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151.
Y. Chung R. Finkel M.P. Bacon J.K. Cochran S. Krishnaswami 《Earth and Planetary Science Letters》1983,65(2):393-405
During reoccupation of the GEOSECS-I test station in May, 1979, more than eighty 30-liter Niskin samples were collected in profile, many as replicates, for210Pb intercomparison measurements by the WHOI, SIO and Yale groups. In addition to the inter-laboratory comparisons, the SIO group also carried out extensive experiments to test the effect of sample scavenging method. Pb equilibration time (storage effect), and filtration process on the measured210Pb results.The intercomparison measurements indicate that there is a general agreement between the various sets of data. The sample set which allows a direct comparison at the same depth was available in most cases only between two of the three groups. The direct paired comparison shows that (1) the WHOI data are systematically 3% lower than the SIO data; (2) there are no systematic differences observed between the SIO and Yale data although the scatter is rather large; (3) the Yale data are systematically higher than the WHOI data by about 8%.The SIO experiments show that (1) the two scavenging methods employed (Fe(OH)3 and Co-APDC co-precipitation) yield identical210Pb results; (2) variation of Pb carrier equilibration time or of storage time has no discernible effect; (3) the filtration apparatus and procedure employed at this station do not result in210Pb loss or contamination.The210Pb profile structure and absolute concentration measured earlier at the same location (GOGO-II test station and GEOSECS station 347) agree with those of station 500 within 10%. The present profile shows a minimum210Pb concentration around 500 m depth, marking the penetration depth of the flux of excess210Pb from the atmosphere. There is a mild mid-depth maximum around 2500–3000 m. The210Pb/226Ra activity ratio decreases monotonically from about 1 at the210Pb minimum to about 0.5 near the bottom. The particulate210Pb profile shows a systematic increase from the subsurface water to the bottom water by a factor of 5. This feature has been observed in many GEOSECS particulate210Pb profiles. 相似文献
152.
We report here on particulate and dissolved210Pb profiles at 16 stations, and on total210Pb profiles at 3 stations, all occupied during the Pacific GEOSECS expedition. Comparison with measurements at Yale on GEOSECS library samples indicates that during separation of particulate lead from dissolved lead, our filtered water samples suffered some loss of210Pb in the filtration system; this effect appears to have reduced the dissolved210Pb activities by ~ 20% in stations where the water was filtered. However, for these first Pacific data on the210Pb distribution between the two phases, this effect does not significantly interfere with our recognition of the major features of both particulate and dissolved210Pb distributions.The dissolved210Pb profiles in general vary geographically, following the226Ra profiles. In deep water,226Ra increases northward and eastward from the southwest Pacific, from ~ 22dpm/100kg, to over 40 dpm/100 kg in the northeast Pacific. Our dissolved210Pb profiles show a similar increase in deep water, varying from about 10 to 20 dpm/100 kg along this line, and are commonly characterized by a mid-depth maximum. This210Pb maximum reflects the mid-depth226Ra maximum of the Pacific Deep Water observed along the western boundary current.In surface water at low latitudes there is a significant210Pb flux from the atmosphere, which produces a210Pb/226Ra activity ratio generally greater than unity. This flux penetrates as deep as 600 m, as indicated by an “induced”210Pb minimum caused by the surface maximum. The surface water210Pb excess decreases toward high southern latitudes and vanishes in the Circumpolar region.The particulate210Pb profiles show a general increase with depth, from ~ 0.3dpm/100kg in subsurface water to ~ 1.5dpm/100kg in bottom water, with or without a mid-depth maximum that reflects the226Ra or dissolved210Pb maximum. The particulate210Pb normally comprises about 2% of the total210Pb in subsurface water, and this fraction increases to about 10% near the bottom. As the filtration loss is not taken into account, the fraction of particulate210Pb quoted here is an upper limit. Since the particulate matter concentrations are quite uniform in the water column below a few hundred meters, the210Pb activity of the particulate matter also increases with depth. The particulate matter has a210Pb concentration of ~ 100dpm/g in subsurface water, but the concentration increases to ~ 500dpm/g or more toward the bottom. This indicates that there is a cumulative adsorption of Pb onto the suspended particles as they are sinking through the water column. 相似文献
153.
154.
155.
Tectono-thermal modeling of the Yinggehai Basin,South China Sea 总被引:1,自引:0,他引:1
Lijuan?HeEmail author Liangping?Xiong Jiyang?Wang Jihai?Yang Weiliang?Dong 《中国科学D辑(英文版)》2001,44(1):7-13
Based on the observed data, the average value of surface heat flow in the Yinggehai Basin is calculated and it turns out to
be 84.1 mW/m2. The thermal evolution of the basin since the Cenozoic era has been attempted by tectono-thermal modeling. Three-phase extension
made the basin become hotter and hotter, reaching its climax in paleo-temperature history since 5.2 Ma. And nowadays, the
basin is in the heat flow decreasing period. During the Cenozoic era, the basement heat flow remained at 50–70 mW/m2 all the time. This is related to the degree of each extension phase, stretching rate mode and also the limited basin scale.
Modeling results also show that, the surface heat flow is controlled mainly by the basement heat flow, and less than 20% comes
from radiogenic heat production in the sediments of the basin 相似文献
156.
