequence and safety margin assessment of expansion joints by shake table testing     

Yu Otsuki  Masahiro Kurata  Konstantinos A. Skalomenos  Yoshiki Ikeda 《地震工程与结构动力学》2019,48(1):3-26

The performance of nonstructural components has attracted attention, and previous large earthquakes have resulted in widespread damage to expansion joints. In contrast to the main structural components, for which ductility beyond the design tolerance is ensured, the safety margin of nonstructural components classified as the product of mechanical engineering, such as expansion joints, is uncertain. This paper investigates the damage sequence and safety margin of expansion joints through shake table testing. The expansion joints were installed to connect 2 rigid steel frames with short and long natural periods. Four commonly used types, high-performance and standard-performance floor and wall expansion joints, were tested. Seven damage patterns of the 4 expansion joints were observed, and most of the damage patterns were considered displacement dependent. The damage mechanisms and relative displacements at the moment of damage were identified by using strain gauges attached near collision and damage locations. The high-performance expansion joints showed only minor damage beyond the design motion range, whereas the standard-performance expansion joints exhibited minor damage below the design motion range and failure at the design motion range or slightly beyond. For each damage state, repair information was obtained through a questionnaire to an expansion joint manufacturer, and the sum of the initial cost and repair cost for high-performance and standard-performance expansion joints was compared. The results will be useful for the selection of expansion joints in the design process.  相似文献   

Three-dimensional shallow velocity structure beneath Taal Volcano,Philippines     

Shuei-Huei You  Konstantinos I. Konstantinou  Yuancheng Gung  Cheng-Horng Lin 《Journal of Seismology》2017,21(6):1427-1438

Based on its numerous historical explosive eruptions and high potential hazards to nearby population of millions, Taal Volcano is one of the most dangerous “Decade Volcanoes” in the world. To provide better investigation on local seismicity and seismic structure beneath Taal Volcano, we deployed a temporary seismic network consisting of eight stations from March 2008 to March 2010. In the preliminary data processing stage, three periods showing linear time-drifting of internal clock were clearly identified from noise-derived empirical Green’s functions. The time-drifting errors were corrected prior to further data analyses. By using VELEST, 2274 local earthquakes were manually picked and located. Two major earthquake groups are noticed, with one lying beneath the western shore of Taal Lake showing a linear feature, and the other spreading around the eastern flank of Taal Volcano Island at shallower depths. We performed seismic tomography to image the 3D structure beneath Taal Volcano using the LOTOS algorithm. Some interesting features are revealed from the tomographic results, including a solidified magma conduit below the northwestern corner of Taal Volcano Island, indicated by high Vp, Vs, and low Vp/Vs ratio, and a large potential hydrothermal reservoir beneath the center of Taal Volcano Island, suggested by low Vs and high Vp/Vs ratio. Furthermore, combining earthquake distributions and tomographic images, we suggest potential existence of a hydrothermal reservoir beneath the southwestern corner of Taal Lake, and a fluid conduit extending to the northwest. These seismic features have never been proposed in previous studies, implying that new hydrothermal activity might be formed in places away from the historical craters on Taal Volcano Island.  相似文献   

Seismic risk assessment of liquid storage tanks via a nonlinear surrogate model          下载免费PDF全文

Konstantinos Bakalis  Dimitrios Vamvatsikos  Michalis Fragiadakis 《地震工程与结构动力学》2017,46(15):2851-2868

A performance‐based earthquake engineering approach is developed for the seismic risk assessment of fixed‐roof atmospheric steel liquid storage tanks. The proposed method is based on a surrogate single‐mass model that consists of elastic beam‐column elements and nonlinear springs. Appropriate component and system‐level damage states are defined, following the identification of commonly observed modes of failure that may occur during an earthquake. Incremental dynamic analysis and simplified cloud are offered as potential approaches to derive the distribution of response parameters given the seismic intensity. A parametric investigation that engages the aforementioned analysis methods is conducted on 3 tanks of varying geometry, considering both anchored and unanchored support conditions. Special attention is paid to the elephant's foot buckling formation, by offering extensive information on its capacity and demand representation within the seismic risk assessment process. Seismic fragility curves are initially extracted for the component‐level damage states, to compare the effect of each analysis approach on the estimated performance. The subsequent generation of system‐level fragility curves reveals the issue of nonsequential damage states, whereby significant damage may abruptly appear without precursory lighter damage states.  相似文献   

