Crustal Thinning of the Northern Continental Margin of the South China Sea

Magnetic data suggest that the distribution of the oceanic crust in the northern South China Sea (SCS) may extend to about 21 °N and 118.5 °E. To examine the crustal features of the corresponding continent–ocean transition zone, we have studied the crustal structures of the northern continental margin of the SCS. We have also performed gravity modeling by using a simple four-layer crustal model to understand the geometry of the Moho surface and the crustal thicknesses beneath this transition zone. In general, we can distinguish the crustal structures of the study area into the continental crust, the thinned continental crust, and the oceanic crust. However, some volcanic intrusions or extrusions exist. Our results indicate the existence of oceanic crust in the northernmost SCS as observed by magnetic data. Accordingly, we have moved the continent–ocean boundary (COB) in the northeastern SCS from about 19 °N and 119.5 °E to 21 °N and 118.5 °E. Morphologically, the new COB is located along the base of the continental slope. The southeastward thinning of the continental crust in the study area is prominent. The average value of crustal thinning factor of the thinned continental crust zone is about 1.3–1.5. In the study region, the Moho depths generally vary from ca. 28 km to ca. 12 km and the crustal thicknesses vary from ca. 24 km to ca. 6 km; a regional maximum exists around the Dongsha Island. Our gravity modeling has shown that the oceanic crust in the northern SCS is slightly thicker than normal oceanic crust. This situation could be ascribed to the post-spreading volcanism or underplating in this region.     

Artificial Upwelling of Deep Seawater Using the Perpetual Salt Fountain for Cultivation of Ocean Desert

Deep seawater in the ocean contains a great deal of nutrients. Stommel et al. have proposed the notion of a “perpetual salt fountain” (Stommel et al., 1956). They noted the possibility of a permanent upwelling of deep seawater with no additional external energy source. If we can cause deep seawater to upwell extensively, we can achieve an ocean farm. We have succeeded in measuring the upwelling velocity by an experiment in the Mariana Trench area using a special measurement system. A 0.3 m diameter, 280 m long soft pipe made of PVC sheet was used in the experiment. The measured data, a verification experiment, and numerical simulation results, gave an estimate of upwelling velocity of 212 m/day. This revised version was published online in July 2006 with corrections to the Cover Date.     

基于规则波波形的超声波非接触测量有关问题探讨

波浪波形的非接触测量近年来获得广泛的应用。本文以规则波为讨论对象，针对介质为空气的超声波测量方式进行波形测量误差分析，并结合实验室和实船试验进行对比分析。理论分析表明：在规则波取为坦谷波和ＳＴＯＫＥＳ波的前提下，超声波技术几乎产生相同的最大误差。定量分析表明，在对测量精度限制的条件下，对文中提及的各项参数应作有效的控制     

Gravity Anomaly and Tectonics in the Northern Part of the North Fiji Basin - Preliminary Result of the 1994 NOFI Cruise under the NEW STARMER Programme

A surface ship gravity survey was carried out in the northern part of the North Fiji Basin during the NOFI cruise by the R/V l'Atalante in August-September, 1994. The two ridges inside the study area, the South Pandora Ridge and the Tripartite Ridge, present different structures and states of isostatic equilibrium in terms of gravity anomaly and its tectonic implications. The former is supported by a restoring force of an imaginary elastic plate in the crust and the latter by the Airy type isostasy. These characteristics can be derived from the difference in magmatic activity, as influenced by the difference in lithospheric structure. The latter is characterised by greater active magmatism and hydrothermalism underneath the ridge than the former. Such a difference in the magmatic activity and the horizontal scale of the shallow subsurface structure is derived from the difference in the stiffness or viscosity of the lithosphere beneath the two ridges.     

