Geo-Characterization at selected accelerometric stations in Crete (Greece) and comparison of earthquake data recordings with EC8 elastic spectra

To estimate the seismic response according to Eurocode (EC8) and almost all other national codes, site conditions have to be properly characterized so that soil amplification and the corresponding peak ground motion can be calculated. In this work, different geophysical and geotechnical methods are combined in order to define the detailed ground conditions in selected sites of the Hellenic Accelerometric Network (HAN) in Crete. For this purpose, the geological information of the sites and shear wave velocity, calculated from surface wave measurements, is used. Additionally, ground acceleration data recorded through HAN have been utilized from intermediate depth earthquakes in the broader area of South Aegean Sea. Using the recorded ground motion data and the procedure defined in EC8, the corresponding elastic response spectrum is calculated for the selected sites. The resulting information is compared to the values defined in the corresponding EC8 spectrum for the seismic zone that includes the island of Crete. The comparison shows that accurate definition of ground type through geological, geotechnical and geophysical investigations is important. However, our current comparison focuses on the distribution of values rather than the absolute values of EC8-prescribed spectra, and the results should be considered in this context.     

马鞍桥金矿床中香沟岩体锆石U-Pb定年、地球化学及其与成矿关系研究

对出露马鞍桥金矿床中香沟二长花岗斑岩进行了单颗粒锆石U-Pb定年和岩石地球化学研究.结果表明,锆石的LA-ICPMS U-Pb年龄值为(242.0±0.8)Ma,与前人确定的秦岭造山带的主造山时间((242±21)Ma)一致,显示香沟岩体可能和印支期华北与扬子板块的碰撞事件有关.香沟岩体以高硅富碱为特征,属于高钾钙碱性系列花岗岩类.香沟岩体高Al(Al2O3=14.49~15.61)和Sr(457.10~630.82μg/g)、亏损Y(<16μg/g)和HREE(Yb<0.45μg/g),并具有较高的Sr/Y(76.24~97.34)和(La/Yb)N(29.65~46.10)比值及强分异的稀土元素组成模式,其地球化学特征显示香沟岩体花岗岩类属于C型埃达克质(adakitic)岩石.岩石初始Sr同位素比值ISr=0.70642~0.70668,εNd(t)=-4.5~-4.0,TDM=1152~1220Ma.香沟岩体具有较低的εNd(t),ISr值和较高的TDM值,同时其Na2O/K2O接近1(Na2O/K2O=0.95~1.10),显示香沟花岗岩不是俯冲洋壳部分熔融形成的Ⅰ型埃达岩或底侵玄武质下地壳熔融所产...     

Bender Elements在测试土样剪切波速中的应用

本文以作者在香港理工大学土木与结构工程系设计制作的一套BenderElements为例,介绍了BenderElements的原理、发展历史、应用范围、使用方法和注意事项等。BenderElements是由压电陶瓷材料制成的,在拉伸、压缩作用下,会产生正、负电荷,反过来,给它施加正、负电荷后,它又可产生弯曲振动,正是利用它的这一特性,将其作成接收和发射装置,来测试土样的剪切波速Vs。BenderElements在安装使用时,防水和静电屏蔽十分关键。Vs可在场地地震反应、液化判别、动力基础设计、检测地基改良效果等方面获得应用。震相识别的原则是接收信号的第一个峰值为到时。     

Funkortung und Wellenausbreitung

Zusammenfassung Die Arbeit will auf die heutigen funktechnischen Hilfsmittel der Navigation hinweisen und die Möglichkeit ihrer Beeinflussung durch die Ausbreitung der Funkwellen aufzeigen. Sowohl auf dem Gebiete des Funkmeßverfahrens (Radar) wie auf den weniger bekannten Gebieten der Hyperbelnavigation und der Richtfunkfeuer sind noch viele Einzelheiten über die Brechung der Funkstrahlen, über die Interferenz und Störungen durch Raumwelleneinflüsse und über die effektive Ausbreitungsgeschwindigkeit zu klären, ehe die Schiffahrt den vollen Nutzen aus allen diesen Methoden ziehen kann.

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Radio direction finding and radio wave propagation

Summary The paper outlines to-day's radio aids to navigation and their eventual dependency on the propagation of radio waves. In the field of radar as well as in the less familiar fields of hyperbolic navigation and radio range many details remain to be cleared with regard to refraction of radio rays, interference and disturbance by sky waves, and the effective velocity of propagation until navigation will be able to derive the full benefit from all these methods.

