Characteristics of water exchange in the Luzon Strait during September 2006

The Luzon Strait is the only deep channel that connects the South China Sea (SCS) with the Pacific. The transport through the Luzon Strait is an important process influencing the circulation, heat and water budgets of the SCS. Early observations have suggested that water enters the SCS in winter but water inflow or outflow in summer is quite controversial. On the basis of hydrographic measurements from CTD along 120 degrees E in the Luzon Strait during the period from September 18 to 20 in 2006, the characteristics of temperature, salinity and density distributions are analyzed. The velocity and volume transport through the Luzon Strait are calculated using the method of dynamic calculation. The major observed results show that water exchanges are mainly from the Pacific to the South China Sea in the upper layer, and the flow is relatively weak and eastward in the deeper layer. The net volume transport of the Luzon Strait during the observation period is westward, amounts to about 3.25 Sv. This result is consistent with historical observations.

长白山火山成因—物理机制和化学演化

This thesis is one of the contributions to NSFC project, “The Changbaishan Volcanism and its Links to the Northeast Asia Tectonic System”. The thesis presents our most recent works on Changbaishan Volcanism, on two aspects as (1) the chemical evolution of the Cenozoic volcanism and the physical links of magma genesis, (2) the Holocene activity of the Tianchi Volcano and risks of potential eruption. 1. Chemical evolution and physical links to the Changbaishan Volcanism Physical links to the Chanbaishan Volcanism, just like origins of most of the volcanisms in eastern China, has long been an enigma. A large scale of volcanic activity has dominated many places of eastern China in Meso-Cenozoic. Activity of these volcanisms in eastern China covers several quite different blocks, covers variety of tectonics, and covers a period of time over 200 million years. Such a large-scale and long-lived volcanism in a continental area challenges our knowledge on dynamics of the Earth’s interior. Some works on “Diwa” hypothesis and “lithospheric thinning” hypothesis present possible links between volcanisms and dynamic evolutions of the earth’s interior, but still cannot interpret where are the sources of the heat and fluid, which are essential to the volcanisms. Based on the study of this thesis, we suggest that dynamics of the deep subduction of western Pacific Plate is the critical factor to the Changbaishan Volcanism and volcanisms in NE China, and maybe even essential to most of the Meso-Cenozoic volcanisms in eastern China. In NE China, stagnant slabs flatted in the mantle transition zone (MTZ, ca. 660 km deep) transport and release significant hydrous fluid to the upper mantle. Metamorphism of the deep-subducted slabs and hence a series of mineral phases play an important role in the water transport, exchange, restore, and release. Dehydrated fluid of the wet slab ascending from the MTZ fertile the upper mantle, and also provide upward heat flow which is essential to the magma genesis. Then magma and volcanism occur with the deep subduction from Mesozoic to mordern time in eastern China. To discribe the exact chemical characteristics of the deep subduction releated volcanics is very difficult, because few researches has contributed to the chemical behaviors of fluid and trace elments in the very deep interior of the Earth, such 660 km deep, 410km or 350km where the fluid may ascend and react. However we can still find some chemical characteristics of oceanic subduction. Basalts of the Changbaishan Volcanism have siginficant characteristics of potassium rich, and even can be called a potassic igneous province. If there are only two possible ways, recycled continentical crust or oceanic crust, to fertile the mantle potossium element as we know now, it’s easy to attribute this to the deep-subducted of the west Pacific Plate. To the eastern China, fluid inclusions in mantle xenoliths from the Cenozic basalts also reveal potassium-rich characteristics. This reveals that the same potassium feritle agents may occur in the mantle sources of eastern China. 2. Holocene activiy of the Tianchi Volcano As one of the large volcanic center and complex volcanic cone, the Tianchi Volcano is a dangerous active volcano, with several Holocene eruptions. Among these eruptions, the Millennium Eruption is regardede as one of the biggist eruptions in the world in the last 2000 years. To estimate the potential danger of volcanic eruption, we discuss two essential factors, as (i) volcanic history of Holocene eruptions, including volcanic geolgy, chronnology and chemistry, (ii) state, evolution and relationship of the magma chambers in mantle and crust beneath the Tianchi Volcano.

