Subsurface Occurrence of Natural Gas Hydrate in the Nankai Trough Area: Implication for Gas Hydrate Concentration

Abstract. The Nankai Trough runs along the Japanese Islands, where extensive BSRs have been recognized in its forearc basins. High resolution seismic surveys and site-survey wells undertaken by the MITI have revealed the gas hydrate distribution at a depth of about 290 mbsf. The MITI Nankai Trough wells were drilled in late 1999 and early 2000. The highlights were successful retrievals of abundant gas hydrate-bearing cores in a variety of sediments from the main hole and the post survey well-2, keeping the cored gas hydrate stable, and the obtaining of continuous well log data in the gas hydrate-dominant intervals from the main hole, the post survey well-1 and the post survey well-3. Gas-hydrate dominant layers were identified at the depth interval from 205 to 268 mbsf. Pore-space hydrate, very small in size, was recognized mostly filling intergranular pores of sandy sediments. Anomalous chloride contents in extracted pore water, core temperature depression, core observations as well as visible gas hydrates confirmed the presence of pore-space hydrates within moderate to thick sand layers. Gas hydrate-bearing sandy strata typically were 10 cm to a meter thick with porosities of about 40 %. Gas hydrate saturations in most hydrate-dominant layers were quite high, up to 90 % pore saturation.
All the gas hydrate-bearing cores were subjected to X-ray CT imagery measurements for observation of undisturbed sedimentary textures and gas-hydrate occurrences before being subjected to other analyses, such as (1) petrophysical properties, (2) biostratigraphy, (3) geochemistry, (4) microbiology and (5) gas hydrate characteristics.     

Determination of the elastic modulus set of foliated rocks from ultrasonic velocity measurements

Ultrasonic measurements of compressional and shear wave velocities under hydrostatic pressure up to 70 MPa were carried out on cylindrical specimens cored across and along the foliation planes. Our measurements revealed that the foliation of the metamorphic rocks induces a clear velocity anisotropy between two orthogonal directions; faster along the foliation plane and slower across the plane in most rock types. All velocity components monotonically increase with the confining pressure, probably due to the closure of microcracks distributed in rock specimens. We determined the complete set of dynamic moduli of foliated metamorphic rocks with two assumptions; transverse isotropy due to the foliation and ellipsoidal seismic energy propagation from a point source. The calculated elastic moduli referring to different directions could be valuable for the design of various engineering structures in planar textured rock mass.     

Thermo-mechanical structure beneath the young orogenic belt of Taiwan

We investigate the thermo-mechanical properties beneath the young orogenic belt of Taiwan by constructing a shear strength profile from a vertical stratified rheological structure. The stratified rheological structure is estimated based on the recently developed thermal structure and its likely composition. Subduction–collision in the young orogenic belts and the thick accretionary wedge make a significant contribution to the growth of sialic crust in the hinterland. The sialic bulk crust not only results in a low seismic velocity but also produces weak crust in the hinterland. The earthquake depth–frequency distribution in the foreland and hinterland correlates very well with the regimes of the brittle/ductile transition revealed in the strength profile. Our results show that the observed two-layer seismicity in the foreland is due to a moderate geotherm and an intermediate mafic bulk composition; while single-layer seismicity in the hinterland is due to its felsic bulk composition. In the foreland, the mechanically strong crust (MSC) and the mechanically strong lithosphere (MSL) coincide with frequent seismicity. The shallow MSC in the hinterland is consistent with the 20- to 25-km seismicity occurring there. The total lithospheric integrated strength (LIS) in the hinterland is only about half of that in the foreland, suggesting a weak lower crust and lithosphere mantle in the hinterland. The results confirm that the earthquake cutoff depth is a proxy for temperature. The calculated decrease of effective elastic thickness (EET) from the orogenic margin (foreland) to the center (hinterland) is consistent with the results of flexure modeling in most orogenic belts. Due to the weak LIS in the hinterland, crustal thinning and rifting may occur in the future. Our results, thus, suggest that the mechanical structure is also closely related to the composition and is not directly reflected in the thermal structure.     

