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1.
Wave number discretization method is applied to study the near-field of seismic sources embedded in a cracked elastic solid. Near-field solutions are obtained for horizontal and vertical line forces. Effects of modifications in cracks of focal region on ground motion, in the near-field, are studied numerically for different
  • ? values of crack density
  • ? saturation of cracks
  • ? width of cracks, and
  • ? regimes of connection between cracks.
    • An earthquake process is assumed to be going through five major stages. These stages represent continuous accumulation of stress, interconnections between cracks leading to eventual failure and drainage of fluid from cracks after the major shock. Variations in the velocity ratio of waves noted from accelerograms verify the process of preparation of an earthquake.P wave contribution to vertical acceleration is negligible when the source is a vertical line force andS wave contributes only a little to horizontal acceleration when the source is a horizontal line force.  相似文献   

    2.
    Fuelwood Development for Energy in Sudan project (GCP/SUD/033/NET) is undertaking research to formulate management plans for Sudan ecologically marginal forests. Rawashda and Wad Kabu forests are taken as examples to initiate sound plans. It is believed that the study of socio-economic parameters of forests users is an essential component to achieve such plan. This study is also fundamental for attaining an integrated land use system, as a prime option of natural resource use. This study is, consequently, aiming at:
    1. Providing the base line information of the different communities identified in Tab 3 and using the two forests.
    2. Examine people's attitude, perception, participation options in maintenance and management of the two forests. Such parameters are also vital for adoption of an integrated land use strategy in the future.
    3. Based on (i) and (ii) to outline broadly the most relevant plan of management land use strategy to be adopted, based on community self-generated options of institutions and objectives of use.
    The main findings in this context can be summarized in the following:
    1. A complex pattern of economic activities (Tab 3) ranging from pure pastoral nomadism to modern mechanized farming, still characterized by combination of related activities of agricultural/livestock breeding, agriculture/forest resource use, etc. This diversity in activities, which is mostly dependent on the natural resource base, gives a sound base for any option of an integrated land use system.
    2. Perception and attitude analysis have revealed a growing awareness of the role of the forest resources in the economy as source of grazing, domestic needs and source of income. This awareness is supported by willingness to participate in any integrated land use plan, yet from a different stand point and objective. Preference of self-generated channels is quite evident, but with a specified role of the government.
    3. The major finding is that, and among all communities, the situation is mature for action, although at different levels.
    Therefore, each community could be approached along relevant lines of action, as an initial phase before attaining a comprehensive land use plan. On-farm trials (OFTs) or in-herd trials seem to be more relevant compared with expert controlled trials. Any plan of action needs to be preceded by revision of present land tenure systems, establishing grass-root institutions, reorientation of concerned government departments, intensive extension programme and careful formulation of projects, execution and follow-up plans. Such steps need to be geared to narrow the ‘Perception gap’ of development between participants or users and planners.  相似文献   

    3.
    Problems of landscape and resource protection resulting from the intensification of land-use can be mastered only by intersectoral planning and a land management considering (landscape-)ecological principles right from the beginning. In the district of Leipzig ecological studies in the '80ies have focussed on:
    1. Determination of the regional pattern of atmospheric immissions;
    2. Registration of heavy metals in soil and vegetation;
    3. Soil compaction, soil erosion;
    4. Study of stress indicators in the aeration zone and in the top-most aquifer in order to examine barrier effects in the percolation process.
    First results are discussed.  相似文献   

    4.
    Prior experimental work has shown that in the laboratory the mineralogy of eclogites is sensitive to the ratio of CaO ∶ MgO ∶ FeO and that the reaction pyroxene + kyanite?garnet + quartz proceeds to the right at high pressures in rocks rich in magnesium and to the left in rocks rich in calcium and iron. Typical basalts crystallized at high pressure never contain kyanite. The chemistry and mineralogy of a large number of naturally occurring eclogites show they belong to three classes.
    1. Kyanite-free magmatic eclogites, rich in magnesium, from:
    2. kimberlites
    3. dunites and serpentinites.
    4. Kyanite-bearing eclogites and grosspydites rich in CaO and low in FeO with intermediate MgO from:
    5. kimberlites
    6. gneisses.
    7. Kyanite-free eclogites of metamorphic origin rich in iron with low magnesium and intermediate amounts of calcium from:
    8. glaucophane schists
    9. gneisses.
      相似文献   