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Radio navigation et propagation des ondes radioélectriques

Résumé Ce travail a pour but d' exposer le radio guidage pour navigation ainsi que sa dépendance eventuelle de la propagation des ondes radioélectriques. Non seulement dans le domaine du radar mais encore dans les domaines moins connus de la navigation hyperbolique et des radiophares directionels il reste beaucoup de détails à éclaircir, détails qui se rapportent à la réfraction du rayon radioélectrique, à l'interférence et aux perturbations causées par des ondes d'espace et, enfin, à la vitesse effective de propagation. Tous ces problèmes doivent être résolus avant que la navigation puisse tirer tout le profit de ces méthodes.

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Vortrag auf der 3. Hamburger geophysikalischen Tagung, 28. 8. 1952.     

Profondità ipocentrali e coefficienti di assorbimento per zone Etnee

Riassunto Si discutono le diverse formule che permettono il calcolo, con i dati macrosismici, delle profondità ipocentrali dei terremoti e dei coefficienti di assorbimento delle zone interessate. Si indicano delle modifiche, nella conduzione dei calcoli richiesti dalla formula delKövesligethy, apportanti notevoli semplificazioni ai calcoli stessi. In base ai metodi indicati vengono studiati i terremoti della regione etnea e particolarmente di quella orientale. Per le profondità ipocentrali i valori ottenuti, compresi fra 0.1 e 2.5 Km, confermano le idee che si hanno sulla genesi dei terremoti della zona. Per i coefficienti di assorbimento invece i risultati, compresi fra 0.03 e 0.35, hanno permesso, di trovare una legge di variazione del coefficiente stesso con la profondità, legge che per la bassa regione orientale ha l'espressione seguente: (x)=0.27e ^–3.5x.

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Summary They discuss the various formulae which enable to calculate, by means of the macrosismical data, the ipocentral earthquake depths and the absorption coefficients. They propose some modifications in the calculus required by theKövesligethy formula, which simplify considerably these calculations. On the basis of the indicated methods, the earthquakes of the Aetna area, especially those of the eastern side, are examined. The values obtained for the ipocentral depths, comprised between 0.1 and 2.5 Km, confirm the opinion they have on the origin of the earthquakes of this area. On the contrary the results for the absorption coefficients comprised between 0.03 and 0.35 enabled to find a variation law of this coefficient with the depth. For the low eastern region this law has the following form: (x)=0.27e ^–3.5x.

     

Solution of H2O in diopside melts: a thermodynamic model

Structural similarities between dry diopside melt and superhydrous albite melt (X _w >0.5) — both lack three-dimensional silicate units — suggest that thermodynamic relations may be similar. A model based on that assumption successfully predicts diopside melting relations and H₂O solubilities. For the model, the three partial differential equations describing solution of H₂O in albite melt for X _w >0.5 have been integrated for diopside melt from X _w =0 to X _w at least as large as 0.76, with two exceptions: an alternative partial differential equation for Henrian solution of H₂O in dilute melts was applied for X _w <0.20, and an alternative differential equation for the pressure dependence of a _w at pressures below 2 kbar was developed. The latter alternative equation yields relatively small ¯V_w's at low pressures rather than the large ¯V_w's calculated from the equation from the albite system. Available experimental solubility data are not precise enough to offer a choice between the small-¯V_w and large-¯V_w equations. Integration of all the partial differential equations was constrained solely by the P and T of a single experimentally-determined point on the H₂O-saturated solidus.Solubilities calculated by a Henrian-analogue solution model (a _di=X _di ² ) from the experimental H₂O saturated solidus lie outside experimental solubility constraints for dilute melts. On the other hand, a Henrian model (a _di=X_di) successfully predicts solubilities in dilute melts. The formulation of the Henrian model and magnitudes of model molar entropies of solution are consistent with the hypothesis that H₂O dissolves in diopside melt as an essentially undissociated species with little ordering on melt structural sites. That species could in turn be consistently, if not uniquely, interpreted to be molecular H₂O or a hydroxylation (OH^–) complex formed from nonbridging oxygens.     

