共查询到20条相似文献，搜索用时 62 毫秒
1.
结合清原地震台台站水准1985年前后观测成果精度的变化，总结了提高台站短水准观测成果精度的几点主要成功措施。它们是：选择最佳视线长度；拓宽线路、增高视线、减弱折光影响；改造仪器站条件；固定观测时间和人员；确定好观测光段。 相似文献
2.
3.
将用于图像处理的光顺技术引用到速度谱能量团曲面的处理环节,借以提高速度谱的分辨率,为最终获得高精确解提供一全新的途径.具体思路是基于路径积分优化法--Viterbi算法所具有的自动搜寻及获取最优解的功能,将其应用于地震资料处理中的速度自动拾取,使其向前做最大"能量团"的积分向后递归计算最优解--叠加速度,但这种解的准确性往往与所定义的目标函数--速度谱的分辨率有关.演算结果表明,Viterbi算法与关顺处理技术的有机结合,不仅提高了速度提取的精度,而且实现了速度的自动拾取,可提高常规地震资料处理的效率,从而可快捷地为叠前深度偏移提供所需初始速度模型. 相似文献
4.
《Advances in water resources》1999,23(1):1-13
The self-calibrated method has been extended for the generation of equally likely realizations of transmissivity and storativity conditional to transmissivity and storativity data and to steady-state and transient hydraulic head data. Conditioning to transmissivity and storativity data is achieved by means of standard geostatistical co-simulation algorithms, whereas conditioning to hydraulic head data, given its non-linear relation to transmissivity and storativity, is achieved through non-linear optimization, similar to standard inverse algorithms. The algorithm is demonstrated in a synthetic study based on data from the WIPP site in New Mexico. Seven alternative scenarios are investigated, generating 100 realizations for each of them. The differences among the scenarios range from the number of conditioning data, to their spatial configuration, to the pumping strategies at the pumping wells. In all scenarios, the self-calibrated algorithm is able to generate transmissivity–storativity realization couples conditional to all the sample data. For the specific case studied here the results are not surprising. Of the piezometric head data, the steady-state values are the most consequential for transmissivity characterization. Conditioning to transient head data only introduces local adjustments on the transmissivity fields and serves to improve the characterization of the storativity fields. 相似文献
5.
The deflection, at a step-shelf fronted coast, of a constant potential vorticity current in a reduced-gravity, inviscid model ocean is studied theoretically. The step shelf, with a depth smaller than the reservoir depth, forces the uplifting of the approaching current and causes water column foreshortening, leading to relative vorticity generation that enhances current deflection to the right (facing the coast). As a consequence, in comparison to the case of a vertical wall coast, the proportion of the transport to the right is increased. For normal incidence for a shelf-depth/reservoir-depth ratio of 0.3 and shelf width to deformation radius ratio of 1.5, more than 90% of the approaching current transport goes to the right and less than 10% to the left. In addition, the (barotropic) dynamic pressure at the coast is low to the right and high to the left (with the highest pressure at the stagnation point). In the vertical wall case, the wall pressures on the flank are equal. For oblique incidence from the left, the deflection to the left is drastically reduced. In fact, there is practically no steady-state flow diverted to the left (less than 2%) when the approach angle is greater than 60° to the left of normal. In the vertical wall case, the same angle would have to be 90° for the flow to the left to vanish, namely only when the approach current is parallel to the coast to the right. 相似文献
6.
Data use and information creation: challenges for marine scientists and for managers 总被引：1，自引：0，他引：1
In the coastal waters of European countries and in the offshore waters of the north-east Atlantic, there is an increasing need for scientists to meet challenging objectives, such as to identify meaningful measures of 'quality', and to recommend 'indicators' to underpin implementation of directives, conventions, statutes and other more informal national and international initiatives. Those indicators may relate to particular species or habitats, to changes in physical and chemical characteristics, and even to the use to which the system is put. The problems to be overcome are difficult, but new and developing approaches will make a significant contribution. The approaches include: criteria to identify 'sensitivity' and 'importance', structures to organise information and electronic information resources to access data.The real challenge is to make the results of the various scientific initiatives relevant to and understandable by a wide range of customers with similar overlapping requirements, and thus make a genuine contribution to protecting the marine environment. Above and beyond that is the need for scientists to drive the agenda to enable real and lasting progress to be made towards ecosystem-based management of our seas and a proper consideration of what 'sustainability' may mean in the marine environment and how we utilise its resources. 相似文献
7.
