Pleistocene 'periglacial' phenomena in southern Africa

True 'periglacial' forms and deposits of late (and middle) Pleistocene age can be recognized in the Drakensberg and the adjacent parts of the Cape Province in the latitudinal zone 28° 30'-31°20' S; lower limits in the eastern Cape and Natal appear to lie near 1500–1800 m, rising from southwest to northeast, and at 2600 m in Lesotho. Significant nivation in the Drakensberg is also indicated, but at higher elevations. Alleged 'periglacial' phenomena in Rhodesia, the Transvaal, the Cape Folded Ranges and their coastal margin are not acceptable as such and include no evidence for cryonival or geliflual proceses. Nonetheless, there is bonafide evidence for several phases of accelerated Pleistocene frost-weathering, including sections of the Cape Coast that experience next to no frost today and would require a winter temperature depression of at least 10° C. It cannot be disputed that southern Africa has experienced cold, glacial-age climates, but there is a serious problem about many of the geomorphological observations or their interpretation.     

Oxidation phenomena in pleonaste bearing titanomagnetites

Transmission electron microscopy revealed that optically homogenous pleonastes occurring in titanomagnetites had been oxidised. The pleonastes had decomposed by a discontinuous mechanism to give an intergrowth of a spinel and an intermediate phase, whose structure was based on a spinel superlattice. The intermediate phase was similar to one previously found in oxidised chromites from Rhum.     

二次生烃的蓝移特征

<正> 二次生烃是指烃源岩在受热温度降低导致一次生烃历程被中止后,受热温度再次增高并达到有机质再次活化所需的临界热动力学条件,烃源岩再次发生生烃演化。广义上,烃源岩在地质历史时期可能经历过多次的生烃中止与活化,发生三次甚至更多次数的生烃作用。李田忠等将一次生烃之后的历次生烃作用统称为二次生烃。伴随荧光分析技术的逐步完善,人们发现了蓝移现象,在进行二次生烃热模拟实验时,发现随着热模拟温度的升高,荧光颜色出现蓝移。当烃源岩原始成熟度超过生油窗上界时,显微组分荧光应该消失,但在试验中却发现显微组分仍具荧光。实际的蓝移现象是两种:一种指的是随着激发时间的增     

Some replacement phenomena in copper-nickel sulphide ores

On the basis of microscopic studies a new mode of formation of monoclinic pyrrhotite (from Norilsk) is proposed whereby the monoclinic polymorph formed through a leakage of solutions which, upon seepage along micro-fissures in an oxidizing environment, affected the hexagonal polymorph by carrying away a certain amount of iron. Experimental evidence is considered to be insufficient for using monoclinic pyrrhotite as a geologic thermometer; we only can say that it formed below 300° to 325°C. A similar interpretation is proposed for the formation of troilite and hexagonal pyrrhotite at Voronezh where troilite is replaced by hexagonal pyrrhotite and the process involves partial substitution of ferric for ferrous ions. Replacement during the hydrothermal stage of Cu-Ni ore deposition includes the following changes: pentlandite and chalcopyrite to mackinawite (Norilsk ores); cubanite and magnetite to valleriite. At Norilsk and Monchegorsk, valleriite and mackinawite were formed during late stages of serpentinization of the country rock. A relation between replacement effects in sulfide ore-bodies and serpentinization processes in basic and ultra-basic country rocks is shown to exist. The bearing of alterations involving olivine, secondary silicates, rutile, magnetite and the sulfides is considered.

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Zusammenfassung Auf Grund mikroskopischer Studien wird eine neue Bildungsweise für den monoklinen Magnetkies von Norilsk vorgeschlagen: Er soll sich beim Durchsickern von Lösungen in Mikrospalten in einer oxidierenden Umgebung aus der hexagonalen Modifikation gebildet haben. Die Verwendung des monoklinen Magnetkieses als geologisches Thermometer auf Grund experimenteller Resultate ist unzulänglich; wir können nur sagen, daß er sich unter 300°–325°C bildete. Eine ähnliche Interpretation wird vorgeschlagen für die Bildung von Troilit und hexagonalem Magnetkies in Voronezh, wo hexagonaler Magnetkies an die Stelle von Troilit tritt und der Vorgang eine partielle Ablösung von zweiwertigem Eisen durch dreiwertiges Eisen nach sich zieht. Folgende Umwandlungen fanden während des hydrothermalen Stadiums der Cu-Ni-Erzablagerung statt: Pentlandit und Chalcopyrit zu Mackinawit (Norilsk Erze); Cubanit und Magnetit zu Valleriit. In Norilsk und Monchegorsk bildeten sich Valleriit und Mackinawit während der letzten Phasen der Serpentinbildung in Nebengesteinen. Es wird bewiesen, daß eine Verbindung besteht zwischen den Umwandlungen der sulfidischen Erzkörper und der Serpentinisierung der basischen und ultra-basischen Nebengesteine. Auch werden Wirkung und Ausmaß der Umwandlungen von Olivin, sekundären Silikaten, Rutil, Magnetit und Sulfiden untersucht.

