Currents in the Luzon Strait during the spring of 2002: observation and computation by modified inverse model

On the basis of the current measurements at 200,500 and 800 m from moored current meters with the time series data from March 17 to April 15 at the mooring station (20°49′57″N, 120°48′ 12″E) and the hydrographic data obtained in the Luzon Strait during the spring of 2002 cruise, the circulation in the investigated     

长江口北支进入南支净盐通量的观测与计

根据 2 0 0 1年 4月 1 0— 1 3日长江口大潮期 5个潮周期 3条测量船的同步连续观测资料 ,计算了长江口北支进入南支的净盐通量为 5 4 5× 1 0 6 t,这一结果为预测长江口南支及青草沙水源地的咸潮入侵强度和开发利用长江口淡水资源提供了重要数据。     

Accretion,structure and hydrology of intermediate spreading-rate oceanic crust from drillhole experiments and seafloor observations

Downhole measurements recorded in the context of the Ocean Drilling Program in Hole 504B, the deepest hole drilled yet into the oceanic crust, are analyzed in terms of accretion processes of the upper oceanic crust at intermediate spreading-rate. The upper part of the crust is found to support the non steady-state models of crustal accretion developed from seafloor observations (Kappel and Ryan, 1986; Gente, 1987). The continuous and vertical nature of borehole measurements provides stratigraphic and structural data that cannot be obtained solely from seafloor studies and, in turn, these models define a framework to analyze the structural, hydrological, and mineralogical observations made in the hole over the past decade.Due to the observed zonation with depth of alteration processes, and its relation to lava morphologies, the 650-m-thick effusive section penetrated in Hole 504B is postulated to be emplaced as the result of two main volcanic sequences. Massive lava flows are interpreted as corresponding to the onset of these sequences emplaced on the floor of the axial graben. The underlying lava made of structures with large porosity values and numerous cm-scale fractures is thus necessarily accreted at the end of the previous volcanic episode. On top of such high heterogeneous and porous intervals, the thick lava flows constitute crustal permeability barriers, thereby constraining the circulation of hydrothermal fluids.Accreted in the near vicinity of the magma chamber, the lower section is that exposed to the most intense hydrothermal circulation (such as black smokers activity). Once capped by a massive flow at the onset of the second volcanic phase, the lower interval is hydrologically separated from ocean-waters. A reducing environment develops then below it resulting, for example, in the precipitation of sulfides. Today, whereas the interval corresponding to the first volcanic episode is sealed by alteration minerals, the second-one is still open to fluid circulation in its upper section. Thus, upper part of the volcanic edifice is potentially never exposed to fluids reaching deep into the crust, while the lower one is near the ridge axis.Considering that most of the extrusives are emplaced within a narrow volcanic zone, the first unit extruded for a given vertical cross-section is necessarily emplaced at the ridge-axis. In Hole 504B, the 250-m-thickTransition Zone from dikes to extrusives is interpreted as the relict massive unit flooding the axial graben at the onset of the first volcanic sequence, and later ruptured by numerous dikes. Further from the axis, the same massive unit constitutes a potential permeability cap for vertical crustal sections accreted earlier. Also, the upper 50 meters of the basement might be considered as the far-end expression of massive outpours extruded near the ridge-axis.     

精密三角高程代替一等水准测量的研究

通过对三角高程测量的原理、误差来源及精度分析，指出了用三角高程测量代替一等水准的关键问题，第一次提出了在特定条件下用三角高程测量代替一等水准是完全可行的，并在生产实践中得到了验证。     

GPS多普勒频移测量速度模型与误差分析

利用GPS多普勒频移观测量可以获得高精度的速度测量结果。文中先给出GPS载波相位观测方程，在此基础上，详细推导了GPS多普勒频移测量载体速度的数学模型。然后在相对测量模式下，讨论各种误差对速度的影响。     

Processes,spatio‐temporal factors and measurements of current erosion in the French Southern Alps: a review

