Enhancement of radon signals in geophysical studies with the track technique     

A. Tidjani  M. Monnin  J -L. Seidel 《Pure and Applied Geophysics》1990,132(3):495-504

The existence of a suspected geological fault has been confirmed using Solid State Nuclear Track Detectors (SSNTDs) by measuring radon concentration variations in the upper soil above its inferred position. The results obtained prompted us to increase the natural radon signal in the soil, using an additional radon source; this enhancement technique, has been experimentally checked with SSNTD detectors.On leave from Faculté des Sciences, Laboratoire des D.S.T.N. Université de Dakar, Dakar-Fann, Sénégal  相似文献   

The effective elastic thickness of the India Plate from receiver function imaging, gravity anomalies and thermomechanical modelling   总被引：2，自引：0，他引：2  

György Hetényi  Rodolphe Cattin  Jérôme Vergne  John L. Náb&#;lek 《Geophysical Journal International》2006,167(3):1106-1118

  相似文献   

RACIALIZED TOPOGRAPHIES: ALTITUDE AND RACE IN SOUTHERN CITIES*     

JEFF UELAND  BARNEY WARF 《Geographical review》2006,96(1):50-78

ABSTRACT. This study examines altitudinal residential segregation by race in 146 cities in the U.S. South. It begins by embedding the topic in recent theorizations of the social construction of nature, the geography of race, and environmental justice. Second, it focuses on how housing markets, particularly in the South, tend to segregate minorities in low‐lying, flood‐prone, and amenity‐poor segments of urban areas. It tests empirically the hypothesis that blacks are disproportionately concentrated in lower‐altitude areas using gis to correlate race and elevation by digital elevation‐model block group within each city in 1990 and 2000. The statistical results confirm the suspected trend. A map of coefficients indicates strong positive associations in cities in the interior South‐where the hypothesis is confirmed‐and an inverse relationship near the coast, where whites dominate higher‐valued coastal properties. Selected city case studies demonstrate these relationships connecting the broad dynamics of racial segregation to the particularities of individual places.  相似文献   

国土资源行业“3S”技术集成研究及实用技术体系构建     

查宗祥  刘聚海  蒋文彪 《国土资源信息化》2005,1(6):2-7

本文面向国土资源信息化建设的实际需求,通过关键技术研究和技术集成,建立基于“3S”的国土资源数据获取、更新、管理、交换与应用的技术体系,通过应用示范研究,形成实用、可推广的技术流程和应用软件。研究结果表明,基于“3S”的技术体系,以其精确的空间定位、快速准确的数据获取、强大的数据管理能力,能够满足国土资源信息化建设的实际需要。  相似文献   

测绘职业教育教学改革探讨     

段莉 《四川测绘》2005,28(2):89-91

随着空间科学技术和计算机技术的发展，以“3S”技术为代表的测绘高新技术已普遍应用于测绘生产中。作为培养测绘实用型人才的测绘职业学校，测绘专业如何重新划分、测绘教育与教学内容如何改革，是测绘教育界普遍关注的问题，本文从教学的角度对有关问题进行了探讨。  相似文献   

Celestite formation, bacterial sulphate reduction and carbonate cementation of Eocene reefs and basinal sediments (Igualada, NE Spain)   总被引：5，自引：0，他引：5  

Conxita Taberner  James D. Marshall†  James P. Hendry‡  Catherine Pierre§  & M. F. Thirlwall¶ 《Sedimentology》2002,49(1):171-190

Petrographic and geochemical studies of an Upper Eocene reef and associated basinal sediments from the mixed carbonate–siliciclastic fill of the south‐eastern Pyrenean foreland basin near Igualada (NE Spain) provide new insights into the evolution of subsurface hydrology during the restriction of a marine basin. The reef deposits are located on delta‐lobe sandstones and prodelta marls, which are overlain by hypersaline carbonates and Upper Eocene evaporites. Authigenic celestite (SrSO₄) is an important component in the observed diagenetic sequences. Celestite is a significant palaeohydrological indicator because its low solubility constrains transportation of Sr²⁺ and SO₄^2? in the same diagenetic fluid. Stable isotopic analyses of carbonates in the reef indicate that meteoric recharge was responsible for aragonite stabilization and calcite cementation. Sulphur and oxygen isotope geochemistry of the celestite demonstrates that it formed from residual sulphate after bacterial sulphate reduction, but also requires that there was a prior episode of sulphate recycling. Meteoric water reaching the reef and basinal areas was most probably charged with SO₄^2? from the dissolution of younger Upper Eocene marine evaporites. This sulphate, combined with organic matter present in the sediments, fuelled bacterial sulphate reduction in the meteoric palaeoaquifer. Strontium for celestite precipitation was partly derived in situ from dissolution of aragonite corals in the reef and basinal counterparts. However, ⁸⁷Sr/⁸⁶Sr data also suggest that Sr²⁺ was partly derived from dissolution of overlying evaporites. Mixing of these two fluids promoted celestite formation. The carbonate stable isotopic data suggest that the local meteoric water was enriched in ¹⁸O compared with that responsible for stabilization of other reefs along the basin margin. Furthermore, meteoric recharge at Igualada post‐dated evaporite deposition in the basin, whereas other parts of the same reef complex were stabilized before evaporite formation. This discrepancy resulted from the spatial distribution of continental siliciclastic units that acted as groundwater conduits.  相似文献   