Mapping landslide susceptibility from small datasets: A case study in the Pays de Herve (E Belgium) 总被引:3,自引:1,他引:3
A landslide susceptibility map is proposed for the Pays de Herve (E Belgium), where large landslides affect Cretaceous clay outcrop areas. Based on a Bayesian approach, this GIS-supported probabilistic map identifies the areas most susceptible to deep landslides. The database is comprised of the source areas of ten pre-existing landslides (i.e. a sample of 154 grid cells) and of six environmental data layers, namely lithology, proximity to active faults, slope angle and aspect, elevation and distance to the nearest valley-floor. A 30-m-resolution DEM from the Belgian National Geographical Institute is used for the analysis. Owing to the small size of the sample, a special cross-validation procedure of the susceptibility map is performed, which uses in an iterative way each of the landslides to test the predictive power of the map derived from the other landslides. Four different sets of variables are used to produce four susceptibility maps, whose prediction curves are compared. While the prediction rates associated with the models not involving the “proximity to active fault” criterion are comparable to those of the models considering this variable, strong weaknesses inherent in the fault data on which the latter rely suggest that the final susceptibility map should be based on a model that excludes any reference to fault. This highlights the difference between a triggering factor and determining factors, and in the same time broadens the scope of the produced map. A single reactivated slide is also used to test the possibility of predicting future reactivation of existing landslides in the area. Finally, the need for geomorphological control over the mathematical treatment is underlined in order to obtain realistic prediction maps. 相似文献
157.
This paper presents results of meticulous laboratory testing and numerical simulations on the effect of reinforcement on the
low-strain stiffness and bearing capacity of shallow foundations on dry sand. The effect of the location and the number of
reinforcement layers is studied in the laboratory, whereas numerical simulations are used to study the reinforcement-foundation
interaction. Laboratory tests show an increase of 100, 200, and 275% not only in bearing capacity but also in low-strain stiffness
(linear load–displacement behaviour) of a square foundation when one, two, and three layers of reinforcement are used, respectively.
The specimen preparation technique is found to be crucial for the repeatability and reliability of the laboratory results
(less than 5% variability). Numerical simulations demonstrate that if reinforcements are placed up to a depth of one footing
width (B) below the foundation, better re-distribution of the load to deeper layers is achieved, thus reducing the stresses and strains
underneath the foundation. Numerical simulations and experimental results clearly identify a critical zone between 0.3 and
0.5B, where maximum benefits not only on the bearing capacity but also on the low-strain stiffness of the foundation are obtained.
Therefore, soil reinforcement can also be used to reduce low-strain vibrations of foundations. 相似文献
158.
Iodine contents of soils developed over the major rock formations of the northern zone of the Eastern Pontide Tectonic Belt
(Northeastern Turkey) have been investigated with respect to soil-parent rock relationship, effect of topography, elevation,
and climate to construe its effect on the health of the local population. Samples were collected from the A and B horizons
of the soils developed over the major stratigraphic units constituting the eastern Pontides, including the Lower Basic Complex
of Jurassic-Lower Cretaceous age, the Berdiga limestone (Jurassic-lower Cretaceous), the Dagbasi granitoid (Upper Cretaceous),
volcano-sedimentary sequence of Upper Cretaceous age, ore-bearing and barren dacites of Upper Cretaceous age, and Neogene
alkaline basalts. Chemical analyses of soil samples indicate significantly lower iodine abundances for all the soils studied
(5–28 ppm) in comparison to the average abundance of iodine in analogous soils of other parts of the world (22–93 ppm). The
concentration of iodine in soils developed over the same geologic formation decrease with increasing elevation. In certain
cases, this decrease may reach up to 70%. Goiter is highly common throughout this region in Turkey. The results of this study
suggest that the iodine deficiency of region’s soils may be a principal underlying cause for this area of Turkey being an
endemic goiter region. 相似文献
159.
Jong-Chan Park Woohan Kim Tae Woong Chung Chang-Eob Baag Jin-Han Ree 《Geophysical Journal International》2007,169(3):1103-1114
We evaluate the stress field in and around the southern Korean Peninsula with focal mechanism solutions, using the data collected from 71 earthquakes ( ML = 1.9–5.2) between 1999 and 2004. For this, the hypocentres were relocated and well-constrained fault plane solutions were obtained from the data set of 1270 clear P -wave polarities and 46 SH / P amplitude ratios. The focal mechanism solutions indicate that the prevailing faulting types in South Korea are strike-slip-dominant-oblique-slip faultings with minor reverse-slip component. The maximum principal stresses (σ1 ) estimated from fault-slip inversion analysis of the focal mechanism solutions show a similar orientation with E–W trend (269°–275°) and low-angle plunge (10°–25°) for all tectonic provinces in South Korea, consistent with the E–W trending maximum horizontal stress (σHmax ) of the Amurian microplate reported from in situ stress measurements and earthquake focal mechanisms. The directions of the intermediate (σ2 ) and minimum (σ3 ) principal stresses of the Gyeongsang Basin are, however, about 90 deg off from those of the other tectonic provinces on a common σ2 –σ3 plane, suggesting a permutation of σ2 and σ3 . Our results incorporated with those from the kinematic studies of the Quaternary faults imply that NNW- to NE-striking faults (dextral strike-slip or oblique-slip with a reverse-slip component) are highly likely to generate earthquakes in South Korea. 相似文献
160.