填土边坡水文作用机理与破坏过程研究—以深圳羊宝地填土滑坡为例

A full understanding of failure mechanism, critical hydrological condition, and process of mobilization and deposition of a landslide is essential for optimal design of stabilization measure and forecasting of landslide hazard. This requires a quantitative study of hydrological response of a slope to rainfall through field monitoring, laboratory test and numerical modelling. At 13:40 on September 18, 2002, a fill slope failed following a period of prolonged rain in Shenzhen, resulting in 5 fatalities and 31 injuries. The failed mass with a volume about 2.5×104m3 traveled about 140m on level ground. Field monitoring, laboratory test, theoretical analysis and numerical modelling were carried out to undestand the hydrological response and failure mechanism of this fill slope. This thesis mainly focuses on the following aspects: (1) The hydrological responses and failure processes of slopes under rainfall infiltration were reviewed. Firstly, the factors influencing on the hydrological responses of slopes were analysed. Secondly, the change of stress state of slope soil and modelling methods of slope failure under rainfall infiltration were reviewed. (2) The characteristics of the Yangbaodi landslide and associated rainfall triggering the failure were presented. The failure was characterized by shallow flowslide, due to an increase of ground water table caused by rainfall infiltration. (3) A fully automated instrumentation was carried out to monitor rainfall, and saturated – unsaturated hydrological response of the fill slope, using a raingauge, piezometers, tensiometers and moisture probes. A conceptual hydrogeological model was presented based on field monitoring and borehole data. Analysis of monitoring data showed that the high pore water pressure in fill slope was caused by upward flow of semiconfined groundwater in the moderately decomposed granite. (4) Laboratory and in-situ testing was performed to study the physical and mechanical properties of fills. Isotropically consolidated undrained compression tests and anisotropically consolidated constant shear stress tests were carried out to understand the failure mechanism of the fill slope. It is indicated that loosely compacted soil is of strain-softening behaviour under undrained conditions, accompanied with a rapid increase in excess pore water pressure. In anisotropically consolidated constant shear stress tests, a very small axial strain was required to induce the failure and the excess pore water pressure increased quickly at failure. This indicated that static liquefaction caused by rise in groundwater table due to rainfall infiltration occurred. (5) The hydraulic conductivity of the highly and moderately decomposed granite was estimated using monitering data of pore water pressure. A saturated – unsaturated flow was modeled to study the hydrological response of the fill slope using rainfall records. It was observed that the lagged failure was due to the geological conditions and the discrepancy of hydraulic conductivity of slope soils. The hydraulic conductivity of moderately decomposed granite is relatively higher than the other materials, resulting in a semiconfied groundwater flow in the moderately decomposed granite, and subsequent upward flow into the upper fill layer. When the ground water table in the fill layer was increased to the critical state, the fill slope failed. (6) Numerical exercises were conducted to replay the failure process of the fill slope, based on field monitoring, laboratory and in-situ testing. It was found that the fill slope was mobilized by a rapid transfer of the concentrated shear stress. The movement of failure mass was characterized by viscosity fluid with a gradual increase in velocity. The failure process, including mobilization and subsequent movement and deposition, was studied using numerical methods.

