Impacts of land cover changes on runoff and sediment in the Cedar Creek Watershed,St. Joseph River,Indiana, United States

The relation between runoff and sediment and land cover is investigated in the Cedar Creek Watershed （CCW）, located in Northeastern Indiana, United States. The major land cover types in this watershed are cultivated land, woodland and pasture /Conservation Reserve Program （CRP）, which account for approximate 90 % of the total area in the region. Moreover, land use was changed tremendously from aooo to 9004, even without regarding the effect of the crop rotation system （corn ＆ soybean）. At least 49 % of land cover types were changed into other types in this period. The land cover types, ranking by changing area from high to low series, are rye, soybean, corn, woodland and pasture/CRP. The CCW is divided into 21 subwatersheds, and soil and water loss in each sub-watershed is computed by using Soil and Water Assessment Tool （SWAT）. The results indicate that the variations in runoff and sediment have positive relation to the area of crops （especially corn and soybean）; sediment is more sensitive to land cover changes than runoff; more heavy rainfall does not always mean more runoff because the combination of different land cover types always modify runoff coefficient; and rye, soybean and corn are the key land cover types, which affected the variation in runoff and sediment in the CCW.     

Revitalization of a mature oil-bearing basin by a paradigm shift in the exploration concept. A case history of Bohai Bay,Offshore China

The Bozhong Depression in Bohai Bay was previously ranked as an unfavorable exploration region due to concerns about reservoir, trapping integrity and top seal risks.     

地壳介质各向异性研究状况,存在问题及进一步研究思路

引言近２０多年来对地球的观测和研究表明地壳介质呈现强烈各向异性。研究地球介质尤其是地壳的各向异性特征,对自然资源开发和地震前兆场演化规律认识都有十分重要的意义。但同时也应看到,地壳介质各向异性研究的各种方法和理论是建立在简化的物理或数学模型上的,因此...     

IP 测深曲线一维快速反演在找矿预测中的应用

一维快速反演的显著特点,是依据ρ＊ｓ和ρｓ在第ｉ个极距γｉ处的梯度,快速计算出体积极化地质体的实际埋深以及所对应的实际η和实际ρ值。通过广西博白东桃、望海嶂铅锌矿区和兴安杨梅铅锌矿区的电阻率／ＩＰ测深剖面资料的一维快速反演处理,结合矿区地质规律,进行找矿预测。对发现的异常经钻探验证,证实ＩＰ测深曲线一维反演技术方法可行,效果明显。     

新疆14C年代测定及数据集(Ⅲ)

每一个14C测定年代数据包括下列内容并按下列位置安排:序号实验室编号样品提供单位及姓名样品名称14C年代(年)14C年代(年)原编号采样日期(距今,5568)(距今,5730)(公元/公元前)(公元/公元前)东经北纬树轮校正年代(年)(公元/公元前)采样地点及物性描述104XZ-218新疆地震局　　　宋和平黄土4500±904630±90花果山-11991-12-00BC2550BC268081°30′43°40′花果山(伊宁—新源公路)槽子黄土山丘,深度为地表下2m105XZ-219新疆地震局宋和平黄土7815±808045±80734厂-2#1991-12-00BC5865BC609581°30′43°伊宁市734厂后沟表层低山,深度在地…     

台风期间南海北部岛礁及下坡海底对水下噪声的影响研究

The correlation of ambient noise with wind speed, and the depth dependence of ambient noise are both investigated, where the ocean noise data were recorded by a vertical line array in the northern South China Sea. It is shown that the correlation coefficients increase with increasing hydrophone depth during typhoon periods when the frequency ≥ 250 Hz, which opposes the generally accepted knowledge that the correlation coefficients of noise level and wind speed decrease with increasing depth during non-typhoon periods. Particularly at frequencies of 250 Hz, 315 Hz and 400 Hz, the correlation coefficients increase by more than 0.05 at depths ranging from 155 m to 875 m. At the three frequencies, the average noise levels also increase with increasing depth during typhoon periods. It is suggested that these differences are attributed to the wind-generated noise in shallow waters and the effect of "downslope enhancement" to sound propagation. During typhoon periods, the surf breaking and surf beat upon the shores and reefs are strengthened, and the source levels are increased. The wind-generated noise in shallow waters interacts with the downslope sea floor, with the noise-depth distribution changed by a "downslope enhancement" effect promoting noise propagation.     

细颗粒泥沙动水絮凝的机理分析

本文首先阐述由环形水槽试验所得出的细颗粒泥沙动水絮凝的若干规律。然后进行絮凝体形成和破碎的机理分析。从而得出产生动水絮凝的充分、必要条件:一是泥沙和电介质的物理、化学性质;二是絮凝体的抗剪能力大于所受到的剪切力,由此引出动水絮凝临界流速的概念。     

Sediment source and environment evolution in Taiwan Island during the Eocene–Miocene

Taiwan Island's outcropping strata can provide important insights into the sedimentary environment and source development of the southeast China margin. This research is based on the Eocene–Miocene strata of the Tsukeng area in the central Western Foothills, northeast shoreline of Taiwan Island and two sites of the East China Sea Shelf Basin(ECSSB), using petrology and detrital zircon U-Pb age for the analysis. Results show that central and northeast Taiwan Island experienced a transformation from continental to marine facies during the Eocene–Miocene, and the sandstone maturity changed with time. Source analysis shows that sediments from the Eocene–early Oligocene strata mainly originated from near-source Mesozoic rocks, whose zircon age is consistent with the igneous rock in the surrounding area and coastal Cathaysia, showing 120 Ma and 230 Ma peaks in the age spectrum diagram. Since the late Oligocene, peaks of 900 Ma and 1 800 Ma are seen, indicating that deposition of matter from the old block began. The sediments could be a mixture of the surrounding Mesozoic volcanic and fewer pre-Cambrian rocks sourced from the coastal river and sporadic old basement in the ECSSB instead of longdistance transportation.     

Spectral aspects of the Gaussian beam method: reflection from a homogeneous half-space

Summary. Use of paraxially approximated Gaussian beams continues to be actively pursued for construction of synthetic seismograms in complicated environments. How to select the beams in the stack remains a source of difficulty which has primarily been addressed by semi-heuristic considerations. In this paper, the classical example of line-source field reflection from a homogeneous half-space that can sustain a head wave is examined from a plane-wave spectral point of view. The individual beam fields are modelled exactly by the complex source point technique, which emphasizes the complex spectral content of these wave objects. The quality of the paraxial approximation of a typical reflected (Gaussian) beam characterized by different parameters is examined from this perspective, and is compared with uniform and non-uniform asymptotics generated from the exact beam field spectral integral. With this information as background, the reflected field for a real line-source is synthesized by beam superposition. Except for the immediate vicinity of the critical reflection angle, the well-known failure of narrow paraxial beams, no matter how densely stacked, to reproduce the head wave effects is shown to be due to the inadequate spectral content of these beams and not to the failure of beam stacking per se. When the rigorous solutions are used for the narrow-waist beams, even relatively few suffice to yield agreement with the exact solution. This circumstance emphasizes the importance of fully understanding the spectral implications of various beam stacking schemes.     

湘湖的形成演变及其发展前景

湘湖的形成、演变和发展在宁绍平原湖泊变迁中为特例.湘湖的存亡和当地的自然、人文条件密切相关,在历史时期作为农业灌溉的湘湖,由于职能转变,目前残剩为河流型的湖泊,但湖内粘土宜制砖瓦的功能,致使水域扩大.湘湖可能发展为风景区.