    5.
    The following facts have supported the origin of the Araguainha circular structure in Central Brazil by a meteoritic impact:
    1. the almost circular contour
    2. the impact-morphologic sequence including a central uplift, ring walls and a basin rim of escarpments
    3. outcrops of suevites and mixed breccias
    4. the evidence of shock metamorphism
    5. the presence of shatter cones, and
    6. negative anomalies of the total intensity of the magnetic field at the center of the ring structure.
      相似文献   

    6.
    《Engineering Geology》2001,59(1-2):1-49
    Geologic concepts and scientific-technical guidance for the planning-design and construction of engineered works was recognized in Europe by the 1800s and by the early 1900s in North America. This early geologic knowledge and experience provided the rudimentary principles that guided practitioners of the 19th century in serving the emerging projects in western United States. Case studies review the scientific-technical lessons learned and the legacy of geologic principles established in the planning and construction of major civil, mining, and military engineered works in the western states. These contributions to GeoScience knowledge and engineering geology practice include:
    • •Tunnels and aqueducts across active fault zones, beneath young volcanic features, groundwater-charged faults, and land subsidence mitigation.
    • •Controversial foundation design, Folsom and Auburn dams, Golden Gate Bridge.
    • •Protective underground construction chambers, safety dependent geologic setting.
    • •Geologic mapping as database management leasing, maintenance railroad trackway.
    • •Causeway Great Salt Lake, geo-risks calculated, mitigated ‘as-constructed’.
    • •Nuclear powerplants seismic design.
    • •Urban Land-Use, on-going processes, acceptable geo-risks.
    • •Dwelling Insurance, insuree's responsibilities.
    • •Selecting technique/method to mitigate risk, preferably based on extensive database, evaluation of characteristics and historical origin adverse features/conditions that constitute a geo-risk.
      相似文献   

    7.
    The author's concept (1970, 1974) of evaluating metamorphic conditions is explained on the basis of most recent petrologic data. The major points treated are:
    1. Instead of usual petrographic mapping, petrographic work in the field is aimed at specific “targets”, i.e., rock compositions. This is so because only specific rocks may give petrogenetically relevant information in the four metamorphic grades.
    2. There are very many mineral reactions in metamorphism but only a few are petrogenetically significant. These are important to know, and they are graphically demonstrated. Any mineral assemblage that is formed by a significant mineral reaction must be verified as a paragenesis of mutually contacting minerals. Only such parageneses deserve to be mapped in the field as isograds or isoreactiongrads.
    3. Crossing isograds or isoreactionsgrads provide data on temperature and pressure during metamorphism for that part of a metamorphic terrane where the crossing has been observed.
    4. The sequence of isograds or isoreaction-grads may be a pressure indicator. Moreover, such a sequence provides geodynamic information whether a larger metamorphic area has been lifted up evenly or has been tilted while it was uplifted after metamorphism.
      相似文献   

    8.
    Shijian Liu 《GeoJournal》1994,34(1):47-54
    Debris flow is a natural phenomenon which occurs on steep slopes of mountain regions. Very often morainic material and nonmorainic sediments, such as debris flow material, fluvial and other sediments, are mixed in the marginal mountain systems of the Tibetan Plateau. The study of quartz-grain surface features of debris flow has an important significance for differentiating between different origins of Quaternary sediments. Features of quartz-grain in debris flow will be described as below:
    1. The predominant shapes of quartz grains are irregular.
    2. The degree of roundness of grains is in general are angular to subangular in shape.
    3. The textures of quartz-grains in debris flows are conchoidal fractures, parallel steps and mechanical V-marks. Parallel steps are especially abundant. Their presence is the most characteristic indicator of debris flow sand, aiding in the differentiation between debris flow and glacial sand.
    4. Fresh cleavage planes are extremely flat.
      相似文献   