     

Pulsation of tectonic phenomena and tectonophysical mechanisms

At present, it is believed that the main tectonic phenomena result from progressive displacements of a small number of rigid plates which form the crust of the Earth. If the plates separate, a rift (of oceanic type) will open; and, if they approach, compression will shorten the crust and form eventually a mountain chain. Both rifting and compression produce earthquakes at the plate borders, and the seismic activity must depict the rate of movement of the plates. There is some indication that this seismic activity occurs in pulses with a period of about 11 years, rifting probably alternating with compression. For long lasting monotonic plate movements, thermal convection and radioactive undations could be adequate causes; but, for these short-period alternating phenomena, gravitational pulsations are considered the best available mechanism. Gravitational pulsations seem to be a necessary consequence of General Relativity, when applied to a convenient cosmological model.     

多波地震勘探中PSV波的识别技术

当地震波非垂直入射并在地下存在波阻抗差时,就会产生转换波。由于转换波和入射波之间存在差异,所以可以利用其差异对其进行分离识别。主要介绍了几种PSV波的分离识别方法,并用极化滤波法对波场进行分离识别。     

Capturing the multifaceted phenomena of socioeconomic vulnerability

Vulnerability and disaster risk assessment has been evaluated from different perspectives with focus on global or national scale. There is a lack of methodologies on city scale, which are able to capture inner-city disparities with regard to socioeconomic aspects. Therefore, the main objective was to develop a transparent and comprehensive indicator-based approach which is flexible in terms of data availability and is not tied to a specific case study side. This research proposes two flexible methodological approaches on how to perform socioeconomic vulnerability assessment. Susceptibility, Coping and Adaptation are the main elements of a modular hierarchical structure to capture the societal sphere of vulnerability. The first method is completely based on official census data at block scale. The second method is an expansion and includes data derived from a field survey to add components of risk perception. The proposed methodologies were developed and applied in the city of Genoa (Italy). The results are displayed spatially explicit on maps. Furthermore statistical analysis, to reveal the driving forces which influence vulnerability, was performed. The census-based approach revealed that vulnerability is forced along the river by the inherent susceptibility, as well as the lack of adaptation. The two approaches can be used effectively in gaining different insights. The flexibility of the framework proved to be suitable to the objective of the research. However, the values computed in this research do not claim completeness, and the aim was to provide useful information for stakeholders in decision making process to reduce vulnerability and risk.     

P-SV波和SS波反射系数之间的近似关系

本文通过对Aki&Richards给出的P-SV波反射系数的一阶近似,给出了一个新的描述P-SV波和SS波反射系数之间关系的近似公式.在4个不同类型的含油气砂岩模型上的定量计算表明:新的近似关系能够反映SS波阻抗和P-SV波反射系数之间的内在关系,而且形式简单、近似效果好、适用范围广,适合于SS波阻抗的定量反演和理论研究;如果再结合PP波AVO信息,还可以简单、准确地进行多参数反演.另外,在20°以内,利用该近似关系,纯SS波零偏移距剖面和P-SV转换波剖面之间可以相互转换.     