Seasonal variations in coastal debris on Awaji Island, Japan 总被引：1，自引：1，他引：0
Shimizu T Nakai J Nakajima K Kozai N Takahashi G Matsumoto M Kikui J 《Marine pollution bulletin》2008,57(1-5):182-186
The subject of our study was Awaji Island, an island located in the west of Japan that is surrounded by sea and that has serious problems relating to coastal debris. We conducted a long-term investigation focusing on three beaches and evaluated the results. The study was designed to develop an understanding of the actual situation, to inform local citizens, and raise their concerns about the problem of debris with a view to taking action against it. We obtained the following results: the amount, type, and ratio of debris changed according to weather and ocean conditions; debris also differs according to geographical conditions; social and economic activities of the surrounding area influence the type of debris encountered. Following this study, we have continued our investigation, and are continuing to gather data. At the same time, it is important to spread our ideas and enlighten people so as to encourage them not to dump debris. We hope that these actions manage to raise the level of consciousness among local citizens and to expand their anti-debris activities. 相似文献
8.
The southwest border of the Parecis Basin (central Brazil) presents several occurrences of gold, copper and zinc. Parallel to this border, there is an alignment of magnetic anomalies with varied size and polarities. In particular, five magnetic anomalies are referred to, in this study, as SJ1 to SJ5. The proximity of these anomalies to each other makes it hard to isolate the magnetic component associated with each source. Furthermore, these anomalies have different magnetization directions, which require the use of a technique which is slightly or not affected by the presence of a remanent magnetization, as the amplitude of the anomalous magnetic field. Considering that, in these intrusions no outcrops are observed, the enhanced horizontal derivative technique was used to estimate the edges location and the depth of these sources. The geological context, allied to the results from the magnetic techniques, allowed to establish binds to restrain the interpretation of the results of the 3D inversion. This procedure permitted to compose three hypothesis to explain the magnetic behavior of the region, from which can be conclusively determined with a borehole analysis. 相似文献
9.
The human eye is an excellent, general-purpose airborne sensor for detecting marine debris larger than 10 cm on or near the surface of the water. Coupled with the human brain, it can adjust for light conditions and sea-surface roughness, track persistence, differentiate color and texture, detect change in movement, and combine all of the available information to detect and identify marine debris. Matching this performance with computers and sensors is difficult at best. However, there are distinct advantages over the human eye and brain that sensors and computers can offer such as the ability to use finer spectral resolution, to work outside the spectral range of human vision, to control the illumination, to process the information in ways unavailable to the human vision system, to provide a more objective and reproducible result, to operate from unmanned aircraft, and to provide a permanent record that can be used for later analysis. 相似文献
10.
The impacts of climate change on storm runoff and erosion in Mediterranean watersheds are difficult to assess due to the expected increase in storm frequency coupled with a decrease in total rainfall and soil moisture, added to positive or negative changes to different types of vegetation cover. This report, the second part of a two‐part article, addresses this issue by analysing the sensitivity of runoff and erosion to incremental degrees of change (from ? 20 to + 20%) to storm rainfall, pre‐storm soil moisture, and vegetation cover, in two Mediterranean watersheds, using the MEFIDIS model. The main results point to the high sensitivity of storm runoff and peak runoff rates to changes in storm rainfall (2·2% per 1% change) and, to a lesser degree, to soil water content (?1·2% per 1% change). Catchment sediment yield shows a greater sensitivity than within‐watershed erosion rates to both parameters: 7·8 versus 4·0% per 1% change for storm rainfall, and ? 4·9 versus ? 2·3% per 1% change for soil water content, indicating an increase in sensitivity with spatial scale due to changes to sediment connectivity within the catchment. Runoff and erosion showed a relatively low sensitivity to changes in vegetation cover. Finally, the shallow soils in one of the catchments led to a greater sensitivity to changes in storm rainfall and soil moisture. Overall, the results indicate that decreasing soil moisture levels caused by climate change could be sufficient to offset the impact of greater storm intensity in Mediterranean watersheds. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
11.
《Journal of Geodynamics》2006,41(4-5):487-493
The focus of this paper is to present the concepts for a new dynamic, i.e. database-driven information system for the International Earth Rotation and Reference Systems Service (IERS). Its goal is to coordinate the data and information flow between the participating institutions. Therefore, all relevant data and products of the IERS should be archived to guarantee their long-term availability. At the same time the consistency and timeliness of the contents of the information system can be guaranteed by managing the information in a database. Additionally, the metadata of all products (including the IERS publications) should be modelled in a database to allow the users to search for specific data or topics with respect to space, time and content. In order to be able to link related data the heterogeneous formats of the products have to be transformed into a common format. The eXtensible Markup Language (XML) is going to be used, to perform this ambitious task. The usage of XML not only allows to link related data but also to easily exchange data and to present them in different ways like Web pages, pdf, etc. The system will be completed by several tools to manage and coordinate the tasks of the Central Bureau (CB) and by an information system with respect to IERS-related topics. The standardised database tools will also allow an easy exchange of information with and links to other databases within the IGGOS project to realize a powerful instrument to serve the Earth observing system. 相似文献
12.
