Detection of underground cavities with monofrequency electromagnetic tomography between boreholes in the frequency range 100 MHz to 1 GHz1

In order to detect underground cavities, we have designed a geophysical method based on the interaction of a monochromatic electromagnetic wave in the frequency band 100 MHz to 1 GHz with the ground situated between two boreholes. Three different approaches are involved in the design of this EM tomographic method.

• 1 The application of an ‘exact’ theory is used to calculate artificial data, based on an integral equation method. These data are inverted using a tomographic algorithm whose basic assumptions are rather coarse. The results show that, however, cavities can very well be detected and their position recovered.
• 2 Data are obtained with a physical reduced-scale model in a water tank, in which all parameters are known in advance. The inversion process confirms the validity of the method.
• 3 Underground cavities are actually detected.

The above approaches are described and discussed and results are shown. The equipment involved and its operation is quite simple: the surface devices are commercially available and only the transmitter and receiver antennae must be specially built. The method is shown to be quite efficient and its cost should be reasonably low.     

Some geological aspects of the conservation project for the Philae Temples in the Aswan Area

In connection with the UNESCO-activity to save the Nubian Monuments several geological and geotechnical problems arising are discussed. Geomorphology, regional geology, capillarity-questions and salt-action are considered and ways of saving the Philae-Monuments are sketched.

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Zusammenfassung Im Zusammenhang mit der UNESCO-Aktion zur Rettung der Nubischen Denkmäler werden verschiedene geologische und geotechnische Probleme dieses Unternehmens beschrieben. Regional-geologische und geomorphologische Fragen, Kapillaritäts- und Salzverwitterungs-Probleme werden angeschnitten und diskutiert. Zum Schluß werden Maßnahmen zur Rettung der Philae-Tempel skizziert.

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Résumé En regard de l'action de l'UNESCO pour le sauvetage des monuments de la Nubie, l'auteur décrit les différents problèmes géologiques et géotechniques relatifs à cette entreprise. Des questions à caractère géologique régional et géomorphologique, des problèmes d'altération par capillarité et à l'intervention de sels sont examinés et discutés. Finalement l'auteur esquisse les mesures à prendre pour la sauvegarde du temple de Philae.

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UNESCO .

     

Sedimentation processes in silt-rich sediment systems

Sediment found in China’s Yangtze and Yellow River systems is characterized by large silt fractions. In contrast to sand and clay, sedimentation and erosion behaviour of silt and silt–clay–sand mixtures is relatively unknown. Therefore, settling and consolidation behaviour of silt-rich sediment from these river systems is analysed under laboratory conditions in specially designed settling columns. Results show that a transition in consolidation behaviour occurs around clay contents of about 10 %, which is in analogy with the transition from non-cohesive to cohesive erosion behaviour. Above this threshold, sediment mixtures consolidate in a cohesive way, whereas for smaller clay percentages only weak cohesive behaviour occurs. The settling behaviour of silt-rich sediment is found to be in analogy with granular material at concentration below 150 g/l. Above 150–200 g/l, the material settles in a hindered settling regime where segregation is limited or even prevented. The results indicate that for modelling purposes, multiple sediment fractions need to be assessed in order to produce accurate modelling results.     

Holocene relative shore-level changes and development of the Ģipka lagoon in the western Gulf of Riga