中国南方热带地区田洋玛珥湖24万年以来的气候变化及湖泊演变

A continuous long (224m) and high-resolution core TY2 was recovered from paleo-maar-lake Tianyang, tropical South China. Based on the diatom records of the upper 130-m core, this paper focuses on exploring climate change and the lake evolution history in tropical South China during the past 240ka. The most typical and unique characteristics of the diatom assemblages is that, Aulacoseira granulata was dominant or absolutely dominant species (80-90%) during most parts of the 130-m core, while Cyclotella stelligera var. tenuis and Fragilaria construens var. venter were subdominant species in only limited parts of the lower and upper core, respectively. Time scale is always the biggest problem for the study of TY2 core, so although diatom is seldom used for establishing time scale, here we attempt this by correlating the diatom-reconstructed temperature sequence with the time scale of ODP core 806B from Equatorial Western Pacific. Verified by the few most reliable ages from TY2 core and the parallel core TYl, a rather reasonable and reliable time scale was established. 01S 7/6 falls at the depth of 100m (ca. 194kaBP), OIS 6/5 at 75m (ca. 132kaBP), OIS 5/4 at 46m (ca. 75kaBP), OIS 4-3 at 35m (ca. 60kaBP). Qualitative and quantitative environmental reconstructions are made on the basis of diatom assemblage ecotype and EDDI dataset. Correlation of diatom-reconstructed temperature and moisture changes of Core TY2 with pollen-reconstructed temperature and rainfall sequence of Core TYl proves that the results are quite consistent in most periods. Thus the reconstruction results from diatom are quite reliable, and probably have a much higher resolution than pollen results. Combined with lithological and magnetic susceptibility variations, the diatom analysis reveals that, the general climate in tropical South China during the past 240ka was warm and wet. On the time scale of glacial-interglacial, warm and wet, cool and dry are not always synchronous. It was relatively warm-wet during the penultimate interglacial, cool-dry during the penultimate glacial, warm-dry during the last interglacial, and cooler-drier during the last glacial. In contrast, on the time scale of subglacial-subinterglacial scales, warm and dry, cool and wet corresponds very obviously, showing very clear 21-23 ka precession cycle. Analysis also shows that, the water of Tianyang paleo-maar-lake was generally warm, turbulent, turbid, meso-trophic, slightly alkaline, low conductivity and fresh during the past 240 kaBP, with small variations in some parts. Tianyang paleolake experienced shallow to semi-deep lake in OIS7d, open shallow lake in OIS7c-OIS5b, shallow coastal lake in OIS5a-OIS4c, swamp in OIS4b, and then completely dried up in OIS3c. The lake evolution was mainly controlled by temperature and precipitation changes in tropical China. While temperature and precipitation changes were probably controlled by the migrations of monsoon rainband and the evaporation rate, which was in turn controlled by the evolution of East Asian monsoon. Therefore, when the summer monsoon was strongest the climate was warm-dry, when stronger the climate was warm-wet; when the winter monsoon was strongest the climate was cool-dry, stronger cool-wet. This mechanism caused the warm-dry sub interglacial and cool-wet subglacial climate in the tropical South China.

APPLICATION OF THE KHOKHLOV-ZABOLOTSKAYA-KUZNETSOV EQUATION TO MODELING HIGH-INTENSITY FOCUSED ULTRASOUND BEAMS

High-intensity focused ultrasound is a form of therapeutic ultrasound which uses high amplitude acoustic waves to heat and ablate tissue. HIFU employs acoustic amplitudes that are high enough that nonlinear propagation effects are important in the evolution of the sound field. A common model for HIFU beams is the Khokhlov-Zabolotskaya-Kuznetsov (KZK) equation which accounts for nonlinearity, diffraction, and absorption. The KZK equation models diffraction using the parabolic or paraxial approximation. Many HIFU sources have an aperture diameter similar to the focal length and the paraxial approximation may not be appropriate. Here, results obtained using the “Texas code,” a time-domain numerical solution to the KZK equation, were used to assess when the KZK equation can be employed. In a linear water case comparison with the O’Neil solution, the KZK equation accurately predicts the pressure field in the focal region. The KZK equation was also compared to simulations of the exact fluid dynamics equations (no paraxial approximation). The exact equations were solved using the Fourier-Continuation (FC) method to approximate derivatives in the equations. Results have been obtained for a focused HIFU source in tissue. For a low focusing gain transducer (focal length 50λ and radius 10λ), the KZK and FC models showed excellent agreement, however, as the source radius was increased to 30λ, discrepancies started to appear. Modeling was extended to the case of tissue with the appropriate power law using a relaxation model. The relaxation model resulted in a higher peak pressure and a shift in the location of the peak pressure, highlighting the importance of employing the correct attenuation model. Simulations from the code that were compared to experimental data in water showed good agreement through the focal plane.