Field measurements and monitoring of wastewater discharge in sea water

This paper reports a study of the field measurements and monitoring of wastewater discharge in sea water at Bari East (Italy). A wastewater sea outfall system is an integral and fundamental part of each wastewater treatment with ultimate sink in the sea water. The design of a water treatment plant and wastewater outfall must take into account the use of the environmental water, the values of physicochemical parameters to be respected in order to safeguard the use itself and the quality of the environmental water where wastewater is issued. In the present study measurements of sea current velocity components were carried out with a VM-ADP (Vessel-Mounted Acoustic Doppler Profiler). Salinity, wind directions and velocities were assessed with, for one survey, the total faecal coliforms and other biochemical parameters. It was emphasized that the measurements necessary for monitoring cannot be concentrated in the wastewater outfall pipe zone only, but should be extended to a neighbouring area of the outfall pipe, with an extension depending on the wastewater discharge, the polluting charge and the magnitude of the sea currents and the winds typical of the zone of interest. The analyses presented in this paper confirm that the sea zones close to the wastewater outfall pipe are particularly sensitive and vulnerable. Such results must be considered in the planning of a wastewater outfall pipe.     

空间扰动引力的谱分析

基于重力场的频谱理论，给出了扰动引力在全球平均意义下的功率谱表达式，揭示了扰动引力的传播特性。通过数值试验，给出了扰动引力随高度变化规律，并分析了不同高度上，扰动引力恢复重力场的最高阶数及相应分辨率。从理论上分析了航空重力测量探测重力场中高频信息的能力，对制定飞行方案有一定参考价值。     

动态基准实时测量系统的开发与应用

介绍了动态基准实时测量系统的硬件组成、站点上全站仪棱镜组合安装与检测方法、系统软件的开发及特点，最后对系统在广州地铁某地铁站结构变形自动监测中的应用情况进行了阐述。通过实际应用表明该系统能应用在自动化、高精度的变形监测领域。     

Crustal Structures of the Northernmost South China Sea: Seismic Reflection and Gravity Modeling

The South China Sea (SCS) is a marginal sea off shore Southeast Asia. Based on magnetic study, oceanic crust has been suggested in the northernmost SCS. However, the crustal structure of the northernmost SCS was poorly known. To elaborate the crustal structures in the northernmost SCS and off southwest Taiwan, we have analyzed 20 multi-channel seismic profiles of the region. We have also performed gravity modeling to understand the Moho depth variation. The volcanic basement deepens southeastwards while the Moho depth shoals southeastwards. Except for the continental margin, the northernmost SCS can be divided into three tectonic regions: the disturbed and undisturbed oceanic crust (8–12 km thick) in the southwest, a trapped oceanic crust (8 km thick) between the Luzon-Ryukyu Transform Plate Boundary (LRTPB) and Formosa Canyon, and the area to the north of the Formosa Canyon which has the thickest sediments. Instead of faulting, the sediments across the LRTPB have only displayed differential subsidence offset of about 0.5–1 s in the northeast side, indicating that the LRTPB is no longer active. The gravity modeling has shown a relatively thin crust beneath the LRTPB, demonstrating the sheared zone character along the LRTPB. However, probably because of post-spreading volcanism, only the transtension-shearing phenomenon of volcanic basement in the northwest and southeast ends of the LRTPB can be observed. These two basement-fractured sites coincide with low gravity anomalies. Intensive erosion has prevailed over the whole channel of the Formosa Canyon.     

南沙群岛海域水体漫衰减系数Kd(490)的特性研究

对南沙群岛海区水体Kd(490）的特性进行了深入分析和探讨,研究结果表明：Kd（490）的垂直分布与同步测量的海水叶绿素a浓度的垂直分布有很强的相关性;Kd（490）的垂直分布反映出该区域海水存在较强的分层现象,研究中还发现上行辐亮度漫衰减系数KL（490）与Kd（490）垂直变化趋势相当一致,但是以二者达到最大值的深度为界,上层水体的KL（490）值稍大于Kd(490）值,在这一深度以下则相反。     

SII型海洋重力仪稳定平台颤动故障与排除方法

S型海洋重力仪是目前海洋重力测量中较为常用的一种仪器，其产品性能也逐步得到提高。介绍了进行全自动化控制升级后，最新引进的SⅡ型海洋重力仪使用中出现的稳定平台颤动故障现象及排除办法。