香港一富营养河港内的底泥耗氧和营养盐释放

Tolo Harbour has received massive discharges of municipal sewage, agricultural wastes and cottage industrial effluents, via three river systems, in the past two decades before the mid Eighties. The Harbour is almost land locked and poorly flushed. The soft sediment acted as a sink for nutrients and organic pollutants. After a decade of efforts in establishing and enforcing water pollution control legislations and upgrading wastewater treatment facilities, the sediments have turned into sources of nutrients and exert a measurable oxygen demand upon the overlying waters. In vitro measurements showed that the sediments oxygen demand (SOD) was between 17.6 and 54.3 mgo₂ · m^-2 · h^-1. The maximum rates of release of ortho-phosphate phosphorus and ammonia nitrogen were 15.0 and 206.0 mg · m^-2 · h^-1, respectively.     

Geodynamic evolution of crust accretion at the axis of the Reykjanes Ridge,Atlantic Ocean

The results of analysis of the anomalous magnetic field of the Reykjanes Ridge and the adjacent basins are presented, including a new series of detailed reconstructions for magnetic anomalies 1–6 in combination with a summary of the previous geological and geophysical investigations. We furnish evidence for three stages of evolution of the Reykjanes Ridge, each characterized by a special regime of crustal accretion related to the effect of the Iceland hotspot. The time interval of each stage and the causes of the variation in the accretion regime are considered. During the first, Eocene stage (54–40 Ma) and the third, Miocene-Holocene stage (24 Ma-present time at the northern Reykjanes Ridge north of 59° N and 17–11 Ma-present time at the southern Reykjanes Ridge south of 59° N), the spreading axis of the Reykjanes Ridge resembled the present-day configuration, without segmentation, with oblique orientation relative to the direction of ocean floor opening (at the third stage), and directed toward the hotspot. These attributes are consistent with a model that assumes asthenospheric flow from the hotspot toward the ridge axis. Decompression beneath the spreading axis facilitates this flow. Thus, the crustal accretion during the first and the third stages was markedly affected by interaction of the spreading axis with the hotspot. During the second, late Eocene-Oligocene to early Miocene stage (40–24 Ma at the northern Reykjanes Ridge and 40 to 17–11 Ma at the southern Reykjanes Ridge), the ridge axis was broken by numerous transform fracture zones and nontransform offsets into segments 30–80 km long, which were oriented orthogonal to the direction of ocean floor opening, as is typical of many slow-spreading ridges. The plate-tectonic reconstructions of the oceanic floor accommodating magnetic anomalies of the second stage testify to recurrent rearrangements of the ridge axis geometry related to changing kinematics of the adjacent plates. The obvious contrast in the mode of crustal accretion during the second stage in comparison with the first and the third stages is interpreted as evidence for the decreasing effect of the Iceland hotspot on the Reykjanes Ridge, or the complete cessation of this effect. The detailed geochronology of magnetic anomalies 1–6 (from 20 Ma to present) has allowed us to depict with a high accuracy the isochrons of the oceanic bottom spaced at 1 Ma. The variable effect of the hotspot on the accretion of oceanic crust along the axes of the Reykjanes Ridge and the Kolbeinsey and Mid-Atlantic ridges adjoining the former in the north and the south was estimated from the changing obliquity of spreading. The spreading rate tends to increase with reinforcing of the effect of the Iceland hotspot on the Reykjanes Ridge.     

Seismotectonic deformations related to the 2010 Maule earthquake at different stages of the seismic cycle from satellite geodetic observations

Doklady Earth Sciences - The interpretation of multiannual satellite geodetic observations after the 2010 Maule earthquake is given on the basis of the keyboard concept of the subduction region...     

A metabolism-based trophic index for comparing the ecological values of shallow-water sediment habitats

We determined fluxes of oxygen and nutrients between water and sediments at 21 sites primarily in Virginia and North Carolina estuaries, over the past 15 yr. These sites represented broad ranges in salinity, tidal amplitude, hydrology, nutrient availability, turbidity, light availability, depth, sediment grain size, and anthropogenic disturbance. In general, we found that heterotrophically dominated sediments had the potential to degrade water quality, whereas photoautotrophy in the sediments ameliorated this impact. We propose a benthic trophic state index as a management tool to make general assessments of the degree to which sediments support ecological processes related to photoautotrophy. The index can be based on simple measurements of metabolic parameters. We also evaluated the relative significance of variability in the index across a number of spatial and temporal scales. Reduced photoautotrophy and/or enhanced heterotrophy tended to be associated with finer-grained, organic-rich sediments. This sediment type was common in oligohaline areas at water depths exceeding 2 m. Temporally, autotrophy declined from winter to spring particularly at sandy sites, while interannual variability was more pronounced for mud sites. *** DIRECT SUPPORT *** A01BY074 00011