This paper presents the analytical properties of the sensitivity of the two-dimensional, steady-state groundwater flow equation to the flow parameters and to the boundary conditions, based on the perturbation approach. These analytical properties are used to provide guidelines for model design, model calibration and monitoring network design. The sensitivity patterns are shown to depend on the nature of both the perturbed parameter and the variable investigated. Indeed, the sensitivity of the hydraulic head to the hydraulic conductivity extends mainly in the flow direction, while the sensitivity to the recharge spreads radially. Besides, the sensitivity of the flow longitudinal velocity to the hydraulic conductivity propagates in both the longitudinal and transverse directions, whereas the sensitivity of the flow transverse velocity propagates in the diagonal directions to the flow. The analytical results are confirmed by application examples on idealized and real-world simulations. These analytical findings allow some general rules to be established for model design, model calibration and monitoring network design. In particular, the optimal location of measurement points depends on the nature of the variable of interest. Measurement network design thus proves to be problem-dependent. Moreover, adequate monitoring well network design may allow to discriminate between the possible sources of error. 相似文献
13.
14.
Nao Kusuhashi Ai Matsumoto Masaki Murakami Takahiro Tagami Takafumi Hirata Tsuyoshi Iizuka Takeshi Handa Hiroshige Matsuoka 《Island Arc》2006,15(3):378-390
Abstract The upper Mesozoic Tetori Group contains numerous fossils of plants and marine and non‐marine animals. The group has the potential to provide key information to improve our understanding of the Middle Jurassic to Early Cretaceous biota of East Asia. However, the depositional age of the Tetori Group remains uncertain, and without good age constraints, accurate correlation with other areas is very difficult. As a first step in obtaining reliable ages for the formations within the Tetori Group, we used laser ablation‐inductively coupled plasma–mass spectrometry to measure the U–Pb ages of zircons collected from tuff beds in the Shokawa district, Takayama City, Gifu Prefecture, central Japan. The youngest reliable U–Pb ages from the tuff beds of the Ushimaru, Mitarai and Okurodani Formations are 130.2 ± 1.7, 129.8 ± 1.0 and 117.5 ± 0.7 Ma, respectively (errors represent 2 SE). These results indicate that the entire Tetori Group in the Shokawa district, which was previously believed to be correlated to the Upper Jurassic to Lower Cretaceous, is in fact correlated to the Lower Cretaceous. The maximum ages of the Ushimaru, Mitarai and Okurodani Formations are late Hauterivian to Barremian, late Hauterivian to Barremian and Barremian to Aptian, respectively. 相似文献
15.
16.
Abdoul R. Ghotbi 《地震工程与工程振动(英文版)》2014,13(3):357-373
The seismic behavior of skewed bridges has not been well studied compared to straight bridges. Skewed bridges have shown extensive damage, especially due to deck rotation, shear keys failure, abutment unseating and columnbent drift. This research, therefore, aims to study the behavior of skewed and straight highway overpass bridges both with and without taking into account the effects of Soil-Structure Interaction(SSI) due to near-fault ground motions. Due to several sources of uncertainty associated with the ground motions, soil and structure, a probabilistic approach is needed. Thus, a probabilistic methodology similar to the one developed by the Pacific Earthquake Engineering Research Center(PEER) has been utilized to assess the probability of damage due to various levels of shaking using appropriate intensity measures with minimum dispersions. The probabilistic analyses were performed for various bridge confi gurations and site conditions, including sand ranging from loose to dense and clay ranging from soft to stiff, in order to evaluate the effects. The results proved a considerable susceptibility of skewed bridges to deck rotation and shear keys displacement. It was also found that SSI had a decreasing effect on the damage probability for various demands compared to the fixed-base model without including SSI. However, deck rotation for all types of the soil and also abutment unseating for very loose sand and soft clay showed an increase in damage probability compared to the fixed-base model. The damage probability for various demands has also been found to decrease with an increase of soil strength for both sandy and clayey sites. With respect to the variations in the skew angle, an increase in skew angle has had an increasing effect on the amplitude of the seismic response for various demands. Deck rotation has been very sensitive to the increase in the skew angle; therefore, as the skew angle increased, the deck rotation responded accordingly. Furthermore, abutment unseating showed an increasing trend due to an increase in skew angle for both fixed-base and SSI models. 相似文献
17.