    9.
    Computer Cartography has gone through many changes during its short life. This article tries to document some of the results of the development. The major conclusions are:

  • - whereas the application of computer mappins is fluurishing, conceptual development is slow;
  • - as a result the applications are simpler than they could be, given the development of computer science, and brute force reigns over elegance.
    • To exemplify these points, the main types of Geographic Information Systems are discussed with respect to their recent achievements: Catastral mapping, Thematic mapping, Topographic mapping, Resource Information Systems, and Digital Terrain Models.  相似文献   

    10.
    H. Kenneweg 《GeoJournal》1994,32(1):47-53
    The development of inventory activities in the field of forest damage assessment and monitoring during the last decade in Germany and the present state are recorded as far as remote sensing has been involved. Any forest inventory is influenced by external factors, and the resulting difficulties for an introduction of new technologies are described. The following tasks and/or methods are discussed:
  • -global approaches to deforestation monitoring
  • -working experience from local and regional case studies
  • -vegetation and vegetation-damage monitoring in ”urban forestry”
  • -sampling approaches for large areas
  • -the contribution of spectral signatures and satellite remote sensing to damage assessment
    •   相似文献   

    11.
    Geologic, petrological and geochemical investigations have been carried out in the western part of the “Zillertaler Alpen”. Important results are:
    1. The premetamorphic material of the Greiner series consists of conglomerates, breccias, arcosic-sandstones or greywackes, bituminous shales, volcanic lavas and tuffs.
    2. The southern part of the “Zentralgneis” shows a differentiation trend from alkaline granite to quarzdiorite with predomination of granodiorite.
    3. Chemical relationships of granodiorite to its restitic inclusions allow the supposition of a palingenetic origin of the granitic rocks.
    4. At least two stages of metamorphism can be differentiated.
    5. Parts of the Greiner series, covered by triassic metasediments, are supposed to be of Permian age. A lower age boundary can not yet be given.
    6. Some vertical, northeast striking faults with throws of more than 1 or 2 kilometers produced southward verging drag folds.
    7. Geodynamic aspects, revealed from regional metamorphism and tectonics, are discussed.
      相似文献   

    12.
    P, T, \(X_{{\text{CO}}_{\text{2}} }\) relations of gehlenite, anorthite, grossularite, wollastonite, corundum and calcite have been determined experimentally at P f =1 and 4 kb. Using synthetic starting minerals the following reactions have been demonstrated reversibly
    1. 2 anorthite+3 calcite=gehlenite+grossularite+3 CO2.
    2. anorthite+corundum+3 calcite=2 gehlenite+3 CO2.
    3. 3anorthite+3 calcite=2 grossularite+corundum+3CO2.
    4. grossularite+2 corundum+3 calcite=3 gehlenite+3 CO2.
    5. anorthite+2 calcite=gehlenite+wollastonite+2CO2.
    6. anorthite+wollastonite+calcite=grossularite+CO2.
    7. grossularite+calcite=gehlenite+2 wollastonite+CO2.
    In the T, \(X_{{\text{CO}}_{\text{2}} }\) diagram at P f =1 kb two isobaric invariant points have been located at 770±10°C, \(X_{{\text{CO}}_{\text{2}} }\) =0.27 and at 840±10°C, \(X_{{\text{CO}}_{\text{2}} }\) =0.55. Formation of gehlenite from low temperature assemblages according to (4) and (2) takes place at 1 kb and 715–855° C, \(X_{{\text{CO}}_{\text{2}} }\) =0.1–1.0. In agreement with experimental results the formation of gehlenite in natural metamorphic rocks is restricted to shallow, high temperature contact aureoles.  相似文献   