Holocene relative shore-level changes and development of the Ģipka palaeolagoon in the western Gulf of Riga are reconstructed using multiproxy analyses by combining litho-, biostratigraphical and chronological data with remote sensing and geophysical data. The results show the development of the Ģipka basin from the Ancylus Lake/Initial Litorina Sea coastal zone (before c. 9.1 cal. ka BP) to coastal fen (c. 9.1 to 8.4 cal. ka BP) and gradual development of the Litorina Sea lagoon (c. 8.4 to 4.8 cal. ka BP) and its transition to a freshwater coastal lake (c. 4.8 to 4.6 cal. ka BP), fen (c. 4.6 to 4.2 cal. ka BP), and river floodplain (since c. 4.2 cal. ka BP). The highest shorelines of the Ancylus Lake and Litorina Sea were mapped at an elevation of 12–11 and 9 m a.s.l., respectively. A new relative shore level (RSL) curve for the western Gulf of Riga was constructed based on RSL data from the Ģipka area and from nearby Ruhnu Island studied earlier. The reconstruction shows that the beginning of the last marine transgression in the western Gulf of Riga started at c. 8.4 cal. ka BP, and concurred with the 1.9 m RSL rise event recorded from the North Sea basin. Diatom analysis results indicate the existence of the Ģipka lagoon between c. 7.7 and 4.8 cal. ka BP, with the highest salinity c. 6.1 cal. ka BP. During the existence of the brackish lagoon, settlement sites of the Neolithic hunter–gatherer groups existed on the shores of the lagoon in the period c. 6.0 to 5.0 cal. ka BP.     

Geosecs North Atlantic radiocarbon and tritium results

Radiocarbon data for 11 stations and tritium data for 16 stations in the North Atlantic Ocean from 74°N to 3°N are presented. For radiocarbon, normal errors inΔ¹⁴C are± 4‰, and in tritium,± 0.09TU or± 3%, whichever is larger. There is a remarkable, but not simply linear, correlation between oceanic bomb transients in¹⁴C and³H. The deep convective mixing in the Greenland Sea is reflected in substantial bomb tracer penetration to all depths, with residence time for the deep, cold core water that seems to be 20 to 30 years. The outflow in the bottom layer southward over the sills of the Denmark Strait and Faroe Passage carries significant tritium concentration, at least to 40°N. Complicated, but coherent, profile structures in the subtropical Atlantic suggest effects of large-scale lateral advection. In particular, a pronounced minimum in both¹⁴C and³H might be associated with the Antarctic intermediate water.     

流体替代技术在北黄海盆地中生界含烃储层识别中的应用

北黄海盆地中生界勘探目的层以陆相碎屑岩储层为主,埋藏较深,受沉积压实和胶结成岩作用的影响,储层物性较差,含油气有利储层识别难度较大。利用流体替代技术,依据已建立的岩石物理模型,结合实际流体温度、压力等参数,对特定泥质含量、孔隙度条件下储层弹性响应特征随不同流体饱和度的变化规律进行正演计算,从而建立了含油气有利储层的弹性参数刻画范围。研究结果表明,对于孔隙度＞8%的物性相对较好的砂岩储层,其中含水的弹性属性与含油的弹性属性有一定的差别,而储层中含气的弹性属性与含油的弹性属性差别较为明显。因此,在研究区可以应用测量的纵波阻抗和模拟的纵横波速比建立含烃储层的解释框架,并利用叠前反演技术对研究区内物性较好有利储层作出预测。     

Background discrimination capabilities of a heat and ionization germanium cryogenic detector

The discrimination capabilities of a 70 g heat and ionization Ge bolometer are studied. This first prototype has been used by the EDELWEISS dark matter experiment, installed in the Laboratoire Souterrain de Modane, for direct detection of WIMPs. Gamma and neutron calibrations demonstrate that this type of detector is able to reject more than 99.6% of the background while retaining 95% of the signal, provided that the background events distribution is not biased towards the surface of the Ge crystal. However, the 1.17 kg day of data taken in a relatively important radioactive environment show an extra population slightly overlapping the signal. This background is likely due to interactions of low energy photons or electrons near the surface of the crystal, and is somewhat reduced by applying a higher charge-collecting inverse bias voltage (−6 V instead of −2 V) to the Ge diode. Despite this contamination, more than 98% of the background can be rejected while retaining 50% of the signal. This yields a conservative upper limit of 0.7 event day⁻¹ kg⁻¹ keV_recoil⁻¹ at 90% confidence level in the 15–45 keV recoil energy interval; the present sensitivity appears to be limited by the fast ambient neutrons. Upgrades in progress on the installation are summarized.