软基沉降观测及其数据处理方法

简述了高速公路软基沉降观测及其数据处理的目的和意义；介绍了沉降观测的布点原则；提出了高速公路软基沉降观测的技术要求；介绍了基于VB的高速公路软基沉降观测数据处理软件；在实际工程中，由于种种原因，会造成沉降观测数据不连续。本文就沉降观测数据不连续时的沉降量估算提出了三种处理方法，在实际工程应用中起到了较大的作用。     

从怀来4井水化学异常变化分析流体在孕震过程中的作用

20世纪60年代，流体在地震孕育与发生过程中的作用就已受到研究者关注。如Evans(1966)发现美国洛基山兵工厂周围地震活动与深井注入废液有关。在我国的地壳流体活动与诱发地震关系的研究方面，也取得了很多成果。针对上地壳流体与地震活动的关系，前人在辽东半岛、东南沿海、红河断裂带、京津地区进行了系统研究。结果表明，地壳热流体活动区的地震活动多，但多为中小地震；而地壳热流体活动弱的地区地震活动数量相对少，但以大震活动为主。近年来，地下流体在孕震过程与构造活动中的作用的研究已有了一些进展。     

大功率激电测深法寻找焦家式深部金矿床的试验应用研究

利用大功率的激电测深法可以寻找焦家式深部金 矿。首先,由物理和数学推导建立多层极化体的数 理模型,其数理模型产生的极化场可由多层若干 个极化单元场相叠加而成。由多次去除极化单元 场的原理而导出大功率激电测深资料进行消除浅 部强激电干扰异常的数据处理公式,从而突出了 深部矿床的激电异常。并利用处理后的激电测深 曲线,定量求取了深部金矿蚀变矿化带的顶界面 埋深。     

Crust and upper mantle structure of the Ailao Shan-Red River fault zone and adjacent regions

Using arrival data of the body waves recorded by seismic stations, we reconstructed the velocity structure of the crust and upper mantle beneath the southeastern edge of the Tibetan Plateau and the northwestern continental margin of the South China Sea through a travel time tomography technique. The result revealed the apparent tectonic variation along the Ailao Shan-Red River fault zone and its adjacent regions. High velocities are observed in the upper and middle crust beneath the Ailao Shan-Red River fault zone and they reflect the character of the fast uplifting and cooling of the metamorphic belt after the ductile shearing of the fault zone, while low velocities in the lower crust and near the Moho imply a relatively active crust-mantle boundary beneath the fault zone. On the west of the fault zone, the large-scale low velocities in the uppermost mantle beneath western Yunnan prove the influence of the mantle heat flow on volcano, hot spring and magma activities, however, the upper mantle on the eas     

Magnetosheath Interaction with the High Latitude Magnetopause

We present both statistical and case studies of magnetosheath interaction with the high-latitude magnetopause on the basis of Interball-1 and other ISTP spacecraft data. We discuss those data along with recently published results on the topology of cusp-magnetosheath transition and the roles of nonlinear disturbances in mass and energy transfer across the high-latitude magnetopause. For sunward dipole tilts, a cusp throat is magnetically open for direct interaction with the incident flow that results in the creation of a turbulent boundary layer (TBL) over an indented magnetopause and downstream of the cusp. For antisunward tilts, the cusp throat is closed by a smooth magnetopause; demagnetized ‘plasma balls’ (with scale ∼ few R_E, an occurrence rate of ∼25% and trapped energetic particles) present a major magnetosheath plasma channel just inside the cusp. The flow interacts with the ‘plasma balls’ via reflected waves, which trigger a chaotization of up to 40% of the upstream kinetic energy. These waves propagate upstream of the TBL and initiate amplification of the existing magnetosheath waves and their cascade-like decays during downstream passage throughout the TBL. The most striking feature of the nonlinear interaction is the appearance of magnetosonic jets, accelerated up to an Alfvenic Mach number of 3. The characteristic impulsive local momentum loss is followed by decelerated Alfvenic flows and modulated by the TBL waves; momentum balance is conserved only on time scales of the Alfvenic flows (1/f_A ∼12 min). Wave trains at f_A∼1.3 mHz are capable of synchronizing interactions throughout the outer and inner boundary layers. The sonic/Alfvenic flows, bounded by current sheets, control the TBL spectral shape and result in non-Gaussian statistical characteristics of the disturbances, indicating the fluctuation intermittency. We suggest that the multi-scale TBL processes play at least a comparable role to that of macro-reconnection (remote from or in the cusp) in solar wind energy transformation and population of the magnetosphere by the magnetosheath plasma. Secondary micro-reconnection constitutes a necessary chain at the small-scale (∼ion gyroradius) edge of the TBL cascades. The thick TBL transforms the flow energy, including deceleration and heating of the flow in the open throat, ‘plasma ball’ and the region downstream of the cusp.     

电子图档的高效管理

通过对前期CAD图档管理系统失败原因进行分析,明确了系统管理的目标,并与软件供应商合作,解决了实施中遇到的问题。