From subsurface to surface: a multidisciplinary approach to decoding uplift histories in tectonically-active karst landscapes     

Christos Pennos  Stein-Erik Lauritzen  Konstantinos Vouvalidis  Patience Cowie  Sofia Pechlivanidou  Charikleia Gkarlaouni  Michael Styllas  Panagiotis Tsourlos  Antonios Mouratidis 《地球表面变化过程与地形》2019,44(9):1710-1721

We present an integrated study of subsurface and surficial karst landforms to unravel the uplift history of karst landscape in a tectonically-active area. To this end, we apply a multidisciplinary approach by combining cave geomorphology and Th/U dating of speleothems with remote sensing plus geophysical imaging of surface landforms. We use as an example Mt. Menikio in northern Greece where four caves share well-defined epiphreatic/shallow phreatic characteristics that are related to the distribution of surface and buried doline fields and provide evidence for three distinct water table stillstands (e.g. expressed as cave levels) now lying at ~130 m, ~800 m and ~1600 m a.m.s.l. Our dating constraints delimit the age of the lower water table stillstand prior to 77 ka ago and imply a maximum rate of relative base level drop of 0.45 mma^-1, which is consistent with relative tectonic uplift rate estimates along currently active normal faults. We interpret the elevation of the higher water table stillstands to reflect earlier phases of uplift related to the regional tectonic events associated with the development of the North Anatolian Fault and the Northern Aegean area. Our analysis shows that the combined study of epiphreatic/shallow phreatic caves and surficial karst landforms together, is a robust way to investigate the uplift history of a karst landscape in a tectonically-active setting. © 2019 John Wiley & Sons, Ltd.  相似文献   

Linking sardine spawning dynamics to environmental variability     

Konstantinos Ganias   《Estuarine, Coastal and Shelf Science》2009,84(3):402

The present paper investigates the effect of environmental variability on the spawning dynamics of sardine, Sardina pilchardus, in the Eastern Mediterranean. To do so, variability in four different reproductive traits, i.e. reproductive activity, incidence of recent spawning, prevalence of early ovarian atresia and relative batch fecundity was tested along a gradient of habitat conditions like water temperature, chlorophyll a (Chl a) concentration and an index of zooplankton production. Apart from atretic prevalence all remaining traits were significantly and positively correlated with Chl a concentration which indicates that sardine in the E. Mediterranean tends to enhance egg production under conditions of increased primary productivity. On the other hand, prevalence of atresia together with spawning incidence were positively affected by water temperature whilst the only factor that correlated significantly with the index of zooplankton production was relative fecundity. These findings were interpreted as an indication of direct energy flow from phytoplankton filter-feeding to gonadal development and egg production, implying that besides capitalized energy sardine also uses current income for supporting reproduction.  相似文献   

Forecasting seismicity rates in western Turkey as inferred from earthquake catalog and stressing history     

Konstantinos Leptokaropoulos  Eleftheria Papadimitriou  Beata Orlecka-Sikora  Vasileios Karakostas 《Natural Hazards》2014,73(3):1817-1842

The spatio-temporal variation in seismicity in western Turkey since the late 1970s is investigated through a rate/state model, which considers the stressing history to forecast the reference seismicity rate evolution. The basic catalog was divided according to specific criteria into four subsets, which correspond to areas exhibiting almost identical seismotectonic features. Completeness magnitude and reference seismicity rates are individually calculated for each subset. The forecasting periods are selected to be the inter-seismic time intervals between successive strong (M ≥ 5.8) earthquakes. The Coulomb stress changes associated with their coseismic slip are considered, along with the constant stressing rate to alter the rates of earthquake production. These rates are expressed by a probability density function and smoothed over the study area with different degrees of smoothing. The influence of the rate/state parameters in the model efficiency is explored by evaluating the Pearson linear correlation coefficient between simulated and observed earthquake occurrence rates along with its 95 % confidence limits. Application of different parameter values is attempted for the sensitivity of the calculated seismicity rates and their fit to the real data to be tested. Despite the ambiguities and the difficulties involved in the experimental parameter value determination, the results demonstrate that the present formulation and the available datasets are sufficient enough to contribute to seismic hazard assessment starting from a point such far back in time.  相似文献