The great majority of marine protected areas (MPAs) fail to meet their management objectives. So MPAs can be effective conservation tools, we recommend two paradigm shifts, the first related to how they are located and the second related to how they are managed. MPAs are unlikely to be effective if they are located in areas that are subject to numerous, and often uncontrollable, external stressors from atmospheric, terrestrial, and oceanic sources, all of which can degrade the environment and compromise protection. MPA effectiveness is also limited by low institutional and community capacity for management and inappropriate size with respect to ecological needs. In particular, the check list approach to management does not ensure that key threats are dealt with, or that management expenditures provide a quantifiable return. We recommend a business planning approach to MPA management, in which managers focus on the viability of the management system, i.e., the ability of the MPA to provide ecological goods and services to its target users over the long term. 相似文献
18.
For wave propagation simulation in piecewise heterogeneous media, Gaussian-elimination-based full-waveform solutions to the generalized Lippmann–Schwinger integral equation (GLSIE) are highly accurate, but involved with extremely time-consuming computations because of the very large size of the resulting boundary–volume integral equation matrix to be inverted. Several flexible approximations to the GLSIE are scaled in an iterative way to adapt numerical solutions to the smoothness of heterogeneous media in terms of incident wavelengths, with a great saving of computing time and memory. Among various typical iterative schemes to the GLSIE matrix, the generalized minimal residual method (GMRES) is an efficient approach to reduce the computational intensity to some degree. The most efficient approximation can be obtained using a Born series, as an alternative iterative solution, to both the boundary-scattering and volume-scattering waves, leading to the Born-series approximation (BSA) scheme and the improved Born-series approximation (IBSA) scheme. These iteration schemes are validated by dimensionless frequency responses to a heterogeneous semicircular alluvial valley, and then applied to a heterogeneous multilayered model by calculating synthetic seismograms to evaluate approximation accuracies. Numerical experiments, compared with the full-waveform numerical solution, indicate that the convergence rates of these methods decrease gradually with increasing velocity perturbations. The comparison also shows that the BSA scheme has a faster convergence than the GMRES method for velocity perturbations less than 10 percent, but converges slowly and even hardly achieves convergence for velocity perturbations greater than 15 percent. The IBSA scheme gives a superior performance over the other methods, with the least iterations to achieve the necessary convergence. 相似文献
19.
An assessment of metal contamination in surface sediments of the Jiaozhou Bay, Qingdao, one of the rapidly developing coastal economic zones in China, is provided. Sediments were collected from 10 stations and a total of 15 heavy metals were analyzed. Concentrations of metals show significant variability and range from 210 to 620 ppm for Ti, 2.7 to 23 ppm for Ni, 4.2 to 28 ppm for Cu, 5.2 to 18 ppm for Pb, 12 to 58 ppm for Zn, 0.03 to 0.11 ppm for Cd, 5 to 51 ppm for Cr, 1.5 to 9.9 ppm for Co, 5.3 to 19 ppm for As, 12 to 32 ppm for Se, and 19 to 97 ppm for Sr. Based on concentration relationships and enrichment factor (EF) analyses, the results indicate that sediment grain size and organic matter played important roles in controlling the distribution of the heavy metals in surface sediments of the Jiaozhou Bay. The study shows that the sediment of the Jiaozhou Bay has been contaminated by heavy metals to various degrees, with prominent arsenic contributing the most to the contamination. The analysis suggests that the major sources of metal contamination in the Jiaozhou Bay are land‐based anthropogenic ones, such as discharge of industrial waste water and municipal sewage and run‐off. Notably, the elevated heavy metal concentrations of the Jiaozhou Bay sediments could have a significant impact on the bay's ecosystem. With the rapid economic development and urbanization around the Jiaozhou Bay, coastal management and pollution control should focus on these contaminant sources, as well as provide ongoing monitoring studies of heavy metal contamination within the bay. 相似文献
20.
Past and future evolution in the Thames Estuary 总被引：1，自引：0，他引：1
In order to manage estuaries effectively, it is important to be able to predict how they are likely to change in the future,
both to natural and anthropogenic forcing. This paper looks at historical morphological development of the Thames Estuary,
taking into account the effect of human intervention, and uses the ASMITA morphological model to predict the long-term evolution
of the estuary into the future, assuming either historic rates of sea-level rise or accelerated sea-level rise. The historical
sediment budget for the Thames Estuary was examined and source and sink terms, including fluvial sediment supply and historical
dredging rates, were included in the ASMITA model. ASMITA predictions showed good overall agreement with the historical data,
highlighting the benefits of detailed historical review and the inclusion of anthropogenic effects in the model. Future ASMITA
predictions for the period 2000 to 2100 suggest that, under both historical and accelerated sea-level rise scenarios, the
estuary will experience accretion, but, for the accelerated sea-level rise scenario, accretion will be at a slower rate than
sea level rise. With accelerated sea-level rise, intertidal profiles were predicted to be up to 0.5 m lower with respect to
high water. 相似文献