    13.
    The kinematics of the deformational events recorded in the catazonal gneisses within the eastern part of the Maures massif (Variscan basement of Provence, southeastern France) has been established. These events can be correlated with both the metamorphic and the magmatic evolution, and the orogenic history of the eastern Maures then consists of the following stages:
    1. -HP-metamorphism preserved only in relict eclogites and quartzites rich in calc-silicates,
    2. -Catazonal metamorphism involving anatectic melting, broadly contemporaneous with large-scale horizontal transport towards the NNE. During this event, the lithologic units were disrupted and intensively mylonitized.
    3. -Intrusion of a first generation of anatectic granitoids.
    4. -A second tectonic event under epi-to mesozonal metamorphism conditions is responsible for the northward displacement of the eastern Maures relative to the western part along a sinistral strike-slip fault 4 km wide (Ramatuelle — Plan de la Tour fault) in which the early anatectic granitoids have been mylonitized. Outside the fault zone, this event is marked by upright to W-vergent open folds trending N-S, i.e. parallel to the transport direction.
    5. -A moderate cataclastic reactivation of the Ramatuelle — Plan de la Tour fault with a dextral sense of shear, locally accompanied in the eastern part of the area by minor lowtemperature thrusting towards the south.
    6. -Intrusion of a second generation of anatectic granites about 320 Ma ago.
    The metamorphic, magmatic and tectonic evolution of the eastern Maures suggests a continuous orogenic history in an area of rapid crustal thickening by large-scale thrusting within the continental crust. This evolution may be related to the development of continental subduction during the continent/continent collision responsible for the Variscan orogeny in southern Europe.  相似文献   

    14.
    Chemical and mineralogical compositions of granitic rocks of the French Massif Central enable us to classify them into two distinct groups: (i) leucogranites, (ii) granodiorites or quartz-monzonites, separated by a natural gap. The differences between these two groups are not only chemical and mineralogical, but are also reflected by:
  • conditions of crystallization as deduced from compositions and from thermal metamorphism of xenoliths.
  • nature of inclusions and, especially, the occurrence of basic fine-grained igneous xenoliths restricted to the granodiorite — quartz-monzonite group
  • relations between intrusive and autochtonous migmatitic masses;
  • levels of formation and of intrusion; the granodioritic and quartz-monzonitic magmas have originated at deeper horizons of the earth's crust than the leucogranitic one, but have risen higher.
    • In our opinion these differences are linked, and the specific characteristics of the granodiorites and quartz-monzonites are related to the presence of basic igneous inclusions. These inclusions are relics of deep basic intrusions in the earth's crust, which have overheated the surrounding acid rocks beyond the minimum temperature of melting. Thus granodioritic or quartz-monzonitic melts were produced and were able to rise to superficial levels. These inclusions are missing in leucogranites. The compositions of the latter and their poor mobility suggest a wet anatectic origin in minimal PT conditions.  相似文献   

    15.
    The paper presents novel information on the Caledonian orogeny in Ireland. A series of Dalradian (Upper Precambrian-Lower Cambrian) metasedimentary rocks occur as an envelope to a granitic igneous complex at Slieve Gamph, Western Ireland. These metasedimentary rocks have been deformed at several distinct times and evidence is shown for the following sequence of events:
    1. formation of major nappe structures and a tectonic slide. The axial-plane traces of the folds probably trended N. E.-S. W.
    2. formation of upright, gently plunging folds with axial-plane traces of the folds trending N. E.-S. W. Emplacement of the components of the Slieve Gamph igneous complex.
    3. formation of a conjugate set of folds:
      1. Open folds with N. N. E.-S. S. W. trending axial-planes which dip to the east,
      2. Open folds with E.W. trending axial-planes which dip to the north.
    4. formation of kink-bands, open and conjugate folds with an axialplane trace trending N. W.-S. E.
    Late phase of faulting. No isotopic dates are available for these structural events.  相似文献   

    16.
    Principe is one of the volcanic centres comprising the Cameroun line in West Africa. The volcanic rocks can be divided into two stratigraphic units:
    1. Younger lava series — basanite and nephelinite overlying.
    2. Older lava series — transitional to mildly alkaline basalt and hawaiite.
    These units lie on a basement of palagonite breccias of tholeiitic affinities. The basic lavas are intruded by plugs ranging in composition from tristanite to phonolite and are overlain by phonolite lavas. These rocks form two chemically and mineralogically distinct suites:
    1. Phonolites which evolved by low pressure crystal fractionation of the younger lava series basanitic magma, and
    2. Tristanite — trachyte — trachyphonolite suite which may have evolved by high pressure crystal fractionation of the older lava series magma.
      相似文献   