Sulfur Content and Isotopic Ratio of Cambro-Ordovician Carbonate Rocks from South Korea: A Possible Source for Mesozoic Magmatic-hydrothermal Ore Sulfur     

Shunso ISHIHARA  Myung–Shik JIN  Yoshimichi KAJIWARA 《Resource Geology》2002,52(1):41-48

Abstract: Carbonate rocks of Cambrian (18 samples) and lower-middle Ordovician (11 samples) ages from South Korea were analyzed for sulfur contents of structurally substituted sulfate (SSS) and sulfides and their δ³⁴S values. The δ³⁴S values of SSS ranging from +25.9 to +45.2 permil, are averaged as +33.6 and +33.5 permil for the Cambrian and Ordovician rocks, respectively, which indicate high δ³⁴S values of the Cambro-Ordovician seawater. The SSS contents in the carbonate rocks are low being 2.9 to 17.3 ppm S (averaged as 7.0 ppm S). Sulfide sulfur, on the contrary, is much abundant containing 3 to 1,880 ppm S and the δ³⁴S values range widely between –17.6 and +31.1 permil. Sulfide sulfur of the studied rocks excluding impure carbonates has an average content of 187 ppm S and δ³⁴S value of +12.8 permil (n=24). The estimated δ³⁴S (sulfate–sulfide) values, which range from 13.8 to 25.4 permil in general with a few exceptions from 36.5 up to 52.3 permil for some impure carbonates, may provide evidence for the persistent oceanic anoxia with its temporary recovery during the Cambro-Ordovician time.
The SSS and sulfide sulfurs have often higher δ³⁴S values than the Mesozoic-Cenozoic ore sulfur (Ishihara et al., 2000). Since carbonate rocks are very reactive with circulating hydrothermal ore solution, high δ³⁴S values of the Korean ore deposits might be caused to some extent by ³⁴S enrichment from the host carbonates, resulting in the low SSS contents observed.  相似文献   

天祝-古浪5.4级地震震源机制和发震断层以及海原西断裂大震危险性讨论          下载免费PDF全文

李亚荣  朱新运 《地震工程学报》2002,24(3):236-240

研究了发生在海西断裂天祝拉分盆地1996年6月1日5.4级地震的震源机制，利用位于天祝－古浪地区的数字式微震监测台网纪录的余震的精确定位确定了本次地震的发震断层，研究表明这次地震是天祝拉分盆地中垂直于主断裂的近南北向断裂所形成，根据破裂模型和海原西断裂的应力积累状况，讨论了海原西断裂近期的大震危险性。  相似文献   

δO of carbonate, quartz and phosphate from belemnite guards: implications for the isotopic record of old fossils and the isotopic composition of ancient seawater     

Antonio Longinelli  Paola IacuminMichele Ramigni 《Earth and Planetary Science Letters》2002,203(1):445-459

Belemnite guards of Cretaceous and Jurassic age were found to contain varying amounts of quartz deposited both on the external surface and inside the rostrum. The oxygen isotopic composition of coexisting carbonate, quartz and phosphate from the same rostrum was measured according to well-established techniques. None of these compounds showed isotopic values in equilibrium with one another. Assuming δ¹⁸O values of the diagenetic water within the range of meteoric waters, the δ¹⁸O(SiO₂) yield temperatures in agreement with the apparent secondary origin of this phase. The δ¹⁸O(CO₃²⁻) range, with a certain continuity, between −10.8 and +0.97 PDB-1 with most of the intermediate values being within the range of the carbonate isotopic values of Mesozoic fossils. The most positive isotopic results obtained from phosphate are close to +23/+24‰ (V-SMOW). They can hardly be related to a secondary origin of the phosphate, or to the presence of diagenetic effects, since these results are among the most positive ever measured on phosphate. As far as we know there is no widespread diagenetic process determining an ¹⁸O enrichment of phosphate. The very low concentration of phosphate did not allow the determination of its mineralogical composition. All the available δ¹⁸O(PO₄³⁻) values from belemnite and non-belemnite fossils of marine origin of Tertiary and Mesozoic age are reported along with the newly measured belemnites. The following conclusions may be drawn from the data reported: (1) the pristine oxygen isotope composition of fossil marine organisms (either carbonate or phosphate) may easily undergo fairly large changes because of oxygen isotope exchange processes with diagenetic water; this process is apparent even in the case of geologically recent fossils; (2) the δ¹⁸O(PO₄³⁻) of belemnite rostra seems to be, at least in the case of the most positive results, in isotopic equilibrium with environmental water because of the similarity between the results from Cretaceous belemnites and the results from Cretaceous and Lower Tertiary pelecypods and fish teeth; 3) if so, the only feasible interpretation that can be suggested for the ¹⁸O enriched data is the possibility of a relatively large variation of the oxygen isotopic composition of ocean paleowater from Jurassic to recent time.  相似文献   

2001年11月14日新疆-青海交界8.1级地震   总被引：3，自引：0，他引：3  

陈学忠  许力生 《国际地震动态》2002,(3):1-4

简要介绍了2001年11月14日新疆－青海交界8．1级地震的预测情况，给出了中、美、日等对此次地震的震源参数测定和震源机制，以及余震的分布和加卸载响应比随时间的变化。进而对震区近期地震趋势进行预测。  相似文献