Heat Wave Hazards: An Overview of Heat Wave Impacts in Canada

Extreme heat events are natural hazards affecting Canada and many other regions of the world. This paper presents an overview of the issues involved in defining heat waves and harmful hot weather events, followed by a spatial and historical overview of heat waves across Canada, and an assessment of heat wave adaptation potential in selected cities. The Prairies, Southern Ontario, and areas in the St. Lawrence River Valley of both Ontario and Quebec demonstrate the highest temperatures and most frequent occurrences of heat waves, with minimal effects in the North, Pacific Coast, and Maritimes. Montreal frequently experiences extreme heat, and based on its low air conditioning rates and older, high-density housing, it demonstrates limited potential for adaptation to heat events. A scientific assessment was done to identify the effects of heat waves on various sectors of Canadian life including agriculture, livestock, fisheries, construction, transportation, utilities, the environment, and human health. Heat stress has been linked to excess human mortality and illness, violent behaviour, drought, forest fires, tornadoes, decreased agricultural and livestock productivity, construction and transportation difficulties, and reduced electrical power supply. Despite limited research on heat waves in Canada, this study demonstrates that the impacts of heat are profound and far-reaching.     

A multiple fracture model of pre-seismic electromagnetic phenomena

Among three main stages of the process of earthquake nucleation long-, middle- and short-term the final stage is characterized by abrupt activation of the process of stress-strain state variation. The strain rates increase by orders of magnitude throughout the whole region of preparation, which increases the signal-to-noise ratio, and therefore the fracture, is easier to detect through monitoring geophysical parameters. The near-critical stresses existing in the Earth's crust and near the surface make it necessary to take into account the real rheology of the rocks, which, as is well known, is characterized by clearly pronounced plastic properties. The condition is favorable for developing creep processes in general and in its avalanche phase immediately before the fracture. The process is completely nonlinear but not chaotic. Based on the assumption that the attenuation of the stress-strain field is proportional to r^− 3, a possible scenario of the final stage of earthquake nucleation process is proposed on the basis of the slip weakening mechanism in the source and the associated mosaic pattern of precursors on the Earth's surface. The formulas for estimating the ultimate distance of precursor detection and the duration of precursor events depending of normalized epicentral distance at the final stage of inelastic deformation preceding brittle failure of rocks are proposed. The data of electromagnetic precursors are interpreted in terms of a multiple fracture model. The results of in situ observations of electric field anomalies in the atmosphere are analyzed in relation to seismic activity. The possibility of constructing a physical model for the generation of a quasi-stable field and electromagnetic emission on the basis of the deformation process prior to an earthquake is discussed. Numerical estimates are obtained for polarization density and life time of an ensemble of electric dipoles generated in surface layers of the crust due to opening of microcracks and other dislocation mechanisms. The origin of quasi-constant electric field along a deformation region on a scale of the preparation zone is advantageous for the propagation of seismic anomalous atmospheric electric fields from the Earth's surface into the ionosphere. The field can be regarded as a physical agent of lithosphere–ionosphere connection.     

On power-law kinetics of transport phenomena in minerals

 Power laws can be written which describe many physical phenomena in materials and can be of great utility. However, they can sometimes provide a false picture of a relationship between two variables when dependence on a third parameter is not taken into account. (For example, electrical conductivity, diffusion, and creep can be shown to have a spurious power-law dependence on oxygen fugacity if the dependence of activation energy on oxygen fugacity is not considered). Extrapolations of data with such spurious power-law dependences can provide a false picture of material behavior under in-situ conditions in the Earth. Received: July 11, 1996 / Revised, accepted: January 23, 1997     

Study of hydrological phenomena by extreme value theory

We describe and give hydrological applications of a probabilistic model based on extreme value theory which can be used to study the values of a hydrologic process that exceed a certain threshold level Q _B .This model is useful in estimating extreme events X _T of return period T based on N years of available hydrologic record. We also present easy-to-use tables which give confidence intervals for X _T .The hydrologic applications reported are a flood frequency analysis, a methodology for estimating flood damage, an estimation of precipitation probabilities, and a prediction of extreme tide levels.     

Debris-flow phenomena in the Central Apennines of Italy

The results of a research project on the extent of debris-flow processes in the Monti Sibillini area (Central Italy) are presented. Debris flows have greatly contributed in shaping the landscape of the Monti Sibillini territory. Based on the dominant active process they can be subdivided into three sections: a source area, a transport area and a depositional area. Four environments can be identified as source areas: landslide deposits, highly fractured rocks, scree or talus deposits, and glacial deposits. The evolution of some of the largest features present in the area is examined. These may have developed from an initial stage of mostly gully erosion and minor landsliding, through an intermediate stage characterized by extensive mass-movement, to a final stage dominated by fluvial processes. Lastly, generalizations on the debris-flow hazard in the study area are made.