    17.
    The “South-Italian city” is characterized at four different levels as an independent cultural-genetic city-type:
    1. The characteristics arrangement of the functional areas and the residential areas of different social groups is represented in a model.
    2. From the model, developments and changes in the arrangement of the functional areas can be identified which clearly deviate from those which are derived from the universal city model.
    3. Some of the structural individuality can be directly explained by the peculiar features of the respective social and economic history.
    4. Some of the special features must, however, be traced back to a wider historico-cultural background. Through this run processes which flow through the universal city development in similar forms, to the deviating structure of the “South-Italian city”.
      相似文献   

    18.
    Detailed sedimentological investigations were performed on sediments from DSDP-Site 594 (Chatham Rise, east of New Zealand) in order to reconstruct the evolution of paleoclimate and paleoceanographic conditions in the Southwest Pacific during the last 6 million years. The results can be summarized as follows:
    1. High accumulation rates of biogenic opal and carbonate and the dominance of smectites in the clay fraction suggest increased oceanic productivity and an equable dominantly humid climate during the late Miocene.
    2. During Pliocene times, decreasing contents of smectites and increasing feldspar/quartz ratios point to an aridification in the source area of the terrigenous sediments, culmunating near 2.5 Ma. At that time, accumulation rates of terrigenous components distinctly increased probably caused by increased sediment supply due to intensified atmospheric and oceanic circulation, lowered sea level, and decreased vegetation cover.
    3. A hiatus (1.45 to 0.73 Ma) suggests intensified intermediate-water circulation.
    4. Major glacial/interglacial cycles characterize the upper 0.73 Ma. During glacial times, oceanic productivity and terrigenous sediment supply was distinctly increased because of intensified atmospheric and oceanic circulations and lowered sea level, whereas during interglacials productivity and terrigenous sediment supply were reduced.
    5. An increased content of amphibols in the sediments of Site 594 indicates increased volcanic activities during the last 4.25 Ma.
      相似文献   

    19.
    According to Sakai-Ohmoto's theory regarding the evolution of sulfur isotopes in hydrothermal systems, in conjunction of new data on chemical resaction equilibrium constants and equilibrium isotopic fractionation factors as well as on individual ion activity coefficients of aqueous sulfur species, the following lgfo2.-pH diagrams are constructed:
    1. mole fractions of aqueous sulfur species (X i ),
    2. stability fields of some minerals in the Fe-S-O system,
    3. diagram depicting the oxidation-reduction-state ratio for aqueous sulfur species (R′)
    4. isotopic compositions of sulfur compounds ( \(\delta S_1 ^{34} \) ).
      相似文献   

    20.
    The earthquake of 6 October 1987 (M = 6.6), which occurred near the Shipunsky Cape, Kamchatka, was the largest crustal event in the vicinity of the main city of Kamchatka — Petropavlovsk-Kamchatsky — during the last three decades. It was followed by numerous aftershocks. This earthquake allowed us to test the effectiveness of the seismic hazard monitoring in Kamchatka, including the seismological, geodetic and hydrogeochemical surveys. The seismic survey provided the location and source nature of the main shock and aftershocks and the seismic environment of the main shock. The geodetic and hydrogeochemical surveys have yielded data on the response to earthquakes of the Earth's surface deformations, water level, and chemical elements concentration in the underground water. As a result, the following data were obtained:

    u

  • The earthquake of 6 October had a seismic moment 4–10 E18 Nm, thrust type of faulting and the source volume of 20 × 20 × 10 km3. The maximum intensity was VI–VII (MSK-64 scale) and maximum acceleration 88 cm/s2.
  • Before this event, a relative increase in the number of the upper mantle (depth more than 100 km) moderate magnitude earthquakes during 5 years and a one-year period of seismic quiescence for small shallow earthquakes, were recognized. Significant anomalies in HCO3 and H3BO3 concentrations in the underground waters were observed in the wells a week before the main shock.
    •   相似文献   

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