Present erosion in mountainous areas of Western Europe causes land management problems, particularly for areas located downstream of erosion zones. Except for transalpine roads and ski resorts, economic activities no longer require as much space as they did in the past. Therefore, natural reforestation has provided signi?cant protection for alpine hillslopes during the 20th century. However, extreme ?oods continue to cause severe damage in intra‐alpine valleys, as well as in piedmont and surrounding plains, making the study of present water erosion phenomena very important. Many studies have investigated the processes and factors of water erosion on slopes at both the catchment and plot scales. They have focused on rock fragmentation and transportation in different ?elds, the spatial and temporal explanatory variables, the consequences downstream (?ooding, sedimentation, river bed evolution) and the impact of ?oods. In the French Alps, present erosion has been studied in a variety of outcrops, with several recent studies conducted in ?elds such as marls, clayey deposits, molasses and moraines. These kinds of outcrops are found throughout the alpine massif, including an area of special interest on the great Jurassic black marl outcrop where badlands are frequently observable. Geomorphologists and hydrologists have been particularly interested in the strong erosion processes in marls, seeking to determine the main patterns and the impact of spatial and temporal factors on soil loss quantities. The main climatic factors of rock disaggregation were found to be the freeze–thaw and wet–dry cycles, which destroy rock cohesion, and the splash effect of rain. The principal site variables are vegetation cover, exposure and dip–slope angle. Erosion rates are two or three orders of magnitude higher on bare soils than on pastures; northern aspect slopes suffer two to four times as much soil loss as southern aspect slopes. Finally, the angle formed by the slope and the dip also determines different behaviours: erosion rates are higher when slope and dip are perpendicular than when they are parallel. The transportation agents are mostly debris ?ows and runoff caused by intense precipitation. Annual erosion depth in the marls is generally assumed to be substantial, up to 10 mm. The high value can be explained by the severity of the climatic conditions and the brittleness of the lithology, which results in numerous fractures. Copyright © 2003 John Wiley & Sons, Ltd.     

三峡水库区工程环境边坡治理方案的选择

为了减少和防止三峡水库区地质灾害的发生，确保库区工程建设的顺利实施，应加强库区工程建设中的环境边坡治理研究。文章结合三峡库区某污水处理厂的工程建设，根据场地工程地质条件，通过对各种不同方案的对比分析，指出常规高填方设计方案存在诸多问题。提出在填方区采用环境边坡治理与主体结构相结合的新设计思路及方法。采用了架空设计方案，尽量保持现有地形地貌，避免了工程建设过程中对山体进行大挖大填，防止人为活动诱发山地灾害。该方案避免了场地高填方，不需修建高填方挡土墙，有效地降低了成本、节约了造价、缩短了工期。上部建筑或构筑物采用框架结构架空支撑，建筑物沉降小。新设计方案的实施，确保了三峡水库区污水处理厂工程建设的顺利进行，取得显著的经济效益及社会效益。     

Intercomparison of Boron Isotope and Concentration Measurements. Part II: Evaluation of Results

The Istituto di Geoscienze e Georisorse (IGG), on behalf and with the support of the International Atomic Energy Agency (IAEA), prepared eight geological materials (three natural waters and five rocks and minerals), intended for a blind interlaboratory comparison of measurements of boron isotopic composition and concentration. The materials were distributed to twenty seven laboratories - virtually all those performing geochemical boron isotope analyses in the world -which agreed to participate in the intercomparison exercise. Only fifteen laboratories, however, ultimately submitted the isotopic and/or concentration results they obtained on the intercomparison materials. The results demonstrate that interlaboratory reproducibility is not well reflected by the precision values reported by the individual laboratories and this observation holds true for both boron concentration and isotopic composition. The reasons for the discrepancies include fractionations due to the chemical matrix of materials, relative shift of the zero position on the δ¹¹B scale and a lack of well characterized materials for calibrating absolute boron content measurements. The intercomparison materials are now available at the IAEA (solid materials) and IGG (waters) for future distribution.     

Petrological model of the northern Izu–Bonin–Mariana arc crust: constraints from high-pressure measurements of elastic wave velocities of the Tanzawa plutonic rocks, central Japan

Ultrasonic compressional wave velocities (Vp) and shear wave velocities (Vs) were measured with varying pressure up to 1.0 GPa in a temperature range from 25 to 400 °C for a suite of tonalitic–gabbroic rocks of the Miocene Tanzawa plutonic complex, central Japan, which has been interpreted as uplifted and exposed deep crust of the northern Izu–Bonin–Mariana (IBM) arc. The Vp values of the tonalitic–gabbroic rocks increase rapidly at low pressures from 0.1 to 0.4 GPa, and then become nearly constant at higher pressures above 0.4 GPa. The Vp values at 1.0 GPa and 25 °C are 6.3–6.6 km/s for tonalites (56.4–71.1 wt.% SiO₂), 6.8 km/s for a quartz gabbro (53.8 wt.% SiO₂), and 7.1–7.3 km/s for a hornblende gabbro (43.2–47.7 wt.% SiO₂). Combining the present data with the P wave velocity profile of the northern IBM arc, we infer that 6-km-thick tonalitic crust exists at mid-crustal depth (6.1–6.3 km/s Vp) overlying 2-km-thick hornblende gabbroic crust (6.8 km/s Vp). Our model shows large differences in acoustic impedance between the tonalite and hornblende gabbro layers, being consistent with the strong reflector observed at 12-km-depth in the IBM arc. The measured Vp of Tanzawa hornblende-bearing gabbroic rocks (7.1–7.3 km/s) is significantly lower than that Vp modeled for the lowermost crustal layer of the northern IBM arc (7.3–7.7 km/s at 15–22 km depth). We propose that the IBM arc consists of a thick tonalitic middle crust and a mafic lower crust.